Transventricular Impedance During Fibrillation

Transventricular impedance during fibrillation was measured with two methods: 1) by injecting a low constant sinusoidal current (obtaining a Z value), and 2) by using the time constant of an exponential defibrillatory discharge (giving an R value). One group of eight dols (Group 300) was normothermic and another group of 14 dogs (Group 400) was hypothermic. The left anterior descending coronary artery was ligated in both groups. For Group 300 (values in ohms), Z = 29.5 (SD 5.1), R = 30.9 (SD 4.7). The paired t-test gave a statistically significant difference (p 0.1 percent). For Group 400, Z = 34.5 (SD 7.3); R = 33.8 (SD 5.8), also with a significant difference, but at a lower level (p 5 percent). Nonetheless, from the practical point of view of calculating the voltage to be applied after establishing an adequate dose current, they (the differences) do not seem to have any important quantitative weight, supporting method 1 (for its easiness) to estimate transventricular impedance in this particular application.