Publications by authors named "Raymond Yee"

229 Publications

A case report of inappropriate inhibition of ventricular pacing due to a unique pacemaker electrogram storage feature.

Eur Heart J Case Rep 2021 Mar 20;5(3):ytab096. Epub 2021 Mar 20.

London Health Sciences Centre, University of Western Ontario, 339 Windermere Road, London, ON N6A 5A5, Canada.

Background: Modern permanent pacemakers (PPMs) have individual features designed to identify cardiac rhythm abnormalities and improve their performance. Inappropriate pacing inhibition may be an undesired outcome from these features and cause symptoms in patients who require frequent pacing, leading to dizziness, and syncope. Inappropriate inhibition can be difficult to identify in circumstances that are intermittent and difficult to reproduce.

Case Summary: A 57-year-old female underwent a mitral valve replacement (MVR) for severe mitral stenosis. One month following MVR, she presented with symptomatic third-degree atrioventricular block, and a dual-chamber PPM (Advisa™, Medtronic, Minneapolis, USA) was implanted and programmed DDD 50-130 b.p.m. At the 3-month follow-up, she reported frequent episodes of lightheadedness. She was found to have intermittent ventricular pacing inhibition on a 48-h Holter monitor due to an internal function of the Advisa™ series of PPMs that attempts to store an electrogram (EGM) every 1 h and 30 s. During the EGM storage, an amplified signal from the storage capacitor can result in oversensing by the ventricular channel and inappropriate pacing inhibition.

Discussion: To rectify the issue, the ventricular lead sensitivity value was increased from 0.9 mV to 1.2 mV. No instances of inappropriate ventricular pacing inhibition were noted on follow-up. To our knowledge, this is a rare case of inappropriate ventricular pacing inhibition caused by a combination of PPM self-adjusting sensitivity algorithm and oversensing every 1 h and 30 s from an amplified storage capacitor. Physicians should be aware of this possible complication and differentiate it from device or lead malfunction.
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http://dx.doi.org/10.1093/ehjcr/ytab096DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7980079PMC
March 2021

Canadian Registry of Electronic Device Outcomes: remote monitoring outcomes in the Abbott battery performance alert-a multicentre cohort.

Europace 2021 Feb 20. Epub 2021 Feb 20.

Department of Medicine, Division of Cardiology, QEII Health Sciences Center, Halifax Infirmary Site, 796 Summer Street, Room 2501D, Halifax NS B3H 3A7, Canada.

Aims: Cardiac implantable electronic devices with device advisories have the potential of device malfunction. Remote monitoring (RM) of devices has been suggested to allow the identification of abnormal device performance and permit early intervention. We sought to describe the outcomes of patients with and without RM in devices subject to the Abbott Premature Battery Depletion (PBD) advisory with data from a Canadian registry.

Methods And Results: Patients with an Abbott device subject to the PBD advisory from nine implantable cardioverter defibrillator (ICD) implanting centres in Canada were included in the registry. The use of RM was identified from baseline and follow-up data in the registry. The primary outcome was detection of PBD and all-cause mortality. A total of 2666 patients were identified with a device subject to the advisory. In all, 1687 patients (63.2%) had RM at baseline. There were 487 deaths during follow-up. At a mean follow-up of 5.7 ± 0.7 years, mortality was higher in those without a remote monitor compared with RM at baseline (24.7% vs. 14.5%; P < 0.001). Pre-mature battery depletion was identified in 36 patients (2.1%) with RM vs. 7 (0.7%) without RM (P = 0.004). Time to battery replacement was significantly reduced in patients on RM (median 5 vs. 13 days, P = 0.001).

Conclusion: The use of RM in patients with ICD and cardiac resynchronization therapy under advisory improved detection of PBD, time to device replacement, and was associated with a reduction in all-cause mortality. The factors influencing the association with mortality are unknown and deserve further study.
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http://dx.doi.org/10.1093/europace/euab025DOI Listing
February 2021

Remote-only monitoring for patients with cardiac implantable electronic devices: a before-and-after pilot study.

CMAJ Open 2021 Jan-Mar;9(1):E53-E61. Epub 2021 Jan 25.

QEII Health Sciences Centre, Dalhousie University (Sapp, AbdelWahab, Parkash), Halifax, NS; Department of Cardiac Sciences (Gillis, Raj), University of Calgary, Calgary, Alta.; Institut universitaire de cardiologie and pneumologie de Quebec (Nault, Philippon), Université Laval, Québec, Que.; University of Ottawa Heart Institute (Nery, Wells), Ottawa, Ont.; Hamilton Health Sciences (Healey), McMaster University, Hamilton, Ont.; CK Hui Heart Centre (Lockwood), Edmonton, Alta.; Vancouver Island Health Authority (Sterns), Victoria, BC; East Carolina University (Sears), Greenville, NC; London Health Sciences Centre (Yee, Tang), University of Western Ontario, London, Ont.

Background: Outcomes for patients with cardiac implantable electronic devices are better when follow-up incorporates remote monitoring technology in addition to in-clinic visits. For patients with implantable devices, we sought to determine the feasibility, safety and associated health care utilization of remote-only follow-up, along with its effects on patients' quality of life and costs.

Methods: This multicentre before-and-after pilot study involved patients with new or existing pacemakers or implantable cardioverter defibrillators. The "before" phase of the study spanned the period October 2015 to February 2017; the "after" phase spanned the period October 2016 to February 2018. The exposure was remote-only follow-up in combination with Remote View, a service that facilitates access to device data, allowing device settings to be viewed remotely to facilitate remote programming. Outcomes at 12 months were feasibility (adherence to remote monitoring), safety (rate of adverse events) and health care utilization (remote and in-clinic appointments). We also assessed quality of life, using 3 validated scales, and costs, taking into account both health care system and patient costs.

Results: A total of 176 patients were enrolled. Adherence (defined as at least 1 successful remote transmission during follow-up) was 87% over a mean follow-up of 11.7 (standard deviation 2.2) months. There was a reduction in in-clinic visits at specialized sites among patients with both implantable defibrillators (26 v. 5, < 0.001, = 48) and pacemakers (42 v. 10, < 0.001, = 51). There was no significant change in visits to community sites for patients with defibrillators (13 v. 17, = 0.3, = 48). The composite rate of death, stroke, cardiovascular hospitalization and device-related hospitalization was 7% ( = 164). No adverse events were linked to the intervention. There was no change in quality-of-life scales between baseline and 12 months. Health care costs were reduced by 31% for patients with defibrillators and by 44% for those with pacemakers.

Interpretation: This pilot study showed the feasibility of remote-only follow-up, with no increase in adverse clinical outcomes and no effect on quality of life, but with reductions in costs and health care utilization. These results support progression to a larger-scale study of whether superior effectiveness and reduced cost can be achieved, with preservation of safety, through use of remote-only follow-up.

Trial Registration: ClinicalTrials.gov, no. NCT02585817.
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http://dx.doi.org/10.9778/cmajo.20200041DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7843075PMC
January 2021

Canadian Registry of Electronic Device Outcomes (CREDO): The Abbott ICD Premature Battery Depletion Advisory, a Multicentre Cohort Study.

CJC Open 2021 Jan 12;3(1):48-53. Epub 2020 Sep 12.

Department of Medicine, Division of Cardiology, QEII Health Sciences Center, Halifax, Nova Scotia, Canada.

Background: Premature or rapid battery depletion may compromise the performance and reliability of an implantable cardioverter defibrillator (ICD), potentially resulting in harm or death to patients. We sought to describe the outcomes and clinical management of devices included in the Abbott ICD Premature Battery Depletion Advisory, using data from a Canadian registry.

Methods: This prospective observational study includes patients with an Abbott device subject to the advisory, from 9 centres in Canada. The incidence and outcomes related to device revision owing to premature battery depletion were identified and adjudicated by a committee.

Results: There were 2678 patients enrolled with a device subject to the advisory. Devices were implanted between 2010 and 2017; follow-up time was 5.7 ± 0.7 years. Device revision occurred in 222 patients (8.3%). Revision for premature battery depletion occurred in 43 patients (1.6%). Devices were revised at physician discretion on notice of the advisory in 16 patients (0.6%), and at patient request in 5 patients (0.2%). A total of 63 (2.4%) devices reached routine end of battery life. A further 95 (3.5%) patients underwent revision for other reasons. There were no reported major complications or adverse events with device revision owing to the advisory. There were no deaths attributed to premature battery depletion.

Conclusions: The rate of premature battery depletion associated with the Abbott ICD Premature Battery Depletion Advisory is low. There were no clinically adverse events identified that were associated with the battery performance of devices under advisory.
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http://dx.doi.org/10.1016/j.cjco.2020.09.008DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7801196PMC
January 2021

Utility of 3-D printing for cardiac resynchronization device implantation in congenital heart disease.

HeartRhythm Case Rep 2020 Oct 22;6(10):754-756. Epub 2020 Jul 22.

Division of Cardiology, Schulich School of Medicine and Dentistry, Western University, London, Ontario, Canada.

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http://dx.doi.org/10.1016/j.hrcr.2020.07.011DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7573375PMC
October 2020

Para-Hisian Pacing During Sinus Rhythm: Establishing Threshold Values to Distinguish Nodal From Septal Pathway Conduction.

JACC Clin Electrophysiol 2020 10 12;6(10):1246-1252. Epub 2020 Aug 12.

London Heart Rhythm Program, Western University, London, Ontario, Canada.

Objectives: This study sought to identify minimum threshold values below which conduction over the atrioventricular (AV) node would be unexpected.

Background: Para-Hisian pacing is used to evaluate for the presence of a septal accessory pathway (AP); however, threshold values to differentiate nodal from AP conduction are unknown.

Methods: The authors performed high- and low-output para-Hisian pacing during sinus rhythm to capture the His and para-Hisian ventricular myocardium (H+V) and para-Hisian ventricular myocardium (V) alone, respectively. The change in stimulation (stim)-to-atrial electrogram interval after loss of His bundle capture in patients with (AP+) and without (AP-) a septal AP was evaluated. Stim-to-proximal coronary sinus (PCS) and stim-to-high right atrium (HRA) intervals were measured and within-patient differences (△) for V and H+V capture were calculated.

Results: A total of 23 AP+ and 45 AP- patients were evaluated. The difference in stimulus to earliest atrial signal in the high right atrial catheter seen with the loss of His bundle capture (△-stim-HRA) (21 ms; interquartile range [IQR]: 3 to 43 ms vs. 64 ms; IQR: 56 to 73 ms; p < 0.001) and difference in stimulus to earliest atrial signal in the proximal coronary sinus catheter seen with the loss of His Bundle capture (△-stim-PCS) (11 ms; IQR: 0 to 30 ms vs. 61 ms; IQR: 52 to 72 ms; p < 0.001) were shorter in AP+ patients. The shortest △-stim-PCS and △-stim-HRA in AP- patients were 37 ms and 32 ms, respectively, whereas the longest corresponding intervals in AP+ patients were 51 ms and 75 ms, respectively.

Conclusions: A △-stim-PCS <37 ms or △-stim-HRA <32 ms confirmed the presence of a septal AP, whereas a value >51 ms for △-stim-PCS or >75 ms for △-stim-HRA excluded it. Alternatively, the minimum △-stim-PCS with loss of His capture compatible with AV nodal conduction in isolation was 37 ms, and a △-stim-PCS >51 ms effectively ruled out the presence of a septal AP.
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http://dx.doi.org/10.1016/j.jacep.2020.05.012DOI Listing
October 2020

A simple maneuver to determine if septal accessory pathway ablation requires a left atrial approach.

J Cardiovasc Electrophysiol 2020 12 24;31(12):3207-3214. Epub 2020 Sep 24.

Division of Cardiology, Schulich School of Medicine and Dentistry, Western University, London, Ontario, Canada.

Introduction: Septal accessory pathway (AP) ablation can be challenging due to the complex anatomy of the septal region. The decision to access the left atrium (LA) is often made after failure of ablation from the right. We sought to establish whether the difference between ventriculo-atrial (VA) time during right ventricular (RV) apical pacing versus the VA during tachycardia would help establish the successful site for ablation of septal APs.

Methods: Intracardiac electrograms of patients with orthodromic reciprocating tachycardia (ORT) using a septal AP with successful catheter ablation were reviewed. The ∆VA was the difference between the VA interval during RV apical pacing and the VA interval during ORT. The difference in the VA interval during right ventricular entrainment and ORT (StimA-VA) was also measured.

Results: The median ∆VA time was significantly less in patients with a septal AP ablated on the right side compared with patients with a septal AP ablated on the left side (12 ± 19 vs. 56 ± 10 ms, p < .001). The StimA-VA was significantly different between the two groups (22 ± 14 vs. 53 ± 9 ms, p < .001). The ∆VA and StimA-VA were always 40 ms in patients with non-decremental septal APs ablated from the right side and always greater than 40 ms in those with septal APs ablated from the left.

Conclusion: ΔVA and StimA-VA values identified with RV apical pacing in the setting of ORT involving a septal AP predict when left atrial access will be necessary for successful ablation.
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http://dx.doi.org/10.1111/jce.14745DOI Listing
December 2020

Double chamber cross-talk, the ultimate double-cross.

Pacing Clin Electrophysiol 2020 12 20;43(12):1599-1604. Epub 2020 Jul 20.

Heart Rhythm Program, London Health Sciences Centre, University of Western Ontario, London, Ontario, Canada.

Cross-talk is a well-described phenomenon in a dual-chamber cardiovascular implantable electronic device. Far-field ventricular events are more commonly sensed in the atrial channel, the reverse is uncommon, and seeing both at the same time has never been reported. We present a case of double cross-talk in a dual-chamber Medtronic ® implantable cardioverter-defibrillator. In this report, we decipher an unusual device response to the cross-talk and describe the programming changes required to resolve it.
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http://dx.doi.org/10.1111/pace.13998DOI Listing
December 2020

Performance of a novel active fixation quadripolar left ventricular lead for cardiac resynchronization therapy: Attain Stability Quad Clinical Study results.

J Cardiovasc Electrophysiol 2020 05 18;31(5):1147-1154. Epub 2020 Mar 18.

Division of Cardiology, Vanderbilt University Heart and Vascular Institute, Nashville, Tennessee.

Introduction: The Medtronic Attain Stability Quad lead is a quadripolar left ventricular (LV) lead with an active fixation helix assembly designed to fixate the lead within the coronary sinus and pace nonapical regions of the LV. The primary objective of this study was to determine the safety and effectiveness of this novel active fixation quadripolar LV lead.

Methods: Patients with standard indications for cardiac resynchronization therapy (CRT) were enrolled. All patients were followed at 3 and 6 months post-implant and every 6 months thereafter until study closure. Pacing capture thresholds (PCTs) were measured at implant and each follow-up and adverse events (AEs) were recorded upon occurrence.

Results: Of the 440 patients who underwent implant procedures, placement of the Attain Stability Quad lead was successful in 426 (96.8%). LV lead-related complications occurred in 10 patients (2.3%), including LV lead dislodgement in three patients (0.7%). The percentage of patients with at least one LV pacing vector with a PCT ≤2.5 V at a 6-month follow-up was 96.3%. The LV lead was successfully fixated to the prespecified pacing location in 97.4% of cases.

Conclusions: This large, multinational study of the Attain Stability Quad lead demonstrated a high rate of implant success with a low complication rate. The active fixation mechanism allowed precise placement of the pacing electrodes at the desired target region with good PCTs and a very low dislodgement rate.
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http://dx.doi.org/10.1111/jce.14439DOI Listing
May 2020

Incremental Value of Implantable Cardiac Device Diagnostic Variables Over Clinical Parameters to Predict Mortality in Patients With Mild to Moderate Heart Failure.

J Am Heart Assoc 2019 07 11;8(14):e010998. Epub 2019 Jul 11.

1 Western University London Ontario Canada.

Background Heart failure remains a leading cause of morbidity and mortality. Clinical prediction models provide suboptimal estimates of mortality in this population. We sought to determine the incremental value of implantable device diagnostics over clinical prediction models for mortality. Methods and Results RAFT (Resynchronization/Defibrillation for Ambulatory Heart Failure Trial) patients with implanted devices capable of device diagnostic monitoring were included, and demographic and clinical parameters were used to compute Meta-Analysis Global Group in Chronic Heart Failure (MAGGIC) heart failure risk scores. Patients were classified according to MAGGIC score into low (0-16), intermediate (17-24), or high (>24) risk groups. Mortality was evaluated from 6 months postimplant in accordance with the RAFT protocol. In a subset of 1036 patients, multivariable analysis revealed that intermediate and high MAGGIC scores, fluid index, atrial fibrillation, and low activity flags were independent predictors of mortality. A device-integrated diagnostic parameter that included a fluid index flag and either a positive atrial fibrillation flag or a positive activity flag was able to significantly differentiate higher from lower risk for mortality in the intermediate MAGGIC cohort. The effect was more pronounced in the high-risk MAGGIC cohort, in which device-integrated diagnostic-positive patients had a shorter time to death than those who were device-integrated diagnostic negative. Conclusions Device diagnostics using a combination of fluid index trends, atrial fibrillation burden, and patient activity provide significant incremental prognostic value over clinical heart failure prediction scores in higher-risk patients. This suggests that combining clinical and device diagnostic parameters may lead to models with better predictive power. Whether this risk is modifiable with early medical intervention would warrant further studies. Clinical Trial Registration URL : http://www.clinicaltrials.gov . Unique identifier: NCT00251251.
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http://dx.doi.org/10.1161/JAHA.118.010998DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6662119PMC
July 2019

Comparison of Ajmaline and Procainamide Provocation Tests in the Diagnosis of Brugada Syndrome.

JACC Clin Electrophysiol 2019 04 27;5(4):504-512. Epub 2019 Mar 27.

Division of Cardiology, University of British Columbia, Vancouver, British Columbia, Canada. Electronic address:

Objectives: The authors studied the response rates and relative sensitivity of the most common agents used in the sodium-channel blocker (SCB) challenge.

Background: A type 1 Brugada electrocardiographic pattern precipitated by an SCB challenge confers a diagnosis of Brugada syndrome.

Methods: Patients undergoing an SCB challenge were prospectively enrolled across Canada and the United Kingdom. Patients with no prior cardiac arrest and family histories of sudden cardiac death or Brugada syndrome were included.

Results: Four hundred twenty-five subjects underwent SCB challenge (ajmaline, n = 331 [78%]; procainamide, n = 94 [22%]), with a mean age of 39 ± 15 years (54% men). Baseline non-type 1 Brugada ST-segment elevation was present in 10%. A total of 154 patients (36%) underwent signal-averaged electrocardiography, with 41% having late potentials. Positive results were seen more often with ajmaline than procainamide infusion (26% vs. 4%, p < 0.001). On multivariate analysis, baseline non-type 1 Brugada ST-segment elevation (odds ratio [OR]: 6.92; 95% confidence interval [CI]: 3.15 to 15.2; p < 0.001) and ajmaline use (OR: 8.76; 95% CI: 2.62 to 29.2; p < 0.001) were independent predictors of positive results to SCB challenge. In the subgroup undergoing signal-averaged electrocardiography, non-type 1 Brugada ST-segment elevation (OR: 9.28; 95% CI: 2.22 to 38.8; p = 0.002), late potentials on signal-averaged electrocardiography (OR: 4.32; 95% CI: 1.50 to 12.5; p = 0.007), and ajmaline use (OR: 12.0; 95% CI: 2.45 to 59.1; p = 0.002) were strong predictors of SCB outcome.

Conclusions: The outcome of SCB challenge was significantly affected by the drug used, with ajmaline more likely to provoke a type 1 Brugada electrocardiographic pattern compared with procainamide. Patients undergoing SCB challenge may have contrasting results depending on the drug used, with potential clinical, psychosocial, and socioeconomic implications.
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http://dx.doi.org/10.1016/j.jacep.2019.01.026DOI Listing
April 2019

Cardiac resynchronization is pro-arrhythmic in the absence of reverse ventricular remodelling: a systematic review and meta-analysis.

Cardiovasc Res 2018 09;114(11):1435-1444

Division of Cardiology, Department of Medicine, Western University, 339 Windermere Road, London, Ontario, Canada.

Aims: Cardiac resynchronization therapy (CRT) has been shown to reduce mortality and heart failure (HF) hospitalization but its effects on the rate of ventricular arrhythmias (VAs) appears to be neutral. We hypothesize that CRT with LV epicardial stimulation is inherently pro-arrhythmic and increases VA rates in the absence of reverse ventricular remodelling while conferring an anti-arrhythmic effect in mechanical responders.

Methods And Results: In this systematic review and meta-analysis, we considered retrospective cohort, prospective cohort, and randomized controlled trials comparing VA rates between cardiac resynchronization therapy-defibrillator (CRT-D) non-responders, CRT-D responders and those with implantable cardioverter-defibrillator (ICD) only. Studies were eligible if they defined CRT-D responders using a discrete left ventricular volumetric value as assessed by any imaging modality. Studies were identified through searching electronic databases from their inception to July 2017. We identified 2579 citations, of which 23 full-text articles were eligible for final analysis. Our results demonstrated that CRT-D responders were less likely to experience VA than CRT-D non-responders, relative risk (RR) 0.49 [95% confidence interval (CI) 0.41-0.58, P < 0.01] and also less than patients with ICD only: RR 0.59 (95% CI 0.50-0.69, P < 0.01). However, CRT-D mechanical non-responders had a greater likelihood of VA compared with ICD only, RR 0.76 (95% CI 0.63-0.92, P = 0.004).

Conclusion: CRT-D non-responders experienced more VA than CRT-D responders and also more than those with ICD only, suggesting that CRT with LV epicardial stimulation may be inherently pro-arrhythmic in the absence of reverse remodelling.
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http://dx.doi.org/10.1093/cvr/cvy182DOI Listing
September 2018

Canadian Registry of Implantable Electronic Device Outcomes: Surveillance of High-Voltage Leads.

Can J Cardiol 2018 06 19;34(6):808-811. Epub 2018 Feb 19.

Cardiovascular Research Methods Center, University of Ottawa Heart Institute, Ottawa, Ontario, Canada.

Background: Cardiac implantable electrical devices (CIEDs) are subject to advisories and complications that can result in morbidity and mortality for patients; there is currently no system in Canada to track these.

Methods: This was a multicenter, prospective cohort study conducted at 5 centers to determine feasibility. Patients with a de novo high-voltage (HV) lead implantation were included and followed for a minimum of 1 year.

Results: There were 611 leads enrolled into the registry over 18 months. The mean age was 62.4 ± 12.8 years; 144 (23.6%) women were enrolled. The indication for lead implantation was for primary prevention in 65.5%. There were 497 (82.1%) de novo devices (single chamber: 54.5%, dual chamber: 20.5%, cardiac resynchronization therapy [CRT] 25.0%); the remainder of the procedures was a system revision for either upgrade (8.1%) or lead revision (9.8%). The lead revision rate at 1 year was 3.4%, with the primary reason being lead dislodgements. Mortality rate was 3.8% at 1 year. The rate of any device-related complication was 2.0% at 30 days, with the highest rate in CRT implants (4.9%, P = 0.0105). At 1 year, the complication rate was 4.5%, with no significant difference among device types.

Conclusions: This study demonstrates that device surveillance is feasible and highlights (1) the need for CIED surveillance to track device-related complications, (2) the scope of this should be larger, and (3) mandatory participation should be considered. This system could predict CIEDs that may be susceptible to higher than usual rates of failure, mitigating adverse outcomes in patients.
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http://dx.doi.org/10.1016/j.cjca.2018.02.009DOI Listing
June 2018

Contemporary Review of the Cardiovascular Implantable Electronic Devices with Future Directions.

Card Electrophysiol Clin 2018 03;10(1):xv

Internal Medicine, UT Southwestern Medical Center, Professional Office Building 1, Suite HP8.110, 5959 Harry Hines Boulevard, Dallas, TX 75390, USA. Electronic address:

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http://dx.doi.org/10.1016/j.ccep.2017.12.002DOI Listing
March 2018

Implantable Cardioverter Defibrillator Implantation with or Without Defibrillation Testing.

Card Electrophysiol Clin 2018 03 14;10(1):119-125. Epub 2017 Dec 14.

Heart Rhythm Program, Department of Medicine, Western University, PO Box 5339, 339 Windermere Road, London, Ontario N6A 5A5, Canada. Electronic address:

Defibrillation testing (DFT) during implantable cardioverter-defibrillator (ICD) implantation is still considered standard of care in some, but in increasingly fewer centers. The goal is to ensure that the device system functions as intended by testing in the controlled laboratory setting. Although safe, complications can occur and DFT is associated with an increased procedural time and cost. DFT is useful in assessing device function when programming changes or patient characteristics raise concerns regarding ICD efficacy. DFT remains standard of practice following implantation of subcutaneous ICDs and other specific circumstances. Implanting physicians should remain familiar with the process of DFT and situations where it is useful for individual patients.
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http://dx.doi.org/10.1016/j.ccep.2017.11.012DOI Listing
March 2018

Initial Clinical Experience With a New Automated Antitachycardia Pacing Algorithm: Feasibility and Safety in an Ambulatory Patient Cohort.

Circ Arrhythm Electrophysiol 2017 Sep;10(9)

From the Department of Medicine, Division of Cardiology, Western University, London, ON, Canada (R.Y.); Department of Medicine, Montefiore-Einstein Center for Cardiovascular Disease, Montefiore Medical Center, Bronx, NY (J.D.F.); Department of Medicine, Division of Cardiology, University of California, San Diego, La Jolla (U.B.-G.); Department of Medicine, Cardiovascular Division, Washington University School of Medicine, St. Louis, MO (T.W.S.); Department of Medicine, Division of Cardiology, Florida Heart Rhythm Specialists, Ft. Lauderdale (D.N.K.); Texas Cardiac Arrhythmia, Austin (R.C.); and Cardiac Rhythm Heart Failure, Medtronic, Inc, Minneapolis, MN (T.J., R.T., P.D.).

Background: Antitachycardia pacing (ATP) in implantable cardioverter-defibrillators (ICD) decreases patient shock burden but has recognized limitations. A new automated ATP (AATP) based on electrophysiological first principles was designed. The study objective was to assess the feasibility and safety of AATP in ambulatory ICD patients.

Methods And Results: Enrolled patients had dual chamber or cardiac resynchronization therapy ICDs, history of ≥1 ICD-treated ventricular tachycardias (VT)/ventricular fibrillation episode, or a recorded, sustained monomorphic VT. Detection was set to ventricular fibrillation number of intervals to detect=24/32, VT number of intervals to detect≥16, and a fast VT zone of 240 to 320 ms. AATP prescribed the components and delivery of successive ATP sequences in real time, using the same settings for all patients. ICD datalogs were uploaded every ≈3 months, at unscheduled visits, exit, and death. Episodes and adverse events were adjudicated by separate committees. Results were adjusted (generalized estimating equations) for multiple episodes. AATP was downloaded into the ICDs of 144 patients (121 men), aged 67.4±11.9 years, left ventricular ejection fraction 33.1±13.6% (n=137), and treated 1626 episodes in 49 patients during 14.5±5.1 months of follow-up. Datalogs permitted adjudication of 702 episodes, including 669 sustained monomorphic VT, 20 polymorphic VT, 10 supraventricular tachycardia, and 3 malsensing episodes. AATP terminated 39 of 69 (59% adjusted) sustained monomorphic VT in the fast VT zone, 509 of 590 (85% adjusted) in the VT zone, and 6 of 10 in the ventricular fibrillation zone. No supraventricular tachycardias converted to VT or ventricular fibrillation. No anomalous AATP behavior was observed.

Conclusions: The new AATP algorithm safely generated ATP sequences and controlled therapy progression in all zones without need for individualized programing.
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http://dx.doi.org/10.1161/CIRCEP.116.004823DOI Listing
September 2017

Ventricular pacing site separation by cardiac computed tomography: validation for the prediction of clinical response to cardiac resynchronization therapy.

Int J Cardiovasc Imaging 2017 Sep 29;33(9):1433-1442. Epub 2017 Mar 29.

Stephenson Cardiac Imaging Centre, Libin Cardiovascular Institute, Calgary, AB, Canada.

Cardiac Resynchronization Therapy (CRT) fails to provide benefit in up to one-third of patients. Maximizing the geographic separation of right and left ventricular pacing lead sites has been suggested as one way to improve response. Cardiac CT provides an opportunity to explore 3-dimensional inter-lead distance (ILD) measures for the prediction of CRT response. The objective of this study was to investigate associations between standardized measures of ILD by cardiac CT and echocardiographic response to CRT. Forty-two consecutive patients undergoing CRT had serial clinical and echocardiographic evaluations performed in addition to a post-procedural cardiac-gated CT with blinded measurement of direct and circumferential (via the myocardium) ILD measures. Clinical response to CRT, the primary clinical outcome, was defined as a ≥15% reduction in LVESV using echocardiography at 6-months. The mean age and ejection fraction was 63.6 ± 8.9 years and 25.2 ± 7.8%, respectively. The primary outcome occurred in 35 of 42 patients (83%). Both direct and circumferential CT-based ILD measures were associated with the primary outcome by univariate analysis. Receiver Operator Characteristic analysis identified Circumferential ILD to have the strongest predictive accuracy (AUC 0.78). Inter- and intra-observer reproducibility of CT-derived ILD measures was excellent. Circumferential ILD measures on cardiac CT are predictive of clinical response to CRT. Incorporation of these measures into the selection of optimal pacing targets, particularly from pre-procedural CT coronary vein imaging may be of therapeutic benefit and warrants further investigation.
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http://dx.doi.org/10.1007/s10554-017-1120-4DOI Listing
September 2017

Right Ventricular Ejection Fraction Is Incremental to Left Ventricular Ejection Fraction for the Prediction of Future Arrhythmic Events in Patients With Systolic Dysfunction.

Circ Arrhythm Electrophysiol 2017 01;10(1)

From the Stephenson Cardiac Imaging Centre (Y.M., B.H., C.P.L., A.G.H., J.W.) and Department of Cardiac Sciences (Y.M., B.H., M.P., C.P.L., A.G.H., J.W.), Libin Cardiovascular Institute of Alberta, University of Calgary, Canada; Department of Diagnostic Imaging, University of Calgary, Alberta, Canada (B.H., C.P.L., A.G.H., J.W.); and Department of Medicine, London Health Sciences Centre, Ontario, Canada (U.J., F.A., M.Z., M.B., J.S., R.Y.).

Background: Left ventricular ejection fraction remains the primary risk stratification tool used in the selection of patients for implantable cardioverter defibrillator therapy. However, this solitary marker fails to identify a substantial portion of patients experiencing sudden cardiac arrest. In this study, we examined the incremental value of considering right ventricular ejection fraction for the prediction of future arrhythmic events in patients with systolic dysfunction using the gold standard of cardiovascular magnetic resonance.

Methods And Results: Three hundred fourteen consecutive patients with ischemic cardiomyopathy or nonischemic dilated cardiomyopathy undergoing cardiovascular magnetic resonance were followed for the primary outcome of sudden cardiac arrest or appropriate implantable cardioverter defibrillator therapy. Blinded quantification of left ventricular and right ventricular (RV) volumes was performed from standard cine imaging. Quantification of fibrosis from late gadolinium enhancement imaging was incrementally performed. RV dysfunction was defined as right ventricular ejection fraction ≤45%. Among all patients (164 ischemic cardiomyopathy, 150 nonischemic dilated cardiomyopathy), the mean left ventricular ejection fraction was 32±12% (range, 6-54%) with mean right ventricular ejection fraction of 48±15% (range, 7-78%). At a median of 773 days, 49 patients (15.6%) experienced the primary outcome (9 sudden cardiac arrest, 40 appropriate implantable cardioverter defibrillator therapies). RV dysfunction was independently predictive of the primary outcome (hazard ratio=2.98; P=0.002). Among those with a left ventricular ejection fraction >35% (N=121; mean left ventricular ejection fraction, 45±6%), RV dysfunction provided an adjusted hazard ratio of 4.2 (P=0.02).

Conclusions: RV dysfunction is a strong, independent predictor of arrhythmic events. Among patients with mild to moderate LV dysfunction, a cohort greatly contributing to global sudden cardiac arrest burden, this marker provides robust discrimination of high- versus low-risk subjects.
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http://dx.doi.org/10.1161/CIRCEP.116.004067DOI Listing
January 2017

Objective criteria for septal fibrosis in non-ischemic dilated cardiomyopathy: validation for the prediction of future cardiovascular events.

J Cardiovasc Magn Reson 2016 Nov 14;18(1):82. Epub 2016 Nov 14.

Stephenson Cardiac Imaging Centre, Libin Cardiovascular Institute of Alberta, University of Calgary, #0700, SSB, Foothills Medical Centre, 1403-29th St. NW, Calgary, AB, T2N2T9, Canada.

Background: Expert subjective reporting of mid-wall septal fibrosis on late gadolinium enhancement (LGE) images has been shown to predict major cardiovascular outcomes in patients with non-ischemic dilated cardiomyopathy (NIDCM). This study aims to establish objective criteria for non-experts to report clinically relevant septal fibrosis and compare its performance by such readers versus experts for the prediction of cardiovascular events.

Methods: LGE cardiovascular magnetic resonance (CMR) was performed in 118 consecutive patients with NIDCM (mean age 57 ± 14, 42 % female) and the presence of septal fibrosis scored by expert readers. CMR-naive readers performed signal threshold-based LGE quantification by referencing mean values of remote tissue and applying these to a pre-defined anatomic region to measure septal fibrosis. All patients were followed for the primary composite outcome of cardiac mortality or appropriate implantable cardioverter-defibrillator (ICD) therapy.

Results: The mean LVEF was 32 ± 12 %. At a median follow-up of 1.9 years, 20 patients (17 %) experienced a primary composite outcome. Expert visual scoring identified 55 patients with septal fibrosis. Non-expert septal fibrosis quantification was highly reproducible and identified mean septal fibrosis burden for three measured thresholds as follows; 5SD: 2.9 ± 3.6 %, 3SD: 6.9 ± 6.3 %, and 2SD: 11.1 ± 7.5 % of the left ventricular (LV) mass, respectively. By ROC analysis, optimal thresholds for prediction of the primary outcome were; 5SD: 2.74 % (HR 8.7, p < 0.001), 3SD: 6.63 % (HR 5.7, p = 0.001) and 2SD: 10.15 % (HR 6.1, p = 0.001). By comparison, expert visual scoring provided a HR of 5.3 (p = 0.001). In adjusted analysis, objective quantification by a novice reader (>5SD threshold) was the strongest independent predictor of the primary outcome (HR 8.7) and provided improved risk reclassification beyond LVEF alone (NRI 0.54, 95 % CI 0.16-0.92, p = 0.005).

Conclusions: Novice readers were able to achieve superior risk prediction for future cardiovascular events versus experts using objective criteria for septal fibrosis in patients with NIDCM. Patients with a septal fibrosis burden >2.74 % of the LV mass (>5SD threshold) were at a 9-fold higher risk of cardiac death or appropriate ICD therapy versus those not meeting this criteria. As such, this study validates reproducible criteria applicable to all levels of expertise to identify NIDCM patients at high risk of future cardiovascular events.
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http://dx.doi.org/10.1186/s12968-016-0300-zDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5108079PMC
November 2016

Experience with bisoprolol in long-QT1 and long-QT2 syndrome.

J Interv Card Electrophysiol 2016 Nov 9;47(2):163-170. Epub 2016 Jul 9.

Heart Rhythm Services, Division of Cardiology, Department of Medicine, University of British Columbia, Vancouver, British Columbia, Canada.

Background: The protective effect of beta-blockers in patients with inherited Long-QT syndrome is well established. Recent reports have suggested that beta-blockers are not equally effective in Long-QT (LQT). Bisoprolol is an attractive candidate for use in LQT because of its cardioselective properties and favorable side-effect profile.

Methods: We performed a retrospective cohort study of 114 consecutive patients with gene-positive Long-QT syndrome type 1 (LQT1) or Long-QT syndrome type 2 (LQT2) treated with bisoprolol, nadolol or atenolol with a total of 580 person-years of follow-up. Electrocardiogram (ECG) parameters and cardiac events during follow-up were compared. In addition, exercise treadmill testing was performed in bisoprolol-treated patients.

Results: Fifty-nine patients were treated with bisoprolol, 39 with atenolol and 16 with nadolol. Overall, 59 % were females and 62 % had LQT1. Baseline heart rate and corrected QT (QTc) interval were similar between the groups. QTc shortening was observed in individuals on bisoprolol (ΔQTc -5 ± 31 ms; p = 0.049) and nadolol (ΔQTc -13 ± 16 ms; p = 0.02) but not on atenolol (ΔQTc +9 ± 24 ms; p = 0.16). Median follow-up was similar for bisoprolol and nadolol (3 years), but longer for atenolol (6 years; p = 0.03); one cardiac event occurred in the bisoprolol group (1.7 %) and two events occurred in the atenolol group (5.1 %; p = 0.45), whereas none occurred in nadolol-treated patients. Beta-blocker efficacy was not affected by the underlying genotype. The antiadrenergic effect of bisoprolol correlated with the reduction of peak heart rates at exercise testing.

Conclusions: Bisoprolol treatment results in QTc shortening in gene-positive LQT1 and LQT2 patients and is well tolerated during long-term administration. The equivalence of bisoprolol for protection from ventricular arrhythmia in LQT patients compared to established beta-blockers remains unknown. Further large-scale studies are required.
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http://dx.doi.org/10.1007/s10840-016-0161-2DOI Listing
November 2016

Canadian Registry of Implantable Electronic Device Outcomes: Surveillance of the Riata Lead Under Advisory.

Circ Arrhythm Electrophysiol 2016 10;9(10)

For the author affiliations, please see the Appendix.

Background: The Riata lead under advisory has posed a unique clinical scenario where inside-out abrasion results in externalization of conductor cables, with a higher risk of electrical failure. We developed a comprehensive registry to assist with clinical management of this lead.

Methods And Results: This Canadian registry reports the findings of 3763 (74.2% of all Riata leads in Canada) Riata leads under advisory, with a mean follow-up time of 8.9±1.5 years. The overall electrical failure rate was 5.2% at 8 years, with no difference between 7-French and 8-French lead models. Cable externalization was found to be more common in the 8-French model (12.3% versus 5.2%, P<0.0001) and was associated with a higher risk of electrical failure. Predictors of electrical lead failure included cable externalization, higher left ventricular ejection fraction, younger age, higher body mass index, and a passive fixation lead. One patient died due to electrical failure, a further 2 patients survived an event where the device failed to deliver high-voltage therapy. Major complications because of lead extraction were higher when compared with lead abandonment, no difference among lead model observed. Two deaths occurred as a consequence of lead extraction, in the context of an underlying infection.

Conclusions: The Riata lead under advisory has a steady electrical failure rate over time. There are identifiable predictors of lead failure that can assist with clinical decisions as to whether lead revision should be performed prophylactically.
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http://dx.doi.org/10.1161/CIRCEP.116.004282DOI Listing
October 2016

Real-World Assessment of Acute Left Ventricular Lead Implant Success and Complication Rates: Results from the Attain Success Clinical Trial.

Pacing Clin Electrophysiol 2016 Nov 4;39(11):1246-1253. Epub 2016 Oct 4.

Massachusetts General Hospital, Boston, Massachusetts.

Background: Left ventricular lead (LVL) implant success rates have historically ranged between 70.5% and 95.5%. To date, there are few large studies that evaluate LVL implant success utilizing a single family of delivery catheters and leads. The Attain Success study was a prospective nonrandomized multicenter global study with the main objectives of assessing single-system LVL implant success and complication rates.

Methods: Patients undergoing cardiac resynchronization therapy implantation were eligible for enrollment. There was no prespecified level of experience for investigator participation. LVL implant success and complication rates were assessed though 3 months of follow-up.

Results: A total of 2,014 patients (69.1 ± 12.0 years, 71% male and 38% atrial fibrillation) were enrolled from 114 centers with a follow-up of 3.5 ± 2.1 months. Coronary sinus cannulation success rate was 96.4% with Attain Family delivery catheters. Implant success rate for Attain Family leads using Attain Family catheters was 94.0%; overall LVL implant success rate was 97.1%. Median procedure time was 4 minutes for cannulation and 9 minutes for LVL placement. Median fluoroscopy time was 17 minutes and median contrast used was 25 cc. There were 55 catheter or LVL-related complications in 53 subjects; the majority were LVL dislodgements (34, 1.7%) and extracardiac stimulation (11, 0.5%). The Kaplan-Meier estimate of the 3-month complication probability was 2.6%.

Conclusion: This study represents the largest prospective evaluation of LVL implantation to date, revealing a high LVL implant success rate and low complication rate using a single family of leads and delivery catheters.
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http://dx.doi.org/10.1111/pace.12939DOI Listing
November 2016

Aerobic Fitness and Risk of Ventricular Arrhythmia Following Physical Exertion.

Can J Cardiol 2016 Apr 28;32(4):533-8. Epub 2015 Dec 28.

Department of Epidemiology and Biostatistics, Schulich Medicine and Dentistry, Western University, London, Ontario, Canada; Division of Cardiology, Western University, London, Ontario, Canada. Electronic address:

Background: Brief episodes of physical exertion are associated with an immediately greater risk of cardiovascular events. Previous studies on the risk of ventricular arrhythmia (VA) shortly after exertion have not assessed if this risk differs according to the level of aerobic fitness or sedentary behaviour. Therefore, we conducted a prospective cohort study of patients with implantable cardioverter-defibrillators (ICDs) with a nested case-crossover analysis to examine the risk of VA shortly after exertion and whether this risk is modified by aerobic fitness and sedentary behaviour.

Methods: Ninety-seven consecutive patients were recruited at the time of ICD implantation and 30 confirmed events occurred among patients who completed interviews about physical exertion preceding ICD therapy. We compared the frequency of exertion within an hour of ICD discharge to each patient's usual frequency of exertion reported at the time of ICD implantation.

Results: Within an hour of episodes of exertion, the risk of VA was 5.3 (95% confidence interval [CI], 2.7-10.6) times greater compared with periods of rest. The association was higher among patients with aerobic fitness below the median (relative risk [RR] = 17.5; 95% CI, 5.2-58.5) than for patients with aerobic fitness above the median (RR, 1.2; 95% CI, 0.4-4.2; P homogeneity = 0.002) and higher among patients who were sedentary (RR, 52.8; 95% CI, 10.1-277) compared with individuals who were not sedentary (RR, 3.2; 95% CI, 1.3-7.6; P homogeneity = 0.0002).

Conclusions: Within 1 hour of episodes of exertion, there is an increased risk of VA, especially among individuals with lower levels of aerobic fitness and with sedentary behaviour.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5087593PMC
http://dx.doi.org/10.1016/j.cjca.2015.12.026DOI Listing
April 2016

Atrial fibrillation management: evaluating rate vs rhythm control.

Expert Rev Cardiovasc Ther 2016 Jun 30;14(6):713-24. Epub 2016 Mar 30.

a Division of Cardiology, Department of Medicine , Western University , London , Canada.

Atrial fibrillation (AF) is an increasing global issue leading to increased hospitalizations, adverse health related events and mortality. This review focuses on the management of atrial fibrillation, in particular in the past decade, comparing two major strategies, rate or rhythm control. We evaluate the evidence for each strategy, pharmacological options and the increasing utilization of invasive techniques, in particular catheter ablation and use of implantable cardiac pacing devices. Pharmacological comparative trials evaluating both strategies have shown rate control being non-inferior to rhythm control for clinical outcomes of mortality and other cardiovascular events (including stroke). Catheter ablation techniques, involving radiofrequency ablation and recently cryoablation, have shown promising results in particular with paroxysmal AF. However, persistent AF provides ongoing challenges and will be a particular focus of continued research.
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http://dx.doi.org/10.1586/14779072.2016.1164033DOI Listing
June 2016

Atrial flutter and atrial fibrillation ablation - sequential or combined? A cost-benefit and risk analysis of primary prevention pulmonary vein ablation.

Heart Rhythm 2016 07 2;13(7):1441-8. Epub 2016 Mar 2.

Arrhythmia Service, University Hospital, Western University, London, Canada.

Background: Recent studies have tested the hypothesis that preventive pulmonary vein isolation (PVI) at time of atrial flutter ablation in patients who have not had atrial fibrillation (AF) will reduce future incidence of AF.

Objective: To model relative procedural costs, risks, and benefits of sequential versus combined ablation strategies.

Methods: The decision model compares a sequential ablation strategy of atrial flutter ablation, followed by future PVI if necessary, with an initial combined flutter and preventive PVI ablation strategy. Assumptions are AF incidence 20% per year, PVI success rate 70%, PVI complication rate 4%, atrial flutter complication rate 1%, and costs $13,056 for PVI and $8,466 for atrial flutter ablation.

Results: The sequential ablation strategy is less expensive, at 1.4 vs 1.6 expected flutter ablation equivalents (FAE) ($11,852 vs $13,545) per patient, and entails less average risk, at 2% vs 4%. A combined ablation strategy is more expensive if the relative cost of PVI is more than 24.6% higher than atrial flutter ablation. A combined ablation strategy has higher total risk if PVI procedural risk is 24.6% more than atrial flutter ablation.

Conclusions: Under base case assumptions of relative cost of PVI to flutter ablation 1.5 and relative risk 4, a sequential ablation approach has less total expected cost and less expected risk. There appears to be no compelling reason to adopt a combined ablation approach into standard practice. Nomograms are presented to allow the reader to assess which strategy is preferred according to local relative costs and risk.
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http://dx.doi.org/10.1016/j.hrthm.2016.02.018DOI Listing
July 2016

ALternate Site Cardiac ResYNChronization (ALSYNC): a prospective and multicentre study of left ventricular endocardial pacing for cardiac resynchronization therapy.

Eur Heart J 2016 Jul 18;37(27):2118-27. Epub 2016 Jan 18.

CHU Bordeaux, Bordeaux University, Bordeaux, France.

Aims: The ALternate Site Cardiac ResYNChronization (ALSYNC) study evaluated the feasibility and safety of left ventricular endocardial pacing (LVEP) using a market-released pacing lead implanted via a single pectoral access by a novel atrial transseptal lead delivery system.

Methods And Results: ALSYNC was a prospective clinical investigation with a minimum of 12-month follow-up in 18 centres of cardiac resynchronization therapy (CRT)-indicated patients, who had failed or were unsuitable for conventional CRT. The ALSYNC system comprises the investigational lead delivery system and LVEP lead. Patients required warfarin therapy post-implant. The primary study objective was safety at 6-month follow-up, which was defined as freedom from complications related to the lead delivery system, implant procedure, or the lead ≥70%. The ALSYNC study enrolled 138 patients. The LVEP lead implant success rate was 89.4%. Freedom from complications meeting the definition of primary endpoint was 82.2% at 6 months (95% CI 75.6-88.8%). In the study, 14 transient ischaemic attacks (9 patients, 6.8%), 5 non-disabling strokes (5 patients, 3.8%), and 23 deaths (17.4%) were observed. No death was from a primary endpoint complication. At 6 months, the New York Heart Association class improved in 59% of patients, and 55% had LV end-systolic volume reduction of 15% or greater. Those patients enrolled after CRT non-response showed similar improvement with LVEP.

Conclusions: The ALSYNC study demonstrates clinical feasibility, and provides an early indication of possible benefit and risk of LVEP.

Clinical Trial: NCT01277783.
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http://dx.doi.org/10.1093/eurheartj/ehv723DOI Listing
July 2016

Outcome of Apparently Unexplained Cardiac Arrest: Results From Investigation and Follow-Up of the Prospective Cardiac Arrest Survivors With Preserved Ejection Fraction Registry.

Circ Arrhythm Electrophysiol 2016 Jan;9(1):e003619

From the Division of Cardiology, Department of Medicine, University of British Columbia, Vancouver, BC, Canada (A.R.M.H., C.C., K.G., M.T.B., C.S., M.J., S.C., A.D.K.); Department of Cardiovascular Sciences, Libin Cardiovascular Institute, University of Calgary, Calgary, AB, Canada (B.G.); Division of Cardiology, Department of Medicine, Queen's University, Kingston, ON, Canada (C.S.S.); University of Ottawa Heart Institute, Ottawa, ON, Canada (D.H.B.); Division of Cardiology, Department of Medicine, Western University, London, ON, Canada (G.J.K., R.Y.); Department of Medicine, Quebec Heart and Lung Institute, Quebec City, QC, Canada (J.C.); Division of Cardiology, Department of Medicine, Population Health Research Institute, Hamilton, ON, Canada (J.S.H.); Department of Medicine, Montreal Heart Institute, Université de Montréal, Montreal, QC, Canada (M.T.); Division of Cardiology, Department of Medicine, QEII Health Sciences Center, Halifax, NS, Canada (M.G.); Division of Cardiology, Department of Medicine, University Health Network, Toronto, ON, Canada (M.H.G., V.S.C.); Division of Cardiology, Department of Medicine, St. Michael's Hospital, University of Toronto, Toronto, ON, Canada (P.A.); Division of Cardiology, Department of Medicine, Royal Jubilee Hospital, Victoria, BC, Canada (R.L.); and Division of Cardiology, Department of Pediatrics, BC Children's Hospital, Vancouver, BC, Canada (S.S.).

Background: The Cardiac Arrest Survivors with Preserved Ejection Fraction Registry (CASPER) enrolls patients with apparently unexplained cardiac arrest and no evident cardiac disease to identify the pathogenesis of cardiac arrest through systematic clinical testing. Exercise testing, drug provocation, advanced cardiac imaging, and genetic testing may be useful when a cause is not apparent.

Methods And Results: The first 200 survivors of unexplained cardiac arrest from 14 centers across Canada were evaluated to determine the results of investigation and follow-up (age, 48.6±14.7 years, 41% female). Patients were free of evidence of coronary artery disease, left ventricular dysfunction, or evident repolarization syndromes. Advanced testing determined a diagnosis in 34% of patients at baseline, with a diagnosis emerging during follow-up in 7% of patients. Of those who were diagnosed, 28 (35%) had an underlying structural condition and 53 (65%) had a primary electric disease. During a mean follow-up of 3.15±2.34 years, 23% of patients had either a shock or an appropriate antitachycardia pacing from their implantable cardioverter defibrillator, or both. The implantable cardioverter defibrillator appropriate intervention rate was 8.4% at 1 year and 18.1% at 3 years, with no clear difference between diagnosed and undiagnosed subjects, or between those diagnosed with a primary electric versus structural pathogenesis.

Conclusions: Obtaining a diagnosis in previously unexplained cardiac arrest patients requires systematic clinical testing and regular follow-up to unmask the cause. Nearly half of apparently unexplained cardiac arrest patients ultimately received a diagnosis, allowing for improved treatment and family screening. A substantial proportion of patients received appropriate implantable cardioverter defibrillator therapy during medium-term follow-up.

Clinical Trial Registration: URL: http://www.clinicaltrials.gov. Unique identifier: NCT00292032.
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http://dx.doi.org/10.1161/CIRCEP.115.003619DOI Listing
January 2016