Effects of Normothermic and Hypothermic Cardiopulmonary Bypass Upon Defibrillation Energy Requirements and Transmyocardial Impedance

摘要

Difficulties in the defibrillation of hypothermic patients may be caused by increased defibrillation threshold, increased tissue impedance or by refibrillation. To evaluate these questions we studied the effect of controlled hypothermia upon defibrillation energy requirements and transcardiac impedance in a canine model of cardiopulmonary bypass in which 26 animals underwent right atrial and femoral arterial cannulation as well as continuous hemodynamic and intramyocardial temperature monitoring. The defibrillation energy requirements were evaluated at 60 minute intervals using an epicardial patch syste and transcardiac impedance was measured before and after the multiple inductions and terminations of ventricular fibrillation In Group 1 defibrillation energy requirements were evaluated immediately after initiation of cardiopulmonary bypass at 37 C (T0), after gradual cooling to 28 C (Ti), and after rewarming to 37 C (T2). Group 2 comprised time controls that were identically instrumented and studied, but maintained at 37 C throughout.