Automatically optimizing pacing output: an excellent idea, but with potentially lethal pitfalls.

AutoCapture (AC) and Ventricular Capture Management (VCM) are pacing algorithms that attempt to automatically optimize pacing output, providing consistent capture and enhancing device longevity. This report describes potentially serious consequences from use of these algorithms. In one pacemaker dependent patient, AC malfunction led to failure of ventricular capture. This was fixed with a software correction. The potential seriousness of AC malfunction leads to the recommendation that this software be downloaded into all susceptible pacemakers. In a second patient, VCM malfunction resulted in unnecessary high output pacing. Our experience illustrates the need for postmarketing surveillance when embracing newer technology.

Pacemakers and store security devices.

The ever-increasing complexity of medical device therapy and installation of public electronic security systems demands vigilance in discerning interactions that may be harmful to patients during typical activities of daily living. Premature pacemaker stimulation, isolated skipped beats, or reversion to backup asynchronous pacing have been observed during in vitro and in vivo testing. To date, no deaths and only minor inconvenience have been reported during extreme exposure of patients with pacemakers when they have come directly in contact with or in close apposition to electronic security systems. Patients with any type of implanted electronic medical system should be forewarned: "Don't lean, don't linger" near any potential source of electromagnetic interference. Changing technologies in implantable electronic medical systems as well as societal sources of electromagnetic interference require continued awareness on the part of physicians and patients alike, with care being taken to distinguish largely theoretical hazards from those that constitute meaningful dangers to patients with implanted cardiac arrhythmia devices.

Transient right bundle branch block causing R wave attenuation postdefibrillation.

Transient and significant decrease in R wave amplitude, associated with transient right bundle branch block, was noted to occur after defibrillation in a defibrillator patient. The mechanism is probably stunning of the right bundle branch, causing right intraventricular conduction delay and decrease in signal amplitude reaching the endocardial sensing dipoles.

Subclavian crush syndrome complicating transvenous cardioverter defibrillator systems.

UNLABELLED: Subclavian crush syndrome, described with pacemaker leads implanted via subclavian puncture, may occur when conductor fractures and insulation breaches develop by compression of a lead between the first rib and clavicle. We reviewed our experience in 164 patients who underwent intended implantation of transvenous defibrillator systems to determine the clinical relevance of subclavian crush syndrome in defibrillator patients. Venous access was obtained via subclavian puncture in 114 patients (70%) and via cephalic cut-down in 50 patients (30%). Nonthoracotomy lead systems, with or without subcutaneous patch, were successfully implanted in 131 of 164 patients (79.9%). Thoracotomy was required in 32 patients (19.5%) and subxiphoid patch in 1 patient (0.6%). Over a mean of 12.9 months (range 1-62 months), 3 patients (1.8%) required revision of the rate sensing lead/coil or superior vena cava coil after development of lead compression fractures in the region of the clavicle and first rib. In all 3 patients the leads had been implanted via subclavian puncture (2.6% of patients in whom the subclavian technique was utilized). Two patients presented with spurious shocks. One patient was asymptomatic. CONCLUSIONS: When venous access is obtained via subclavian puncture, subclavian crush syndrome may develop in patients with transvenous defibrillator systems. Patients may be asymptomatic and lead fractures may go unrecognized. When implanting transvenous defibrillator systems, strong consideration should be given to obtaining venous access primarily via the cephalic cut-down technique.

Ventricular pacing induced ventricular tachycardia in patients with implantable cardioverter defibrillators.

Appropriately timed noncompetitive ventricular pacing potentially may initiate ventricular tachycardia in patients prone to these arrhythmias. The combination of bradycardia pacing and stored electrograms in a currently available cardioverter defibrillator provides an opportunity to evaluate the occurrence of such pacing induced ventricular tachycardia. During a surveillance period of 18.7 +/- 11.4 months, stored electrograms documented 302 episodes of ventricular tachycardia in 77 patients. Five patients (6.5%) demonstrated 25 episodes (1-16 per patient) of ventricular tachycardia that were immediately preceded by an appropriately paced ventricular beat (8.3% of all episodes of ventricular tachycardia). All five patients had prior myocardial infarctions and a history of monomorphic ventricular tachycardia occurring both spontaneously and in response to programmed electrical stimulation. Antitachycardia pacing terminated pacing induced ventricular tachycardia in 22 episodes; in one episode antitachycardia pacing accelerated ventricular tachycardia. In two cases shock therapy was aborted for nonsustained ventricular tachycardia. We conclude that, in selected nonsustained ventricular tachycardia. We conclude that, in selected postinfarction patients with recurrent sustained monomorphic ventricular tachycardia treated with implantable cardioverter defibrillators, appropriately timed ventricular pacing may induce ventricular tachycardia.

Submammary pacemaker implantation: a unique tunneling technique.

Submammary pacemaker implantation offers women a cosmetically acceptable alternative to the standard pectoral implant. We present a novel method of submammary implantation performed on ten women aged 13-54 years. The lead electrodes are tunneled from the infraclavicular to the inframammary incision using a long needle, guidewire, and introducers/dilators in a manner analogous to the retained guidewire technique used for standard lead insertion. The procedure can generally be performed under local anesthesia. All patients tolerated the procedure well without acute complications. Over 2- to 23-month follow-up, there were no lead dislodgments. No patients developed mastitis or incisional complications, and all have been extremely satisfied with the cosmetic results. With proper technique, submammary pacemaker implantation can be performed under local anesthesia with minimal patient discomfort and optimal cosmesis.

A comparison of VVIR and DDDR pacing following cardiac transplantation.

UNLABELLED: We compared the clinical course of patients paced in VVIR versus DDDR mode to determine the most appropriate method of pacing following cardiac transplantation. Pacemaker implantation was required in 9 of 90 orthotopic cardiac transplants (10%). Indications included sinus bradycardia or sinus arrest (8 patients) and AV node dysfunction (1 patient). VVIR pacemakers were implanted in four patients and DDDR in five patients. DDDR patients: The mean P wave was 1.7 mV and the mean atrial stimulation threshold was 0.8 V (at 0.5 msec). During follow-up of 20 months, two atrial lead complications developed (29% of leads in 33% of patients). No lead complications were directly related to endomyocardial biopsy. VVIR patients: All four patients developed VA conduction with mean VA time 180 msec (160-240 msec). Two patients developed pacemaker syndrome. CONCLUSIONS: VA conduction and pacemaker syndrome may develop in cardiac transplant recipients paced in the VVIR mode. Dual chamber pacing is technically feasible and preferable following cardiac transplantation.

The automatic implantable cardioverter-defibrillator: efficacy, complications and survival in patients with malignant ventricular arrhythmias.

Ninety-four patients underwent surgery for automatic implantable cardioverter-defibrillator implantation. Ninety patients were discharged from the hospital with the device and were followed up for a mean period of 17 +/- 10 months. Forty-six patients experienced at least one discharge of the device under circumstances consistent with a malignant ventricular arrhythmia. One sudden death occurred. Complications included perioperative death (3 patients), post-operative ventricular tachycardia (12 patients) and atrial fibrillation (8 patients), perioperative myocardial infarction (1 patient) and device discharges for sinus tachycardia and supraventricular arrhythmias (17 patients). Six and 12 month survival rates by life table analysis were 98.7 and 95.4%, respectively. Thus, the automatic implantable cardioverter-defibrillator is a highly effective and relatively low risk treatment modality for patients with refractory life-threatening ventricular arrhythmias.

Performance of implantable cardiac rhythm management devices.

Our data represent use, follow-up, and management decisions from eight independently functioning centers and most importantly, actuarial survival of ICRMD's that have been implanted for a 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. Furthermore, these data 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.

Clinical and hemodynamic comparison of VVI versus DDD pacing in patients with DDD pacemakers.

To identify better those subgroups of pacemaker recipients who will benefit from dual chamber pacing, 19 patients with DDD pacemakers that were physiologically paced were entered into a blinded, randomized protocol comparing long-term VVI versus DDD pacing. Patients were evaluated in each of the pacing modes for exercise performance, cardiac chamber size, cardiac output, functional status and health perception. Eight patients (42%) insisted on early crossover, from VVI to DDD pacing, after only 1.8 +/- 1.4 weeks because of symptoms consistent with pacemaker syndrome. Overall, 12 patients preferred DDD pacing and no patient preferred VVI pacing (p = 0.001). Percent fractional shortening (30 +/- 8 vs 24 +/- 6%, p = 0.009) and cardiac output (6.3 +/- 2.6 vs 4.4 +/- 2.2 liters/min, p = 0.0001) where significantly greater in the DDD mode. Exercise duration was greater during DDD compared with VVI pacing (11.3 +/- 3.7 vs 10.1 +/- 3.7 minutes, p = 0.006). However, it was only in the crossover subgroup that DDD pacing resulted in significant improvement in exercise performance and health perception compared with VVI pacing. This subgroup of patients was characterized by an intrinsic sinus rate of less than 60 beats/min (4/8 vs 0/11, p = 0.006), ventriculoatrial (VA) conduction (4/8 vs 1/11, p = 0.048), greater increase in exercise peak systolic blood pressure from VVI to DDD mode (21 +/- 12 vs 4 +/- 13 mm Hg, p = 0.02) and greater improvement in exercise capacity from VVI to DDD pacing (2.2 +/- 1.2 vs 0.6 +/- 1.4 minutes, p = 0.03) compared with the other 11 patients.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Single-chamber and dual-chamber cardiac pacemakers. A formal cost comparison.

Dual-chamber pacemakers, more sophisticated and costly than single-chamber pacemakers, are being used with increasing frequency, often with unclear indications. Proponents of dual-chamber devices have focused on initial differences in cost without considering additional induced costs. We examined the incremental cost of dual-versus single-chamber pacemakers over the expected lifetime of a pacemaker recipient. In addition to initial costs, we included the costs of pacemaker malfunction, reimplantation, generator replacement, and follow-up. Expected differences in cumulative costs per patient were calculated over a 12-year period. Dual-chamber pacing is $2500 more costly at implantation. The difference in cumulative cost increases to $5100 by year 12, reflecting shorter functional life for dual-chamber pacemaker generators and increased cost of follow-up. The incremental cost of dual-chamber pacemaking is neither short-term nor trivial. Dual-chamber pacemakers should be reserved for those who clearly benefit from its advanced technology.

Pacemaker-mediated tachycardias: an unresolved problem.

The advent of dual chamber pacing systems that restore atrioventricular synchrony and allow rate variability in response to physiologic stress has provided a major advance in pacing therapy. Undesirable pacemaker-mediated tachycardias may arise when the atrial sensing amplifier of a VDD or DDD device detects a retrogradely conducted P-wave, ectopic atrial tachycardia, myopectoral contractions, or environmental electromagnetic interference. The rate of the resultant tachycardia is determined by the programmed upper tracking rate of the pacemaker. Although seldom life-threatening, troublesome myocardial ischemia may ensue in patients with coronary artery disease. In most instances, the incidence and rate of pacemaker-mediated tachycardias may be minimized by judicious programming.