Tovar O H, Jones J L
Department of Physiology and Biophysics, Georgetown University, Washington, District of Columbia 20422, USA.
Am J Physiol. 1997 Feb;272(2 Pt 2):H1011-9. doi: 10.1152/ajpheart.1997.272.2.H1011.
The "extension of refractoriness" hypothesis, which suggests that the shock halts fibrillation by extending the refractory period, has not been directly tested. Defibrillation (5 isolated rabbit hearts; 111 episodes) was attempted by 8-ms pulses (65% tilt) delivered through epicardial patches. Monophasic action potentials were recorded in a low current density region (6.3 V/cm at 90% success). Fifty shocks failed to convert; 61 shocks successfully defibrillated. Postshock response duration (from shock to repolarization) was significantly longer for successful type A (with no postshock activations) defibrillation (102.3 +/- 7.5 ms) than for unsuccessful defibrillation (47.6 +/- 4.3 ms; P < 0.0001) for shocks occurring during the last 40% of the fibrillation action potential. Probability of success and postshock response duration both increased with current intensity. However, at each intensity, response durations for successful defibrillation were significantly longer than those for unsuccessful defibrillation. A minimum prolongation of 75 ms was associated with type A defibrillation. These results suggest that shock-induced response duration correlates with successful defibrillation and that a response of 75 ms is required to completely block fibrillation wavefronts.
“不应期延长”假说认为电击通过延长不应期来终止颤动，但该假说尚未得到直接验证。通过心外膜贴片施加8毫秒脉冲（65%倾斜度），对5只离体兔心脏进行了111次除颤尝试。在低电流密度区域（90%成功率时为6.3伏/厘米）记录单相动作电位。50次电击未能转复；61次电击成功除颤。对于在颤动动作电位最后40%期间发生的电击，成功的A型（电击后无激活）除颤的电击后反应持续时间（从电击到复极化）（102.3±7.5毫秒）显著长于未成功除颤的情况（47.6±4.3毫秒；P<0.0001）。成功概率和电击后反应持续时间均随电流强度增加。然而，在每种强度下，成功除颤的反应持续时间均显著长于未成功除颤的情况。A型除颤相关的最小延长时间为75毫秒。这些结果表明，电击诱导的反应持续时间与成功除颤相关，且需要75毫秒的反应来完全阻断颤动波前。
