Biomedical subjects

J N Wetherbee

Publications and source records attributed to J N Wetherbee.

At least 19 recordsLinked to original sources

PubMed1996

Direct comparison of monophasic, biphasic and sequential pulse defibrillation over a single current pathway.

BACKGROUND: Defibrillation waveform and its spatial and temporal distribution are important determinants of its efficacy. Previous comparisons of monophasic, biphasic and sequential waveforms have used one current pathway for monophasic and biphasic defibrillation and two pathways for sequential defibrillation thus confounding a direct comparison of the waveforms. DESIGN: This study compared monophasic, biphasic and sequential pulse defibrillation over a single current pathway using a nonthoracotomy and a thoracotomy lead system in a dog model. MAIN RESULTS: Eight mongrel dogs (mean weight 21.6+/-2.9 kg) first underwent nonthoracotomy defibrillation testing followed by a median sternotomy and implantation of two 13.9 cm2 epicardial patch electrodes posterior = cathode). Nonthoracotomy electrode configuration consisted of a right ventricular catheter (cathode) and a chest wall subcutaneous patch (anode). After 10 s of alternating current induced ventricular fibrillation, defibrillation was attempted with a test shock. Monophasic, biphasic and sequential shocks of 10 ms total duration were compared. Biphasic and sequential shocks consisted of two 5 ms components separated by 0.25 ms switch time constant. Four trials of five leading edge voltages were performed for each waveform and stepwise logistic regression analysis was used to determine 80% probability of successful defibrillation (E80). For epicardial defibrillation, E80s were monophasic 11.3+/-1.5 J; biphasic 7.9+/-1.2 J; and sequential 12.1+/-1.4 J. For nonthoracotomy defibrillation, E80s were monophasic 17.7+/-3.4 J; biphasic 13.8+/-3.3 J; and sequential 18.2+/-3.5 J. The mean E80 for biphasic pulses was significantly lower than monophasic or sequential pulses for either lead system. CONCLUSIONS: Biphasic pulses are superior to monophasic or sequential pulses delivered over a single current pathway.

Animals↗

PubMed1995

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.

Animals↗

PubMed1994

Electrode polarity is an important determinant of defibrillation efficacy using a nonthoracotomy system.

Experimental and clinical data using epicardial patch electrodes and monophasic waveform suggest that electrode polarity may be an important determinant of defibrillation efficacy. Our objective was to examine the effect of electrode polarity in an animal model using a nonthoracotomy system and monophasic and biphasic waveforms for defibrillation. We examined the effect of lead polarity in 14 pentobarbital anesthetized dogs (21.1 +/- 2.4 kg) using monophasic and biphasic shocks and a nonthoracotomy system. Monophasic and single capacitor biphasic shocks of 10-msec total duration were used. The lead system consisted of a right ventricular catheter electrode with 4-cm2 surface area and a left chest wall subcutaneous patch electrode with 13.9-cm2 surface area. Electrode polarities RV(-)-Patch(+) and RV(+)Patch(-) were tested using both monophasic and biphasic waveforms. Alternating current was used to induce ventricular fibrillation and test shocks were delivered after 10 seconds of ventricular fibrillation. Each polarity configuration for monophasic and biphasic waveforms was tested four times at five different capacitor voltage levels (200-600 V, in 100-V increments). Defibrillation efficacy curves were constructed using logistic regression analysis for each animal and energies associated with 80% probability of successful defibrillation (E80) were determined. The mean E80 +/- SD values were as follows. Monophasic waveform: RV(-)Patch(+) 23.4 +/- 7.5 J; RV(+)Patch(-) 20.9 +/- 7.9 J (P < 0.03). Biphasic waveform: RV(-)Patch(+) 15.8 +/- 6.8 J; RV(+)Patch(-) 12.5 +/- 6.0 J (P < 0.03). The mean impedance values for both waveforms using either polarity ranged from 65.4 to 67 ohms and were not significantly different.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1993

Increased prevalence of abnormal signal-averaged electrocardiograms in older patients who have hypertension with low diastolic blood pressure.

Greater mortality in hypertensive patients with the lowest diastolic blood pressure (DBP) values has been reported and may be partially explained by more fatal arrhythmias. The records of 135 patients were reviewed to determine whether the prevalence of an abnormal signal-averaged electrocardiogram (SAECG+), a risk marker for ventricular arrhythmias, was greater in patients who have hypertension with DBP < 85 mm Hg. SAECG+ was present in 31 (39%) of 80 patients with hypertension and 13 (24%) of 55 subjects with normotension p < 0.05. Hypertensive patients were more likely than normotensive subjects to have left ventricular hypertrophy (LVH, p = 0.01) and LV dysfunction (p < 0.01). In multivariate analysis only age and systolic dysfunction emerged as significant predictors of SAECG+. Among 68 hypertensive patients and for whom recent DBP data were available, SAECG+ was present in 18 of 37 with DBP < 85 mm Hg (group 1), 1 of 12 with DBP 85 to 94 mm Hg (group 2, p < 0.05 vs group 1), and 4 of 19 with DBP > 95 mm Hg (group 3, p < 0.05 vs group 1, p = 0.08 vs group 2). There were no significant differences between the three groups of hypertensive patients for coronary artery disease, LVH, systolic dysfunction, or left-sided cardiac chamber enlargement. Multivariate analysis in hypertensive patients indicated that age and DBP were each independently predictive of SAECG+, whereas the indexes of heart disease were not. Within group 1, those with SAECG+ were significantly older (68 +/- 1 vs 59 +/- 1 years, p < 0.01) and more likely to have LVH (p < 0.03).(ABSTRACT TRUNCATED AT 250 WORDS)

Arrhythmias, Cardiac↗

PubMed1993

Long-term complications of implantable cardioverter defibrillator lead systems.

Over a period of 8.5 years in 255 patients with full-system implantable cardioverter defibrillators, lead-specific complications requiring reoperation developed in 32 patients. A total of 36 leads were affected. Lead fracture was the cause of failure in half of these patients. Refinement and improvement in structural designs of these leads, use of endocardial leads, and attention to technical details during implantation should decrease the incidence of these complications.

Arrhythmias, Cardiac↗

PubMed1993

Pericardial effusion increases defibrillation energy requirement.

Pericardial effusion may increase defibrillation energy requirements. We examined the effect of pericardial effusion in seven pentobarbital anesthetized dogs (25.3 +/- 3.4 kg) using monophasic and biphasic shock. A median sternotomy was performed and two 13.9 cm2 patch electrodes were sewn extrapericardially; 3 cc/kg of 0.9% NaCl was instilled through an intrapericardial catheter used to create a hemodynamically insignificant pericardial effusion. Four trials of five leading edge voltages (200-600 volts, in 100 volt increments) were performed for monophasic and biphasic shocks of 10 msec total duration and defibrillation efficacy curves were determined by logistic regression analysis. Baseline impedance was 68.1 and 66.2 Ohms for monophasic and biphasic waveforms, respectively, and decreased to 52.9 and 49.9 Ohms, respectively, with pericardial effusion (P < 0.01). Energy associated with 80% probability of successful defibrillation (E80) for monophasic shock was 16.0 joules at baseline and increased to 18.5 joules with pericardial effusion (P < 0.016). Similarly, E80 for biphasic shocks increased from 10.6 joules to 13.0 joules (P < 0.016). Removal of pericardial effusion was associated with impedance and E80 returning to baseline. In this model, pericardial effusion increased defibrillation energy requirements and may explain early postimplant defibrillator failure.

Animals↗

PubMed1992

Optimal lead positioning for postoperative atrial pacing.

Temporary atrial pacing leads have uncontested utility for diagnosis and treatment of postoperative supraventricular arrhythmias. Sensing and capture thresholds may be inconsistent, however. We evaluated intraoperative atrial sensing amplitude and capture thresholds in 25 patients after coronary bypass using six bipolar and four unipolar lead combinations based on four lead positions: A, atrial appendage; B, 1 cm above the presumed sinoatrial node at the atrial-superior-vena caval junction; C, interatrial groove at the right superior pulmonary vein; and D, caudal inferolateral free wall. Unipolar lead B and bipolar lead B-D had the best voltage pacing threshold and system resistance (p less than 0.05). The lowest current was also observed with unipolar lead B and bipolar lead B-D, but the difference was not significant (p greater than 0.05). P-wave amplitude was not significantly different for any lead combination. Location C, in unipolar or bipolar combinations, frequently paced the phrenic nerve. These data provide new guidelines for establishment of postoperative temporary atrial pacing leads.

Arrhythmias, Cardiac↗

PubMed1991

Comparison of efficacy of automatic implantable cardioverter defibrillator in patients older and younger than 65 years of age.

PURPOSE: The efficacy of the automatic implantable cardioverter defibrillator (AICD) was compared in elderly patients and younger patients with life-threatening ventricular tachyarrhythmias. Clinical characteristics, surgical complications, and long-term survival rates were compared between the two age groups. PATIENTS AND METHODS: A retrospective study was conducted of 54 elderly patients (greater than 65 years) and 79 younger patients (less than 65 years) who had had AICDs implanted for recurrent symptomatic ventricular tachycardia and/or ventricular fibrillation. RESULTS: In 85% of elderly patients and 78% of younger patients, coronary artery disease was the underlying disease (NS). The mean left ventricular ejection fraction was 31.4 +/- 14.3% in the elderly patients and 35.7 +/- 17.6% in the younger patients (NS). Concomitant myocardial revascularization was performed in 37% of elderly patients and 29% of younger patients (NS); however, only 4% of elderly patients had concomitant left ventricular resection or cryoablation, compared with 15% of younger patients (p less than 0.001). Two patients in each age group died perioperatively (4% versus 3%, NS), and no significant difference in surgical morbidity or length of hospital stay following AICD implantation was noted between the age groups. In conjunction with AICD, elderly patients more commonly received antiarrhythmic drugs, with 54% of elderly patients taking amiodarone at the time of hospital discharge compared with 29% of the younger patients (p less than 0.008). In contrast, beta-blockers were more commonly used in younger patients (16% versus 2%, p less than 0.03). At a mean follow-up of 25 months, 11 (20%) elderly patients and 16 (20%) younger patients had died. Six deaths in elderly patients and five deaths in younger patients were classified as arrhythmic deaths (NS); however, only one younger patient and three elderly patients died suddenly (NS). Calculated survival curves demonstrated similar survival rates in the two age groups with approximately 90%, 87%, and 80% of the patients alive at 1, 2, and 3 years, respectively. Theoretic survival curves calculated from appropriate AICD shocks demonstrated significantly lower survival compared with actual survival. CONCLUSION: It is concluded that AICD is a very effective treatment for life-threatening ventricular tachyarrhythmias, and this benefit applies to elderly patients as well as younger patients.

Adolescent↗

PubMed1989

Comparison of monophasic with single and dual capacitor biphasic waveforms for nonthoracotomy canine internal defibrillation.

Monophasic and single capacitor and dual capacitor biphasic truncated exponential shocks were tested in pentobarbital-anesthetized dogs with use of a nonthoracotomy internal defibrillation pathway consisting of a right ventricular catheter electrode and a subcutaneous chest wall patch electrode. Seven dogs weighing 20.2 +/- 0.5 kg were utilized. Monophasic pulses of 10 ms duration were compared with three biphasic pulses. All biphasic waveforms had an initial positive phase (P1) followed by a terminal negative phase (P2) and the total duration of P1 plus P2 was 10 ms. The dual capacitor biphasic waveform (P1 9 ms, P2 1 ms) had equal initial voltages of P1 and P2. Two simulated single capacitor biphasic waveforms were also tested, the first designed to minimize the magnitude of P2 (P1 9 ms, P2 1 ms with initial voltage of P2 equal to 0.3 of the initial voltage of P1) and the second to maximize P2 (P1 5 ms, P2 5 ms with initial voltage of P2 = 0.5 P1). Alternating current was used to induce ventricular fibrillation and four trials of eight initial voltages from 100 to 800 V were performed for each of the four waveforms. Stepwise logistic regression was utilized to construct curves relating probability of successful defibrillation and energy. In the logistic model, the dual capacitor biphasic and single capacitor biphasic waveforms that maximized P2 were associated with significantly (p less than 0.001) lower energy requirements for defibrillation than those of the monophasic waveform. The single capacitor biphasic waveform that minimized P2 was not significantly better than the monophasic waveform.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1989

Long-term internal cardiac defibrillation threshold stability.

The automatic implantable cardioverter-defibrillator is tested intraoperatively with defibrillation trials to ensure effectiveness. It is unknown if the energy requirement for internal defibrillation remains stable and that once demonstrated effective, if the device will continue to be effective in terminating lethal ventricular arrhythmias. In this study, the defibrillation energy requirement was compared in 56 patients at the time of lead implantation to that obtained at the time of generator replacement. Mean time to generator replacement was 17. +/- 6.6 months. The defibrillation threshold was stable over that time (11.9 +/- 6.7 joules compared to 12.7 +/- 8.4 joules, NS). There was no relation between transmyocardial impedance and defibrillation threshold. In addition, no effect on defibrillation threshold was demonstrated by the use of various cardiac medications, concomitant surgery or the occurrence of clinical shocks during follow-up.

Electric Countershock↗

PubMed1989

Complications of automatic implantable cardioverter defibrillators: radiographic, CT, and echocardiographic evaluation.

Automatic implantable cardioverter defibrillators (AICDs) were studied in three groups: (a) Serial radiographs were reviewed in 51 clinic patients. Twenty of 96 (21%) AICD patches distorted with time. (b) Thirty-six postoperative computed tomographic (CT) scans of asymptomatic patients revealed that pericardial fluid collections were frequent during the month after surgery but rare beyond that. Echocardiography was insensitive for these collections. CT also demonstrated dense fibrosis around some distorted patches, months after surgery. (c) Five other patients with pericardial infection had distorted patches, and the four studied with CT had fluid beneath their patches. (d) A case of constrictive pericarditis had distorted patches but was not diagnosed with CT. The authors conclude that distorted patches may indicate postoperative complications and that CT is the imaging modality of choice.

Arrhythmias, Cardiac↗

PubMed1988

Comparison of ST segment depression in upright treadmill and supine bicycle exercise testing.

Significant differences in the hemodynamic response to upright and supine exercise have been reported in patients with coronary artery disease. The purpose of the present study was to compare the degree of myocardial ischemia as assessed by ST segment depression during upright treadmill and supine bicycle exercise in 98 patients with coronary artery disease and in 34 patients with normal coronary arteries. The amount of ST segment depression at maximal exercise in patients with coronary artery disease was 0.90 +/- 0.80 mm for treadmill and 1.34 +/- 1.09 mm for supine bicycle (p less than 0.001). The amount of ST segment depression during treadmill and supine bicycle exercise tests was also compared at highest similar heart rates (0.68 +/- 0.77 versus 1.17 +/- 1.01, p less than 0.001), at highest similar rate-pressure products (0.71 +/- 0.77 versus 1.08 +/- 1.04, p less than 0.001), at highest similar metabolic equivalents of oxygen consumption (MET) levels (0.69 +/- 0.75 versus 1.20 +/- 1.05 mm, p less than 0.001) and at the onset of angina (0.84 +/- 0.73 versus 1.18 +/- 0.88 mm, p less than 0.001). The rate-pressure product achieved at maximal exercise was similar in both tests (18.74 +/- 5.80 x 10(3) versus 18.81 +/- 5.17 x 10(3), p = NS). The occurrence of angina during treadmill and supine bicycle exercise tests was similar (47 of 98 versus 48 of 98, respectively, p = NS). For the detection of coronary artery disease, the sensitivity was 50.0% for treadmill and 63.3% for supine bicycle (p less than 0.05) and the specificity was 73.5 versus 70.6%, respectively (p = NS).(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗

PubMed1988

Comparative efficacy of monophasic and biphasic truncated exponential shocks for nonthoracotomy internal defibrillation in dogs.

Pentobarbital-anesthetized dogs were studied to determine the relative efficacy of monophasic and biphasic truncated exponential shocks employing a nonthoracotomy internal defibrillation pathway that consisted of a right ventricular catheter electrode (cathode) and a subcutaneous chest wall patch electrode (anode). In part 1 of the experiments, six dogs (19.6 +/- 1.1 kg) were utilized. Monophasic pulses of 5, 7.5, 10 and 12.5 ms duration were compared with biphasic pulses of the same total duration. The biphasic pulses had an initial positive phase (P1) followed by a terminal negative phase (P2) with the initial voltage equal for each phase. For each biphasic total pulse width, five relative P1 versus P2 durations were tested (50 and 50%, 75 and 25%, 90 and 10%, 25 and 75%, 10 and 90%). Ventricular fibrillation was induced by alternating current and pulse configurations were tested randomly to determine the minimal voltage and energy for defibrillation (threshold). Biphasic shocks with P1 longer than P2 were associated with significantly lower (p less than 0.01) energy thresholds than were monophasic shocks. Additionally, there was no significant relation between pulse width and voltage or energy thresholds. In part 2 of the experiments, six dogs (20.2 +/- 1.6 kg) were studied. Monophasic shocks were compared with biphasic shocks with P1 versus P2 durations of 75 and 25% and 90 and 10% for total pulse widths of 7.5, 10 and 12.5 ms. Threshold determinations were performed as in part 1. Subsequently, five initial voltages clustered about threshold were randomly tested four times and dose-response curves constructed for each pulse configuration with the use of stepwise logistic regression. Biphasic shocks resulted in significantly lower energy (p less than 0.0001) and voltage (p less than 0.001) requirements than did monophasic shocks.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1988

Strength-duration curves of fixed pulse width variable tilt truncated exponential waveforms for nonthoracotomy internal defibrillation in dogs.

Six anesthetized dogs (wgt 19.6 + 1.1 kg) underwent defibrillation trials using truncated monophasic pulses of 2.5-20 msec in duration. The current pathway consisted of a 4 cm2 RV catheter electrode (cathode) and a 13.9 cm2 subcutaneous chest wall patch (anode). Fibrillation was induced by alternating current and defibrillation attempted 10 seconds later. Only one test shock was assessed for each fibrillation episode. The various durations were tested randomly, and the minimum peak voltage and energy resulting in defibrillation was determined for each. Shorter pulse durations were associated with lower energies with pulses of 2.5-15 msec having significantly lower energy thresholds than shocks of 20 msec (P less than 0.05). The relationship between duration and voltage threshold is hyperbolic with minimum voltage between 7.5 and 12.5 msec while the shortest and longest pulses were associated with the highest voltage thresholds. Shocks of 5 to 15 msec were associated with significantly lower voltage threshold than 2.5 msec pulses (P less than 0.05). The threshold average current (Iav) reached a nadir at 10 msec. Shocks in the midrange of those tested resulted in the best combination of low average current and energy requirements for defibrillation using this nonthoracotomy lead system.

Animals↗

PubMed1988

Sequential shocks are comparable to single shocks employing two current pathways for internal defibrillation in dogs.

Sequential pulse defibrillation using two current pathways was compared with single shocks simultaneously utilizing both pathways in 16 dogs to assess the effects of temporal summation. A cardioverter-defibrillator catheter was positioned via the external jugular vein with the distal 4 cm2 shocking electrode located in the right ventricular apex and the proximal 8 cm2 electrode located in the superior vena cava. Three electrode configurations were tested: (1) single pulse, distal electrode (cathode) to proximal electrode and chest wall patch (common anode), (2) sequential 5 ms pulses with 1 ms interpulse delay, distal electrode (cathode) to proximal electrode (anode) followed by distal electrode (cathode) to chest wall patch (anode), and (3) sequential 10 ms pulses with 1 ms interpulse delay using same current pathways described for configuration 2. The lowest energies resulting in termination of AC induced ventricular fibrillation on four trials were 27.9, 26.6, and 42.3 joules respectively for configurations 1, 2, and 3. The mean energy levels were not significantly different for configurations 1 and 2, both of which were significantly lower than that for configuration 3. The lowest peak voltages terminating ventricular fibrillation on four trials were 595 +/- 176, 521 +/- 134 and 579 +/- 171 volts for configuration 1, 2, and 3. The mean voltage level for configuration 2 was significantly lower than that for configurations 1 and 3, which were not significantly different.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1987

Catheter ablation: relationship of defibrillator waveform to the production of postshock ventricular tachyarrhythmias and myocardial damage.

The myocardial damage and arrhythmogenicity of percutaneous transcatheter shocks utilizing two different defibrillator waveforms (truncated exponential and damped sinusoidal) were compared. Ten dogs (33.7 +/- 3.6 kg) were studied. Five received left ventricular damped sinusoidal R-synchronous shocks during sinus rhythm and the other five received truncated exponential waveform shocks. Each dog received four energies (60, 120, 180, and 240 joules) randomly assigned to four left ventricular sites. The immediate postshock rhythms were recorded. Ventricular tachycardia occurred after 90% of the damped sinusoidal shocks compared to only 25% of the truncated exponential shocks (p less than 0.005). The animals were sacrificed 14 days later. Infarct size as determined by planimetry was not significantly different for the two waveforms. Thus intracavitary shocks utilizing a truncated exponential waveform are less arrhythmogenic than damped sinusoidal waveform shocks but produce similar morphologic changes and therefore may offer a significant safety advantage for catheter ablation procedures.

Animals↗

PubMed1987

Relationship of left ventricular mass to defibrillation threshold for the implantable defibrillator: a combined clinical and animal study.

Defibrillation results when a critical mass of myocardium is depolarized. The relationship between echocardiographic determinations of left ventricular mass, volume, and cavity radius to wall thickness ratio and defibrillation threshold for the implantable defibrillator was examined. Ten patients with two large patch defibrillating lead systems were studied. Defibrillation threshold was determined intraoperatively as the lowest energy terminating ventricular fibrillation. Left ventricular mass, volume, and radius/posterior wall thickness ratio were calculated from two-dimensional echocardiograms. A significant correlation was found between left ventricular mass and defibrillation threshold (r = 0.78, p less than 0.01). The correlations between defibrillation threshold and left ventricular volume (r = 0.59) and radius/wall thickness ratio (r = 0.55) were not significant. Subsequently, 11 dogs undergoing defibrillation trials with a transvenous catheter and a chest wall patch were studied. Defibrillation threshold was defined as the lowest energy-terminating ventricular fibrillation (four separate attempts). Subsequently, the heart was dissected, and the left ventricle (including the septum) was weighed. The correlation between left ventricular weight and defibrillation threshold (r = 0.76) was significant (p less than 0.01). We conclude that noninvasive assessment of left ventricular mass and direct measurement of left ventricular weight are significantly correlated with defibrillation threshold and consistent with the critical mass hypothesis.

Animals↗

PubMed1987

Nonthoracotomy internal defibrillation in dogs: threshold reduction using a subcutaneous chest wall electrode with a transvenous catheter electrode.

The efficacy of truncated exponential waveform shocks using a cardioverter-defibrillator catheter with and without a 13.9 cm2 subcutaneous thoracic patch electrode was examined in 10 pentobarbital-anesthetized dogs. The cardioverter-defibrillator catheter was positioned through the external jugular vein with the distal 4 cm2 shocking electrode located in the right ventricular apex and the 8 cm2 proximal electrode located in the superior vena cava. Four electrode configurations were tested: 1) distal electrode (cathode) to proximal electrode and chest wall patch (common anodes), 2) distal electrode (cathode) to chest wall patch (anode), 3) distal electrode (cathode) to proximal electrode (anode), and 4) chest wall patch (cathode) to proximal electrode (anode). The lowest randomized energy resulting in termination of alternating current-induced ventricular fibrillation on four trials at that energy was 20.2, 21.3, 27.4 and greater than 40 J, respectively, for configurations 1 through 4. The energy requirements for configurations 1, 2 and 3 were significantly lower than for configuration 4 (p less than 0.001). Additionally, configurations incorporating the distal electrode and the patch electrode (configurations 1 and 2) were significantly better than the catheter alone (configuration 3; p less than 0.05). There was no significant difference between configurations 1 and 2. In conclusion, the addition of a subcutaneous chest wall electrode to the cardioverter-defibrillator catheter significantly lowered energy requirements for defibrillation, suggesting that a nonthoracotomy approach for the automatic implantable cardioverter-defibrillator is feasible.

Animals↗