EFFECTS OF RESPIRATION PHASE ON VENTRICULAR DEFIBRILLATION THRESHOLD IN A HOT CAN ELECTRODE SYSTEM

The impedance of defibrillation pathways is an important determinant o f ventricular defibrillation efficacy. The hypothesis in this study wa s that the respiration phase (end-inspiration versus end-expiration) m ay alter impedance and/or defibrillation efficacy in a ''hot can'' ele ctrode system. Defibrillation threshold (DFT) parameters were evaluate d at end-expiration and at end-inspiration phases in random order by a biphasic waveform in ten anesthetized pigs (body weight: 19.1 +/- 2.4 kg; heart weight: 97 +/- 10g). Pigs were intubated with a cuffed endo tracheal tube and ventilated through a Drager SAV respirator with tida l volume of 400-500 mt. A transvenous defibrillation lead (6 cm long, 6.5 Fr) was inserted into the right ventricular apex. A titanium can e lectrode (92-cm(2) surface area) was placed in the left pectoral area. The right ventricular lead was the anode for the first phase and the cathode for the second phase. The DFT was determined by a ''doun-up do wn-up'' protocol. Statistical analysis was performed with a Wilcoxon m atched pair test. The median impedance at DFT for expiration and inspi ration phases were 37.8 +/- 3.1 Omega and 39.3 +/- 3.6 Omega, respecti vely (P = 0.02). The stored energy at DFT for expiration and inspirati on phases were 5.7 +/- 1.9 J and 6.0 +/- 1.0 J respectively (P = 0.594 ). Shocks delivered at end-inspiration exhibited a statistically signi ficant increase in electrode impedance in a ''hot can'' electrode syst em. The finding that DFT energy was not significantly different at bot h respiration phases indicates that respiration phase does not signifi cantly affect defibrillation energy requirements.