Hou C J, Chang-Sing P, Flynn E, Martinez L, Peterson J, Ottoboni L K, Liem L B, Sung R J
Cardiac Electrophysiology Service, Stanford (Calif) University Medical Center 94305, USA.
Circulation. 1995 Nov 1;92(9):2558-64.
This study was designed to characterize the ventricular vulnerable period (VVP) and ventricular fibrillation (VF) threshold by use of T-wave shocks in patients undergoing implantation of cardioverter/defibrillators. A premature condensed shock applied during the VVP can induce VF. Most studies on the VVP and VF threshold have been conducted in animals rather than in humans.
Twenty-one patients undergoing implantation of Medtronic PCD Jewel 7219D cardioverter/defibrillators because of ventricular tachycardia and/or VF were enrolled. All had structural heart disease. Their ages ranged from 42 to 85 years (mean, 69 +/- 11.3 years). Seventeen (80.9%) had atherosclerotic coronary artery disease. The right ventricle (RV) was driven at a cycle length (S1) of 400 ms, and monophasic shocks (S2) of 0.6 J were delivered through an RV apex lead (cathode) and a superior vena cava lead (anode) during the T wave of each cardiac cycle. The longest and shortest S1-S2 intervals that were capable of inducing sustained VF were defined as the outer and inner limits of the VVP at an energy level of 0.6 J, respectively. To determine the VF threshold, a shock of 0.2 J was applied at the midpoint of the VVP at 0.2-J increments until sustained VF was induced. The lowest energy setting capable of inducing sustained VF was defined as the VF threshold. Of the 21 patients, the VVP at an energy level of 0.6 J averaged 53.8 +/- 26.0 ms. Characteristically, the VVP started from the ascending limb of the T wave and ended at or slightly beyond the peak of the T wave, occupying 12.2 +/- 5.8% of the QT interval. The midpoint of the VVP used for determination of the VF threshold measured 0 to 90 ms (mean, 32.9 +/- 26.0 ms) before the peak of the T wave. Of the 21 patients, 16 (76.2%) had a VF threshold at < or = 0.2 J (estimated 57 V), 3 at 0.4 J (estimated 81 V), and 2 at 0.6 J (estimated 99 V).
The VF threshold is low (< or = 0.2 J) in the majority of patients requiring implantation of cardioverter/defibrillators. Further studies are needed to define clinical usefulness of the study technique relative to its potential role for risk stratification and for assessing antifibrillatory properties of antiarrhythmic drugs in this subset group of patients.
本研究旨在通过对接受心脏转复除颤器植入术的患者使用T波电击来确定心室易损期（VVP）和心室颤动（VF）阈值。在VVP期间施加的过早密集电击可诱发VF。大多数关于VVP和VF阈值的研究是在动物而非人类中进行的。
纳入21例因室性心动过速和/或VF而接受美敦力PCD Jewel 7219D心脏转复除颤器植入术的患者。所有患者均有结构性心脏病。年龄范围为42至85岁（平均69±11.3岁）。17例（80.9%）患有动脉粥样硬化性冠状动脉疾病。右心室（RV）以400 ms的周期长度（S1）驱动，在每个心动周期的T波期间，通过RV心尖导联（阴极）和上腔静脉导联（阳极）施加0.6 J的单相电击（S2）。能够诱发持续性VF的最长和最短S1-S2间期分别被定义为能量水平为0.6 J时VVP的外限和内限。为确定VF阈值，在VVP中点以0.2 J的增量施加0.2 J的电击，直至诱发持续性VF。能够诱发持续性VF的最低能量设置被定义为VF阈值。21例患者中，能量水平为0.6 J时VVP平均为53.8±26.0 ms。其特征是，VVP从T波的上升支开始，在T波峰值处或略超过T波峰值结束，占QT间期的12.2±5.8%。用于确定VF阈值的VVP中点在T波峰值前0至90 ms（平均32.9±26.0 ms）。21例患者中，16例（76.2%）的VF阈值≤0.2 J（估计57 V），3例为0.4 J（估计81 V），2例为0.6 J（估计99 V）。
在大多数需要植入心脏转复除颤器的患者中，VF阈值较低（≤0.2 J）。需要进一步研究来确定该研究技术相对于其在该亚组患者风险分层及评估抗心律失常药物抗纤颤特性方面潜在作用的临床实用性。
