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(Circulation Research. 1996;79:461-473.)
© 1996 American Heart Association, Inc.

Articles

Cellular and Ionic Basis of Arrhythmias in Postinfarction Remodeled Ventricular Myocardium

Dayi Qin, Zhi-Hao Zhang, Edward B. Caref, Mohamed Boutjdir, Praveer Jain, Nabil El-Sherif

the Cardiology Division, Department of Medicine, State University of New York Health Science Center, and Veterans Affairs Medical Center, Brooklyn, NY.

Correspondence to Nabil El-Sherif, MD, Cardiology Division, Box 1199, SUNY Health Science Center, 450 Clarkson Ave, Brooklyn, NY 11203. E-mail el-sherif.nabil@brooklyn.va.gov.

After myocardial infarction (MI), the noninfarcted myocardium undergoes significant hypertrophy as part of the post-MI structural remodeling. Electrophysiological changes associated with the hypertrophied remodeled myocardium may play a key role in arrhythmia generation in the post-MI heart. We investigated the cellular and ionic basis of arrhythmias in remodeled left ventricular (LV) myocardium 3 to 4 weeks after MI in the rat. We analyzed (1) the incidence of induced ventricular tachyarrhythmias (VTs) in the in vivo heart, (2) action potential characteristics and arrhythmia mechanisms in multicellular preparations and isolated remodeled LV myocytes, and (3) the density and kinetics of the L-type Ca²⁺ current (I_Ca-L) and the fast and slow components of transient outward K⁺ currents (I_to-f and I_to-s, respectively). The results were compared with those from sham-operated rats. In vivo, programmed stimulation induced sustained VT in 80% of post-MI rats but not in sham-operated rats. The capacitance of post-MI hypertrophied myocytes was significantly increased compared with myocytes from sham-operated rats. Post-MI myocytes had prolonged action potential duration (APD) with marked heterogeneity of the time course of repolarization. The prolongation of APD could be explained by the significant decrease of the density of both I_to-f and I_to-s. There was no change in the kinetics of both currents compared with control. Both the density and kinetics of I_Ca-L were not significantly different in post-MI remodeled myocytes compared with control. The cellular studies showed that reentrant excitation secondary to dispersion of repolarization and triggered activity from both early and delayed afterdepolarizations are potential mechanisms for VT in the post-MI remodeled heart.

Key Words: myocardial infarction • hypertrophy • patch clamp • single cell • ion channel