Epicardial Patch Electrodes Research Articles

Animal Model of Cardiac Reperfusion Injury to Evaluate the Effects of Electrical Microcurrent Application: Preliminary Results

Reperfusion injury (RI) occurs after cardiac surgery, myocardial infarction or heart transplantation, however effective treatment strategies are still lacking. Cardiac micro intensity electrical current (C-MIC) modulates inflammation, myocardial remodeling and recovery in failing hearts in vivo and in vitro. This study aimed to establish a large animal model of RI to test C-MIC application on RI after cardiopulmonary bypass (CPB). Seven swines underwent CPB with 120 mins crossclamp time, and were assigned to a control (n=3) or treatment group (n=4). The treatment group received a C-MIC device consisting of an epicardial patch electrode placed on the left ventricular lateral free wall, a transvenous right ventricular counter electrode, and a current generator. C-MIC treatment was continued until CPB weaning. Reperfusion on full CPB flow lasted 20 mins, followed by a stepwise weaning process. Inotropes or pacing were not allowed. Noradrenaline was used to maintain arterial pressure and xylocaine for arrhythmia treatment. Defibrillation was performed as needed. Primary end-point was survival at 20 mins after CPB weaning. Baseline characteristics and pre-CPB hemodynamics were comparable between groups. All C-MIC devices were successfully implanted, without observed malfunction. A microcurrent in the upper µA range was delivered. In the C-MIC group, CPB weaning was successful in all animals, and survival with stable hemodynamics was observed in 50% of cases (Table 1). Weaning and survival rates were lower in the control group. Noradrenaline was required in 50% of the C-MIC animals and in 100% of control animals to maintain arterial pressure after CPB. Our study presents an animal model which allows evaluation of RI treatment strategies. In this pilot trial, the C-MIC device was safely and successfully implanted. Our data suggest a potential benefit of C-MIC treatment for RI and further studies are needed to test this promising therapy.

Chronic performance of a novel radiofrequency ablation device on the beating heart: Limitations of conduction delay to assess transmurality

The creation of consistently transmural lesions with epicardial ablation on the beating heart has represented a significant challenge for current technology. This study examined the chronic performance of the AtriCure Coolrail device (AtriCure Inc, West Chester, Ohio), an internally cooled, bipolar radiofrequency ablation device designed for off-pump epicardial ablation. The study also examined the reliability of using acute intraoperative conduction delay to evaluate lesion integrity. Seven swine underwent median sternotomy. The right atrial appendage and inferior vena cava were isolated with a bipolar radiofrequency clamp. Linear ablation lines were created between these structures with the AtriCure Coolrail. Paced activation maps were recorded with epicardial patch electrodes acutely before and after ablation and after keeping the animals alive for 4 weeks. The conduction time across the linear ablation was calculated from these maps. The lesions were histologically evaluated with trichrome staining. Only 76% of cross-sections of Coolrail lesions were transmural, and only 1 of 12 ablation lines was transmural in every cross-section examined. Mapping data were available in 5 of the animals. Significant conduction delay was present after the creation of each line of ablation acutely; however, after 4 weeks, conduction time returned to preablation values, demonstrating lack of transmurality. The AtriCure Coolrail failed to reliably create transmural lesions. Although the Coolrail was able to create acute conduction delay, its failure to transmurally ablate the atrial myocardium left gaps along the length of the lesion, which resulted in neither chronic conduction block nor delay across any line of ablation.

Epicardial application of an amiodarone-releasing hydrogel to suppress atrial tachyarrhythmias

Background Amiodarone is currently the most effective antiarrhythmic drug for sinus rhythm maintenance. However, due to serious extracardiac adverse effects, prophylactic amiodarone therapy is only appropriate for patients at high risk for postoperative atrial fibrillation (AF). We hypothesized that epicardial application of an amiodarone-releasing hydrogel would produce therapeutic myocardial drug concentrations, while systemic levels would remain low. Methods Goats were fitted with right atrial epicardial patch electrodes. A poly(ethylene glycol)-based hydrogel with amiodarone (1 mg/kg bw) ( n = 10) or without drug ( n = 6) was applied to the right atrial epicardium. Atrial effective refractory period (AERP), conduction time and atrial response to burst pacing (rapid atrial response, RAR) were assessed up to 28 days in awake goats. Myocardial, plasma and extracardiac tissue amiodarone concentrations were analysed by high-performance liquid chromatography. Results The amiodarone-loaded hydrogel produced therapeutic drug concentrations in the right atrium up to 21 days after application. In this period, AERP and conduction time were prolonged, while RAR inducibility was reduced ( P < 0.05) compared to animals treated with drug-free hydrogel. Mean amiodarone concentrations in the right atrium were 1 order of magnitude higher than in other heart chambers and 2 orders of magnitude higher than in extracardiac tissues. Plasma amiodarone levels remained below the detection limit (< 10 ng/mL) during the 28-day follow-up. Conclusions Epicardial application of an amiodarone-releasing hydrogel reduces atrial vulnerability to tachyarrhythmias up to 3 weeks, while extracardiac drug levels remain low. Therefore, amiodarone-releasing hydrogel could be applied during cardiac surgery to prevent postoperative AF at minimal risk for extracardiac adverse side effects.

Abstract 4098: Epicardial Amiodarone-Releasing Hydrogel Reduces Inducibility of Atrial Fibrillation in Goats

Amiodarone (AM) is one of the most effective anti-arrhythmic drugs to prevent postoperative atrial fibrillation (AF). However, due to systemic side effects, prophylactic AM therapy is only appropriate for patients at high risk for postoperative AF. This study addressed the hypothesis that local epicardial delivery of AM produces therapeutic myocardial drug concentrations, while systemic levels remain low. Goats (n=14) were instrumented with right atrial epicardial patch electrodes, and a PEG-based hydrogel with AM (1 mg/kg bw) (n=9) or without drug (n=5) was applied to the right atrial epicardium. AF inducibility was assessed up to 28 days in awake goats by applying burst stimuli. Myocardial and plasma AM concentrations were analysed by HPLC. AM-hydrogel produced higher subepicardial than subendocardial drug concentrations, which both remained therapeutic up to 21 days after hydrogel application (fig. 1a ). In this period, AF inducibility was significantly lower in the AM-hydrogel group compared to hydrogel alone (fig. 1b ; p&lt;0.05). Plasma AM and metabolite levels were below detection limits (&lt;30 ng/L) during the 28-day follow-up. Epicardial AM-releasing hydrogel produces sufficient myocardial drug concentrations to reduce AF inducibility up to 3 weeks, whereas plasma drug levels remain undetectably low. This study demonstrates that local delivery of anti-arrhythmic drugs is a feasible approach to obtain therapeutically effective myocardial drug concentrations, while minimizing risk for systemic side effects. Locally applied AM-releasing hydrogel may be a novel strategy to prevent postoperative AF. Figure 1a. Amiodarone Distribution in Right Atrium (n=5) Figure 1b. AF Inducibility After Hydrogel Application (mean + SD)

Map-guided surgery for atrial fibrillation

Although current surgical procedures result in a high success rate for atrial fibrillation, they are not guided by electrophysiologic findings in individual patients and thus might include unnecessary incisions in some patients or be inappropriate for other patients. We sought to determine whether intraoperative mapping is beneficial for the surgical treatment of atrial fibrillation. A 256-channel 3-dimensional dynamic mapping system with custom-made epicardial patch electrodes was used to examine the atrial activation during atrial fibrillation and to determine the optimal procedure in 37 patients with continuous and 9 patients with intermittent atrial fibrillation intraoperatively. Surgical intervention for atrial fibrillation was not indicated in 3 patients in whom the atrial electrograms had a low voltage over a broad area. Concurrent, multiple, and repetitive activations arising from the pulmonary veins or left atrial appendage were observed in all patients. A simple left atrial procedure consisting of pulmonary vein isolation and left atrial incisions without any right atrial incisions was performed in 8 patients in whom the right atrial activation was passive, and all (100%) were cured of atrial fibrillation. The radial procedure was performed in the remaining 35 patients, and 31 (89%) of the patients were cured of atrial fibrillation. In this subset of patients, 10 exhibited reentrant or focal activation in the posterior left atrium between the right and left pulmonary veins and required an additional linear ablation on the posterior left atrium. The total amount of postoperative bleeding after the simple left atrial procedure was significantly less than after the radial procedure (378 +/- 135 vs 711 +/- 364 mL, P = .03). The right and left atrial transport functions were well preserved after both the radial and simple left atrial procedures. Intraoperative mapping facilitates determining the optimal procedure for atrial fibrillation in each patient.

Implantation of cardioverter device in young children: the perirenal approach

Placement of Implantable cardioverter devices in young children is complicated because of the relatively large size and heavy weight of these devices. A technique is described where the device is implanted in the left perirenal space while an endovascular lead is used instead of an epicardial patch electrode.

Pectoral implantation of single-lead implantable cardioverter-defibrillators in patients without transvenous access

With the introduction of the single-lead “Active-Can” implantable cardioverter-defibrillators, the implantation of the internal defibrillators has become a technically easy procedure. With these systems lowest defibrillation thresholds are achieved with a very low complication rate. For patients with thrombosis of both subclavian veins, however, a transvenous implantation technique is not possible. These patients are still equipped with epicardial patch electrodes. This article describes an alternative technique for implantation of this system in such patients, eliminating the need for epicardial patches and related complications.

Lead-related complications in 340 patients with an implantable cardiverter/defibrillator

From February 1991 to May 1998, 340 patients had a cardioverter/defibrillator (ICD) implanted. Mean age was 64 +/- 9 years, 278 male and 62 female. 60% of patients had coronary artery disease and 31% dilatative cardiomyopathy. Ejection fraction was 38 +/- 14%. The indication for an implantable cardioverter/defibrillator was in 57% of patients ventricular tachycardia, in 43% ventricular fibrillation. 298 patients had a single-chamber cardioverter/defibrillator implanted, 42 patients a dual-chamber cardioverter/defibrillator. In 25 patients additional subcutaneous patch or array electrodes and in 2 patients additional epicardial patch electrodes were implanted. Implantation site was in 92 patients abdominal and in 248 pectoral. Over a period of 7 years 34 lead-related complications occurred in 33 patients (9.7%), after a median of 2 months after implantation. Diagnosis was made by routine chest x-ray in about 55% of lead-related complications, by clinical presentation (inadequate therapy, pain) in 24%, and by electrical parameters in 21%. In patients with an abdominal implantation site, lead-related complications occurred in 20%, in contrast to 6% in patients with a pectoral implantation site. Regarding patients with pectoral implantation site, lead-related complications were observed in 12% of patients with a dual-chamber ICD vs 4% with a single-chamber ICD (p = 0.05), due to dislocation of atrial electrodes with dual-chamber ICD. There were no differences in clinical parameters between patients with pectoral vs abdominal and between single vs dual-chamber ICD. There were no deaths due to lead-related complications.

Left ventricular pseudoaneurysm after epicardial patch electrode placement

There are many known complications of implantable cardioverter-defibrillator placement. We treated a patient in whom a left ventricular pseudoaneurysm developed secondary to epicardial patch electrode placement and cardioverter-defibrillator implantation. The presenting symptoms, diagnostic evaluation, and surgical repair are described.

Effect of preexisting epicardial patch electrodes on defibrillation thresholds of unipolar defibrillators

We conclude that patients with failing epicardial lead systems can be safely and effectively treated with the implantation of a fourth generation unipolar implantable cardioverter defibrillator.

Effect of changing capacitors between phases of a biphasic defibrillation shock.

In this study, we examined the effect of changing capacitor values between phases of a biphasic waveform with the goal of lowering leading edge voltage (LEV), total delivered energy (TDE), and total stored energy (TSE). Defibrillation thresholds were determined in 18 open-chest swine using epicardial patch electrodes. In part I, three combinations of capacitors were tested: 150:150 microF; 150:300 microF; and 300:150 microF. Waveform durations were 6/0, 6/2, 6/4, 6/6, and 6/8 ms. In part II, phase 1 capacitance was 150 microF. Three phase 2 capacitance values were used: 150 microF; 75 microF; and 37.5 microF. Phase 2 LEV was a multiple of phase 1 trailing edge voltage: x 0.5; x 0.75; x 1; x 2; x 3; and x 4. A 3.5/2.0 ms biphasic waveform was used. In part III, thresholds were determined for two sets of capacitor values, which can be created by switching a pair of capacitors from in parallel to in series, 150:37.5 microF and 300:75 microF, and nine waveform durations, 4/0, 4/2, 4/4, 6/0, 6/3, 6/6, 8/0, 8/4 and 8/8 ms. In part I, the 300:150 microF system defibrillated with the lowest LEV, TDE and TSE were not different for any of the biphasic waveforms tested except for the 6/8 ms, which was higher. In part II, there was no difference in LEV among any of the three phase 2 capacitor values. LEV was lowest for the x 2, x 3, x 4 multipliers. Peak voltage was lowest for the x 1 and x 2 multipliers. TDE was lowest for the x 0.5, x 0.75, x 1, and x 2 multipliers. In part III, the 300:75 microF system defibrillated at a lower LEV than did the 150:37.5 microF system. The 150:37.5 microF system defibrillated at a lower total delivered energy than did the 300:75 microF. These results suggest that defibrillation can be accomplished with lower LEV, TDE, and TSE if two capacitors are switched from a parallel configuration to a series configuration between phases of the biphasic waveform.

Defibrillation Shocks Over Epicardial Patches Produce Sympathetic Neural Dysfunction in Man

The purpose of this study was to determine the effect of direct current (DC) shocks on cardiac sympathetic innervation in humans using I-123-metaiodobenzylguanidine (MIBG) scintigraphy. Decreased efferent sympathetic neural function has been demonstrated following > 10-J DC shocks delivered through epicardial patch electrodes in dogs. To evaluate the effect of DC shocks on cardiac sympathetic innervation in humans, we performed MIBG scintigraphy in 11 patients (ages 46 to 75 years) prior to and after receiving shocks from an implantable cardioverter defibrillator (ICD). This study was performed during an ICD generator change in 7 patients with epicardial patch electrodes and at the time of initial ICD implantation in 4 patients: 2 with epicardial patch electrodes, and 2 with a transvenous ICD system. All patients had spontaneous and inducible ventricular tachycardia. Prior to ICD implantation and remote from any cardioversions or shocks, baseline MIBG and thallium-201 scintigraphy were performed. Repeat MIBG scintigraphy was performed after delivery of ICD shocks and compared with the baseline scans to determine the effect of the shock on sympathetic neural function. The baseline scans revealed focal areas of reduced MIBG uptake in areas of thallium perfusion defects in all patients except the patient without structural heart disease whose scans were normal. Postshock, patients with epicardial patch electrodes who received at least one 24-J shock and had the postshock MIBG scan performed within 4 hours demonstrated no cardiac uptake of MIBG. Two patients with epicardial patch electrodes had no change in the postshock MIBG scans: 1 had a maximal shock of 20 J, and the other had the postshock scan delayed for 11 hours. The 2 patients with a transvenous lead system demonstrated no change in the postshock MIBG scan when compared with baseline. This study demonstrates that following DC shocks delivered over epicardial patch electrodes, there is diffuse reduction in MIBG uptake that probably represents cardiac sympathetic neural dysfunction that appears to be transient. Sympathetic function does not appear to be affected by shocks delivered over a transvenous lead system.

714-2 Diffuse Cardiac Sympathetic Dysfunction Follows Implantable Defibrillator Shocks Delivered Through Epicardial Patch Electrodes

Decreased efferent sympathetic neural function has been demonstrated following &gt; 10J DC shocks delivered through epicardial patch electrodes in dogs. To evaluate the effect of DC shocks on cardiac sympathetic innervation in humans, we performed 1–123-metaiodobenzylguanidine (MIBG) scintigraphy in 5 patients (age 46–73 years, mean 64) prior to and after receiving shocks from implanted cardiac defibrillators (ICD). Four patients had coronary artery disease (CAD) with prior myocardial infarction and one had an idiopathic dilated cardiomyopathy (IDCM). All patients had spontaneous and inducible ventricular tachycardia. One patient was receiving amiodarone at the time of this study. One patient had had prior coronary artery bypass surgery (CABG), and two had concurrent CABG at the time of ICD implantation. This study was performed during an ICD generator change in 2 patients and at the time of initiallCD implantation in 3 patients. Four patients (3 CAD, 1 IDCM) received epicardial patch electrodes, and one patient had a transvenous lead system. Baseline MIBG and thallium-201 scintigraphy performed &gt; 1 week preoperatively and remote from any cardioversions or shocks revealed focal areas of reduced MIBG uptake in areas of thallium perfusion defects in all patients. Repeat MIBG scans were performed &gt; four hours after shocks delivered during either the surgical implantation orfollow-up EPS. All patients had received at least one 24J shock (mean 2.4 shocks, range 1–4), In all patients with epicardial patch electrodes, there was minimal or no cardiac uptake of MIBG post-Shock, consistent with diffuse sympathetic dysfunction. In the patient with a transvenous lead system the post-shock MIBG scan was unchanged from baseline. This study demonstrates that following DC shocks delivered through epicardial patches there is diffuse cardiac sympathetic neural dysfunction, which may contribute to the arrhythmic “storm” that has been reported following some ICD implantations.

805-4 Mechanism of Epinephrine in Defibrillation After Prolonged Ventricular Fibrillation

Administration of Epinephrine (EPi) is an integral part of resuscitation of ventricular fibrillation (VF). The mechanism of its action is not known. To evaluate this, 20 open chested pigs were studied using Endocardial (EN) and Epicardial (EP) Monophasic Action potentials (MAP) recordings. Defibrillation is achieved by using two EP patch electrodes, Each animal is fibrillated by using AC current and allowed to fibrillate for 10 minutes, ECG, BP, RV, LV, EN, and EP MAPs were recorded every minute during VF and resuscitation. At 10’ of VF, each animal is randomized either to EPi or saline and cardiac massage was instituted for 5 minutes. The heart was then defibrillated. In both groups. cycle lengths of MAPs and synchronization of repolarization which is the interval between EN and EP MAPs were measured during VF and resuscitation. The results were 10/10 of EPi and 1/10 saline animals were resuscitated. Successful defibrillation with EPi is because of: 1) shortening of cycle length, and 2) synchronization of repolarization.

Position of epicardial patch electrodes for implantable defibrillation significantly affects shock strength requirements.

To assess the impact of epicardial patch electrode position on internal defibrillation efficacy. Two mesh patch electrodes (13 cm2) were positioned on the epicardium of acute, isoflurane-anesthetized pigs (n = 7, 40-47 kg). Defibrillation efficacy was determined for three different patch positions: P1 = anterior-basal right ventricle (RV) and lateral-apical left ventricle (LV); P2 = lateral RV and lateral LV; and P3 = anterior-basal septal region and posterior-apical septal region. To quantify defibrillation efficacy, single capacitor discharge, fixed-tilt (68%) biphasic waveforms were delivered to the heart 10 seconds after initiation of ventricular fibrillation. Initial shock intensities were selected using an up/down protocol. Conversion data were used to construct sigmoidal curves relating probability of defibrillation to energy delivered, peak voltage, and peak current in each animal. Mean peak voltage and current at 50% defibrillation probability were 40% higher for P2 than they were for either P1 or P3 (p < 0.05). Similarly, mean energy delivered was 75% higher for P2. In this pig model, position of epicardial patch electrodes affects defibrillation efficacy. Apical-to-basal shock vectors (P1 and P3) yielded significantly lower defibrillation shock strength requirements than did a lateral-wall-to-lateral-wall vector (P2), which was perpendicular to the intraventricular septum. These data may help explain the disparity in defibrillation thresholds observed in the human population of patients undergoing implantable cardioverter defibrillator testing with epicardial patch electrodes.

A Direct Comparison of Epicardial and Nonthoracotomy Defibrillation Using Monophasic and Biphasic Shocks

Defibrillation using epicardial patches may be associated with lower energy requirements than nonthoracotomy defibrillation although a direct comparison using various waveforms has not been reported. To directly compare defibrillation efficacy using these two configurations, nine mongrel dogs (20.9 +/- 2.3 kg) first underwent nonthoracotomy defibrillation testing followed by a thoracotomy and implantation of epicardial patch electrodes and redetermination of defibrillation efficacy. Each dog served as its own control. Nonthoracotomy electrode configuration consisted of a right ventricular catheter (cathode) and a chest wall subcutaneous patch (anode). The epicardial configuration consisted of two 13.9 cm2 epicardial patches. Alternating current induced ventricular fibrillation was allowed to persist for 10 seconds, followed by either a monophasic or a single capacitor biphasic shock of 10-msec total duration. Four trials of five leading edge voltages were performed for monophasic and biphasic pulses and stepwise logistic regression analysis was used to determine 80% probability of successful defibrillation (E80). For epicardial defibrillation E80s were: monophasic 19.2 +/- 4.2 J and biphasic 12.6 +/- 4.0 J; nonthoracotomy defibrillation E80s were: monophasic 24.2 +/- 4.4 J and biphasic 17.8 +/- 4.1 J. Epicardial patch defibrillation required less energy than nonthoracotomy electrode configuration. However, using biphasic pulses nonthoracotomy defibrillation could achieve lower defibrillation energy requirements than epicardial defibrillation with monophasic pulses.

Low Voltage Shocks Have a Significantly Higher Tilt of the Internal Electric Field Than Do High Voltage Shocks

Typically, an implantable cardioverter defibrillator (ICD) uses a cardioversion shock that is a lower voltage pulse of the same morphology and tilt as its defibrillation pulse. We investigated the internal electric field resulting from an ICD low voltage shock to determine whether its field characteristics matched those of the internal electric field of a high voltage shock. We attached epicardial patch electrodes, for shock delivery, to five fresh pig hearts placed in a diluted, heparinized saline bath. We inserted two plunge electrodes into the myocardium to measure an internal voltage proportional to the electric field. Monophasic 20-msec shocks, from a 140-microF capacitor, ranging from 0.1-30 joules, were delivered through the patches. We measured the current, external voltage, and internal voltage every 0.1 msec throughout the duration of a shock. For each shock, we calculated the time point that represented the 65% tilt position as measured across the patch electrodes. At this 65% tilt time position, we measured the pulse widths and calculated the internal tilt from the internal voltage. We found that the initial internal voltage for the 30-joule shock was 173 +/- 40 volts compared to 10 +/- 2 volts for the 0.1-joule shock. Similarly, we found that the final internal voltage for the 30-joule shock was 56 +/- 14 volts compared to 2 +/- 1 volts for the 0.1-joule shock. Thus, the internal tilt for the 30-joule shock was 68 +/- 1% versus 82 +/- 3% for the 0.1-joule shock (P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison and frequency of ventricular arrhythmias after defibrillator implantation by thoracotomy versus nonthoracotomy approaches

Postoperative exacerbation of ventricular arrhythmias has been reported in some patients treated with thoracotomy implantable cardioverter-defibrillators (ICDs). This phenomenon, which may be related to epicardial patch electrodes, may be less frequent after nonthoracotomy ICD implantation. In this nonrandomized study, postoperative arrhythmias in thoracotomy approaches (n = 52) were compared with those in nonthoracotomy approaches (n = 59). Preoperatively, all patients were clinically stable receiving an antiarrhythmic regimen chosen by serial drug testing. Nine of 52 patients in the thoracotomy group developed sustained ventricular tachycardia postoperatively while receiving the same antiarrhythmic regimen chosen preoperatively, and 1 patient eventually died. Two additional patients developed frequent and prolonged episodes of nonsustained ventricular tachycardia requiring changes in the antiarrhythmic regimen. In the nonthoracotomy group, only 3 of 59 patients developed sustained ventricular tachycardia and 1 developed frequent nonsustained ventricular tachycardia. Thus, only 4 of 59 patients in the nonthoracotomy group developed clinically significant ventricular arrhythmia during the postoperative period compared with 11 of 52 patients in the thoracotomy group (p < 0.05). Surgical mortality was 6% in the thoracotomy group, and 0% in the nonthoracotomy group. In the remaining clinically stable patients, a marked (sevenfold) increase in asymptomatic ventricular arrhythmias was noted in 15 of 39 patients in the thoracotomy group, and in 3 of 55 patients in the nonthoracotomy group (p < 0.05). Thus, postoperative exacerbation of ventricular arrhythmia, sometimes noted with thoracotomy approaches, is very rare with nonthoracotomy approaches.

Sudden death in recipients of first-generation implantable cardioverter defibrillators: analysis of terminal events. Participating investigators.

Clinical factors and terminal events associated with sudden death in 51 patients were analyzed from among a multicenter experience of 864 recipients of first generation automatic implantable cardioverter defibrillator (AICD) devices (single zone, committed, monophasic pulse with > or = 1 epicardial patch electrode) during the period May 1982-February 1988. For these 51 patients, mean age was 58 years and atherosclerotic heart disease was present in 84%, with a history of ventricular fibrillation (VF) in 61%, and inducible sustained ventricular tachycardia (VT) in 84%; mean left ventricular ejection fraction was 0.26. Nearly 80% experienced one or more appropriate AICD shocks during the median 9 month (range 0-46 months) period prior to death. Of 30 monitored deaths, the first documented terminal rhythm was VF in 12 (40%), VT in 8 (27%), and asystole or electromechanical dissociation in the remaining 10 (33%). Shocks were documented during terminal events in 21 (66%) of 32 witnessed cases of sudden death with activated devices. The proportion of monitored or witnessed sudden deaths that were known or presumed to be tachyarrhythmic (based on terminal VT, VF, or shocks) ranged from 69% (11/16 cases with activated/nondepleted devices and a defibrillation threshold [DFT] < or = 20 J) to 81% (29/36 cases on intention-to-treat basis). Of 27 patients with known or presumed sudden tachyarrhythmic death, the AICD had been deactivated prior to death in 4 (15%); activated, but depleted in 4 (15%); activated/nondepleted, but with DFT of 25 J in 4 (15%); and activated/nondepleted, but without DFT testing in 4 (15%). The remaining 11 (41%) known or presumed sudden tachyarrhythmic deaths occurred in patients with activated/nondepleted devices and DFT < or = 20 J; however, definite or suspected contributory factors (e.g., hematoma under epicardial patch, generator component failure, or drug-induced DFT rise) could be identified in 6 (55%) of 11 cases. Thus, in this first-generation AICD experience: 1) most sudden deaths occurred on the basis of a known or presumed tachyarrhythmia; and 2) an understanding of apparent "failure" of ICD therapy could often be gained through an integrated analysis of associated clinical factors and management practices, as well as device "hardware" function. These observations are likely to remain relevant, even with respect to newer generation ICDs.

Smaller capacitors improve the biphasic waveform.

Current implantable cardioverter defibrillators (ICDs) use relatively large capacitance values. Theoretical considerations suggest, however, that improved defibrillation energy requirements may be obtained with smaller capacitance values. We compared the energy requirement for defibrillation in a porcine model using a biphasic waveform generated from two capacitance values of 140 microF and 85 microF. Phase 1 reversal of the shock waveform occurred at 65% tilt. Phase 2 pulse width was equal to phase 1. Shocks were delivered through epicardial patch electrodes after 10 seconds of induced ventricular fibrillation. The defibrillation threshold (DFT) was determined by a "down-up" technique requiring three reversals of defibrillation success or failure. The DFT was defined as the average of the values obtained with all trials starting from the successful shock prior to the first failure to defibrillate to the last successful defibrillation. In eight experiments, the measured parameters at DFT were as follows. The average stored and delivered DFT energies for the 85 microF capacitor were 6.1 +/- 2.1 and 6.0 +/- 2.0 J, respectively, compared to 7.5 +/- 1.3 and 7.4 +/- 1.3 J for the 140 microF capacitor (P < 0.04). The phase 1 pulse widths were significantly shorter for the 85 microF capacitor (5.1 +/- 0.8 msec vs 9.2 +/- 1.3 msec) and the impedances were lower (54.4 +/- 5.8 omega vs 59.9 +/- 6.3 omega). The mean leading edge voltage was trending higher for the 85 microF capacitor, but this difference did not reach statistical significance (374 +/- 63 V vs 326 +/- 30 V; P = 0.055). Smaller capacitance values do result in lower energy requirements for the biphasic waveform, at a possibly higher leading edge voltage and a much shorter pulse width. Smaller capacitance values could represent a significant enhancement of well-established benefits demonstrated with the biphasic waveform.