Measurement of cardioversion/defibrillation thresholds in man by a truncated exponential waveform and an apical patch-superior vena caval spring electrode configuration.

Abstract

Defibrillation/cardioversion thresholds were measured in 33 patients undergoing defibrillator implants. Each patient had a 12 cm2 patch placed near the left ventricular apex via a thoracotomy and a 10 cm2 spring lead placed pervenously at the right atrial-superior vena caval junction. Ventricular tachycardia of stable morphology, polymorphic ventricular tachycardia, or ventricular fibrillation was induced four times in each patient and 1, 5, 10, and 25 J truncated exponential shocks with 60% tilt were given in a random sequence. The conversion rate was constant (77%, 86%, 87%, 85%) with increasing energy for ventricular tachycardia but progressively increased for polymorphic ventricular tachycardia and ventricular fibrillation (8%, 33%, 58%, 92%). The ventricular tachycardia acceleration rates for 1, 5, 10, and 25 J were 23%, 14%, 10%, and 15%. Patients not reliably converted with 25 J may require repositioning of leads or two patches. We conclude that for the springpatch electrodes, increasing energy from 1 to 25 J improves the conversion rate for polymorphic ventricular tachycardia and ventricular fibrillation; the ventricular tachycardia conversion rate is constant. Acceleration of ventricular tachycardia occurs at all energies. Defibrillator implantation requires extensive intraoperative electrophysiologic testing to ensure safe and reliable termination of ventricular tachycardia and fibrillation. Circulation 69, No. 4, 766-771, 1984.

Mechanistic inquiry into decrease in probability of defibrillation success with increase in complexity of preshock reentrant activity

“…The study by Kerber et al (16) demonstrated that the degree of organization of ventricular tachyarrhythmia determines the energy and current requirements for successful transthoracic cardioversion and defibrillation. Similar were the conclusions by Winkle et al (28), which were derived from their internal defibrillation studies. However, the mechanisms by which the organization of the arrhythmia affects the probability of success for a given shock strength remain unclear.…”

“…Cardioversion of a monomorphic ventricular tachycardia (VT) typically requires less energy than termination of ventricular fibrillation (VF). The American Heart Association recommends using lower currents and energies for termination of VT (1); these recommendations are supported by clinical studies (16,28). The study by Kerber et al (16) demonstrated that the degree of organization of ventricular tachyarrhythmia determines the energy and current requirements for successful transthoracic cardioversion and defibrillation.…”

Clinical experience, complications, and survival in 70 patients with the automatic implantable cardioverter/defibrillator.

“…Testing included the induction and termination of ventricular fibrillation in patients who have experienced ventricular tachycardia only clinically, since there is an unavoidable incidence of ventricular tachycardia acceleration even with R wave synchronous pulse discharges. 8 We also prefer that an arrhythmia be terminated with the initial pulse discharge rather than by one of the three subsequent backup discharges. This extensive testing with optimization of electrode configuration may also contribute to the high survival rates in our series.…”

Effect of duration of ventricular fibrillation on defibrillation efficacy in humans.

“…Ventricular tachycardia is generally more easily terminated with lower energy shocks than is ventricular fibrillation. 13 Our data should not be extrapolated beyond the 15-second duration of ventricular fibrillation that we evaluated. The difference in defibrillation efficacy between 5 and 15 seconds seen only at 300 V in this study could possibly be observed at higher energies if the duration of fibrillation is longer than 15 seconds.…”