Regional electrical activation and mechanical function in the partially ischemic left ventricle of the dog. Delhaas, Tammo, Theo Arts, Frits W. Prinzen, and Robert S. Reneman. Departments of Physiology and Biophysics, Cardiovascular Research Institute Maastricht, University of Limburg, Maastricht, The Netherlands
APStracts 3:0377H, 1996.
During normoxia, asynchronous electrical activation of the left ventricle significantly affects regional mechanical performance. Regional fiber strain and external work during the ejection phase are found to be lower in early-activated than in late-activated regions. Because electrical activation is known to be delayed during ischemia, the present study was designed to investigate the influence of this electrical asynchrony on regional fiber strain, if any, during moderate and severe myocardial ischemia. Regional electrical activation time (tea) and fiber strain during the ejection phase (ef) were measured in the epicardial layers of the left ventricular anterior wall during normoxia, and after 15 min of total occlusion (n=5) or 30, 60, 120 and 180 min of partial occlusion of the left anterior interventricular coronary artery (LAICA; n=11). Myocardial blood flow (MBF) was assessed with radioactive microspheres. Blood gases, pH, and lactate and inorganic phosphate content were determined in arterial, local venous and coronary sinus blood. During normoxia, tea and ef were similar in various epicardial regions of the left ventricular anterior wall. During total LAICA occlusion, in the ischemic area subepicardial MBF decreased from 0.860.36 to 0.180.09 ml.g1.min1 (meanSD), subepicardial ef decreased from 0.110.02 to 0.010.01, whereas the delay in tea between the normoxic basal-lateral and the ischemic apical-medial area increased slightly but statistically significant from 1.98.0 to 7.58.0 ms. After 180 min partial occlusion of the LAICA, in the ischemic area subepicardial MBF decreased from 0.620.17 to 0.490.18 ml.g1.min1 and ef from 0.080.01 to 0.030.01. No significant change in the difference in tea between the normoxic and the ischemic area could be detected, being 5.14.8 and 5.25.8 ms in the control situation and after 180 min partial occlusion, respectively. These findings indicate that in the ischemic epicardium 1) mechanical function is more affected than electrical impulse conduction; 2) delayed activation, if any, is accompanied by decreased instead of increased fiber strain as found in the normoxic left ventricle. 

Received 28 August 1995; accepted in final form 3 April 1996.
APS Manuscript Number H807-5.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 19 September 1996