Biphasic Shocks (biphasic + shock)

Distribution by Scientific Domains


Selected Abstracts


Electrophysiologic Deterioration After One-Minute Fibrillation Increases Relative Biphasic Defibrillation Efficacy

JOURNAL OF CARDIOVASCULAR ELECTROPHYSIOLOGY, Issue 6 2000
OSCAR H. TOVAR M.D.
Biphasic Shocks and One-Minute Fibrillation. Introduction: The probability of survival decreases to 70% after 2 minutes of ventricular fibriltation. Bipliasic shocks are more effective than monophasic shocks in terminating short-duration (<30 sec) ventricular fibrillation. We tested the hypotheses that developing ischemia changes the electrophysiologic characteristics of fibrillation and that the relative efficacy of biphasic shocks increases as electrophysiologic characteristics deteriorate. Methods and Results: Monophasic (12 msec) and biphasic (6/6 msec) shocks (1 to 4 A) were tested in random order in isolated rabbit hearts after 1-minute ischemic fibrillation. Monophasic action potentials showed only a sporadic occurrence of electrical diastole after 5 seconds of fibrillation (24% of action potentials in the right ventricle and 18% in the left ventricle). After 60 seconds of fibrillation, diastole (17.83 ± 1.14 msec in the right ventricle and 21.52 ± 1.16 msec in the left ventricle) appeared after almost every action potential (P < 0.0001 compared with 5 sec), despite a lack of change in fibrillation cycle length and dominant frequency. Monophasie I50 was 2.89 A, and biphasic I50 was 1.4 A (77% reduction in energy). Normalized curve width decreased 28%. Retrospective analysis showed that shocks delivered early in the fibrillation action potential bad a greater probability of succeeding (89%) than shocks delivered late (30%; P < 0.001). Conclusion: After l-minute ischemic fibrillation, diastolic intervals occur during fibrillation. Therefore, defibrillation shocks have an approximately 29% probability of interacting with the fibrillation action potential during diastole. At this time, biphasic shocks produced a more deterministic defibrillation threshold and became even more efficacious (I50B/M = 0.48) than at short fibrillation durations (I50 B/M = 0.7). [source]


Biphasic versus Monophasic Cardioversion in Shock-Resistant Atrial Fibrillation:

JOURNAL OF CARDIOVASCULAR ELECTROPHYSIOLOGY, Issue 8 2003
A Randomized Clinical Trial
Introduction: Cardioversion of atrial fibrillation using monophasic transthoracic shocks occasionally is ineffective. Biphasic cardioversion requires less energy than monophasic cardioversion, but its efficacy in shock-resistant atrial fibrillation is unknown. Thus, we compared the efficacy of cardioversion using biphasic versus monophasic waveform shocks in patients with atrial fibrillation previously refractory to monophasic cardioversion. Methods and Results: Fifty-six patients with prior failed monophasic cardioversion were randomized to either a 360-J monophasic damped sinusoidal shock or biphasic truncated exponential shocks at 150 J, followed by 200 J and then 360 J, if necessary. If either waveform failed, patients were crossed over to the other waveform. The primary endpoint was defined as the proportion of patients achieving sinus rhythm following initial randomized therapy. Stepwise multivariate logistic regression examined independent predictors of shock success, including patient age, sex, left atrial diameter, body mass index, drug therapy, and waveform. Twenty-eight patients were randomized to the biphasic shocks and 28 to the monophasic shocks. Sinus rhythm was restored in 61% of patients with biphasic versus 18% with monophasic shocks (P = 0.001). Seventy-eight percent success was achieved in patients who crossed over to the biphasic shock after failing monophasic cardioversion, whereas only 33% were successfully cardioverted with a monophasic shock after crossover from biphasic shock (P = 0.02). Overall, 69% of patients who received a biphasic shock at any point in the protocol were cardioverted successfully, compared to 21% with the monophasic shock (P < 0.0001). The type of shock was the strongest predictor of shock success (P = 0.0001) in multivariate logistic regression. Conclusion: An ascending sequence of 150-, 200-, and 360-J transthoracic biphasic cardioversion shocks are successful more often than a single 360-J monophasic shock. Thus, biphasic shocks should be the recommended configuration of choice for all cardioversions. (J Cardiovasc Electrophysiol, Vol. 14, pp. 868-872, August 2003) [source]


Reentry Site During Fibrillation Induction in Relation to Defibrillation Efficacy for Different Shock Waveforms

JOURNAL OF CARDIOVASCULAR ELECTROPHYSIOLOGY, Issue 5 2001
Ph.D., RAYMOND E. IDEKER M.D.
Reentry Site and Defibrillation Waveform Efficacy.Introduction: Unsuccessful defibrillation shocks may reinitiate fibrillation by causing postshock reentry. Methods and Results: To better understand why some waveforms are more efficacious for defibrillation, reentry was induced in six dogs with 1-, 2-, 4-, 8-, and 16-msec monophasic and 1/1- (both phases 1 msec) 2/2-, 4/4-, and 8/8-msec biphasic shocks. Reentry was initiated by 141 ± 15 V shocks delivered from a defibrillator with a 150- , F capacitance during the vulnerable period of paced rhythm (183 ± 12 msec after the last pacing stimulus). The shock potential gradient field was orthogonal to the dispersion of refractoriness. Activation was mapped with 121 electrodes covering 4 × 4 cm of the right ventricular epicardium, and potential gradient and degree of recovery of excitability were estimated at the sites of reentry. Defibrillation thresholds (DFTs) were estimated by an up-down protocol for the same nine waveforms in eight dogs internally and in nine other dogs externally. DFT voltages for the different waveforms were positively correlated with the magnitude of shock potential gradient and negatively correlated with the recovery interval at the site at which reentry was induced by the waveform during paced rhythm for both internal (DFT = 1719 + 64.5 , V , 11.1RI; R2= 0.93) and external defibrillation (DFT = 3445 + 150 , V , 22RI; R2= 0.93). Conclusion: The defibrillation waveforms with the lowest DFTs were those that induced reentry at sites of low shock potential gradient, indicating efficacious stimulation of myocardium. Additionally, the site of reentry induced by waveforms with the lowest DFTs was in myocardium that was more highly recovered just before the shock, perhaps because this high degree of recovery seldom occurs during defibrillation due to the rapid activation rate during fibrillation. [source]


Electrophysiologic Deterioration After One-Minute Fibrillation Increases Relative Biphasic Defibrillation Efficacy

JOURNAL OF CARDIOVASCULAR ELECTROPHYSIOLOGY, Issue 6 2000
OSCAR H. TOVAR M.D.
Biphasic Shocks and One-Minute Fibrillation. Introduction: The probability of survival decreases to 70% after 2 minutes of ventricular fibriltation. Bipliasic shocks are more effective than monophasic shocks in terminating short-duration (<30 sec) ventricular fibrillation. We tested the hypotheses that developing ischemia changes the electrophysiologic characteristics of fibrillation and that the relative efficacy of biphasic shocks increases as electrophysiologic characteristics deteriorate. Methods and Results: Monophasic (12 msec) and biphasic (6/6 msec) shocks (1 to 4 A) were tested in random order in isolated rabbit hearts after 1-minute ischemic fibrillation. Monophasic action potentials showed only a sporadic occurrence of electrical diastole after 5 seconds of fibrillation (24% of action potentials in the right ventricle and 18% in the left ventricle). After 60 seconds of fibrillation, diastole (17.83 ± 1.14 msec in the right ventricle and 21.52 ± 1.16 msec in the left ventricle) appeared after almost every action potential (P < 0.0001 compared with 5 sec), despite a lack of change in fibrillation cycle length and dominant frequency. Monophasie I50 was 2.89 A, and biphasic I50 was 1.4 A (77% reduction in energy). Normalized curve width decreased 28%. Retrospective analysis showed that shocks delivered early in the fibrillation action potential bad a greater probability of succeeding (89%) than shocks delivered late (30%; P < 0.001). Conclusion: After l-minute ischemic fibrillation, diastolic intervals occur during fibrillation. Therefore, defibrillation shocks have an approximately 29% probability of interacting with the fibrillation action potential during diastole. At this time, biphasic shocks produced a more deterministic defibrillation threshold and became even more efficacious (I50B/M = 0.48) than at short fibrillation durations (I50 B/M = 0.7). [source]


Atrial Activation Occurring Immediately after Successful Cardioversion of Atrial Fibrillation

PACING AND CLINICAL ELECTROPHYSIOLOGY, Issue 1 2008
ARTURO MARTÍN PEÑATO MOLINA M.D.
Background and Objective: Electrical defibrillation is very effective in interrupting atrial fibrillation (AF). However, its mechanism is not completely understood. We report our observations in patients subjected to external electriocardioversion (ECV) of atrial fibrillation and contrast them with recent theories about defibrillation mechanism. Methods: In 13 consecutive patients transthoracic electrical cardioversion for AF was performed during an electrophysiological study (11 monophasic -200,360 J- and 9 biphasic shocks -50,150 J-). About 10,16 electrograms were obtained with multipolar catheters recording right atrium, coronary sinus, and right pulmonary artery. AF was defined by interelectrogram intervals and changing sequences among recordings, indicating complete lack of organization. We evaluated the presence of propagated activations immediately (<300 ms) after successful shocks (,1 discrete electrogram in all recordings). In unsuccessful shocks we evaluated changes in electrogram morphology (discrete/fragmented) and interelectrogram intervals before and after defibrillation. Results: About 16/20 shocks terminated AF. In 6/16 one or two cycles of atrial activation were recorded just after the shock and before AF ended. In 10/16 AF was interrupted immediately after the shock. 4/20 shocks did not interrupt the arrhythmia. After these shocks, transient organization of recorded activity with longer interelectrogram cycle length and disappearance of fragmented activity were transiently observed. Conclusion: Our clinical findings in atrial defibrillation in vivo reproduce experimental data that show myocardial activations early after successful direct current shocks. These observations suggest that successful defibrillation depends not only on the immediate effects of the shock, but also on transient effects on electrophysiological properties of the myocardium, capable of interrupting persistent or reinitiated activations. [source]


Open-Chest Epicardial "Surgical" Defibrillation:

PACING AND CLINICAL ELECTROPHYSIOLOGY, Issue 3 2003
Biphasic Versus Monophasic Waveform Shocks
ZHANG, Y., et al.: Open-Chest Epicardial "Surgical" Defibrillation: Biphasic Versus Monophasic Waveform Shocks. The aim of the study was to compare biphasic versus monophasic shocks for open-chest epicardial defibrillation. Transthoracic biphasic waveform shocks require less energy to terminate ventricular fibrillation compared to monophasic waveform shocks. However, if biphasic shocks are effective for open-chest epicardial ("surgical") defibrillation has not been established. Twenty-eight anesthetized adult swine (15,25 kg) underwent a midline sternotomy. Ventricular fibrillation was electrically induced. After 15 seconds of ventricular fibrillation, each pig in group 1(n = 16)randomly received damped sinusoidal monophasic epicardial shocks and truncated exponential biphasic epicardial shocks from large(44.2 cm2)paddle electrodes at eight energy levels(2,50 J). Pigs in group 2(n = 12)received monophasic and truncated exponential biphasic shocks from small(15.9 cm2)paddle electrodes. In group 1 (large paddle electrodes), the overall percent shock success rose from15 ± 9%at 2 J to97 ± 3%at 50 J. In this group there was no significant difference in percent of shock success between damped sinusoidal monophasic and biphasic waveform shocks. In group 2 (small paddle electrodes), biphasic shocks yielded a significantly higher percent of shock success than monophasic shocks at mid-energy levels from 7 to 20 J (allP < 0.01). With small surgical paddle electrodes, biphasic waveform shocks demonstrated a significantly higher percent of shock success rate compared to monophasic waveform shocks. With large paddle electrodes, the two waveforms were equally effective. (PACE 2003; 26:711,718) [source]