Epicardial activation after unsuccessful defibrillation shocks in dogs

Abstract

To study defibrillation, shocks were given to seven dogs during electrically induced fibrillation, while recordings were made from 56 epicardial electrodes. Shocks were given via electrodes on the left ventricular apex and the right atrium, creating an uneven shock field with much higher potential gradients in the apex than in the base of the ventricles. For unsuccessful 0.01- to 0.05-J shocks, activation occurred soon after the shock at many sites in both the base and the apex. For 0.1- to 0.5-J shocks, the number of early activation sites was greatly decreased, and the latency from the shock until earliest recorded activation was greatly increased at the apex but not at the base. For 1- to 5-J shocks, one to three early sites were present and confined to the base, with a long latency between the shock and the appearance of these early sites. The latency and location of earliest activation were similar to those after 1- to 5-J shocks given to induce fibrillation during normal paced rhythm. Shocks of 10 J successfully defibrillated. These findings suggest that the shock field can have at least three effects. One, a weak field fails to halt the activation fronts of fibrillation. Two, a stronger field halts but then reinduces fibrillation in a manner similar to that of the same strength field during the vulnerable period of normal rhythm. Three, a still higher field halts fibrillation without reinitiating it. Successful defibrillation requires a shock strong enough to create this third field intensity throughout the ventricles.

Tunnel Propagation of Postshock Activations as a Hypothesis for Fibrillation Induction and Isoelectric Window

“…IW increased as shock strength increased. 4,6,13 3. For both monophasic (MS) and biphasic (BS) shock waveforms, earliest PAs arose, following weak shocks, in areas of high extracellular potential gradient, but moved to areas of low extracellular potential gradient as shock strength increased.…”

“…The presence of an isoelectric window (IW) following unsuccessful defibrillation attempts [3][4][5] led to the understanding that an electric shock terminates ongoing fibrillation but then reinitiates it; hence the mechanisms of fibrillation induction and its reinitiation (unsuccessful defibrillation) are the same. Indeed, striking similarities between these mechanisms have been found, particularly with regard to propagation of the first global postshock activation (PA) and IW duration.…”

Left ventricular geometry immediately following defibrillation: shock-induced relaxation

“…deexcitation; ultrasound; cardiac mechanics MUCH RESEARCH has concentrated on determining the electrical phenomenon that can predict either the success or failure of ventricular defibrillation. Many studies suggest that excitation (depolarization) of the myocardium plays an important role in defibrillation (2,13,14,16,18) by extinguishing fibrillatory wave fronts [critical mass theory (18)] or by preventing any new fibrillatory wave fronts from forming after the defibrillation shock (2). However, recent studies (4, 11) suggest that deexcitation (repolarization) may be an important factor in determining the success or failure of defibrillation.…”

Right Atrial Septal Electrode for Reducing the Atrial Defibrillation Threshold

“…7,11 With this electrode configuration (RAA3 CS), it has been demonstrated that after a failed shock near the ADFT, the recurrent atrial activation originates from the posterior left atrial wall near the pulmonary veins, 12 a region distant from the defibrillation electrodes, where the shock potential gradient is low. 13 In an effort to reduce the ADFT of the standard RAA3 CS configuration, the benefit of an additional electrode situated across the interatrial septum (SP) was assessed in an earlier study. 14 The delivered-energy ADFT of the configuration with the RAA and CS electrodes in common shocking to the SP electrode (RAAϩCS3 SP) was significantly lower than that of RAA3 CS, and the configuration tested with the lowest mean ADFT was the sequential-shock configuration RAA3 SP/CS3 SP (first shock pathway/second shock pathway).…”