Depolarization changes early in the course of myocardial infarction: Significance of changes in the terminal portion of the QRS complex

AbstractStudies of patients during variant angina have revealed that there are specific changes in the terminal part of the QRS complex that provide information regarding the location of the ischemic. Extending these studies to acute myocardial infarction, the electrocardiogram (ECG) obtained from 32 patients within 5 h of the onset of chest pain was analyzed to determine if similar inferences could be made. A preinfarction ECG was available from each patient for comparison and 30 patients underwent coronary arteriography within 3 weeks of the infarction.The 10 patients with anterior infarction had a decrease (p < 0.05) in the S wave in leads V2(0.80 ±0.50 mV) and V3(0.65 ± 0.43 mV). In 23 patients with inferior infarction an increase (p < 0.05) in the R wave of lead III (0.47 ± 0.35 mV), S wave of lead aVL (0.31 ± 0.23 mV) and R wave of lead aVF (0.37 ± 0.30 mV) occurred. A strong positive correlation between the R wave changes in leads III and aVF and the S wave in lead aVL (r = 0.94 and 0.91, respectively) suggests that the R and S wave changes in these leads are expressions of the same phenomenon and indicates that the terminal QRS complex is chiefly affected.Eight of 23 patients with inferior infarction and ST depression in the anterior precordial leads had a normal left anterior descending coronary artery. All had an increase in S wave amplitude in leads V2and V3. Eight patients had inferior infarction, ST depression in anterior leads and severe lesions in the left anterior descending artery or anterior wall motion abnormalities. These patients had variable changes in the S wave amplitude in leads V2and V3(in four patients the S waves increased; in four the S waves decreased, a response usually seen in anterior infarction). Two of the four patients with decreased S wave in leads V2and V3died after a subsequent anterior infarction.It is concluded that QRS changes early in the course of acute myocardial infarction are similar to those occurring during variant angina and are due to decreased intramyocardial conduction velocity in the ischemic region. Analysis of the terminal portion of the QRS complex early during infarction has value in determining the location of the ischemic zone