Michael Glikson

The Implantable Cardioverter-Defibrillator

Implantable cardioverter defibrillators (ICDs) have evolved from the treatment of last resort to the gold standard therapy for patients at high risk for ventricular tachyarrhythmias. High-risk patients include those who have survived life-threatening arrhythmias, and individuals with cardiac diseases who are at risk for such arrhythmias, but are symptomless. Use of an ICD will affect the patients quality of life. Some drugs can substantially affect defibrillator function and efficacy, and possible drug-device interactions should be considered. Patients with ICDs may encounter cell phones, antitheft detectors, and many other sources of potential electromagnetic Interference. In addition to treating ventricular tachyarrhythmias, new defibrillators provide full featured dual chamber pacing, and could treat atrial arrhythmias, and congestive heart failure by means of biventricular pacing.

The Response of the QT Interval to the Brief Tachycardia Provoked by Standing: A Bedside Test for Diagnosing Long QT Syndrome

OBJECTIVES This study was undertaken to determine whether the short-lived sinus tachycardia that occurs during standing will expose changes in the QT interval that are of diagnostic value. BACKGROUND The QT interval shortens during heart rate acceleration, but this response is not instantaneous. We tested whether the transient, sudden sinus tachycardia that occurs during standing would expose abnormal QT interval prolongation in patients with long QT syndrome (LQTS). METHODS Patients (68 with LQTS [LQT1 46%, LQT2 41%, LQT3 4%, not genotyped 9%] and 82 control subjects) underwent a baseline electrocardiogram (ECG) while resting in the supine position and were then asked to get up quickly and stand still during continuous ECG recording. The QT interval was studied at baseline and during maximal sinus tachycardia, maximal QT interval prolongation, and maximal QT interval stretching. RESULTS In response to brisk standing, patients and control subjects responded with similar heart rate acceleration of 28 +/- 10 beats/min (p = 0.261). However, the response of the QT interval to this tachycardia differed: on average, the QT interval of controls shortened by 21 +/- 19 ms whereas the QT interval of LQTS patients increased by 4 +/- 34 ms (p < 0.001). Since the RR interval shortened more than the QT interval, during maximal tachycardia the corrected QT interval increased by 50 +/- 30 ms in the control group and by 89 +/- 47 ms in the LQTS group (p < 0.001). Receiver-operating characteristic curves showed that the test adds diagnostic value. The response of the QT interval to brisk standing was particularly impaired in patients with LQT2. CONCLUSIONS Evaluation of the response of the QT interval to the brisk tachycardia induced by standing provides important information that aids in the diagnosis of LQTS.

Long-Term Outcome of Patients Who Received Implantable Cardioverter Defibrillators for Stable Ventricular Tachycardia

Introduction: Evidence is inconclusive concerning the role of implantable cardioverter defibrillators (ICDs) to treat patients with hemodynamically stable ventricular tachycardia (VT). The goal of this study was to estimate future risk of unstable ventricular arrhythmias in patients who received ICDs for stable VT.

Adenosine-5'-triphosphate test for the noninvasive diagnosis of concealed accessory pathway.

OBJECTIVES This study assessed the use of adenosine triphosphate (ATP) in the noninvasive diagnosis of concealed accessory pathway (AP) and dual atrioventricular (AV) node physiology in patients with inducible AV reentrant tachycardia (AVRT). BACKGROUND Administration of ATP during sinus rhythm identifies dual AV node physiology in 76% of patients with inducible sustained slow/fast AV nodal reentry tachycardia (AVNRT). METHODS Incremental doses of ATP were intravenously administered during sinus rhythm to 34 patients with inducible sustained AVRT involving a concealed AP and to 27 control patients without AP or dual AV node physiology. One study group patient could not complete the study and was excluded from analysis. RESULTS The AV reentrant echo beats (AVRE), or AVRT, suggestive of the presence of concealed AP, were observed after ATP administration in 24 (73%) study patients and in none of the control group. Electrocardiographic signs suggestive of dual AV node physiology were observed after ATP administration in 7 (21%) study patients and in none of the control group. Most instances of AVRE/AVRT were preceded by a slight increase (<50 ms) in PR interval. In 8 of 9 patients tested, neither AVRE nor AVRT was no longer observed following ATP administration after successful radiofrequency ablation of the AP. In the remaining patient, a different AVRE due to the presence of an additional AP was observed. CONCLUSIONS Administration of ATP during sinus rhythm may be a useful bedside test for identifying patients with concealed AP who are prone to AVRT and those with associated dual AV node pathways.

Pneumothorax: an unusual cause of ICD defibrillation failure.

We describe two patients with defibrillation failure of implantable cardioverter defibrillators (ICDs) resulting from large left pneumothoraxes following subclavian vein puncture during the implantation. Following pneumothorax drainage, low defibrillation thresholds (DFTs) were attained without further manipulations. The absence of other signs and symptoms of pneumothorax and the presence of satisfactory pacing function during the procedure, resulted in a significant delay in diagnosis. Pneumothorax should be included in the differential diagnosis when unexpected high DFTs are found during ICD implantation or predischarge testing. This complication is avoidable by a different surgical approach, cephalic vein cutdown.

Adaptive cardiac resynchronization therapy device: a simulation report.

We report the results of a simulation of an adaptive cardiac resynchronization therapy (CRT) device performing biventricular pacing in which the atrioventricular (AV) delay and interventricular (VV) interval parameters are changed dynamically in response to data provided by the simulated IEGMs and simulated hemodynamic sensors. A learning module, an artificial neural network, performs the adaptive part of the algorithm supervised by an algorithmic deterministic module, internally or externally from the implanted CRT or CRT‐D. The simulated cardiac output obtained with the adaptive CRT device is considerably higher (30%) especially with higher heart rates than in the nonadaptive CRT mode and is likely to be translated into improvement in quality of life of patients with congestive heart failure.

Safety and efficacy of strategic implantable cardioverter-defibrillator programming to reduce the shock delivery burden in a primary prevention patient population

AIMS Strategically chosen ventricular tachycardia (VT)/ventricular fibrillation (VF) detection and therapy parameters aimed at reducing shock deliveries were proven effective in studies that utilized single manufacturer devices with a follow-up of up to 1 year. Whether these beneficiary effects can be generalized to additional manufacturers and be maintained for longer periods is to be determined. Our aim was to evaluate the durability and applicability of the programming of strategic implantable cardioverter-defibrillators (ICDs) of various manufacturers, which is aimed at reducing the shock delivery burden in primary prevention ICD recipients. METHODS AND RESULTS A retrospective analysis of prospectively collected data of 300 ICD recipients of various manufacturers was conducted; 160 devices were strategically programmed to reduce shocks and 140 were not. The primary endpoint was the composite of death and appropriate shocks. Additional outcomes were inappropriate shocks, syncope events, and non-sustained VTs. At a median follow-up of 24 months, 19 patients died, 31 received appropriate shocks, and 41 received inappropriate shocks. Multivariate analysis showed that strategic programming dedicated to shock reduction was associated with a 64% risk reduction in the primary endpoint [hazard ratio (HR): 0.13-0.93; P = 0.03] and a 70% reduction in inappropriate shock deliveries (HR: 0.16-0.72; P = 0.01). Very few syncope events occurred (five patients, 1.6%), and there was no between-group difference in this outcome. CONCLUSION Utilization of strategically chosen VT/VF detection and therapy parameters was found to be effective and safe in ICDs of various manufacturers at a median follow-up period of 2 years among primary prevention patients.

Multipole analysis of heart rate variability as a predictor of imminent ventricular arrhythmias in ICD patients.

Contemporary implantable cardiac defibrillators (ICD) enable storage of multiple, preepisode R‐R recordings in patients who suffered from ventricular tachyarrhythmia (VTA). Timely prediction of VTA, using heart rate variability (HRV) analysis techniques, may facilitate the implementation of preventive and therapeutic strategies.

Poor Heart Rate Recovery Is Associated With the Development of New-Onset Atrial Fibrillation in Middle-Aged Adults

OBJECTIVE To investigate the association between heart rate recovery (HRR) and new-onset atrial fibrillation (AF) in middle-aged adults. PATIENTS AND METHODS Heart rate recovery was calculated using the exercise stress test in 15,729 apparently healthy self-referred men and women who attended periodic health screening examinations between January 2000, and December 2015. All participants completed the maximal exercise stress test according to the Bruce protocol and were followed clinically on a yearly basis for a median of 6.4±4 years. The primary end point was new-onset AF. Participants were grouped according to HRR at 5 minutes, dichotomized at the median value (<73 beats/min). RESULTS Participants with low HRR were older, were more commonly men, had a higher rate of comorbidities, and were less fit. Kaplan-Meier survival analysis revealed that the cumulative probability of AF at 6 years was higher in participants with low HRR (2.1%) than in those with high HRR (0.6%) (log-rank, P<.001). Older age, male sex, obesity resting heart rate, and ischemic heart disease were all associated with increased AF risk in a univariate Cox regression model (P<.05 for all). Multivariate Cox regression analysis revealed that low HRR was independently associated with increased AF risk (hazard ratio, 1.92; 95% CI, 1.3-2.8; P<.001) after adjustment for multiple confounders. CONCLUSION Lower HRR is independently associated with the development of new-onset AF during long-term follow-up in middle-aged adults.

Ethnic Differences Among Implantable Cardioverter Defibrillators Recipients in Israel

Heart failure is an increasingly common condition arising from a variety of different pathophysiological processes. Little is known about the unique features of Israeli Arabs who present with heart failure and who undergo cardiac device implantation. The study population comprised of 4,671 patients who were enrolled in the national Israeli Implantable Cardioverter Defibrillator registry. We compared demographic, clinical, and echocardiographic characteristics; device-related indications; and outcomes between Israeli Arabs (n = 733) and Jews (n = 3,938), who were enrolled in the registry from July 2010 through December 2013. Israeli Arabs constituted 15.7% of the study population. They were younger at presentation compared with Jews (57 ± 15 vs 66 ± 12 years, respectively; p <0.001), with a greater burden of co-morbidities, including diabetes mellitus and chronic obstructive lung disease and smoking. In addition, Arab patients had a greater frequency of non-ischemic cardiomyopathy (40.2% vs 24.6%, respectively; p <0.001), which was associated with a greater frequency of familial history of sudden cardiac death. During 15 ± 9 month follow-up, the mortality rates and appropriate device therapy were similar in both ethnic groups. In conclusion, Israeli Arab patients implanted with implantable cardioverter defibrillators display unique clinical features with greater prevalence of non-ischemic cardiomyopathy characterized by an early-onset and rapid deterioration.