Abstract: Biphasic shocks defibrillate more effectively than monophasic shocks, however, the mechanisms are still unknown. Isolated Langendorff-perfused rabbit hearts were paced at a cycle length of 500ms and the myocardial responses to shocks were recorded by MAP technique. A total of (84±11) biphasic T wave shocks were administered to each heart through two large shock plate electrodes flanking the bath to describe the area of vulnerability(AOV). The AOV was characterized by the induction of VF and was defined two-dimensionally by shock strength and coupling interval. ULV and LLV, which represent the upper and lower coner of AOV, respetively, occurred at shock strength of (373±62)V and (213±39)V, respectively. The coupling interval for ULV and LLV were (187±9) vs. (175±12)ms, p < 0.01, which resulted in a more complete repolarization level for ULV (84±9)% compare to that for LLV ((73±7)%, p < 0.01). The left and right borders of AOV (LBV, RBV) were (170±13)ms and (194±5)ms. The shock strength for RBV had a vertical upshift of (64±51)V (p < 0.01) compare to that for LBV. The rightward shift of the ULV timing compare to the LLV and the shock strength upshift of RBV vs. LBV resulted in a right-tilt of the AOV for biphasic shocks. This rightward shift of ULV timing vs. LLV might be responsible for its high defibrillation efficacy.

Key words: biphasic shock, area of vulnerability (AOV), upper limit of vulnerability (ULV), monophasic action potential(MAP)

摘要： 兔离体心脏用Langendorff方法灌流，500ms周长起搏。通过两只方形钢板电极对每只心脏平均施加(84±11)个电震强度(SS)和偶联间期(CI)随机组合的双相电震。心脏对电震的反应用单相动作电位(MAP)来记录。易损区(AOV)由诱发室性纤颤(VF)的数据点组成，为SS和CI的二维函数。由易损性上下限(ULV，LLV)和易损区左右边界(LBV，RBV)4个点所限定的AOV是均一的。ULV和LLV发生的SS分别为(373±62)和(213±39)V；发生时间分别为(187±9)和(175±12)ms，p＜0.01，这导致ULV的复极水平(84%±9%)比LLV(73%±7%)更完全(p＜0.01)。易损区左右边界分别为(170±13)和(194±5)ms；且右边界的SS比左边界抬高了(64±51)V(p＜0.01)。ULV发生时间较LLV的右移以及右边界比左边界SS的抬高导致双相电震AOV呈现向右倾斜。ULV发生时间较LLV的右移可能是其除颤高效的原因之一。

关键词: 双相电震, 易损区, 易损性上限, 单相动作电位