Shmuel Inbar

Improving SVT Discrimination in Single‐Chamber ICDs: A New Electrogram Morphology‐Based Algorithm

Introduction: Wide‐spread adoption of ICD therapy has focused efforts on improving the quality of life for patients by reducing “inappropriate” shock therapies. To this end, distinguishing supraventricular tachycardia from ventricular tachycardia remains a major challenge for ICDs. More sophisticated discrimination algorithms based on ventricular electrogram morphology have been made practicable by the increased computational ability of modern ICDs.

Utility of predischarge and one-month transvenous implantable defibrillator tests

We evaluated the utility of performing predischarge implantable cardioverter-defibrillator (ICD) testing and ICD testing at 1 month in detecting ICD-related problems, identifying 4 patients with an unacceptable increase in defibrillation threshold. Given that ICD testing is noninvasive and has minimal (if any) associated risk, we recommend that predischarge and 1-month follow-up ICD testing should be performed after implantation.

Uncertainty Principle of Signal-Averaged Electrocardiography

BACKGROUND Signal-averaged ECG (SAECG) reproducibility is reported to have a component that is independent of residual noise. Methods and Results-In group 1, multiple paired SAECGs were obtained to noise levels of 0.3+/-0.1 and 0.5+/-0.2 microV. For the 0.5- and 0. 3-microV noise recordings, QRS duration (QRSd) was 101.2+/-11.3 and 104.6+/-9.6 ms, respectively (P<0.0001), and the differences in paired QRSd (DeltaQRSd) were normally distributed, with variances of 11.4 and 26.2 ms(2) (P<0.0001). Paired SAECGs were obtained in group 2 patients without and with late potentials; DeltaQRSd variance was 3.3 and 217.9 ms(2) (P<0.0001). In group 3, >/=10 SAECGs were acquired at noise levels of 0.2 to 0.8 microV, in 0.1-microV increments. QRSd increased as noise level decreased. The variance was greater in low-noise (0.2 to 0.4 microV) versus higher-noise (0. 5 to 0.8 microV) recordings. In group 4, SAECGs were analyzed with bidirectional and Bispec filters, with no difference in QRSd between the 2 filters and a normally distributed DeltaQRSd. A computer simulation demonstrated that alterations in the phase relationship of noise to signal results in a normal distribution of signal end points. CONCLUSIONS Within the acceptable noise range for SAECG, lower noise results in longer QRSd and larger variance, suggesting that more accurate recordings may have less reproducibility. The random timing of noise relative to signal results in the distribution/variance of repeated measurements. Statistical strategies may be used to reduce some of this variance and may enhance the diagnostic utility of SAECG.

Late Recurrence of Atrial Flutter Following Radiofrequency Catheter Ablation

The success rate for catheter ablation of atrial flutter has been reported to be approximately 90%, but recurrences are common and can be seen in up to 20% of cases. Most of these recurrences are seen within a few weeks following ablation. We report on a patient who developed a recurrence of type I atrial flutter 2 years after an initially successful radiofrequency catheter ablation procedure. Whether the recurrent atriai flutter is due to a new reentrant circuit resulting from slow progression of atrial disease or due to the changes produced by radiofrequency energy in the nearby myocardium is not clear. Further work to define the electrophvsiological changes in the atrial myocardium produced by radiofrequency energy, as well as long‐term follow‐up of patients undergoing radiofrequency catheter ablation for atrial flutter may help in answering these questions.

Local Electrogram Changes in Response to a High‐Voltage Intracardiac Shock in Humans

Electrogram Changes Following ICD Shocks. Introduction: Transvenous defibrillators may have difficulty sensing ventricular fibrillation following an unsuccessful shock. This study was undertaken to characterize the changes that occur in intracardiac electrograms following a defibrillator shock that may contribute to the failure to redetect arrhythmias.

Deadly proposal: a case of catecholaminergic polymorphic ventricular tachycardia.

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a rare adrenergically mediated arrhythmogenic disorder classically induced by exercise or emotional stress and found in structurally normal hearts. It is an important cause of cardiac syncope and sudden death in childhood. Catecholaminergic polymorphic ventricular tachycardia is a genetic cardiac channelopathy with known mutations involving genes affecting intracellular calcium regulation. We present a case of a 14-year-old boy who had cardiopulmonary arrest after an emotionally induced episode of CPVT while attempting to invite a girl to the school dance. Review of his presenting cardiac rhythm, induction of concerning ventricular arrhythmias during an exercise stress test, and genetic testing confirmed the diagnosis of CPVT. He recovered fully and was treated with &bgr;-blocker therapy and placement of an implantable cardioverter-defibrillator. In this report, we discuss this rare but important entity, including its molecular foundation, clinical presentation, basics of diagnosis, therapeutic options, and implications of genetic testing for family members. We also compare CPVT to other notable cardiomyopathic and channelopathic causes of sudden death in youth including hypertrophic cardiomyopathy, arrhythmogenic right ventricular dysplasia, long QT syndrome, short QT syndrome, and Brugada syndrome.

Autonomic Effects on Noise Recorded During Signal‐Averaged Electrocardiography

The purpose of this study was to assess the effects of autonomic stimulation and blockade on noise levels and to compare the noise measurements in the ST and TP segments of the signal‐averaged ECG. Five‐minute electrocardiographic data were recorded in 14 normal volunteers (8 males and 6 females; mean age 28.5 ± 5.0 years) on two separate days (day 1—baseline, epinephrine infusion, isoproterenol infusion, β‐blockade, and combined adrenergic and parasympathetic blockade; day 2—baseline, phenylephrine infusion, parasympathetic blockade, and during phenylephrine infusion following atropine). Signal averaging was done off‐line on 100 beats and noise was measured in both the ST and TP segments as the standard deviation of voltage in the segment of interest. For all conditions tested, the mean noise level measured in the ST segment (0.46 ± 0.16 μV) was significantly less than that measured in the TP segment (0.52 ± 0.24 μV; P = 0.0003). but there was good correlation between the noise measured in the STand the TP segment (R2= 0.62, P < 0.0001). Noise increased with isoproterenol infusion and decreased following adrenergic blockade. In addition, day 2 baseline noise was less than baseline noise on day 1. Finally, neither parasympathetic stimulation or blockade nor α‐adrenergic stimulation significantly affected signal‐averaged electrocardiography (SAECG) noise levels. Thus, the data support the notion that enhanced sympathetic tone increases noise levels and β‐adrenergic blockade may decrease noise levels, likely due to effects from muscle sympathetic nerve activity. These findings are important since the target population for the SAECG are patients with myocardial infarction and congestive heart failure, conditions associated with increased sympathetic tone, which may in turn impact on the reproducibility or technical aspects of the SAECG. In addition, because noise in the ST and TP segments are highly correlated and the noise measured in the ST segment is less than that in the TP segment, uniform adoption of noise measurement in the ST segment seems most appropriate.

A Novel Solution for the High Defibrillation Threshold in Patients with a DF-4 Lead: Adding a High Voltage Adaptor/Splitter.

A high defibrillation threshold occurs in approximately 6% of implants. The defibrillation threshold can be improved by addition of a defibrillation lead. However, the DF-4 high energy ICD header precludes the addition of a defibrillation lead. Here we report on use of a new high voltage adaptor/splitter that enables the addition of an extra defibrillation lead.

Ventricular fibrillation induced by high-output ICD shock: report of cases and review of literature

This report highlights the importance of realising that even the modern-day implantable cardioverter defibrillators (ICDs) with R wave synchronised appropriate shocks have a potential proarrhythmic effect. We present two cases of ventricular fibrillation induction resulting from an appropriate ICD shock observed in two different patients at our institution. Such cases have not been reported before. We discuss the possible reasons for our observations and are also submitting a pertinent literature review with our reports.

Challenges of device therapy for ventricular tachycardia in the rate range of sinus rhythm

A method is described for patient-activated detection of ventricular tachycardia, under circumstances in which automatic algorithms fail. We present a case of a patient with an implanted defibrillator (Jewel PCD) who presented with symptomatic exercise-induced ventricular tachycardia that was only marginally faster than the preceding sinus tachycardia. Programming the sudden onset criterion avoided delivery of therapy into sinus tachycardia, but failed to detect ventricular tachycardia. Brief application of a magnet resulted in successful detection and therapy. This method is device-specific and requires a co-operative, insightful patient. The benefits and risks of such an approach are discussed.