Ventricular Fibrillation and Shortening, Alternans and Afterdepolarizations of Epicardial Monophasic Action Potentials During Coronary Occlusion and Reperfusion

Shinji Ito, Toshihisa Miyazaki, Shunichiro Miyoshi, Yoshiko Furukawa, Shunsuke Takagi, Kazunori Moritani, Hideo Mitamura, Satoshi Ogawa
1999 Japanese Circulation Journal - English Edition  
entricular fibrillation (VF) occurs frequently in a setting of acute coronary occlusion and reperfusion, and constitutes a major cause of sudden cardiac death. The mechanisms of the induction of VF by coronary occlusion have been investigated in animal models by recording unipolar electrograms, 1 bipolar electrograms, 2 composite electrograms, 3 and by a mapping technique. 4 According to Kaplinsky et al, there are 2 peaks in the occurrence of ventricular arrhythmias early after acute coronary
more » ... clusion: the first peak occurs within 10 min (immediate ventricular arrhythmias) and the second peak occurs between 15 and 20 min (delayed ventricular arrhythmias). 3 The former is attributed to reentry based on a marked conduction delay in the subepicardial layer of the ischemic myocardium. However, ventricular arrhythmias can occur immediately after acute coronary occlusion even without a marked increase in activation time. 4 In such cases, reentry based on repolarization abnormalities, such as shortening or increased dispersion of repolarization, or other mechanisms, including triggered activity and abnormal automaticity, may be involved in the arrhyth- The relationship between the occurrence of ventricular fibrillation (VF) and repolarization abnormalities of the ischemic and reperfused myocardium is poorly understood. The present study examined the temporal relationship between ischemia-and reperfusion-induced changes in monophasic action potential (MAP) configurations and the occurrence of VF, and assessed the effects of repetition of ischemia. The left anterior descending coronary artery of 32 anesthetized dogs was occluded twice for 5 min, 30 min apart, during constant atrial pacing while recording MAPs from the epicardial ischemic zone. During the first occlusion, shortening of the MAP duration at 90% repolarization (APD90) and an increase in MAP alternans, defined as the maximal difference in APD90 between 2 consecutive beats, were observed. Afterdepolarizations also occurred transiently in 35% of the animals during occlusion and in 29% upon reperfusion. VF occurred in 28% (9/32 of the dogs) during the first sequence, and the incidence was higher in the subgroups with maximal alternans ≥20 ms (p<0.05), maximal shortening rate ≥30%, and afterdepolarizations. During the second sequence, the incidence of VF was reduced to 9% (3/32, p<0.05), associated with a significant reduction in the MAP changes. Thus, repolarization abnormalities of the ischemic and reperfused myocardium appear to be related to the occurrence of VF. The amelioration of the repolarization abnormalities by repetition of ischemia may be involved in its antifibrillatory effect. (Jpn Circ J 1999; 63: 201 -208)
doi:10.1253/jcj.63.201 pmid:10201622 fatcat:xjpzx7y4r5ek7mqdi2dbb5pece