Electrocardiographic " Peri 4 nfarction Block " A Clinical and Pathologic Correlation

THE TERM "peri-infarction block" was suggested by First, Bayley, and Bedford1 in 1950 to describe a type of intraventricular conduction defect that develops following myocardial infarction. They described alteration in the direction of the early portion of the QRS complex (initial QRS forces) that produced definite manifestations of myocardial infarction (i.e., Q waves) and slurring and prolongation of the terminal portion of the QRS complex (terminal QRS forces), giving rise to a total QRS duration of 0.11 second or greater. The authors postulated that the normal radial spread of excitation to the epicardium was interrupted by subendocardial infarction and that the overlying active myocardium was activated through circuitous routes of slower conducting myocardial fibers. Grant and associates2proposed different criteria for "peri-infarction block," which are (1) an abnormality of the direction of initial QRS forces of a type characteristic of myocardial infarction (accounting for Q waves); (2) an abnormality of direction of terminal QRS forces so that they point in a direction away from the initial QRS forces, the angle between the direction of the initial and terminal forces being 1000 or more; (3) little or no prolongation of the QRS interval. These criteria represent a substantial departure from those proposed by First et al.1 Grant interpreted the defect in excitation of the left ventricle in "peri-infarction block" to represent involvement by infarction or scarring of one or the other of the two divisions of the left bundle. In this circumstance im-