Publications by authors named "Nick W F Linton"

30 Publications

  • Page 1 of 1

OpenEP: A Cross-Platform Electroanatomic Mapping Data Format and Analysis Platform for Electrophysiology Research.

Front Physiol 2021 26;12:646023. Epub 2021 Feb 26.

Imperial College London, London, United Kingdom.

Background: Electroanatomic mapping systems are used to support electrophysiology research. Data exported from these systems is stored in proprietary formats which are challenging to access and storage-space inefficient. No previous work has made available an open-source platform for parsing and interrogating this data in a standardized format. We therefore sought to develop a standardized, open-source data structure and associated computer code to store electroanatomic mapping data in a space-efficient and easily accessible manner.

Methods: A data structure was defined capturing the available anatomic and electrical data. OpenEP, implemented in MATLAB, was developed to parse and interrogate this data. Functions are provided for analysis of chamber geometry, activation mapping, conduction velocity mapping, voltage mapping, ablation sites, and electrograms as well as visualization and input/output functions. Performance benchmarking for data import and storage was performed. Data import and analysis validation was performed for chamber geometry, activation mapping, voltage mapping and ablation representation. Finally, systematic analysis of electrophysiology literature was performed to determine the suitability of OpenEP for contemporary electrophysiology research.

Results: The average time to parse clinical datasets was 400 ± 162 s per patient. OpenEP data was two orders of magnitude smaller than compressed clinical data (OpenEP: 20.5 ± 8.7 Mb, vs clinical: 1.46 ± 0.77 Gb). OpenEP-derived geometry metrics were correlated with the same clinical metrics (Area: = 0.7726, < 0.0001; Volume: = 0.5179, < 0.0001). Investigating the cause of systematic bias in these correlations revealed OpenEP to outperform the clinical platform in recovering accurate values. Both activation and voltage mapping data created with OpenEP were correlated with clinical values (mean voltage = 0.8708, < 0.001; local activation time = 0.8892, < 0.0001). OpenEP provides the processing necessary for 87 of 92 qualitatively assessed analysis techniques (95%) and 119 of 136 quantitatively assessed analysis techniques (88%) in a contemporary cohort of mapping studies.

Conclusions: We present the OpenEP framework for evaluating electroanatomic mapping data. OpenEP provides the core functionality necessary to conduct electroanatomic mapping research. We demonstrate that OpenEP is both space-efficient and accurately representative of the original data. We show that OpenEP captures the majority of data required for contemporary electroanatomic mapping-based electrophysiology research and propose a roadmap for future development.
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http://dx.doi.org/10.3389/fphys.2021.646023DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7952326PMC
February 2021

Targeting the ectopy-triggering ganglionated plexuses without pulmonary vein isolation prevents atrial fibrillation.

J Cardiovasc Electrophysiol 2021 Feb 19;32(2):235-244. Epub 2021 Jan 19.

Myocardial Function Section, National Heart and Lung Institute, Imperial College London, London, UK.

Background: Ganglionated plexuses (GPs) are implicated in atrial fibrillation (AF). Endocardial high-frequency stimulation (HFS) delivered within the local atrial refractory period can trigger ectopy and AF from specific GP sites (ET-GP). The aim of this study was to understand the role of ET-GP ablation in the treatment of AF.

Methods: Patients with paroxysmal AF indicated for ablation were recruited. HFS mapping was performed globally around the left atrium to identify ET-GP. ET-GP was defined as atrial ectopy or atrial arrhythmia triggered by HFS. All ET-GP were ablated, and PVs were left electrically connected. Outcomes were compared with a control group receiving pulmonary vein isolation (PVI). Patients were followed-up for 12 months with multiple 48-h Holter ECGs. Primary endpoint was ≥30 s AF/atrial tachycardia in ECGs.

Results: In total, 67 patients were recruited and randomized to ET-GP ablation (n = 39) or PVI (n = 28). In the ET-GP ablation group, 103 ± 28 HFS sites were tested per patient, identifying 21 ± 10 (20%) GPs. ET-GP ablation used 23.3 ± 4.1 kWs total radiofrequency (RF) energy per patient, compared with 55.7 ± 22.7 kWs in PVI (p = <.0001). Duration of procedure was 3.7 ± 1.0 and 3.3 ± 0.7 h in ET-GP ablation group and PVI, respectively (p = .07). Follow-up at 12 months showed that 61% and 49% were free from ≥30 s of AF/AT with PVI and ET-GP ablation respectively (log-rank p = .27).

Conclusions: It is feasible to perform detailed global functional mapping with HFS and ablate ET-GP to prevent AF. This provides direct evidence that ET-GPs are part of the AF mechanism. The lower RF requirement implies that ET-GP targets the AF pathway more specifically.
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http://dx.doi.org/10.1111/jce.14870DOI Listing
February 2021

Electrocardiographic predictors of successful resynchronization of left bundle branch block by His bundle pacing.

J Cardiovasc Electrophysiol 2021 Feb 4;32(2):428-438. Epub 2021 Jan 4.

National Heart and Lung Institute, Imperial College London, Hammersmith Hospital, London, UK.

Background: His bundle pacing (HBP) is an alternative to biventricular pacing (BVP) for delivering cardiac resynchronization therapy (CRT) in patients with heart failure and left bundle branch block (LBBB). It is not known whether ventricular activation times and patterns achieved by HBP are equivalent to intact conduction systems and not all patients with LBBB are resynchronized by HBP.

Objective: To compare activation times and patterns of His-CRT with BVP-CRT, LBBB and intact conduction systems.

Methods: In patients with LBBB, noninvasive epicardial mapping (ECG imaging) was performed during BVP and temporary HBP. Intrinsic activation was mapped in all subjects. Left ventricular activation times (LVAT) were measured and epicardial propagation mapping (EPM) was performed, to visualize epicardial wavefronts. Normal activation pattern and a normal LVAT range were determined from normal subjects.

Results: Forty-five patients were included, 24 with LBBB and LV impairment, and 21 with normal 12-lead ECG and LV function. In 87.5% of patients with LBBB, His-CRT successfully shortened LVAT by ≥10 ms. In 33.3%, His-CRT resulted in complete ventricular resynchronization, with activation times and patterns indistinguishable from normal subjects. EPM identified propagation discontinuity artifacts in 83% of patients with LBBB. This was the best predictor of whether successful resynchronization was achieved by HBP (logarithmic odds ratio, 2.19; 95% confidence interval, 0.07-4.31; p = .04).

Conclusion: Noninvasive electrocardiographic mapping appears to identify patients whose LBBB can be resynchronized by HBP. In contrast to BVP, His-CRT may deliver the maximum potential ventricular resynchronization, returning activation times, and patterns to those seen in normal hearts.
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http://dx.doi.org/10.1111/jce.14845DOI Listing
February 2021

Discriminating electrocardiographic responses to His-bundle pacing using machine learning.

Cardiovasc Digit Health J 2020 Jul-Aug;1(1):11-20

National Heart and Lung Institute, Imperial College London, Hammersmith Hospital, London, United Kingdom.

Background: His-bundle pacing (HBP) has emerged as an alternative to conventional ventricular pacing because of its ability to deliver physiological ventricular activation. Pacing at the His bundle produces different electrocardiographic (ECG) responses: selective His-bundle pacing (S-HBP), non-selective His bundle pacing (NS-HBP), and myocardium-only capture (MOC). These 3 capture types must be distinguished from each other, which can be challenging and time-consuming even for experts.

Objective: The purpose of this study was to use artificial intelligence (AI) in the form of supervised machine learning using a convolutional neural network (CNN) to automate HBP ECG interpretation.

Methods: We identified patients who had undergone HBP and extracted raw 12-lead ECG data during S-HBP, NS-HBP, and MOC. A CNN was trained, using 3-fold cross-validation, on 75% of the segmented QRS complexes labeled with their capture type. The remaining 25% was kept aside as a testing dataset.

Results: The CNN was trained with 1297 QRS complexes from 59 patients. Cohen kappa for the neural network's performance on the 17-patient testing set was 0.59 (95% confidence interval 0.30 to 0.88; <.0001), with an overall accuracy of 75%. The CNN's accuracy in the 17-patient testing set was 67% for S-HBP, 71% for NS-HBP, and 84% for MOC.

Conclusion: We demonstrated proof of concept that a neural network can be trained to automate discrimination between HBP ECG responses. When a larger dataset is trained to higher accuracy, automated AI ECG analysis could facilitate HBP implantation and follow-up and prevent complications resulting from incorrect HBP ECG analysis.
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http://dx.doi.org/10.1016/j.cvdhj.2020.07.001DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7484933PMC
September 2020

Improving ultrasound video classification: an evaluation of novel deep learning methods in echocardiography.

J Med Artif Intell 2020 Mar;3

National Heart and Lung Institute, Imperial College London, Hammersmith Hospital, London, UK.

Echocardiography is the commonest medical ultrasound examination, but automated interpretation is challenging and hinges on correct recognition of the 'view' (imaging plane and orientation). Current state-of-the-art methods for identifying the view computationally involve 2-dimensional convolutional neural networks (CNNs), but these merely classify individual frames of a video in isolation, and ignore information describing the movement of structures throughout the cardiac cycle. Here we explore the efficacy of novel CNN architectures, including time-distributed networks and two-stream networks, which are inspired by advances in human action recognition. We demonstrate that these new architectures more than halve the error rate of traditional CNNs from 8.1% to 3.9%. These advances in accuracy may be due to these networks' ability to track the movement of specific structures such as heart valves throughout the cardiac cycle. Finally, we show the accuracies of these new state-of-the-art networks are approaching expert agreement (3.6% discordance), with a similar pattern of discordance between views.
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http://dx.doi.org/10.21037/jmai.2019.10.03DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7100611PMC
March 2020

Granger Causality-Based Analysis for Classification of Fibrillation Mechanisms and Localization of Rotational Drivers.

Circ Arrhythm Electrophysiol 2020 03 16;13(3):e008237. Epub 2020 Feb 16.

National Heart & Lung Institute, Imperial College London, United Kingdom (B.S.H., X.L., N.A.Q., I.M., R.A.C., Z.I.W., N.W.F.L., P.B.L., P.K., N.S.P., F.S.N.).

Background: The mechanisms sustaining myocardial fibrillation remain disputed, partly due to a lack of mapping tools that can accurately identify the mechanism with low spatial resolution clinical recordings. Granger causality (GC) analysis, an econometric tool for quantifying causal relationships between complex time-series, was developed as a novel fibrillation mapping tool and adapted to low spatial resolution sequentially acquired data.

Methods: Ventricular fibrillation (VF) optical mapping was performed in Langendorff-perfused Sprague-Dawley rat hearts (n=18), where novel algorithms were developed using GC-based analysis to (1) quantify causal dependence of neighboring signals and plot GC vectors, (2) quantify global organization with the causality pairing index, a measure of neighboring causal signal pairs, and (3) localize rotational drivers (RDs) by quantifying the circular interdependence of neighboring signals with the circular interdependence value. GC-based mapping tools were optimized for low spatial resolution from downsampled optical mapping data, validated against high-resolution phase analysis and further tested in previous VF optical mapping recordings of coronary perfused donor heart left ventricular wedge preparations (n=12), and adapted for sequentially acquired intracardiac electrograms during human persistent atrial fibrillation mapping (n=16).

Results: Global VF organization quantified by causality pairing index showed a negative correlation at progressively lower resolutions (50% resolution: =0.006, =0.38, 12.5% resolution, =0.004, =0.41) with a phase analysis derived measure of disorganization, locations occupied by phase singularities. In organized VF with high causality pairing index values, GC vector mapping characterized dominant propagating patterns and localized stable RDs, with the circular interdependence value showing a significant difference in driver versus nondriver regions (0.91±0.05 versus 0.35±0.06, =0.0002). These findings were further confirmed in human VF. In persistent atrial fibrillation, a positive correlation was found between the causality pairing index and presence of stable RDs (=0.0005,=0.56). Fifty percent of patients had RDs, with a low incidence of 0.9±0.3 RDs per patient.

Conclusions: GC-based fibrillation analysis can measure global fibrillation organization, characterize dominant propagating patterns, and map RDs using low spatial resolution sequentially acquired data.
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http://dx.doi.org/10.1161/CIRCEP.119.008237DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7069398PMC
March 2020

Ripple-AT Study: A Multicenter and Randomized Study Comparing 3D Mapping Techniques During Atrial Tachycardia Ablations.

Circ Arrhythm Electrophysiol 2019 08 9;12(8):e007394. Epub 2019 Aug 9.

Imperial College Healthcare, London (V.L., M.K.-W., G.K., P.B.L., N.S.P., N.Q., Z.W., N.W.F.L., P.K.).

Background: Ripple mapping (RM) is an alternative approach to activation mapping of atrial tachycardia (AT) that avoids electrogram annotation. We tested whether RM is superior to conventional annotation based local activation time (LAT) mapping for AT diagnosis in a randomized and multicenter study.

Methods: Patients with AT were randomized to either RM or LAT mapping using the CARTO3v4 CONFIDENSE system. Operators determined the diagnosis using the assigned 3D mapping arm alone, before being permitted a single confirmatory entrainment manuever if needed. A planned ablation lesion set was defined. The primary end point was AT termination with delivery of the planned ablation lesion set. The inability to terminate AT with this first lesion set, the use of more than one entrainment manuever, or the need to crossover to the other mapping arm was defined as failure to achieve the primary end point.

Results: One hundred five patients from 7 centers were recruited with 22 patients excluded due to premature AT termination, noninducibility or left atrial appendage thrombus. Eighty-three patients (pts; RM=42, LAT=41) completed mapping and ablation within the 2 groups of similar characteristics (RM versus LAT: prior ablation or cardiac surgery n=35 [83%] versus n=35 [85%], P=0.80). The primary end point occurred in 38/42 pts (90%) in the RM group and 29/41pts (71%) in the LAT group (P=0.045). This was achieved without any entrainment in 31/42 pts (74%) with RM and 18/41 pts (44%) with LAT (P=0.01). Of those patients who failed to achieve the primary end point, AT termination was achieved in 9/12 pts (75%) in the LAT group following crossover to RM with entrainment, but 0/4 pts (0%) in the RM group crossing over to LAT mapping with entrainment (P=0.04).

Conclusions: RM is superior to LAT mapping on the CARTO3v4 CONFIDENSE system in guiding ablation to terminate AT with the first lesion set and with reduced entrainment to assist diagnosis.

Clinical Trials Registration: https://www.clinicaltrials.gov. Unique identifier: NCT02451995.
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http://dx.doi.org/10.1161/CIRCEP.118.007394DOI Listing
August 2019

Quantification of Electromechanical Coupling to Prevent Inappropriate Implantable Cardioverter-Defibrillator Shocks.

JACC Clin Electrophysiol 2019 06 27;5(6):705-715. Epub 2019 Mar 27.

Department of Cardiology, Imperial College Hospitals National Health Service Trust, London, United Kingdom; National Heart and Lung Institute, Imperial College London, London, United Kingdom.

Objectives: This study sought to test specialized processing of laser Doppler signals for discriminating ventricular fibrillation (VF) from common causes of inappropriate therapies.

Background: Inappropriate implantable cardioverter-defibrillator (ICD) therapies remain a clinically important problem associated with morbidity and mortality. Tissue perfusion biomarkers, implemented to assist automated diagnosis of VF, sometimes mistake artifacts and random noise for perfusion, which could lead to shocks being inappropriately withheld.

Methods: The study tested a novel processing algorithm that combines electrogram data and laser Doppler perfusion monitoring as a method for assessing circulatory status. Fifty patients undergoing VF induction during ICD implantation were recruited. Noninvasive laser Doppler and continuous electrograms were recorded during both sinus rhythm and VF. Two additional scenarios that might have led to inappropriate shocks were simulated for each patient: ventricular lead fracture and T-wave oversensing. The laser Doppler was analyzed using 3 methods for reducing noise: 1) running mean; 2) oscillatory height; and 3) a novel quantification of electromechanical coupling which gates laser Doppler relative to electrograms. In addition, the algorithm was tested during exercise-induced sinus tachycardia.

Results: Only the electromechanical coupling algorithm found a clear perfusion cut off between sinus rhythm and VF (sensitivity and specificity of 100%). Sensitivity and specificity remained at 100% during simulated lead fracture and electrogram oversensing. (Area under the curve running mean: 0.91; oscillatory height: 0.86; electromechanical coupling: 1.00). Sinus tachycardia did not cause false positive results.

Conclusions: Quantifying the coupling between electrical and perfusion signals increases reliability of discrimination between VF and artifacts that ICDs may interpret as VF. Incorporating such methods into future ICDs may safely permit reductions of inappropriate shocks.
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http://dx.doi.org/10.1016/j.jacep.2019.01.025DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6597902PMC
June 2019

Evaluation of a new algorithm for tracking activation during atrial fibrillation using multipolar catheters in humans.

J Cardiovasc Electrophysiol 2019 09 2;30(9):1464-1474. Epub 2019 Jul 2.

Department of Bioengineering, Imperial College London, London, UK.

Background: Conventional mapping techniques during atrial fibrillation (AF) are difficult to apply because of cycle length irregularity. Mapping studies are usually restricted to short durations of AF in limited regions because of the laborious manual annotation of local activation time (LAT). The purpose of this study was to test an automated algorithm to map activation during AF, with comparable accuracy to manual annotation.

Methods: Left atrial (LA) mapping was performed using a 20-pole double loop catheter (AFocusII) in 30-second data segments from 16 patients. The new algorithm (RETRO-Mapping) was designed to detect wavefront propagation between electrodes, and display activating wavefronts on a two-dimensional representation of the catheter. Activation patterns were validated against their bipolar electrograms and with isochronal maps. The mapping protocol was approved by the research ethics committee (13/LO1169 and 14/LO1367).

Results: During AF, uniform wavefront activation direction (mean ± SD, degrees) from manually constructed isochronal maps was comparable to RETRO-Propagation Map (RETRO-PM) and RETRO-Automated Direction (RETRO-AD): 1 ± 6.9 for RETRO-PM; and 2 ± 6.6 for RETRO-AD. There was no significant difference in activation direction assigned to 1373 uniform wavefronts during AF when comparing RETRO-PM with RETRO-AD (Bland-Altman mean difference: -0.1 degrees; limits of agreement: -8.0 to 8.3; 95% CI -0.4 to 0.2; (r = 0.01) R2 = < 0.005; P = .77).

Conclusion: We have developed and validated a new technique to map activation during AF. This technique shows comparable accuracy to that of conventional isochronal mapping with careful manual adjustment of LAT.
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http://dx.doi.org/10.1111/jce.14033DOI Listing
September 2019

Voltage during atrial fibrillation is superior to voltage during sinus rhythm in localizing areas of delayed enhancement on magnetic resonance imaging: An assessment of the posterior left atrium in patients with persistent atrial fibrillation.

Heart Rhythm 2019 09 3;16(9):1357-1367. Epub 2019 Jun 3.

Imperial College Healthcare NHS Trust, Hammersmith Hospital, London, United Kingdom. Electronic address:

Background: Bipolar electrogram voltage during sinus rhythm (V) has been used as a surrogate for atrial fibrosis in guiding catheter ablation of persistent atrial fibrillation (AF), but the fixed rate and wavefront characteristics present during sinus rhythm may not accurately reflect underlying functional vulnerabilities responsible for AF maintenance.

Objective: The purpose of this study was determine whether, given adequate temporal sampling, the spatial distribution of mean AF voltage (V) better correlates with delayed-enhancement magnetic resonance imaging (MRI-DE)-detected atrial fibrosis than V.

Methods: AF was mapped (8 seconds) during index ablation for persistent AF (20 patients) using a 20-pole catheter (660 ± 28 points/map). After cardioversion, V was mapped (557 ± 326 points/map). Electroanatomic and MRI-DE maps were co-registered in 14 patients.

Results: The time course of V was assessed from 1-40 AF cycles (∼8 seconds) at 1113 locations. V stabilized with sampling >4 seconds (mean voltage error 0.05 mV). Paired point analysis of V from segments acquired 30 seconds apart (3667 sites; 15 patients) showed strong correlation (r = 0.95; P <.001). Delayed enhancement (DE) was assessed across the posterior left atrial (LA) wall, occupying 33% ± 13%. V distributions were (median [IQR]) 0.21 [0.14-0.35] mV in DE vs 0.52 [0.34-0.77] mV in non-DE regions. V distributions were 1.34 [0.65-2.48] mV in DE vs 2.37 [1.27-3.97] mV in non-DE. V threshold of 0.35 mV yielded sensitivity of 75% and specificity of 79% in detecting MRI-DE compared with 63% and 67%, respectively, for V (1.8-mV threshold) CONCLUSION: The correlation between low-voltage and posterior LA MRI-DE is significantly improved when acquired during AF vs sinus rhythm. With adequate sampling, mean AF voltage is a reproducible marker reflecting the functional response to the underlying persistent AF substrate.
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http://dx.doi.org/10.1016/j.hrthm.2019.05.032DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6722483PMC
September 2019

His Resynchronization Versus Biventricular Pacing in Patients With Heart Failure and Left Bundle Branch Block.

J Am Coll Cardiol 2018 12;72(24):3112-3122

National Heart and Lung Institute, Imperial College London, London, United Kingdom.

Background: His bundle pacing is a new method for delivering cardiac resynchronization therapy (CRT).

Objectives: The authors performed a head-to-head, high-precision, acute crossover comparison between His bundle pacing and conventional biventricular CRT, measuring effects on ventricular activation and acute hemodynamic function.

Methods: Patients with heart failure and left bundle branch block referred for conventional biventricular CRT were recruited. Using noninvasive epicardial electrocardiographic imaging, the authors identified patients in whom His bundle pacing shortened left ventricular activation time. In these patients, the authors compared the hemodynamic effects of His bundle pacing against biventricular pacing using a high-multiple repeated alternation protocol to minimize the effect of noise, as well as comparing effects on ventricular activation.

Results: In 18 of 23 patients, left ventricular activation time was significantly shortened by His bundle pacing. Seventeen patients had a complete electromechanical dataset. In them, His bundle pacing was more effective at delivering ventricular resynchronization than biventricular pacing: greater reduction in QRS duration (-18.6 ms; 95% confidence interval [CI]: -31.6 to -5.7 ms; p = 0.007), left ventricular activation time (-26 ms; 95% CI: -41 to -21 ms; p = 0.002), and left ventricular dyssynchrony index (-11.2 ms; 95% CI: -16.8 to -5.6 ms; p < 0.001). His bundle pacing also produced a greater acute hemodynamic response (4.6 mm Hg; 95% CI: 0.2 to 9.1 mm Hg; p = 0.04). The incremental activation time reduction with His bundle pacing over biventricular pacing correlated with the incremental hemodynamic improvement with His bundle pacing over biventricular pacing (R = 0.70; p = 0.04).

Conclusions: His resynchronization delivers better ventricular resynchronization, and greater improvement in hemodynamic parameters, than biventricular pacing.
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http://dx.doi.org/10.1016/j.jacc.2018.09.073DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6290113PMC
December 2018

A novel approach to mapping the atrial ganglionated plexus network by generating a distribution probability atlas.

J Cardiovasc Electrophysiol 2018 12 5;29(12):1624-1634. Epub 2018 Oct 5.

Myocardial Function Section, Imperial Centre for Translational and Experimental Medicine, Imperial College London, London, UK.

Introduction: The ganglionated plexuses (GPs) of the intrinsic cardiac autonomic system are implicated in arrhythmogenesis. GP localization by stimulation of the epicardial fat pads to produce atrioventricular dissociating (AVD) effects is well described. We determined the anatomical distribution of the left atrial GPs that influence atrioventricular (AV) dissociation.

Methods And Results: High frequency stimulation was delivered through a Smart-Touch catheter in the left atrium of patients undergoing atrial fibrillation (AF) ablation. Three dimensional locations of points tested throughout the entire chamber were recorded on the CARTO™ system. Impact on the AV conduction was categorized as ventricular asystole, bradycardia, or no effect. CARTO maps were exported, registered, and transformed onto a reference left atrial geometry using a custom software, enabling data from multiple patients to be overlaid. In 28 patients, 2108 locations were tested and 283 sites (13%) demonstrated (AVD-GP) effects. There were 10 AVD-GPs (interquartile range, 11.5) per patient. Eighty percent (226) produced asystole and 20% (57) showed bradycardia. The distribution of the two groups was very similar. Highest probability of AVD-GPs (>20%) was identified in: inferoseptal portion (41%) and right inferior pulmonary vein base (30%) of the posterior wall, right superior pulmonary vein antrum (31%).

Conclusion: It is feasible to map the entire left atrium for AVD-GPs before AF ablation. Aggregated data from multiple patients, producing a distribution probability atlas of AVD-GPs, identified three regions with a higher likelihood for finding AVD-GPs and these matched the histological descriptions. This approach could be used to better characterize the autonomic network.
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http://dx.doi.org/10.1111/jce.13723DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6369684PMC
December 2018

Intra-Atrial Conduction Delay Revealed by Multisite Incremental Atrial Pacing is an Independent Marker of Remodeling in Human Atrial Fibrillation.

JACC Clin Electrophysiol 2017 09;3(9):1006-1017

Division of Imaging Sciences and Biomedical Imaging, King's College London, London, United Kingdom.

Objectives: This study sought to characterize direction-dependent and coupling interval-dependent changes in left atrial conduction and electrogram morphology in uniformly classified patients with paroxysmal atrial fibrillation (AF) and normal bipolar voltage mapping.

Background: Although AF classifications are based on arrhythmia duration, the clinical course, and treatment response vary between patients within these groups. Electrophysiological mechanisms responsible for this variability are incompletely described.

Methods: Intracardiac contact mapping during incremental atrial pacing was used to characterize atrial conduction, activation dispersion, and electrogram morphology in 15 consecutive paroxysmal AF patients undergoing first-time pulmonary vein isolation. Outcome measures were vulnerability to AF induction at electrophysiology study and 2-year follow-up for arrhythmia recurrence.

Results: Conduction delay showed a bimodal distribution, occurring at either long (high right atrium pacing: 326 ± 13 ms; coronary sinus pacing: 319 ± 16 ms) or short (high right atrium pacing: 275 ± 11 ms; coronary sinus pacing: 271 ± 11 ms) extrastimulus coupling intervals. Arrhythmia recurrence was found only in patients with conduction delay at long extrastimulus coupling intervals, and patients with inducible AF were characterized by increased activation dispersion (activation dispersion time: 168 ± 29 ms vs. 136 ± 11 ms). Electrogram voltage and duration varied throughout the left atrium, between patients, and with pacing site but were not correlated with AF vulnerability or arrhythmia recurrence.

Conclusions: Within the single clinical entity of paroxysmal AF, incremental atrial pacing identified a spectrum of activation patterns correlating with AF vulnerability and arrhythmia recurrence. In contrast, electrogram morphology (characterized by electrogram voltage and duration) was highly variable and not associated with AF vulnerability or recurrence. An improved understanding of the electrical phenotype in AF could lead to improved mechanistic classifications.
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http://dx.doi.org/10.1016/j.jacep.2017.02.012DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5612260PMC
September 2017

Visualizing Localized Reentry With Ultra-High Density Mapping in Iatrogenic Atrial Tachycardia: Beware Pseudo-Reentry.

Circ Arrhythm Electrophysiol 2017 Apr;10(4)

From the Department of Cardiology, Imperial College Healthcare NHS Trust, Hammersmith Hospital, London, United Kingdom (V.L., M.S., K.L., N.Q., F.S.N., S.A.H., S.M.A.S., L.M.-L., E.L., I.W., M.K.-W., D.C.L., N.W.F.L., Z.W., P.K., D.W.D., N.S.P., P.B.L.); and Boston Scientific Ltd, Marlborough, MA (N.B., F.G.).

Background: The activation pattern of localized reentry (LR) in atrial tachycardia remains incompletely understood. We used the ultra-high density Rhythmia mapping system to study activation patterns in LR.

Methods And Results: LR was suggested by small rotatory activations (carousels) containing the full spectrum of the color-coded map. Twenty-three left-sided atrial tachycardias were mapped in 15 patients (age: 64±11 years). 16 253±9192 points were displayed per map, collected over 26±14 minutes. A total of 50 carousels were identified (median 2; quartiles 1-3 per map), although this represented LR in only n=7 out of 50 (14%): here, rotation occurred around a small area of scar (<0.03 mV; 12±6 mm diameter). In LR, electrograms along the carousel encompassed the full tachycardia cycle length, and surrounding activation moved away from the carousel in all directions. Ablating fractionated electrograms (117±18 ms; 44±13% of tachycardia cycle length) within the carousel interrupted the tachycardia in every LR case. All remaining carousels were pseudo-reentrant (n=43/50 [86%]) occurring in areas of wavefront collision (n=21; median 0.5; quartiles 0-2 per map) or as artifact because of annotation of noise or interpolation in areas of incomplete mapping (n=22; median 1, quartiles 0-2 per map). Pseudo-reentrant carousels were incorrectly ablated in 5 cases having been misinterpreted as LR.

Conclusions: The activation pattern of LR is of small stable rotational activations (carousels), and this drove 30% (7/23) of our postablation atrial tachycardias. However, this appearance is most often pseudo-reentrant and must be differentiated by interpretation of electrograms in the candidate circuit and activation in the wider surrounding region.
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http://dx.doi.org/10.1161/CIRCEP.116.004724DOI Listing
April 2017

Simultaneous display of multiple three-dimensional electrophysiological datasets (dot mapping).

Europace 2017 Oct;19(10):1743-1749

Division of Imaging Sciences and Biomedical Imaging, King's College London, 4th Floor, North Wing, St. Thomas' Hospital, 249 Westminster Bridge Road, London SE1 7EH, UK.

Aims: Complex ablation procedures are supported by accurate representation of an increasing variety of electrophysiological and imaging data within electroanatomic mapping systems (EMS). This study aims to develop a novel method for representing multiple complementary datasets on a single cardiac chamber model. Validation of the system and its application to both atrial and ventricular arrhythmias is examined.

Methods And Results: Dot mapping was conceived to display multiple datasets by utilizing quantitative surface shading to represent one dataset and finely spaced dots to represent others. Dot positions are randomized within triangular (surface meshes) or tetrahedral (volumetric meshes) simplices making the approach directly transferrable to contemporary EMS. Test data representing uniform electrical activation (n = 10) and focal scarring (n = 10) were used to test dot mapping data perception accuracy. User experience of dot mapping with atrial and ventricular clinical data is evaluated. Dot mapping ensured constant screen dot density for regions of uniform dataset values, regardless of user manipulation of the cardiac chamber. Perception accuracy of dot mapping was equivalent to colour mapping for both propagation direction (1.5 ± 1.8 vs. 4.8 ± 5.3°, P = 0.24) and focal source localization (1.1 ± 0.7 vs. 1.4 ± 0.5 mm, P = 0.88). User acceptance testing revealed equivalent diagnostic accuracy and display fidelity when compared with colour mapping.

Conclusion: Dot mapping provides the unique ability to display multiple datasets from multiple sources on a single cardiac chamber model. The visual combination of multiple datasets may facilitate interpretation of complex electrophysiological and imaging data.
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http://dx.doi.org/10.1093/europace/euw190DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5834094PMC
October 2017

A Prospective Study of Ripple Mapping the Post-Infarct Ventricular Scar to Guide Substrate Ablation for Ventricular Tachycardia.

Circ Arrhythm Electrophysiol 2016 06;9(6)

From the Imperial College Healthcare NHS Trust, London, United Kingdom.

Background: Post-infarct ventricular tachycardia is associated with channels of surviving myocardium within scar characterized by fractionated and low-amplitude signals usually occurring late during sinus rhythm. Conventional automated algorithms for 3-dimensional electro-anatomic mapping cannot differentiate the delayed local signal of conduction within the scar from the initial far-field signal generated by surrounding healthy tissue. Ripple mapping displays every deflection of an electrogram, thereby providing fully informative activation sequences. We prospectively used CARTO-based ripple maps to identify conducting channels as a target for ablation.

Methods And Results: High-density bipolar left ventricular endocardial electrograms were collected using CARTO3v4 in sinus rhythm or ventricular pacing and reviewed for ripple mapping conducting channel identification. Fifteen consecutive patients (median age 68 years, left ventricular ejection fraction 30%) were studied (6 month preprocedural implantable cardioverter defibrillator therapies: median 19 ATP events [Q1-Q3=4-93] and 1 shock [Q1-Q3=0-3]). Scar (<1.5 mV) occupied a median 29% of the total surface area (median 540 points collected within scar). A median of 2 ripple mapping conducting channels were seen within each scar (length 60 mm; initial component 0.44 mV; delayed component 0.20 mV; conduction 55 cm/s). Ablation was performed along all identified ripple mapping conducting channels (median 18 lesions) and any presumed interconnected late-activating sites (median 6 lesions; Q1-Q3=2-12). The diastolic isthmus in ventricular tachycardia was mapped in 3 patients and colocated within the ripple mapping conducting channels identified. Ventricular tachycardia was noninducible in 85% of patients post ablation, and 71% remain free of ventricular tachycardia recurrence at 6-month median follow-up.

Conclusions: Ripple mapping can be used to identify conduction channels within scar to guide functional substrate ablation.
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http://dx.doi.org/10.1161/CIRCEP.116.004072DOI Listing
June 2016

A Prospective Study of Ripple Mapping in Atrial Tachycardias: A Novel Approach to Interpreting Activation in Low-Voltage Areas.

Circ Arrhythm Electrophysiol 2016 Jan;9(1):e003582

From the Department of Cardiac Electrophysiology, Imperial College Healthcare NHS Trust, London, United Kingdom.

Background: Post ablation atrial tachycardias are characterized by low-voltage signals that challenge current mapping methods. Ripple mapping (RM) displays every electrogram deflection as a bar moving from the cardiac surface, resulting in the impression of propagating wavefronts when a series of bars move consecutively. RM displays fractionated signals in their entirety thereby helping to identify propagating activation in low-voltage areas from nonconducting tissue. We prospectively used RM to study tachycardia activation in the previously ablated left atrium.

Methods And Results: Patients referred for atrial tachycardia ablation underwent dense electroanatomic point collection using CARTO3v4. RM was played over a bipolar voltage map and used to determine the voltage "activation threshold" that differentiated functional low voltage from nonconducting areas for each map. Ablation was guided by RM, but operators could perform entrainment or review the isochronal activation map for diagnostic uncertainty. Twenty patients were studied. Median RM determined activation threshold was 0.3 mV (0.19-0.33), with nonconducting tissue covering 33±9% of the mapped surface. All tachycardias crossed an isthmus (median, 0.52 mV, 13 mm) bordered by nonconducting tissue (70%) or had a breakout source (median, 0.35 mV) moving away from nonconducting tissue (30%). In reentrant circuits (14/20) the path length was measured (87-202 mm), with 9 of 14 also supporting a bystander circuit (path lengths, 147-234 mm). In breakout tachycardias, splitting of wavefronts resulted in 2 to 4 incomplete circuits. RM-guided ablation interrupted the tachycardia in 19 of 20 cases with the first ablation set.

Conclusions: RM helps to define activation through low-voltage regions and aids ablation of atrial tachycardias.
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http://dx.doi.org/10.1161/CIRCEP.115.003582DOI Listing
January 2016

Atrioventricular Optimized Direct His Bundle Pacing Improves Acute Hemodynamic Function in Patients With Heart Failure and PR Interval Prolongation Without Left Bundle Branch Block.

JACC Clin Electrophysiol 2015 Dec 23;1(6):582-591. Epub 2015 Oct 23.

National Heart & Lung Institute, Imperial College London, London, United Kingdom; Imperial College Healthcare NHS Trust, Hammersmith Hospital, London, United Kingdom.

Objectives: The purpose of this study was to investigate whether heart failure patients with narrow QRS duration (or right bundle branch block) but with long PR interval gain acute hemodynamic benefit from atrioventricular (AV) optimization. We tested this with biventricular pacing and (to deliver pure AV shortening) direct His bundle pacing.

Background: Benefits of pacing for heart failure have previously been indicated by acute hemodynamic studies and verified in outcome studies. A new target for pacing in heart failure may be PR interval prolongation, which is associated with 58% higher mortality regardless of QRS duration.

Methods: We enrolled 16 consecutive patients with systolic heart failure, PR interval prolongation (mean, 254 ± 62 ms) and narrow QRS duration (n = 13; mean QRS duration: 119 ± 17 ms) or right bundle branch block (n = 3; mean, QRS duration: 156 ± 18 ms). We successfully delivered temporary direct His bundle pacing in 14 patients and temporary biventricular pacing in 14 participants. We performed AV optimization using invasive systolic blood pressure obtaining parabolic responses (mean R: 0.90 for His, and 0.85 for biventricular pacing).

Results: The mean increment in systolic BP compared with intrinsic ventricular conduction was 4.1 mm Hg (95% confidence interval [CI]: +1.9 to +6.2 mm Hg for His and 4.3 mm Hg [95% CI: +2.0 to +6.5 mm Hg] for biventricular pacing. QRS duration lengthened with biventricular pacing (change = +22 ms [95% CI: +18 to +25 ms]) but not with His pacing (change = +0.5 ms [95% CI: -2.6 to +3.6 ms).

Conclusions: AV-optimized pacing improves acute hemodynamic function in patients with heart failure and long PR interval without left bundle branch block. That it can be achieved by single-site His pacing shows that its mechanism is AV shortening. The improvement is ∼60% of the effect size previously reported for biventricular pacing in left bundle branch block. Randomized, blinded trials are warranted to test for long-term beneficial effects.
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http://dx.doi.org/10.1016/j.jacep.2015.08.008DOI Listing
December 2015

Atrial tachycardia: when the going gets tough...

Authors:
Nick W F Linton

Pacing Clin Electrophysiol 2014 Aug 1;37(8):925-6. Epub 2014 May 1.

Department of Cardiology, Charing Cross Hospital, Imperial College Healthcare NHS Trust, London, UK.

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http://dx.doi.org/10.1111/pace.12411DOI Listing
August 2014

A practical criterion for the rapid detection of single-loop and double-loop reentry tachycardias.

J Cardiovasc Electrophysiol 2013 May 25;24(5):544-52. Epub 2013 Mar 25.

King's College London, UK.

Introduction: Entrainment criteria for the diagnosis of reentrant atrial tachycardia can be difficult to apply and cannot detect double-loop reentry. We sought to develop and clinically test a new criterion for the diagnosis of single- and double-loop reentry.

Methods And Results: (1) Proposed criterion: after sequential overdrive pacing at 2 different locations and assessing the first ensuing beats of tachycardia, the difference in activation time recorded between 2 appropriate stationary positions changes by 1 or 2 tachycardia cycle lengths; a change of 2 tachycardia cycle lengths usually indicates double-loop reentry rather than only a single-loop. (2) Clinical testing: multiple overdrive pacing maneuvers were undertaken and analyzed in 5 patients with common flutter (single-loop reentry). In total, 23 pairs of overdrive pacing maneuvers were performed using electrodes in the coronary sinus and a distribution of positions in the right atrium. In 22/23 pairs of maneuvers, the change in Activation Difference was within 2.6 ± 12.4 milliseconds of the tachycardia cycle length, confirming single loop reentry. For double-loop reentry, the literature was reviewed and 3 cases of double-loop reentry were identified with sufficient data. In all of these cases, double-loop reentry was detected and also the zone containing the common isthmus was identified.

Conclusion: The proposed criterion can diagnose single- and double-loop reentry atrial tachycardia using intracardiac recordings from any pair of well separated positions. The criterion does not require precise electrode placement or extensive activation mapping.
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http://dx.doi.org/10.1111/jce.12076DOI Listing
May 2013

Arrhythmia and left ventricular ejection fraction: once broken, always broken?

Authors:
Nick W F Linton

Heart Rhythm 2013 Jun 15;10(6):847-8. Epub 2013 Mar 15.

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http://dx.doi.org/10.1016/j.hrthm.2013.03.018DOI Listing
June 2013

Alternating RBBB and LBBB post-AV node ablation: what is the mechanism?

Pacing Clin Electrophysiol 2012 Dec 14;35(12):1505-6. Epub 2012 Sep 14.

Cardiothoracic Department, Guy's and St. Thomas' NHS Foundation Trust, London, United Kingdom.

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http://dx.doi.org/10.1111/j.1540-8159.2012.03512.xDOI Listing
December 2012

Fast pathway ablation using cryotherapy for a patient with a long PR interval in sinus rhythm and AVNRT.

Pacing Clin Electrophysiol 2012 Feb 30;35(2):e47-51. Epub 2010 Sep 30.

Imperial College Healthcare NHS Trust, London, UK.

A 53-year-old man with previous aortic valve surgery presented with paroxysmal narrow complex tachycardia, induced by exercise. His PR interval was greater than 400 ms when in sinus rhythm and atrioventricular nodal reentry tachycardia (AVNRT) was diagnosed with invasive electrophysiological studies. Single echoes were repeatedly inducible with single-paced extrastimuli. Cryotherapy was then used to ablate the fast pathway using single echoes to monitor anterograde slow pathway and retrograde fast pathway function during ablation.
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http://dx.doi.org/10.1111/j.1540-8159.2010.02910.xDOI Listing
February 2012

Cardiac ripple mapping: a novel three-dimensional visualization method for use with electroanatomic mapping of cardiac arrhythmias.

Heart Rhythm 2009 Dec 3;6(12):1754-62. Epub 2009 Sep 3.

Imperial College Healthcare NHS Trust, London, UK.

Background: Mapping of regular cardiac arrhythmias is frequently performed using sequential point-by-point annotation of local activation relative to a fixed timing reference. Assigning a single activation for each electrogram is unreliable for fragmented, continuous, or double potentials. Furthermore, these informative electrogram characteristics are lost when only a single timing point is assigned to generate activation maps.

Objective: The purpose of this study was to develop a novel method of electrogram visualization conveying both timing and morphology as well as location of each point within the chamber being studied.

Methods: Data were used from six patients who had undergone electrophysiological study with the Carto electroanatomic mapping system. Software was written to construct a three-dimensional surface from the imported electrogram locations. Electrograms were time gated and displayed as dynamic bars that extend out from this surface, changing in length and color according to the local electrogram voltage-time relationship to create a ripple map of cardiac activation.

Results: Ripple maps were successfully constructed for sinus rhythm (n = 1), atrial tachycardia (n = 3), and ventricular tachycardia (n = 2), simultaneously demonstrating voltage and timing information for all six patients. They showed low-amplitude continuous activity in four of five tachycardias at the site of successful ablation, consistent with a reentrant mechanism.

Conclusion: Ripple mapping allows activation of the myocardium to be tracked visually without prior assignment of local activation times and without interpolation into unmapped regions. It assists the identification of tachycardia mechanism and optimal ablation site, without the need for an experienced computer-operating assistant.
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http://dx.doi.org/10.1016/j.hrthm.2009.08.038DOI Listing
December 2009

Robotically assisted ablation produces more rapid and greater signal attenuation than manual ablation.

J Cardiovasc Electrophysiol 2009 Dec;20(12):1398-404

Imperial College Healthcare NHS Trust; National Heart and Lung Institute, Imperial College London, St. Mary's Hospital, London, UK.

Introduction: Robotic remote catheter ablation potentially provides improved catheter-tip stability, which should improve the efficiency of radiofrequency energy delivery. Percentage reduction in electrogram peak-to-peak voltage has been used as a measure of effectiveness of ablation. We tested the hypothesis that improved catheter-tip stability of robotic ablation can diminish signals to a greater degree than manual ablation.

Methods: In vivo NavX maps of 7 pig atria were constructed. Separate lines of ablation were performed robotically and manually, recording pre- and postablation peak-to-peak voltages at 10, 20, 30, and 60 seconds and calculating signal amplitude reduction. Catheter ablation settings were constant (25W, 50 degrees , 17 mL/min, 20-30 g catheter tip pressure). The pigs were sacrificed and ablation lesions correlated with NavX maps.

Results: Robotic ablation reduced signal amplitude to a greater degree than manual ablation (49 +/- 2.6% vs 29 +/- 4.5% signal reduction after 1 minute [P = 0.0002]). The mean energy delivered (223 +/- 184 J vs 231 +/- 190 J, P = 0.42), power (19 +/- 3.5 W vs 19 +/- 4 W, P = 0.84), and duration of ablation (15 +/- 9 seconds vs 15 +/- 9 seconds, P = 0.89) was the same for manual and robotic. The mean peak catheter-tip temperature was higher for robotic (45 +/- 5 degrees C vs 42 +/- 3 degrees C [P < 0.0001]). The incidence of >50% signal reduction was greater for robotic (37%) than manual (21%) ablation (P = 0.0001).

Conclusion: Robotically assisted ablation appears to be more effective than manual ablation at signal amplitude reduction, therefore may be expected to produce improved clinical outcomes.
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http://dx.doi.org/10.1111/j.1540-8167.2009.01590.xDOI Listing
December 2009

Robotic catheter ablation of ventricular tachycardia in a patient with congenital heart disease and Rastelli repair.

J Cardiovasc Electrophysiol 2009 Oct 26;20(10):1163-6. Epub 2009 Feb 26.

Imperial College Healthcare NHS Trust, London W2 1NY, UK.

Robotically assisted catheter ablation has been proven feasible in patients with a variety of atrial arrhythmias. The potential to provide improved catheter tip maneuvering and stability potentially makes it ideal for complex ablation procedures. We present the case of a patient with complex congenital heart disease with previous Rastelli repair and recurrent ventricular tachycardia (VT) who underwent robotically assisted mapping and ablation for right ventricular VT, utilizing substrate mapping techniques.
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http://dx.doi.org/10.1111/j.1540-8167.2009.01436.xDOI Listing
October 2009

His delay: a case of ice on the path?

J Cardiovasc Electrophysiol 2008 Sep 8;19(9):995-6. Epub 2008 Jul 8.

From the Imperial College Healthcare NHS Trust, St. Mary's Hospital, London, United Kingdom.

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http://dx.doi.org/10.1111/j.1540-8167.2008.01237.xDOI Listing
September 2008

Is clinical assessment of the circulation reliable in postoperative cardiac surgical patients?

J Cardiothorac Vasc Anesth 2002 Feb;16(1):4-7

Rayne Institute, St. Thomas' Hospital, London, United Kingdom.

Objective: To study adult patients in the immediate postoperative period after cardiac surgery and determine whether cardiac output (CO) and systemic vascular resistance (SVR) are generally within normal limits and whether clinical assessment of CO provides an adequate approximation to guide treatment.

Design: Prospective study.

Setting: Overnight intensive recovery unit, St Thomas' Hospital, London.

Participants: Fifty patients who had undergone cardiac surgery within the previous 5 hours and whose COs were not being measured.

Interventions: The physician (if present) or nurse managing the patient was asked to make a clinical estimate (as low, normal, or high) of CO and of SVR. CO was measured by lithium dilution. The clinically estimated values were compared with the measured values, after adjusting for patient size.

Measurements And Main Results: In 29 of 50 (58%) patients, cardiac index (CI) (20 of 50 [40%] patients) or systemic vascular resistance index (SVRI) (22 of 50 [44%] patients) was outside normal limits (CI, 2.7 (plus minus 30%) L/min/m(2); SVRI, 2,500 (plus minus 30%) dyne center dot sec center dot cm(minus sign 5)/m(2)). When CI was outside the normal range, the clinical estimate was usually wrong (13 of 20 [65%]); when SVRI was outside the normal range, the clinical estimate was also usually wrong (16 of 22 [73%]).

Conclusions: In the early postoperative period after cardiac surgery, clinical assessment of the circulatory state is frequently misleading, and there should be a low threshold for measuring CO.
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http://dx.doi.org/10.1053/jcan.2002.29631DOI Listing
February 2002