Vectorcardiographic diagnosis of diaphragmatic myocardial infarction.

Vectorcardiograms of 31 patients with arteriographic evidence of complete occlusion of the right coronary artery were analyzed in order to evaluate and attempt to improve the vectorcardiographic criteria for the diagnosis of an old diaphragmatic myocardial infarction. The electrocardiogram showed no evidence of a diaphragmatic infarction in 48 percent of these patients. This was advantageous, since the intent of the study was to develop vectorcardiographic criteria that exceeded the capability of the electrocardiogram. The criteria that appeared optimal were: (1) an instantaneous 0.02 second QRS vector equal or superior to 315 degrees (-45 degrees) in the sagittal plane, or (2) ratio of voltages of 0 to left x-intercept to maximal QRS vector greater than 0.22 in the frontal plane. These criteria identified a diaphragmatic infarction in 77 percent of patients (24 of 31) with complete occlusion of the right coronary artery. There were no false positive findings in 40 normal subjects. A group of criteria previously defined by others, based upon rotation, contour of initial forces, duration of superior forces relative to the contour, magnitude of 0 to left x-intercept, and maximal QRS vecotr, was equally sensitive. Other previously defined criteria were less sensitive. The criteria developed in this study, when tested in 22 patients with prominent Q waves indicative of an old diaphragmatic infarction, properly diagnosed the infarction in all 22 patients. All previous criteria also successfully detected infarction in these patients. However, the new criteria identified a greater number of patients without electrocardiographic evidence of diaphragmatic infarction than were identified with previously defined vectorcardiographic criteria unless the latter were complex.