Natural course of the S-T segment and QRS complex in patients with acute anterior myocardial infarction

Sums of the S-T segment elevation from the 35 lead precordial electrocardiographic map (∑ST₃₅) and Standard 6 lead precordial electrocardiogram (∑ST₆) were obtained from 20 patients after acute anterior myocardial infarction and the calculations repeated 2, 4, 12, 24, 48, 72 and 240 hours later. Q and R wave areas were summed (∑Q₃₅, ∑Q₆, ∑R₃₅ and ∑R₆). ∑ST₃₅ and ∑ST₆ values decreased significantly in patients without pericarditis 7 to 12 hours after the onset of symptoms (P < 0.02), but increased significantly from these reduced values 25 to 48 hours after the onset of symptoms. An increase in ∑ST₃₅ and ∑ST₆ (P < 0.05) occurred 13 to 24 hours after the onset of symptoms in four patients with pericarditis before a pericardial rub was heard. No significant change in ∑Q₃₅ occurred from the initial to the final map study; a decrease in ∑R₃₅ (P < 0.02) occurred only in a group of patients studied at or before 5 hours after initial symptoms. No correlation was found between the initial level of S-T segment elevation and subsequent change in Q or R wave areas except in two patients whose initial electrocardiographic studies were performed at or within 5 hours of initial symptoms. Good correlation was found between ∑ST₃₅ and ∑ST₆ (r = +0.906, P < 0.001), ∑Q₃₅ and ∑Q₆ (r = +0.864, P < 0.001), and ∑R₃₅ and ∑R₆ (r = +0.903, P < 0.001). The course of the S-T segment and QRS complex after anterior myocardial infarction depends on the time of study after initial symptoms. The Standard 6 lead precordial electrocardiogram may offer a practical alternative to the 35 lead map for patients with anterior myocardial infarction.