Unexpected ICD pulse generator failure due to electronic circuit damage caused by electrical overstress.

Because it is a lifesaving device, the unexpected failure of an ICD can be catastrophic. We report ICD electronic circuit failure due to electrical overstress damage (EOS) to the high voltage hybird circuit and other electronic components in a series of ICD pulse generator models. Data were obtained from the Multicenter Registry of Pacemaker and ICD Pacemaker and Lead Failures, and from the manufactures' adverse event reports, that were in the FDA's Manufacturer and User Facility Device Experience (MAUDE) database. Of 16 nonbattery Guidant/CPI ICD pulse generator failures reported to the registry, 6 (38%) have been confirmed by the manufacturer to be EOS related, and Guidant/CPI has reported 273 such failures to the FDA as of 12/29/00. The signs of failure included loss of telemetry and inability to deliver therapy, and some patients have experienced serious adverse events. Hybrid circuit damage may have occurred during capacitor charging or reform, and the majority appears to have happened during normal ICD function. While the incidence of this problem is unknown, a management strategy should be adopted that includes routine follow-up every 3 months and device evaluation after a shock or exposure to external defibrillation or electrosurgical devices. This study suggests that additional data are needed to determine the incidence of this problem, and that our present methods for monitoring the performance of ICD's following market release are inadequate.

Hypertrophic cardiomyopathy with left ventricular apical diverticulum.

In summary, 3 patients with HC and LV apical diverticula of various sizes are described. All 3 had morphologic evidence of severe midventricular obstruction, including 2 with documentation of greatly elevated LV systolic pressure and marked LV outflow pressure gradients.

Clinical results with nonthoracotomy ICD systems.

The results of two separate US Food and Drug Administration clinical trials that involved endocardial and epicardial leads were compared with regard to patient demographics, detection and conversion characteristics, and subsequent clinical course including long-term survival experience. The patient groups, although not strictly contemporaneous, were sufficiently similar to allow meaningful comparisons. There were no significant differences in detection of induced arrhythmias and ability to convert them. The surgical mortality, infection rate, and incidence of other morbid complications were lower in patients who had received endocardial leads; however, the differences did not reach statistical significance. Survivals through 1 year of follow-up were uniformly high. These results suggest that the performance of the endocardial lead system is comparable to existing epicardial leads in similar patient populations.

Carotid sinus hypersensitivity in patients with unexplained syncope: clinical, electrophysiologic, and long-term follow-up observations.

To assess the incidence and clinical characteristics of carotid sinus hypersensitivity and the relationship to electrophysiologic findings, 76 patients with unexplained syncope underwent carotid sinus massage during electrophysiologic studies for syncope evaluation. Twenty-one patients (28%) were found to have carotid sinus hypersensitivity. Of these 21 patients, 11 (52%) had coronary artery disease, two (10%) had hypertensive heart disease, and eight (38%) had no organic heart disease. During electrophysiologic studies, abnormal sinus node function was found in three patients (14%), abnormal atrioventricular (AV) node function was noted in four (19%), and combined abnormal sinus node and AV node functions were seen in three (14%). Eleven patients (53%) had a normal electrophysiologic study. During carotid sinus massage, sinus arrest alone was observed in 12 patients (57%), and combined sinus arrest and AV nodal block was seen in nine (43%). Thirteen patients were treated with a permanent pacemaker, in whom either carotid sinus massage reproduced the symptom or concomitant sinus node or AV node abnormality, or organic heart disease was present. With a mean follow-up of 42 +/- 19 months, none of these 13 patients had recurrent syncope. However, one of eight patients (13%) who did not receive a pacemaker had recurrence of syncope. Subsequently, this patient has done well after implantation of a pacemaker. These observations suggest that there is a significant incidence of carotid sinus hypersensitivity in patients with unexplained syncope. Permanent pacing appears to be beneficial in selected patients based on clinical and electrophysiologic findings.

Electrocardiographic manifestations of the rapid recharge function of pulse generators after sensing.

In this report, we present our observations in three patients with Medtronic Spectrax VVI pulse generators that exhibited unusually clear electrocardio-Spectrax VVI pulse generators that exhibited unusually clear electrocardiographic artifacts, due to the rapid recharge function upon sensing. Although many contemporary pulse generators contain rapid recharge circuits operative after the delivery of a pacemaker stimulus, only certain Medtronic Spectrax pulse generators also possess a rapid recharge capability after sensing. Rapid recharge upon sensing may produce electrocardiographic deflections that should not be misinterpreted as pacemaker malfunction.

The automatic implantable cardioverter-defibrillator. Clinical experience, complications, and follow-up in 25 patients.

Twenty-five patients with recurrent ventricular tachyarrhythmias underwent implantation of an automatic implantable cardioverter-defibrillator. The mean length of follow-up was 11.9 +/- 10.8 months. Before the implantation, the patients had survived one or more cardiac arrests (mean, 1.7; range, 1 to 4) and episodes of syncope (mean, 2.2; range, 2 to 3) and had received 6.0 +/- 1.0 antiarrhythmic drug trials. The in-hospital complications included death (two patients), reoperation (one patient), intraoperative myocardial infarction (one patient), sensing-failure (one patient), infection (five patients), and pocket seroma (two patients). The posthospital complications included device failure (four patients), device deactivation (one patient), and inappropriate discharge (two patients). The device discharged appropriately in seven patients due to sustained ventricular tachycardia. During electrophysiologic measurements, the energy requirement for successful cardioversion-defibrillation was related to the type of ventricular arrhythmia induced (monomorphic or pleomorphic ventricular tachycardia or fibrillation). Ventricular tachycardia acceleration occurred in ten patients (40%). No significant changes were found in the size of the electrograms or in the cardioversion threshold during early and late follow-up measurements. Life table analysis showed a 12-month survival rate of 86% and an arrhythmic death survival rate of 100%. We confirm the improved rate of survival in this high-risk group of patients, despite significant complications.

Performance of implantable cardiac rhythm management devices.

Our data represent use, follow-up, and management decisions from seven independently functioning centers and most importantly, actuarial survival of ICRMDs that have been implanted for sufficient time period to allow assessment of time versus failure. General patterns of possible target durations for adequate performance for present or future generations of similar clinical devices may be suggested by the data that we have presented. However, it would be inappropriate to conclude from these data that any presently implanted ICRMD would have a particular functional reliability. These data, furthermore, only summarized device hardware performance and cannot and must not be used to determine either short-term or long-term individual patient status, management, or outcome.

Twelve years of clinical experience with lithium pulse generators.

The clinical performance of 9,651 lithium pulse generators, which were implanted at our registry hospitals since 1973, was assessed by analysis of actuarial survival data and information obtained at the time of pacemaker failure. Cumulative survival estimates for all units were: 5 years, 94 percent, 7 years, 81 percent, 10 years, 62 percent. Discriminant actuarial analysis revealed no differences between lithium iodine and lithium cupric sulfide longevity. Battery depletion was found in 49.1 percent of 277 units subjected to detailed explant analysis, while 31 percent and 8.7 percent had component and hermetic seal defects, respectively. Of the pulse generators with battery depletion, all but two units exhibited normal end-of-battery life behavior. We conclude that the lithium iodine and lithium cupric sulfide batteries are safe, long-term energy sources; however, the impact of reduced battery size and dual chamber pacing on these performance parameters is unknown.

Temporary pacing. Indications, modes, and techniques.

This article reviews the indications for temporary pacing, describes and illustrates the techniques, discusses the fundamentals of electrical stimulation, and explores special applications, including overdrive and dual-chamber DDD pacing.

Programmability: a clinical approach.

Programmability is a vital characteristic of any implantable pacing system. It allows the physician to alter or adjust pulse-generator behavior at any time during or after pacemaker insertion. This capability has been shown to reduce the need for reoperation to correct sensing and pacing malfunctions. Moreover, programmability can be utilized to prolong battery life, evaluate lead-electrode performance, and individualize the pacemaker prescription.

The cost of tachyarrhythmia management.

Health economy measures in the United States demand that physicians develop more cost effective approaches to the management of patients who have tachyarrhythmias. Accordingly, the hospital records of 47 patients admitted for electrophysiologic evaluations were reviewed. The average length hospital stay for patients who had ventricular tachycardia was 32 days (range: 7-75) and the average cost of hospitalization was $41,988 (range: $6,299-131,259) per patient. Hospitalization costs were significantly less for 14 patients who had supraventricular tachycardia and for 10 patients who were evaluated for syncope of uncertain etiology. The cost of hospitalization correlated significantly with the length of hospital stay (r = 0.98). Therefore, new approaches to managing critical arrhythmias are needed; these include outpatient surveillance and intervention systems, use of potentially curative therapies; e.g. resection or ablation application of electrical devices capable of detecting and terminating lethal arrhythmias.

Techniques for improving cardiac performance with implantable devices.

A variety of pacing techniques are available to improve cardiac performance in patients who have bradyarrhythmias. These approaches include the preservation of AV synchrony and rate responsiveness, whereby pacing rate is varied according to some physiologic marker such as the atrial rate. New rate responsive pacemakers utilize other sensors to govern pacing rate and these units may monitor QT interval duration, respiratory rate, activity, venous oxygen saturation, temperature, or pH. Additional sensors are presently being investigated and prototype stroke volume and pressure monitoring devices should be available in the near future. All of these approaches require clinical evaluation and their eventual widespread application must be preceded by thorough studies of benefit, risk, and cost.