Biomedical subjects
Publications and source records attributed to G L Dolack.
Runaway pacemaker occurred in a patient undergoing high-energy neutron radiation therapy despite adherence to published safety guidelines. The very low estimated dose of 0.9 Gy received by the pacemaker demonstrates the extreme sensitivity of integrated circuits to this new modality of radiation therapy.
A 49-year-old woman underwent a successful radiofrequency catheter ablation of a left-sided accessory pathway using a retrograde approach across the aortic valve. Routine echocardiography performed 20 hours after the procedure revealed a new aortic valve mass. Five blood cultures were negative. An echocardiogram after 2 days of heparin therapy showed complete resolution of the mass. There was no clinical evidence of embolization. Echocardiography may need to be performed routinely after catheter ablations performed retrograde across the aortic valve so that this potentially devastating complication can be diagnosed and treated early in its course.
BACKGROUND: Implantable transvenous cardioverter-defibrillators offer a significant opportunity to decrease procedural morbidity and medical costs in the care of patients with life-threatening ventricular arrhythmias who otherwise would have required a sternotomy or thoracotomy for device insertion. The purpose of this study was to examine prospectively the safety, efficacy, and limitations associated with the use of a transvenously implanted, tiered-therapy cardioverter-defibrillator with antitachycardia pacing function in a consecutive population of 84 ventricular fibrillation (VF) and sustained ventricular tachycardia (VT) survivors. METHODS AND RESULTS: The index arrhythmia promoting transvenous cardioverter-defibrillator implantation was VF in 41 patients, VT in 27, and both VF and VT in 16. In each patient, transvenous defibrillation via a coronary sinus, a right ventricular, a superior vena caval, and/or a subcutaneous chest patch lead system was attempted. The pulsing methods used include two-electrode single-pathway pulsing or three-electrode dual-pathway simultaneous or sequential pulsing. A transvenous cardioverter-defibrillator was inserted if the defibrillation threshold (DFT) was < or = 20 J. Successful implantation of a transvenous cardioverter-defibrillator was possible in 80 of 84 (95%) patients. The mean implant DFT was 10.9 +/- 4.8 J. After cardioverter-defibrillator implantation, all patients were extubated in the operating room and sent to a standard telemetry ward for monitoring. No patient suffered a postoperative pulmonary complication or perioperative flurry of cardiac arrhythmias. Postoperative complications included lead dislodgments in eight, transient long thoracic nerve injury in one, asymptomatic left subclavian vein occlusion in two, asymptomatic small pericardial effusion in one, subcutaneous patch pocket hematomas in four, pulse generator pocket infection in one, and lead fracture in one. As experience was gained with the procedure, it was routine to discharge patients 3 days after surgery. The mean hospital stay was 6.0 +/- 2.4 days. Upon discharge, all patients returned to their prehospital activities including those with complications except for the patient with a pocket infection, who required intravenous antibiotic therapy. Patient survival using an intention-to-treat analysis was 98% over an 11 +/- 7-month follow-up period. During this time period, 31 of the 80 patients (39%) with transvenous lead systems were successfully treated by their device for sustained VT or VF. Antitachycardia pacing was used in 424 episodes of monomorphic VT and was successful in 371 (88%). All episodes of VF were aborted by the device. Antiarrhythmic drugs were used after device implantation in only eight of 80 patients (10%). CONCLUSIONS: Transvenous cardioverter-defibrillator implantation is practical in most candidates. Implant DFTs are usually low, surgical morbidity and postoperative complications are modest, therapy of VT and VF is efficient, and survival is excellent.
BACKGROUND: Multiprogrammable antiarrhythmia devices can treat monomorphic ventricular tachycardia (VT) with autodecremental overdrive pacing and/or with low-energy cardioversion. These two methods provide the opportunity to decrease patient discomfort typically experienced with high-energy pulses. Although both therapies are known to be effective, controversy persists over their relative safety and efficacy. METHODS AND RESULTS: The purpose of this study was to examine the safety and efficacy of autodecremental overdrive pacing and low-energy cardioversion in reproducibly terminating monomorphic VT in 24 patients with multiprogrammable antiarrhythmia devices. The protocol required that identical ECG morphology VT be reproducibly induced four times to assess the outcome of antitachycardia pacing and cardioversion twice for each patient in a randomized fashion. Each episode of VT was induced via the implanted device. Autodecremental overdrive pacing initially began with seven stimuli at 97% of the VT cycle length, decrementing by 10 msec per stimulus to a minimum coupling interval of 200 msec. If ineffective, autodecremental overdrive pacing was allowed to iterate three more times for a total of four pacing interventions. With each iteration, one stimulus was added to the pacing train. Similarly, with low-energy cardioversion, up to four therapeutic attempts were made, beginning with a 0.2-J pulse. If ineffective, pulse energy was increased to 0.4, 1.0, and finally 2.0 J. All interventions were automatic without human interference. VT (cycle length, 306 +/- 42 msec) was repeatedly terminated in 15 of 24 patients (63%) by autodecremental overdrive pacing and in 18 of 24 patients (75%) by low-energy cardioversion (p = 0.53). Eight of the 24 patients (33%) had their VT terminated repeatedly by both therapies. VT accelerated to faster VT or ventricular fibrillation by autodecremental overdrive pacing in four of 24 patients (17%) and by low-energy cardioversion in five of 24 (21%) (p = 0.88). Only one of the 24 patients (4%) accelerated with both therapies. No patient was unaffected by either therapy. CONCLUSIONS: In the manner programmed, autodecremental overdrive pacing and low-energy cardioversion have similar efficacy and acceleration rates. Response to one therapy does not predict response to the other.
BACKGROUND: Transvenous implantable cardioverter-defibrillators provide significant advantages in the treatment of patients with life-threatening ventricular arrhythmias. However, present technology requires considerable electrophysiology expertise, multiple incisions, and long operative times for successful implementation. METHODS AND RESULTS: In this study, we present a prototype of a new, easy-to-insert unipolar transvenous defibrillation system that has the reliability of epicardial defibrillation but the ease of pacemaker insertion. This system incorporates a single anodal right ventricular defibrillation electrode using a 65% tilt biphasic pulse delivered to a 108-cm2 surface area pulse generator titanium alloy shell as an active cathode placed in a left infraclavicular pocket. Testing of this system was performed before implantation of a standard nonthoracotomy-transvenous defibrillation system in 40 consecutive patients with a history of ventricular tachycardia or fibrillation. The simplified unipolar single-lead system resulted in a defibrillation threshold of 9.3 +/- 6.0 J with 37 of 40 patients (93%) having a defibrillation threshold of less than 20 J. Moreover, the unipolar defibrillation system was efficiently used requiring only 3.4 +/- 0.8 ventricular fibrillation inductions to measure the defibrillation threshold and 100 +/- 28 minutes to implement. CONCLUSIONS: This new unipolar transvenous defibrillation system is as simple to insert as a pacemaker, requires few ventricular fibrillation inductions, demands less technical expertise, and provides defibrillation at energy levels comparable to that reported with epicardial lead systems. It should substantially reduce the morbidity, time, and cost of defibrillator implantation.
BACKGROUND: The purpose of this report is to describe our initial experience with a tiered-therapy, variable detection criteria, multiprogrammable antiarrhythmia device capable of antitachycardia pacing, cardioversion, and defibrillation in 50 cardiac arrest survivors. METHODS AND RESULTS: An epicardial lead system was used in 35 patients. A transvenous lead system was used in 15 patients. The index arrhythmia leading to device implantation was ventricular fibrillation (VF) in 23 patients, ventricular tachycardia (VT) in 21 patients, and both VT and VF in six patients. Postoperatively, all 50 patients benefited from the additional functions available in the new device compared with a device capable only of high-energy termination of arrhythmias using a simple rate detection algorithm. Total patient survival over a mean follow-up period of 15 +/- 5 months was 96%, with no patient succumbing to sudden arrhythmic death, cardiac death, or surgical death. Nine patients (18%) avoided the need for a bradycardia pacemaker because of the device's backup bradycardia pacing function. A programmable tachycardia cycle length stability algorithm prevented inappropriate device intervention into atrial fibrillation in 11 patients (22%). Detection schema flexibility, antitachycardia pacing capabilities, and low-energy cardioversion options allowed the elimination or avoidance of antiarrhythmic drugs in 41 patients (82%). Device data storage facilitated troubleshooting and reprogramming of detection algorithms and therapeutic schema in all 50 patients. Finally, the ability to perform noninvasive programmed electrical stimulation obviated the need for invasive cardiac catheterization in 35 of 35 patients who required electrophysiological testing after device implantation. CONCLUSIONS: These findings indicate that a multiprogrammable antiarrhythmia device can provide a substantial advance in the treatment of patients with disabling or life-threatening ventricular arrhythmias by minimizing the use of painful shocks, reducing the need for antiarrhythmic drugs, lowering the incidence of inappropriate shocks, facilitating electrophysiological evaluation, and obviating the need for dual-device therapy.
BACKGROUND: Several clinical studies have demonstrated a general superiority of biphasic waveform defibrillation compared with monophasic waveform defibrillation using epicardial lead systems. To test the breadth of utility of biphasic waveforms in humans, a prospective, randomized evaluation of defibrillation efficacy of monophasic and single capacitor biphasic waveform pulses was performed for two distinct nonthoracotomy lead systems as well as for an epicardial electrode system in 51 cardiac arrest survivors undergoing automatic defibrillator implantation. METHODS AND RESULTS: The configurations tested consisted of a right ventricular-left ventricular (RV-LV) epicardial patch-patch system, an RV catheter-chest patch (CP) nonthoracotomy system, and a coronary sinus (CS) catheter-RV catheter nonthoracotomy system. For each configuration, the defibrillation current and voltage waveforms were recorded via a digital oscilloscope to measure defibrillation threshold voltage, current, resistance, and stored energy. Biphasic waveform defibrillation proved more efficient than monophasic waveform defibrillation for the epicardial RV-LV system (4.8 +/- 4.1 versus 6.7 +/- 4.9 J, p = 0.047) and the nonthoracotomy RV-CP system (23.4 +/- 11.1 versus 34.3 +/- 10.4 J, p = 0.0042). Biphasic waveform defibrillation thresholds were not significantly lower than monophasic waveform defibrillation thresholds for the CS-RV nonthoracotomy system (15.6 +/- 7.2 versus 20.0 +/- 11.5 J, p = 0.11). Biphasic waveform defibrillation proved more efficacious than monophasic waveform defibrillation in 13 of 20 patients (65%) with RV-LV epicardial patches, 10 of 15 patients (67%) with an RV-CP nonthoracotomy system, and nine of 16 patients (56%) with an RV-CS nonthoracotomy system. CONCLUSIONS: Biphasic pulsing was useful with nonthoracotomy lead systems as well as with epicardial lead systems. However, the degree of biphasic waveform defibrillation superiority appeared to be electrode system dependent. Furthermore, for a few individuals, biphasic waveform defibrillation proved less efficient than monophasic waveform defibrillation, regardless of the lead system used.
The results of signal-averaged electrocardiography and programmed electrical stimulation were evaluated in 25 patients with recurrent sustained ventricular tachycardia (VT) and 46 patients with a history of out-of-hospital ventricular fibrillation (VF) to characterize the electrophysiologic substrate responsible for these different clinical arrhythmia presentations. Patients with VT had a higher incidence of late potentials (VT 83%, VF 50%, p = 0.005). Significant differences between these groups were also noted in response to programmed electrical stimulation. A sustained ventricular arrhythmia was induced in 24 of 25 (96%) patients with a history of VT but in only 27 of 46 (59%) of VF patients (p = 0.005). In addition, VF was induced in 11 (24%) patients in the VF group but in none of the patients in the VT group (p = 0.005). When the 2 groups were compared on the basis of select clinical characteristics, no significant difference in age, sex, presence of coronary artery disease or ejection fraction was noted. The frequency of prior myocardial infarction was significantly higher in the VT group (VT 20 of 25, 80%; VF 24 of 46, 52%; p = 0.03). Finally, no significant relation between the presence of late potentials and induced arrhythmias was noted in either group. The inability of signal-averaged electrocardiography to predict inducibility in VF patients may represent a significant limitation of this technique in identifying patients at risk for sudden cardiac death.