Vectorcardiographic changes following coronary artery bypass surgery

Myocardial infarction (MI) has been reported to occur in about 15 per cent of patients following coronary artery bypass (CAB) surgery. Preoperative and postoperative electrocardiograms (ECG) were evaluated in 85 patients. Thirty-four of these patients also had pre- and postoperative vectorcardiograms (VCG). Fifteen additional patients undergoing open heart surgery were used as controls. These included aortic valve replacement (in 4), mitral valve commissurotomy (in 6), mitral valve replacement (in 1), atrial septal defect repair (in 3), and repair SVC to LA shunt (in 1). Pre- and postoperative VCG's were analyzed in three planes. The angle of each 10 msec. vector was measured. The maximal voltage was determined along each axis in each plane. Mean changes in these parameters were determined for the controls. Change exceeding two standard deviations from the control mean was considered abnormal and not explainable by trauma of open heart surgery itself. Excluding the six intraoperative deaths, $\text{19}\text{79}$ (24 per cent) had QRS changes of myocardial infarction by ECG. Changes were considered significant in the postoperative VCG if they occurred in at least two consecutive angles in one plane or in the maximum voltage in one axis. The postoperative VCG depicted MI in 34 per cent ($\text{12}\text{34}$). In the absence of classic criteria for MI a significant change in VCG angle occurred in 26.4 per cent ($\text{9}\text{34}$). The voltage in at least one axis changed significantly in 11.8 per cent ($\text{4}\text{34}$). A change in the postoperative VCG was demonstrated in 73.5 per cent ($\text{25}\text{34}$). The pre- and postoperative VCG is a sensitive method of detecting subtle changes in conduction or loss of myocardium seen in the majority of patients following CAB surgery.