Relationship between epicardial and intramyocardial ST-segment voltage and myocardial blood flow during graded coronary constriction in the dog.

This study was undertaken to examine the relationship between electrographic ST-elevation and regional myocardial blood flow during graded coronary constriction. Electrograms from the epicardial surface, outer and inner layers of the myocardium were recorded. Regional blood flow to the outer and inner layers of the myocardium was measured by means of a heat-clearance method. With the application of a coronary constriction, myocardial blood flow to the inner layer began to decrease with a 75% coronary constriction, while flow to the outer layer was maintained at near normal up to least an 80% coronary constriction. Non-linear squares curve of between ST-elevation and the decrease in myocardial flow resulted in y = 18.80 exp-0.06x - 0.02 in the outer layer and y = 9.22 exp-0.02x - 1.54 in the inner layer. Also the non-linear squares curve of between epicardial ST-elevation and the decrease in myocardial flow resulted in y = 50.91 exp-0.11 x + 0.04 in the inner layer and y = 10.29 exp-0.07 x + 0.03 in the outer layer. The standard deviations of the coefficients of the latter two equations were higher than those of the former two equations. The higher values indicated larger variations of the parameter coefficients and data points. These results clearly demonstrated that a regional intramyocardial electrogram more closely reflects local ischemia than does an epicardial electrogram.