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G H Bardy

Publications and source records attributed to G H Bardy.

At least 55 records · Page 3Linked to original sources
PubMed1995

Serial defibrillation threshold measures in man: a prospective controlled study.

UNLABELLED: Serial DFT Measures in Man. INTRODUCTION: The defibrillation threshold (DFT) may change throughout the first year following implantation of a cardioverter defibrillator, but it remains uncertain if changes are a consequence of changes in clinical condition or are related to fundamental alterations at the electrode-tissue interface. The purpose of this study was to evaluate the extent and time course of DFT changes over the first year following implantable cardioverter defibrillator (ICD) surgery when extraneous clinical and device variables potentially affecting the DFT were excluded. METHODS AND RESULTS: We prospectively enrolled 61 patients undergoing epicardial or nonthoracotomy/transvenous ICD therapy into a series of follow-up studies where the DFT was measured at implant and at 1, 6, 12, and 52 weeks following implantation in a uniform manner. Stored energy DFT was measured and recorded for all patients. Patient exclusion criteria were: (1) inability to complete all five measures of the DFT; (2) institution of Class I or Class III antiarrhythmic drugs at any time during the study; (3) lead system changes (relocation or new leads) or programming changes in pulse width or current pathway; or (4) development of a significant change in their clinical status, such as decompensated congestive heart failure or acute ischemia. Only 20 of the 61 patients satisfied the criteria required to complete the study. Two of the excluded patients developed high DFTs, which required reprogramming of the current pathway. Eight patients had an epicardial lead system, and 12 had a nonthoracotomy lead system.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

Considerations for ventricular fibrillation detection by implantable cardioverter defibrillators.

Implantable cardioverter defibrillator detection of ventricular fibrillation is inherently a complicated process. Nevertheless, there is a clinical imperative that ventricular fibrillation be detected with 100% sensitivity. Incumbent with the need for such a high sensitivity is a trade-off that results in diminished ventricular fibrillation detection specificity, which in turn results in unnecessary delivery of high-energy shocks. In this review we look in generic terms at the different lead and detection systems available and the effect of these systems on both undersensing and oversensing of ventricular fibrillation. In addition, several clinical and programming issues that affect sensitivity and specificity of ventricular fibrillation detection are reviewed.

Algorithms↗
PubMed1994

Advances in implantable cardioverter-defibrillator therapy.

The use of implantable defibrillation systems in patients with cardiac arrest has resulted in lower mortality than expected from studies of similar patients not receiving defibrillators. Nonthoracotomy lead systems have led to a decrease in operative mortality and lowered the cost of defibrillator implantation, but these systems have a higher energy requirement for defibrillation than do epicardial ones. The recent introduction of single-lead systems and bipolar defibrillation pulses has simplified nonthoracotomy defibrillator implantation and improved defibrillation efficiency. A prototype unipolar, single-lead pectoral implant defibrillation system is described that may significantly improve the reliability, safety, and cost effectiveness of nonthoracotomy defibrillators. This and other improved nonthoracotomy systems may expand the indications for defibrillator implantation to prophylactic use in high-risk patients who have not yet experienced life-threatening ventricular arrhythmias.

Defibrillators, Implantable↗
PubMed1994

Biphasic waveform defibrillation using a three-electrode transvenous lead system in humans.

INTRODUCTION: Biphasic waveform defibrillation is not always more efficacious than monophasic waveform defibrillation. METHODS AND RESULTS: Waveform efficacy appears to vary with the lead system used. In this prospective, randomized study, defibrillation efficacy with biphasic and monophasic single capacitor 120-microF, 65% tilt pulses was compared for a lead system consisting of right ventricular (RV), chest patch (CP), and superior vena cava (SVC) electrodes. Although this lead system is commonly used with monophasic pulses in transvenous defibrillators, few studies have examined the defibrillation efficacy of this lead system in man for biphasic waveform defibrillation. Fourteen cardiac arrest survivors undergoing defibrillator implantation were included in the study using pulses delivered from a cathodal RV electrode simultaneously to anodal SVC and CP electrodes. Biphasic and monophasic waveforms were recorded oscilloscopically to acquire defibrillation threshold (DFT) data on leading edge voltage requirements and for stored energy. The monophasic DFT voltage was 661 +/- 177 V compared to the biphasic DFT voltage of 451 +/- 185 V (P < 0.0001). The monophasic DFT stored energy was 28.0 +/- 13.4 J compared to the biphasic DFT stored energy of 14.1 +/- 12.4 J (P < 0.0001). The stored energy DFT was < or = 15 J in only 2 of 14 patients (15%) with monophasic defibrillation but < or = 15 J in 10 of 14 (71%) patients with biphasic defibrillation. CONCLUSION: These findings indicate that biphasic defibrillation with an RV, SVC, CP transvenous electrode system is substantially more efficient than monophasic defibrillation, allowing for higher numbers of patients to receive transvenous defibrillators with a relatively simple lead system at a satisfactory cutoff DFT safety margin of 15 J.

Adolescent↗
PubMed1994

A prospective randomized comparison of defibrillation efficacy of truncated pulses and damped sine wave pulses in humans.

INTRODUCTION: Damped sine wave pulses have been used for nearly 50 years in transthoracic defibrillation systems. The purpose of this study was to determine whether damped sine wave pulses have a role in implantable defibrillators. METHODS AND RESULTS: In 21 survivors of cardiac arrest, we prospectively compared defibrillation efficacy of a standard truncated capacitor (RC) monophasic pulse with a damped sine wave inductor-capacitor (LRC) pulse using a right ventricular-left ventricular epicardial patch-patch electrode system. The RC pulse was a standard 65% tilt monophasic waveform generated from a 120 mu F capacitor. The LRC pulse was designed to simulate the waveform currently used in transthoracic defibrillators and was generated by passing the charge stored on a 40 mu F capacitor through a 37-mH inductor. Capacitor voltage, peak delivered voltage, peak delivered current, discharge pathway resistance, delivered energy, and stored energy were compared for the two waveforms at the defibrillation threshold. There was no difference in defibrillation efficacy for the two waveforms. Peak delivered voltage was similar at the defibrillation threshold: 313 +/- 101 V for the RC pulse and 342 +/- 119 V for the LRC pulse (P = 0.16). Similarly, no differences were found in defibrillation threshold peak delivered current: 8.6 +/- 2.5 (RC) versus 9.3 +/- 2.7 (LRC) amperes (A) (P = 0.20); discharge pathway resistance: 37 +/- 11 (RC) versus 38 +/- 13 (LRC) omega (P = 0.71); delivered energy: 7.0 +/- 4.5 (RC) versus 7.0 +/- 4.0 (LRC) joules (J) (P = 0.88); and stored energy: 8.7 +/- 5.7 (RC) versus 9.8 +/- 5.4 (LRC) J (P = 0.35). Although both waveforms performed the same, it was necessary to use substantially higher stored voltages with the damped sine wave delivery system than with the truncated waveform delivery system: 356 +/- 110 V for the RC pulse and 675 +/- 192 V for the LRC pulse (P < 0.0001). CONCLUSION: This study demonstrates that RC monophasic pulses provide equally effective epicardial defibrillation as LRC pulses with respect to delivered voltage and current and stored and delivered energy. However, in order for LRC pulses to provide comparable delivered voltage, current, and energy to that of RC pulses, nearly twice the voltage must be stored on the capacitor to accomplish the same task. These findings suggest that despite the nearly 50-year experience with damped sine wave pulses with transthoracic defibrillators, there is no need to begin using damped sine wave pulses for implantable defibrillators. Moreover, these data raise a question regarding the need for inductors in transthoracic defibrillators.

Aged↗
PubMed1994

The implantable pace-maker-cardioverter-defibrillator: radiographic aspects.

Safer and easier placement, recent approval by the U.S. Food and Drug Administration of several models, and increasing availability have expanded the use of implantable cardioverter-defibrillators (ICDs) for treatment of life-threatening ventricular tachyarrhythmia. Modern ICDs generally use a combination of two transvenously placed electrodes and one subcutaneous electrode; therefore, they do not require a thoracotomy for placement. The authors evaluated the radiographic aspects of one particular ICD--the pacemaker-cardioverter-defibrillator (PCD)--including the normal appearance and variations, confusing findings, and such complications as deformity of the subcutaneous patch electrode, lead fracture, and electrode malposition and migration. The PCD can also be combined with a preexisting, surgically placed automatic ICD or with a pacemaker. Familiarity with the PCD and other ICDs is essential, since the radiologist may be the first to recognize a complication that can render the device inoperative and leave the patient vulnerable to sudden death.

Defibrillators, Implantable↗
PubMed1994

Prospective, randomized comparison in humans of a unipolar defibrillation system with that using an additional superior vena cava electrode.

BACKGROUND: A unipolar defibrillation system using a single right ventricular (RV) electrode and the active shell or "CAN" of the implantable cardioverter-defibrillator itself situated in a left infraclavicular pocket has been shown to be as efficient in defibrillation as an epicardial lead system. The purpose of this study was to determine whether defibrillation efficacy can be improved further by adding a superior vena cava (SVC) electrode to this already efficient defibrillation system. METHODS AND RESULTS: We prospectively and randomly compared the defibrillation efficacy of a simplified unipolar defibrillation system, RV-->CAN, with that of one incorporating a high SVC electrode, RV-->SVC + CAN, in 15 consecutive cardiac arrest survivors undergoing implantation of a presently available transvenous defibrillation system. The RV defibrillation electrode was a 5-cm coil located on a 10.5F lead used as the anode in both lead configurations examined. The active CAN was a 108-cm2 surface area shell of a titanium alloy pulse generator used as the cathode in both configurations and placed in a left infraclavicular pocket. The SVC electrode was a 6F 5-cm-long coil and was used as an additional cathode positioned at the junction of the SVC and the left innominate vein. The defibrillation pulse used was a 65% tilt, asymmetric biphasic waveform delivered from a 120-microF capacitor. The defibrillation threshold (DFT) stored energy, leading edge voltage, current, and pulsing resistance were measured for both lead systems. The single-lead unipolar system, RV-->CAN, resulted in a stored energy DFT of 7.4 +/- 5.2 J, and the three-electrode dual pathway system, RV-->SVC + CAN, resulted in a DFT of 6.0 +/- 3.4 J (P = .20). There was no difference in defibrillation efficacy with the more complicated three-electrode system over the unipolar system despite a decrease in pulsing resistance to 48.6 +/- 3.5 omega compared with 61.2 +/- 5.9 omega for the unipolar system (P < .0001) and a slight rise in delivered current to 6.3 +/- 1.8 A compared with 5.5 +/- 2.0 A for the unipolar system (P = .062). CONCLUSIONS: The unipolar single-lead transvenous defibrillation system provides defibrillation at energy levels comparable to that reported with present epicardial lead systems. Coupling of this lead system to a third SVC electrode increases system complexity but offers little defibrillation advantage despite a large decrease in pulsing resistance and a modest increase in delivered current.

Defibrillators, Implantable↗
PubMed1994

Efficacy of a single-lead unipolar transvenous defibrillator compared with a system employing an additional coronary sinus electrode. A prospective, randomized study.

BACKGROUND: Recent development of a prototype single-lead unipolar transvenous defibrillator offers the possibility of device implantation with the ease of a permanent pacemaker. Lowering defibrillation energy requirements would allow for a further reduction in defibrillator generator size and enhance the feasibility of pacemaker-like placement. However, if achieving a lower defibrillation energy requires placing additional intracardiac leads, the potential advantage of a smaller generator may be offset by the disadvantages of a more complex lead system. The purpose of this study was to compare defibrillation energy requirements of a single-lead unipolar defibrillator with a three-electrode system employing an additional lead in the coronary sinus. METHODS AND RESULTS: Testing of a single-lead unipolar biphasic pulse defibrillation system versus a three-electrode system with an additional coronary sinus lead was performed in prospective, randomized fashion in 15 patients with a history of ventricular tachycardia or fibrillation. Ventricular fibrillation was induced with alternating current, and defibrillation threshold was measured by a pulse given 10 seconds after arrhythmia induction. The mean defibrillation threshold stored energy and mean leading edge voltage did not significantly differ between the two systems (11.3 +/- 5.9 J versus 9.9 +/- 5.2 J and 418 +/- 118 V versus 390 +/- 112 V, respectively; P > .4). Using either defibrillation system, all patients were successfully defibrillated by < 24 J and over half of patients by < 10 J. CONCLUSIONS: A unipolar transvenous biphasic defibrillation system is an effective means of treating ventricular fibrillation. The added complexity of additional leads is not offset by any significant improvement in defibrillation efficacy or energy requirements. Given the simplicity and effectiveness of a single-lead system coupled with a small generator, placement of defibrillation systems may now approach the ease of pacemaker implantation.

Adult↗
PubMed1994

Runaway pacemaker during high-energy neutron radiation therapy.

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.

Adenocarcinoma↗
PubMed1993

Development of an aortic valve mass after radiofrequency catheter ablation.

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.

Aortic Valve↗
PubMed1993

Implantable transvenous cardioverter-defibrillators.

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.

Algorithms↗
PubMed1993

A prospective randomized repeat-crossover comparison of antitachycardia pacing with low-energy cardioversion.

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.

Algorithms↗
PubMed1993

A simplified, single-lead unipolar transvenous cardioversion-defibrillation system.

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.

Adult↗
PubMed1992

Further evidence supporting the concept of T-wave memory: observation in patients having undergone high-energy direct current catheter ablation of the Wolff-Parkinson-White syndrome.

Following successful high-energy direct current catheter ablation of posterior septal accessory pathways, serial T-wave changes were observed in seven patients with Wolff-Parkinson-White syndrome, but not in two patients with a concealed accessory bypass pathway. Following catheter ablation in the patients with Wolff-Parkinson-White syndrome, the previously upright T-waves in the inferior electrocardiographic leads became inferiorly directed. Serial electrocardiograms following catheter ablation revealed slow regression of these T-wave changes over time. In contrast, in the two patients in whom a concealed accessory pathway was present, the T-waves prior to and following the procedure were upright. In these two patients, serial electrocardiograms showed no evolution of the T-wave vector over the same time period. Although a small rise in myocardial CK enzymes was observed, ischaemic injury in the area of catheter ablation could not be documented by post-procedure echocardiography, tomographic thallium scintigraphy, technetium pyrophosphate scintigraphy or coronary angiography with left ventriculography. We conclude that the observed T-wave changes in the patients with Wolff-Parkinson-White syndrome may be a result of the change in depolarization sequence resulting from loss of pre-excitation, and that the time-dependent nature of these T-wave changes is consistent with the concept of T-wave 'memory'.

Adult↗