Publications by authors named "Robert D Nass"

14 Publications

  • Page 1 of 1

Performance of ECG-based seizure detection algorithms strongly depends on training and test conditions.

Epilepsia Open 2021 Sep 20;6(3):597-606. Epub 2021 Jul 20.

Department of Epileptology, University Hospital Bonn, Bonn, Germany.

Objective: To identify non-EEG-based signals and algorithms for detection of motor and non-motor seizures in people lying in bed during video-EEG (VEEG) monitoring and to test whether these algorithms work in freely moving people during mobile EEG recordings.

Methods: Data of three groups of adult people with epilepsy (PwE) were analyzed. Group 1 underwent VEEG with additional devices (accelerometry, ECG, electrodermal activity); group 2 underwent VEEG; and group 3 underwent mobile EEG recordings both including one-lead ECG. All seizure types were analyzed. Feature extraction and machine-learning techniques were applied to develop seizure detection algorithms. Performance was expressed as sensitivity, precision, F score, and false positives per 24 hours.

Results: The algorithms were developed in group 1 (35 PwE, 33 seizures) and achieved best results (F score 56%, sensitivity 67%, precision 45%, false positives 0.7/24 hours) when ECG features alone were used, with no improvement by including accelerometry and electrodermal activity. In group 2 (97 PwE, 255 seizures), this ECG-based algorithm largely achieved the same performance (F score 51%, sensitivity 39%, precision 73%, false positives 0.4/24 hours). In group 3 (30 PwE, 51 seizures), the same ECG-based algorithm failed to meet up with the performance in groups 1 and 2 (F score 27%, sensitivity 31%, precision 23%, false positives 1.2/24 hours). ECG-based algorithms were also separately trained on data of groups 2 and 3 and tested on the data of the other groups, yielding maximal F scores between 8% and 26%.

Significance: Our results suggest that algorithms based on ECG features alone can provide clinically meaningful performance for automatic detection of all seizure types. Our study also underscores that the circumstances under which such algorithms were developed, and the selection of the training and test data sets need to be considered and limit the application of such systems to unseen patient groups behaving in different conditions.
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http://dx.doi.org/10.1002/epi4.12520DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8408591PMC
September 2021

Informed DEcision for cerebrospinal fluid analysis after epiLeptic seizures- the IDEAL-score: A development and validation study.

Seizure 2021 Oct 29;91:228-232. Epub 2021 Jun 29.

Department of Neurology, Epilepsy Center, University Medicine Greifswald, Greifswald, Germany.

Background: This observational study was done to develop a score based on clinical predictors that enables a guided decision for the necessity of cerebrospinal fluid (CSF) analysis after first unprovoked epileptic seizures and to validate this score in a retrospective patient cohort.

Methods: Clinical predictors were identified by two panels of epilepsy experts and selected according to content validity ratios. Based on these predictors a score was created and applied to a cohort of patients with first epileptic seizures.

Results: The "IDEAL score" consists of 9 items (fever, prolonged disturbance of consciousness, headache, imaging results, cognitive dysfunction, status epilepticus, malignancy, autoimmune encephalitis symptoms) that are collected at two different time points (< 3 h [A-score]; > 3 h [B-score] after hospital admittance). A CSF analysis is recommended, if at least one clinical finding is present, either one of the items evaluated during the acute phase (A-score) or later in the diagnostic process (B-score). In 41 patients (13%) CSF analysis provided essential clues to the cause of the seizure. The combined IDEAL score reached a sensitivity of 98%, a specificity of 53%, a positive predictive value of 24% and a negative predictive value of 99% in this patient cohort.

Conclusions: A CSF analysis after first epileptic seizures provided decisive etiological findings in only 13% of all investigated patients. The IDEAL score offers clinicians a simple and easy-to-implement algorithm to assess the necessity of a CSF analysis, and to prevent unnecessary diagnostic procedures.
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http://dx.doi.org/10.1016/j.seizure.2021.06.019DOI Listing
October 2021

Does the accumulated antiepileptic drug load in chronic epilepsy reflect disease severity?

Epilepsia 2020 12 15;61(12):2685-2695. Epub 2020 Oct 15.

Department of Epileptology, University Hospital Bonn (UKB), Bonn, Germany.

Objective: To ascertain factors that are related to the antiepileptic drug load in epilepsy.

Methods: In this cross-sectional study, we analyzed a large cohort of conservatively treated patients with epilepsy (n = 1135) and a smaller homogeneous group of presurgical patients with neuropathologically confirmed unilateral hippocampal sclerosis (n = 91). Considered clinical variables comprised (1) presence of an underlying cerebral lesion, (2) onset and (3) duration of epilepsy, (4) seizure frequency, (5) generalized or focal to bilateral tonic-clonic seizures, (6) ictal impairment of awareness, and (7) a history of convulsive status epilepticus. In the presurgical sample, we additionally considered (8) the degree of pathology (hippocampal neuronal cell densities) instead of (1) presence of a cerebral lesion and (9) an overall rating of epilepsy severity (GASE scale). Drug load was quantified as (a) the number of concomitant antiepileptic drugs (AEDs) and (b) the total defined daily dose (DDD).

Results: Analyses disclosed only small correlations between clinical variables and drug load indices. In the conservatively treated cohort, the multiple regression analyses revealed that epilepsy onset, cerebral lesion, history of convulsive status epilepticus, and seizure frequency combined explained only 6%-10% of variance in drug load. Nearly the same variance (5%-8%) could be explained by duration of epilepsy alone. Degree of hippocampal pathology and the epilepsy severity ratings were not related to drug load indices.

Significance: Clinical markers of epilepsy severity were only marginally associated with drug load. Findings rather indicate that patients seem to accumulate drugs due to the chronicity of epilepsy. Overall, the drug load remained largely unexplained. The findings nevertheless call for scrutinizing multidrug therapies in patients with long-lasting epilepsies.
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http://dx.doi.org/10.1111/epi.16720DOI Listing
December 2020

Time courses of HMGB1 and other inflammatory markers after generalized convulsive seizures.

Epilepsy Res 2020 05 26;162:106301. Epub 2020 Feb 26.

Institute of Clinical Chemistry and Clinical Pharmacology, University Hospital Bonn, Bonn, Germany; Institute of Laboratory Medicine, German Heart Centre Munich, Munich, Germany.

Purpose: Neuroinflammation and disruption of blood brain barrier (BBB) are important players in epileptogenesis, ictogenesis and pharmacoresistance. In this context, we investigated blood levels of HMGB1 and other inflammatory and BBB markers after generalized and focal to bilateral tonic-clonic seizures in serum, summarized under the term generalized convulsive seizures (GCS).

Methods: We included consenting adults who were admitted to the epilepsy monitoring unit. Blood samples were drawn at baseline and immediately after a GCS as well as after 2, 6 and 24 h. We measured leukocytes, c-reactive protein (CRP), the danger-associated molecular patterns (DAMPs) high mobility group box 1 (HMGB1) and S100, receptor of advanced glycation end products (RAGE) alongside the BBB markers intercellular adhesion molecule-1 (ICAM1) and matrix metalloproteinase 9 (MMP9). Noradrenaline and lactate measurements were available from a previous study. P-levels <0.05 were regarded as significant.

Results: Twenty-eight patients with 28 GCS were included. Leukocytosis occurred immediately after GCS and normalized within two hours (p < 0.001). S100 and HMGB1 both increased by ∼80 % (p < 0.001). MMP9 peaked after six hours with levels at 48.6 % above baseline. RAGE decreased by 17.6 % with a nadir at 24 h. CRP increased by 118 % with a peak at 24 h. ICAM1 remained stable (p = 0.068). Postictal HMGB1 correlated with postictal leukocytosis (r = 0.42; p = 0.025) and with MMP9 levels six hours later (r = 0.374; p = 0.05). Postictal lactate levels correlated with MMP9 at 6 h (r = 0.48; p = 0.01) and CRP at 24 h (r = 0.39; p = 0.04). Postictal noradrenaline correlated with lactate (r = 0.57; p = 0.02) and leukocytes (r = 0.39; p = 0.047).

Discussion: The serum level of the DAMPs HMGB1 and S100 increase immediately after GCS. The hypothetical mechanism includes central nervous processes, such as glutamate toxicity and ROS release from seizing neurons but also muscular tissues. BBB breakdown is marked by the release of MMP9. Further research is needed to understand the complex interactions between electrical and metabolic stress, neuroinflammation and BBB mechanics in seizures and epilepsy.

Conclusion: Our study reveals signs of inflammation, neuronal damage and transitory disruption of BBB following single GCS, underscoring the widespread and possibily detrimental effects of recurrent seizures on brain properties. The long term impact on the disease course, however, is unclear.
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http://dx.doi.org/10.1016/j.eplepsyres.2020.106301DOI Listing
May 2020

Acute metabolic effects of tonic-clonic seizures.

Epilepsia Open 2019 Dec 22;4(4):599-608. Epub 2019 Oct 22.

Department of Epileptology University of Bonn Medical Center Bonn Germany.

Objective: Tonic-clonic seizures (TCS) lead to metabolic stress and changes in related blood markers. Such markers may indicate harmful conditions but can also help to identify TCS as a cause of transient loss of consciousness. In this study, we hypothesized that the alterations of circulating markers of metabolic stress depend on the clinical features of TCS.

Methods: Ninety-one adults undergoing video-EEG monitoring participated in this prospective study. Electrolytes, renal parameters, creatine kinase (CK), prolactin (PRL), lactate, ammonia, glucose, and other parameters were measured at inclusion and different time points after TCS.

Results: A total of 39 TCS were recorded in 32 patients (six generalized onset tonic-clonic seizures in 6 and 33 focal to bilateral tonic-clonic seizures in 26 patients). Shortly after TCS, mean lactate, ammonia, and PRL levels were significantly increased 8.7-fold, 2.6-fold, and 5.1-fold, respectively, with levels of more than twofold above the upper limits of the normal (ULN) in 90%, 71%, and 70% of the TCS and returned to baseline levels within 2 hours. Only postictal lactate levels were significantly correlated with the total duration of the tonic-clonic phase. In contrast, CK elevations above the ULN were found in three TCS (~10%) only with a peak after 48 hours. Immediately after the TCS, hyperphosphatemia occurred in one third of the patients, whereas hypophosphatemia was observed in one third 2 hours later. TCS led to subtle but significant alterations of other electrolytes, creatinine, and uric acid, whereas glucose levels were moderately increased.

Significance: Lactate is a robust metabolic marker of TCS with elevations found in ~90% of cases within 30 minutes after seizure termination, whereas ammonia rises in ~ 70%, similarly to PRL. Phosphate levels show an early increase and a decrease 2 hours after TCS in a third of patients. CK elevations are rare after video-EEG-documented TCS, challenging its value as a diagnostic marker.
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http://dx.doi.org/10.1002/epi4.12364DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6885665PMC
December 2019

Blood Pressure in Seizures and Epilepsy.

Front Neurol 2019 14;10:501. Epub 2019 May 14.

Department of Epileptology, University Hospital Bonn, Bonn, Germany.

In this narrative review, we summarize the current knowledge of neurally mediated blood pressure (BP) control and discuss how recently described epilepsy- and seizure-related BP alterations may contribute to premature mortality and sudden unexpected death in epilepsy (SUDEP). Although people with epilepsy display disturbed interictal autonomic function with a shift toward predominant sympathetic activity, prevalence of arterial hypertension is similar in people with and without epilepsy. BP is transiently increased in association with most types of epileptic seizures but may also decrease in some, illustrating that seizure activity can cause both a decrease and increase of BP, probably because of stimulation or inhibition of distinct central autonomic function by epileptic activity that propagates into different neuronal networks of the central autonomic nervous system. The principal regulatory neural loop for short-term BP control is termed baroreflex, mainly involving peripheral sensors and brain stem nuclei. The baroreflex sensitivity (BRS, expressed as change of interbeat interval per change in BP) is intact after focal seizures, whereas BRS is markedly impaired in the early postictal period following generalized convulsive seizures (GCS), possibly due to metabolically mediated muscular hyperemia in skeletal muscles, a massive release of catecholamines and compromised brain stem function. Whilst most SUDEP cases are probably caused by a cardiorespiratory failure during the early postictal period following GCS, a profoundly disturbed BRS may allow a life-threatening drop of systemic BP in the aftermath of GCS, as recently reported in a patient as a plausible cause of SUDEP in a few patients.
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http://dx.doi.org/10.3389/fneur.2019.00501DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6527757PMC
May 2019

Blood markers of cardiac stress after generalized convulsive seizures.

Epilepsia 2019 02 15;60(2):201-210. Epub 2019 Jan 15.

Department of Epileptology, University Hospital Bonn, Bonn, Germany.

Objective: Generalized convulsive seizures (GCS) are associated with high demands on the cardiovascular system, thereby facilitating cardiac complications. To investigate occurrence, influencing factors, and extent of cardiac stress or injury, the alterations and time course of the latest generation of cardiac blood markers were investigated after documented GCS.

Methods: Adult patients with refractory epilepsy who underwent video-electroencephalography (EEG) monitoring along with simultaneous one-lead electrocardiography (ECG) recordings were included. Cardiac biomarkers (cardiac troponin I [cTNI]; high-sensitive troponin T [hsTNT]; N-terminal prohormone of brain natriuretic peptide [NT-proBNP]; copeptin; suppression of tumorigenicity-2 [SST-2]; growth differentiation factor 15, [GDF-15]; soluble urokinase plasminogen activator receptor [suPAR]; and heart-type fatty acid binding protein [HFABP]) and catecholamines were measured at inclusion and at different time points after GCS. Periictal cardiac properties were assessed by analyzing heart rate (HR), HR variability (HRV), and corrected QT intervals(QTc).

Results: Thirty-six GCS (6 generalized-onset tonic-clonic seizures and 30 focal to bilateral tonic-clonic seizures) were recorded in 30 patients without a history of cardiac or renal disease. Postictal catecholamine levels were elevated more than twofold. A concomitant increase in HR and QTc, as well as a decrease in HRV, was observed. Elevations of cTNI and hsTNT were found in 3 of 30 patients (10%) and 6 of 23 patients (26%), respectively, which were associated with higher dopamine levels. Copeptin was increased considerably after most GCS, whereas SST-2, HFABP, and GDF-15 displayed only subtle variations, and suPAR was unaltered in the postictal period. Cardiac symptoms did not occur in any patient.

Significance: The use of more sensitive biomarkers such as hsTNT suggests that signs of cardiac stress occur in about 25% of the patients with GCS without apparent clinical symptoms. SuPAR may indicate clinically relevant troponin elevations. Copeptin could help to diagnose GCS, but specificity needs to be tested.
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http://dx.doi.org/10.1111/epi.14637DOI Listing
February 2019

Evidence for peri-ictal blood-brain barrier dysfunction in patients with epilepsy.

Brain 2018 10;141(10):2952-2965

Department of Epileptology, University of Bonn Medical Center, Bonn, Germany.

Epilepsy has been associated with a dysfunction of the blood-brain barrier. While there is ample evidence that a dysfunction of the blood-brain barrier contributes to epileptogenesis, blood-brain barrier dysfunction as a consequence of single epileptic seizures has not been systematically investigated. We hypothesized that blood-brain barrier dysfunction is temporally and anatomically associated with epileptic seizures in patients and used a newly-established quantitative MRI protocol to test our hypothesis. Twenty-three patients with epilepsy undergoing inpatient monitoring as part of their presurgical evaluation were included in this study (10 females, mean age ± standard deviation: 28.78 ± 8.45). For each patient, we acquired quantitative T1 relaxation time maps (qT1) after both ictal and interictal injection of gadolinium-based contrast agent. The postictal enhancement of contrast agent was quantified by subtracting postictal qT1 from interictal qT1 and the resulting ΔqT1 was used as a surrogate imaging marker of peri-ictal blood-brain barrier dysfunction. Additionally, the serum concentrations of MMP9 and S100, both considered biomarkers of blood-brain barrier dysfunction, were assessed in serum samples obtained prior to and after the index seizure. Fifteen patients exhibited secondarily generalized tonic-clonic seizures and eight patients exhibited focal seizures at ictal injection of contrast agent. By comparing ΔqT1 of the generalized tonic-clonic seizures and focal seizures groups, the anatomical association between ictal epileptic activity and postictal enhancement of contrast agent could be probed. The generalized tonic-clonic seizures group showed significantly higher ΔqT1 in the whole brain as compared to the focal seizures group. Specific analysis of scans acquired later than 3 h after the onset of the seizure revealed higher ΔqT1 in the generalized tonic-clonic seizures group as compared to the focal seizures group, which was strictly lateralized to the hemisphere of seizure onset. Both MMP9 and S100 showed a significantly increased postictal concentration. The current study provides evidence for the occurrence of a blood-brain barrier dysfunction, which is temporally and anatomically associated with epileptic seizures. qT1 after ictal contrast agent injection is rendered as valuable imaging marker of seizure-associated blood-brain barrier dysfunction and may be measured hours after the seizure. The observation of the strong anatomical association of peri-ictal blood-brain barrier dysfunction may spark the development of new functional imaging modalities for the post hoc visualization of brain areas affected by the seizure.
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http://dx.doi.org/10.1093/brain/awy242DOI Listing
October 2018

Laboratory markers of cardiac and metabolic complications after generalized tonic-clonic seizures.

BMC Neurol 2017 Sep 19;17(1):187. Epub 2017 Sep 19.

Department of Epileptology, University Hospital Bonn, Bonn, Germany.

Background: Generalized tonic-clonic seizures (GTCS) frequently lead to emergency inpatient referrals. Laboratory blood values are routinely performed on admission to detect underlying causes and metabolic or cardiac complications. Our goal was to assess the nature and frequency of complications occurring in association with GTCS.

Methods: We retrospectively extracted data from emergency protocols and discharge letters of adult patients admitted to the Department of Epileptology between 01/2010 and 06/2015. Inclusion criteria were diagnosis of GTCS and admission via emergency services. Exclusion criteria were status epilepticus prior to admission to hospital and non-generalized seizures.

Results: A total of 223 patients (of 986 screened cases) were included. Overall, 1.8% required intubation while 1.3% had less severe respiratory problems. In 5.6% of patients, a transient hypoxemia was measured. Hypertensive urgencies affected 7.8% of the patients, sinus tachycardia occurred in 41.2%. Troponin I (cTNI) was determined in 75 patients and was increased in 12% of these cases. Occurrence of elevated cTNI levels was significantly correlated with patient's age. Four patients were diagnosed with NSTEMI and one patient with STEMI. Creatine kinase (CK) was increased in 59.4% of the patients, with <5-fold increases in 47%, <10-fold in 5.8% and >10-fold increases in 4.3%. Rhabdomyolysis with an >50 fold increase in CK was detected in 1.9% of patients. Prolonged disturbances of consciousness affected 5% of cases while agitation, delirium, and psychotic episodes occurred in 6.3%. Minor traumatic injuries affected 45.7% of patients.

Conclusions: Troponin elevations in association with GTCS are one of the more common complications after emergency admissions especially in older patients. In our selected patient population, serious complications such as intracranial hemorrhage, myocardial infarction and acute renal failure occurred in <1% of GTCS only.
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http://dx.doi.org/10.1186/s12883-017-0965-4DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5605980PMC
September 2017

The role of postictal laboratory blood analyses in the diagnosis and prognosis of seizures.

Seizure 2017 Apr 27;47:51-65. Epub 2017 Feb 27.

Department of Epileptology, University Hospital of Bonn, Bonn, Germany.

Background: Epileptic seizures (ES) lead to alterations in the blood laboratory values and reflect changes in different organ systems. Here, we review the diagnostic and prognostic value of various blood laboratory values within the context of epilepsy.

Methods: Narrative review and literature search on PubMed using the term, "seizure" and various laboratory values.

Results: Laboratory markers can help clinicians determine whether an unwitnessed event was more likely to be epileptic or non-epileptic. Prolactin testing helps differentiate ES from psychogenic non-epileptic seizures (PNES) in adults and adolescents, and is associated with high specificity and moderate sensitivity. Elevations in the creatine kinase (CK) levels are common after generalized tonic-clonic seizures (GTCS) and display high specificity and moderate sensitivity. Metabolic markers such as ammonia and lactate may have diagnostic potential for postictal blood tests. Analyzing blood postictally is important for identifying the cause of the symptomatic seizures due to endocrine, metabolic, toxic or infectious etiologies. Finally, laboratory analyses are used for identifying patients who are at risk for developing rare, threatening complications such as rhabdomyolysis, acute renal failure (ARF) or cardiomyopathy.

Conclusions: Presently, no postictal laboratory values can definitively prove or rule out the diagnosis of an epileptic seizure. For seizures with unknown causes, simple blood tests can be a valuable aid for quickly defining the etiology, particularly with certain metabolic and toxic encephalopathies. For this reason, CK, electrolytes, creatinine, liver and renal function tests should be measured on at least one occasion. Further research is needed in order to identify new biomarkers that improve the diagnosis and prognosis of seizures and seizure-related complications.
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http://dx.doi.org/10.1016/j.seizure.2017.02.013DOI Listing
April 2017

Optical imaging of mitochondrial function uncovers actively propagating waves of mitochondrial membrane potential collapse across intact heart.

J Mol Cell Cardiol 2010 Oct 16;49(4):565-75. Epub 2010 Jul 16.

Cardiovascular Research Center, Mount Sinai School of Medicine, New York, NY 10029, USA.

Polarization of the mitochondrial membrane potential (DeltaPsi(m)) is critical for normal mitochondrial function and cellular energetics. Mitochondrial dysfunction, manifesting as disrupted DeltaPsi(m) polarization (i.e. depolarization or hyperpolarization), underlies several important and highly prevalent diseases, including a variety of cardiac and neurological disorders. As such, DeltaPsi(m) instability might form a unifying mechanism for a class of metabolic disorders affecting excitable tissues. Here, we measured the spatio-temporal kinetics of DeltaPsi(m) changes across the intact heart using high-resolution optical DeltaPsi(m) imaging and uncovered surprisingly complex spatial patterns and dynamically fluctuating changes in DeltaPsi(m) that developed into actively propagating waves of mitochondrial depolarization during global ischemia. Our data further indicated that the recovery of DeltaPsi(m) upon reperfusion is dictated by the duration of the preceding ischemic insult. Post-ischemic electrical and functional recovery was dependent on early DeltaPsi(m) recovery but independent of overall cellular injury measured using a standard assay of lactate dehydrogenase release. These findings reveal a novel mechanism by which instabilities in cellular energetic properties that are independent of irreversible cellular injury can scale to the level of the intact organ via an organized process of active conduction involving the multi-cellular network. This highlights the importance of investigating cellular metabolic properties in the context of the intact organ.
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http://dx.doi.org/10.1016/j.yjmcc.2010.07.002DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3081287PMC
October 2010

Altered spatiotemporal dynamics of the mitochondrial membrane potential in the hypertrophied heart.

Biophys J 2010 May;98(10):2063-71

Cardiovascular Research Center, Division of Cardiology, Mount Sinai School of Medicine, New York, New York, USA.

Chronically elevated levels of oxidative stress resulting from increased production and/or impaired scavenging of reactive oxygen species are a hallmark of mitochondrial dysfunction in left ventricular hypertrophy. Recently, oscillations of the mitochondrial membrane potential (DeltaPsi(m)) were mechanistically linked to changes in cellular excitability under conditions of acute oxidative stress produced by laser-induced photooxidation of cardiac myocytes in vitro. Here, we investigate the spatiotemporal dynamics of DeltaPsi(m) within the intact heart during ischemia-reperfusion injury. We hypothesize that altered metabolic properties in left ventricular hypertrophy modulate DeltaPsi(m) spatiotemporal properties and arrhythmia propensity.
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http://dx.doi.org/10.1016/j.bpj.2010.01.045DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2872265PMC
May 2010

Mechanisms of disease: ion channel remodeling in the failing ventricle.

Nat Clin Pract Cardiovasc Med 2008 Apr 4;5(4):196-207. Epub 2008 Mar 4.

Cardiovascular Research Center, Mount Sinai School of Medicine, New York, NY 10029, USA.

In an attempt to compensate for compromised hemodynamics in heart failure, neurohumoral mechanisms are activated that trigger fundamental changes in gene expression and in protein processing, trafficking and post-translational regulation, resulting in myocyte hypertrophy. Unfortunately, over time these changes become maladaptive, predisposing to myocyte loss, chamber dilatation, interstitial hyperplasia and intercellular uncoupling. Intrinsic and peripheral responses to mechanical dysfunction alter the expression and function of key ion channels and calcium-handling proteins, thereby remodeling the cellular action potential and the intracellular calcium transient. This electrophysiological remodeling renders the heart more vulnerable to ventricular arrhythmias that underlie sudden cardiac death. In this Review, we consider key ventricular ionic changes that are associated with heart failure, with the intention of identifying molecular targets for antiarrhythmic therapy.
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http://dx.doi.org/10.1038/ncpcardio1130DOI Listing
April 2008

Dynamic changes in conduction velocity and gap junction properties during development of pacing-induced heart failure.

Am J Physiol Heart Circ Physiol 2007 Aug 13;293(2):H1223-30. Epub 2007 Apr 13.

Division of Cardiology and Institute for Computational Medicine, Johns Hopkins University, 720 Rutland Ave., Ross 844, Baltimore, MD 21205, USA.

End-stage heart failure (HF) is characterized by changes in conduction velocity (CV) that predispose to arrhythmias. Here, we investigate the time course of conduction changes with respect to alterations in connexin 43 (Cx43) properties and mechanical function during the development of HF. We perform high-resolution optical mapping in arterially perfused myocardial preparations from dogs subjected to 0, 3, 7, 14, and 21 days of rapid pacing to produce variable degrees of remodeling. CV is compared with an index of mechanical function [left ventricular end-diastolic pressure (LVEDP)] and with dynamic changes in the expression, distribution, and phosphorylation of Cx43. In contrast to repolarization, CV was preserved during early stages of remodeling (3 and 7 days) and significantly reduced at later stages, which were associated with marked increases in LVEDP. Measurements of differentially phosphorylated Cx43 isoforms revealed early, sustained downregulation of pan-Cx43 that preceded changes in CV and LVEDP, a gradual rise in a dephosphorylated Cx43 isoform to over twofold baseline levels in end-stage HF, and a late abrupt increase in pan-Cx43, but not dephosphorylated Cx43, lateralization. These data demonstrate that 1) CV slowing occurs only at advanced stages of remodeling, 2) total reduction of pan-Cx43 is an early event that precedes mechanical dysfunction and CV slowing, 3) changes in Cx43 phosphorylation are more closely associated with the onset of HF, and 4) Cx43 lateralization is a late event that coincides with marked CV reduction. These data reveal a novel paradigm of remodeling based on the timing of conduction abnormalities relative to changes in Cx43 isoforms and mechanical dysfunction.
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http://dx.doi.org/10.1152/ajpheart.00079.2007DOI Listing
August 2007
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