Myocardial blood flow as a determinant factor in the electrical stability of the myocardium

The role of regional myocardial blood flow on the electrical stability as determined by ventricular fibrillation threshold (VFT) was evaluated in 12 dogs during subendocardial and transmural ischemia. With selective subendocardial ischemia produced by partial stenosis of left anterior descending coronary artery (LAD), both VFT and myocardial blood flow (MBF) decreased 66.6 per cent (p < .001) and 44.7 per cent (p < .001), respectively from the control values in the LAD subendocardium. VFT and MBF were not significantly different from control values in LAD subepicardium and remote circumflex regions during partial stenosis of LAD. After ligation of LAD, VFT in the subepicardium and subendocardium of LAD fell 74.6 per cent (p < .001) and 74 per cent (p < .001), respectively, from control values with an associated decrease in MBF of 98.2 per cent and 91 per cent in each of the regions. Following ligation of LAD, VFT was also decreased in the circumflex subendocardium and subepicardium 62.2 per cent (p < .001) and 59.1 per cent (p < .001), respectively, from control values while there was no change in MBF from control values in both these regions. This study demonstrates the following patterns in electrical instability with ischemia: 1. 1. During selective subendocardial ischemia produced by partial stenosis of the LAD, VFT and MBF showed a parallel decline in the LAD subendocardial zone, suggesting a direct relationship between these parameters. 2. 2. Following LAD ligation with production of transmural ischemia, the entire left ventricle became electrically unstable, as measured by VFT, independent of regional myocardial blood flow. This suggests that factors other than MBF significantly influence electrical instability during transmural ischemia.