Implantable cardioverter-defibrillator in a German shepherd dog with ventricular arrhythmias

Evaluation of shock waveform configuration on the defibrillation capacity of implantable cardioverter defibrillators in dogs

“…Alternatively, earlier ICD placement attempts in dogs suggest that an adequate shock vector can be obtained by delivering a shock between the distal coil secured in the right ventricle and the generator positioned on the left side of the thorax at the point of maximal cardiac impulse. 4,5 In this study, the mean DFT value was 9.2 J and never exceeded 17.6 J, which is consistent with the recommended 10-J safety margin. This finding is in contrast with DFT values previously obtained in clinical dogs.…”

“…This finding is in contrast with DFT values previously obtained in clinical dogs. 4,5 It is possible that DFT values are lower in healthy dogs than animals with cardiac disease. Some studies in dogs with experimentally induced heart failure did not conclude a decrease in shock efficacy, while others found an increase in DFT up to 180% from baseline.…”

“…2,3 There are only two published reports of ICD implantation in dogs with ventricular arrhythmias. 4,5 Our group implanted a third ICD in a Doberman Pinscher with dilated cardiomyopathy that died within 36 h of the procedure after the defibrillator failed to terminate an episode of unstable ventricular tachycardia, despite successive delivery of six maximum energy shocks. In all three cases, the defibrillation threshold (DFT), which is the minimum energy necessary to reliably terminate VF at the time of initial implant testing, equaled the maximum energy deliverable by the device.…”

“…6,7 This seems achievable by securing the pulse generator on the left side of the thorax in a subcutaneous pocket located in the precordial area, and by delivering the shock between the device and the lead's distal coil, positioned deep in the right ventricular apex. 4,5,8 Defibrillation shock waveform morphology and duration have been identified as key determinants of defibrillation efficacy. Current ICDs deliver truncated biphasic shocks: the first phase of the exponential waveform charges the cell membranes to the same potential, while the second phase, which is opposite polarity, removes the residual charge from marginally stimulated cells and returns the membrane voltage to zero.…”