Internal cardiac defibrillation in man: Pronounced improvement with sequential pulse delivery to two different lead orientations

Abstract

Wider applicability of an implantable automatic defibrillator depends on achieving internal cardiac defibrillation consistently with the lowest possible energy. In animal studies, we have found that the cardiac defibrillation threshold could be reduced when sequential shocks separated in time and spacially arranged were delivered to the heart. We compared internal cardiac defibrillation using a single pulse shock delivered through an intravascular catheter with this new method for internal cardiac defibrillation in patients undergoing cardiac surgery for the correction of arrhythmias. For the single pulse shock and the first pulse of the sequential pulse shock, current was passed thourgh an intravascular catheter with the catheter cathode at the apex of the right ventricle and the anode at the superior vena cava-atrial junction region. The second pulse of the sequential pulse countershock was delivered between the catheter cathode in the right ventricular apex and an oval plaque electrode secured on the laterobasal left ventricular epicardium as anode. With the single pulse alone for shock delivery, 12 patients could be defibrillated with an average of 20.1 ± 16.8 J, with a corresponding leading-edge peak voltage and current of 836 ± 319 V and 9.4 ± 4.5 A, respectively. However, two of the patients could not be defibrillated with energies below 50 J. With the sequential pulse shock delivery, a significant reduction in all values were recorded. Mean total energy for defibrillation averaged 7.7 ± 6.0 J. Leading-edge peak voltage and current from the catheter averaged 430 ± 148 V and 5.0 ± 2.8 A, respectively. In addition, all patients could be defibrillated with less than 23 J, and nine of the 12 patients (75%) could be defibrillated with less than 7.5 J. In contrast, only two of these same 12 patients (17%) could be defibrillated with less than 7.5 J using the single pulse alone (binomial exact test, p = .0156). We conclude that sequential pulse defibrillation provides a pronounced reduction in the total energy necessary for defibrillation compared with the single pulse delivered through a catheter alone. Furthermore, the sequential pulse system provides a reduction in the current density at the electrodes, potentially reducing myocardial damage. This system may be important in the design of a totally implantable automatic defibrillator.