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 through 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. Circulation 73, No. 3, 484-491, 1986. THE DEVELOPMENT of the automatic internal defibrillator by Mirowski and co-workers'-' has provided the impetus for a search for the optimum electrode system4 5 for internal cardiac defibrillation. We

Effect of capacitor size and pathway resistance on defibrillation threshold for implantable defibrillators.

“…The size of output capacitors is constrained by the combined requirements to store sufficient energy to defibrillate reliably and to operate below voltages at which components of the output circuit fail or myocardial damage occurs.10,262829 The output circuits of current pulse generators can operate safely at voltages over 1000 V.1 10 There is substantial reason to believe that voltages higher than 750 V (corresponding to 34 J from a 120-,F capacitor) may be safe. During defibrillator implantation, internal 815-V (40 J) rescue shocks are given routinely, pulses up to 1000 V have been shown to be safe in dogs,30 and humans have been defibrillated safely with voltages up to 1420 V. 31 In the present study, we detected no adverse effects from 910-V pulses (25 J from 60-,uF capacitors). However, additional safety studies are required before voltages greater than 750 V can be recommended for implanted pulse generators.…”

Transvenous Biventricular Defibrillation Halves Energy Requirements in Patients

“…Prior studies also showed sequential shock schemes can produce lower DFTs than single shock schemes, but none placed a lead transvenously on the middle of the LV free wall. 12,13 Animal and clinical studies demonstrated substantial reductions in DFT using a small epicardial patch on the LV free wall and a sequential shock waveform, but this approach is no longer clinically acceptable due to the need for transthoracic patch insertion. 3,13 Other sequential shock studies used small, temporary defibrillation catheters that bear little resemblance to modern ICD leads, and most studies used 2 monophasic shocks delivered with equal amplitudes.…”

“…12,13 Animal and clinical studies demonstrated substantial reductions in DFT using a small epicardial patch on the LV free wall and a sequential shock waveform, but this approach is no longer clinically acceptable due to the need for transthoracic patch insertion. 3,13 Other sequential shock studies used small, temporary defibrillation catheters that bear little resemblance to modern ICD leads, and most studies used 2 monophasic shocks delivered with equal amplitudes. 12 The present study bears closest resemblance to that of Exner et al, 14 who reported a 44% reduction in DFT with sequential biphasic waveforms.…”

Prediction of defibrillation success from a single defibrillation threshold measurement with sequential pulses and two current pathways in humans.

“…Energy was calculated by the integrated area under the curve and the correction for the logarithmic decay of the capacitive discharge. 4 Although the value for the mean defibrillation threshold of the group receiving test shocks greater than 2.25 times defibrillation threshold was the lowest, there was no statistical difference between the groups (F= 2.01 at 4 and 44 df, p>0.05) of the 51 patients, 50 of whom were undergoing surgical ablation of the accessory pathway for Wolff-ParkinsonWhite syndrome. The additional patient was having an internal defibrillator implanted.…”

“…Defibrillation threshold was defined as the minimum energy required to cause defibrillation. 4 Once defibrillation threshold had been determined, estimated stored voltage for a test shock was calculated, which would correspond to that necessary to deliver the randomly selected ratio of defibrillation threshold energy for that patient. The initial stored voltage was set at the test shock voltage level.…”