Comparative Effect of Shocks on the Endocardial Rate-sensing Signals from Transvenous Lead Systems

We evaluated transvenous defibrillation lead systems (Medtronic TransveneTM, CPI EndotakTM 60 series, CPI EndotakTM 70 series, Ventritex TVLTM) in random order in each of 6 large (30-60 kilogram) pigs. Defibrillation coils were positioned at the right ventricular apex (cathode) and in the superior ven cav (anode). The effect of biphasic shocks of graded magnitude on the bipolar right ventricular endocardial sinus peak-peak R wave amplitude recorded from each lead was measured at 1-60 seconds after the shock. Post-shock amplitudes (R′) were expressed as fraction of the value just prior to each shock (R). Values shown are the means for all 6 animals. Results: Post-shock R wave amplitude reduction was most severe with the EndotakTM 60 and TVLTM leads and was most marked at leading edge voltages > 400. This pattern was present but less marked with the EndotakTM 70 lead. No significant reduction was noted at any shock voltage with the TransveneTM lead. Conclusions: Post-shock sinus R wave amplitude is least affected in the TransveneTM system, which is the only system which senses in true bipolar fashion. These dat may have implications for post-shock sensing by devices.