VECTORCARDIOGRAPHY IN EXPERIMENTAL MYOCARDIAL-INFARCTION - SERIAL CHANGES AND CORRELATION BETWEEN QRS LOOP CHANGE AND THE INFARCTION SIZE

The objectives of this study were to examine the serial vectorcardiogr aphic changes following acute myocardial infarct and to assess the rel ationship between QRS loop changes and infarct size. Fifty adult male Long-Evans rats of 250-350 gm body weight were used to study experimen tal acute myocardial infarction induced by coronary artery ligation. V ectorcardiograms (VCG) of the Frank lead system were recorded before, and 1 day and 7 days after operation. Animals were sacrificed on the 7 th day for histological quantitation of infarct area ratios. We found that (1) before operation, rats have ST elevation, probably due to ear ly repolarization. (2) After coronary artery ligation, ECG showed char acteristic dome-shaped ST elevation at 1 hr after ligation which retur ned to normal during the first day. Abnormal Q waves appeared thereaft er. (3) After ligation, maximum QRS-vector, ST vector and maximum T ve ctor were reduced in magnitude the first day and recovered by the 7th day. The vectors tended to shift their direction to the right and to t he posterior. QRS-T angle, however, widened as time went on. About hal f of the rats revealed changes in the inscription direction of the QRS loop and abnormal QRS morphology also appeared in about half of the l igated rats. (4) Those in whom abnormal QRS loop morphology and/or bit ing appeared had significantly larger infarct area ratios (p<0.01). (5 ) Change in QRS loop inscription direction seemed not to be related to the infarct size. (6) In the LS plane, the difference in max QRS vect or magnitude between the 1st and 7th days significantly correlated wit h the infarct area ratio (r=0.533, P<0.05). In the H plane, the change in the max QRS vector magnitude at the 7th day correlated with the in farct area ratio (r=-0.531, P<0.05). In the F plane, changes in the di rection of the max QRS vector were significantly correlated to the inf arct area ratio both on the first (r=0.431, P<0.05) and 7th days (r=0. 531, p<0.05). It is concluded that the VCG, like the EGG, had evolutio nal changes in AMI and that the QRS loop seen on vectorcardiography ha s only a slight correlation with the histological myocardial infarct s ize.