Evolution of vectorcardiographic QRS changes during myocardial infarction in dogs and their relation to infarct size.

The ability of vectorcardiographic QRS changes to quantify myocardial ischaemia and necrosis in dogs was studied. Myocardial infarction was produced in 21 anaesthetised dogs by inflating a balloon inserted into the right, left anterior descending, or left circumflex coronary artery. A Frank vectorcardiogram was recorded before and every 15-30 minutes for 10 hours after the occlusion. ST vector magnitude (ST-VM), QRS summation vectors, and QRS integral differences (QRS-VD) between the preocclusion recording and subsequent recordings were computed. Twenty four hours after occlusion two vectorcardiograms were obtained, the hearts removed, and the infarcts cut out and weighed. Four dogs were excluded from the study because of persistent arrhythmias, major conduction defects, or sudden death. In the remaining 17 dogs the QRS summation vectors rotated maximally towards the site of infarction 7 minutes after occlusion corresponding to a median minimum QRS-VD of -19 (range -2 to -29) microVs. This coincided with the maximum ST-VM, median 0.43 (range 0.12-0.68) mV. The QRS summation vectors subsequently rotated away from the infarct producing a median maximum QRS-VD of 20 (range 6-28) microVs. The maximum QRS-VD correlated significantly with the percentage of infarcted myocardium (r = 0.82). The correlation between the early minimum QRS-VD and the maximum ST-VM was r = 0.83. The QRS-VD was recomputed with a reference taken 2 or 4 hours after occlusion. The relation between maximum QRS-VD and infarct percentage was not significantly changed with the reference at 2 hours, but with the reference at 4 hours the ability to predict infarct size was lost.(ABSTRACT TRUNCATED AT 250 WORDS)