THE DIAGNOSTIC QRS PATTERNS IN MYOCARDIAL INFARCTION

Abstract

In an endeavor to increase the diagnostic value of the Ecg, the QRS patterns of 369 series of records with chest leads from cases of definite myocardial infarction were classified. Ninety % of the 141 cases of posterior wall infarction showed a Q3 (or Q2 and Q3) or its equivalent. It was concluded that an entirely inverted QRS3 was equivalent to a Q3 in the presence of a Q2 (either a diphasic QRS2 or a triphasic W-shaped QRS2 with a deeply inverted initial phase). Only 28% of the 190 cases of anterior wall infarction showed a Q1 pattern, either with a diphasic or triphasic QRS in this lead. It was concluded that an entirely inverted QRS1, when notched on the downstroke, was equivalent to a Q1. The QRS patterns encountered in anterior wall infarction could be grouped into 5 categories beside a miscellaneous group. These are described. The two most common QRS contours encountered in anterior wall infarction were (a) the small upright QRS1 (or inverted QRS1) and (b) the diphasic QRS2 and QRS3 with deep S waves. At times each occurred alone without the other, often they occurred together. Thus a small upright or inverted QRS1 was encountered in 64 of the 190 cases, and diphasic QRS2 and QRS3 with deep S2 and S3 were encountered in 63 of the 190 cases. These QRS contours in the limb leads can be caused by the anterior wall infarct per sc. This was indicated in cases with control records before infarction and in cases checked by necropsy. The occurrence of these QRS contours in the presence of anterior wall infarction, therefore, does not indicate respectively either right ventricular preponderance when QRS1 is inverted or left preponderance when S2 and S3 are present. In such cases these diagnoses should be avoided even though it appears that deep S2 and S3 are more apt to be present in cases with preexisting left ventricular hypertrophy. The chest leads were found to be essential in the diagnosis of anterior wall infarction in 9% of cases in which the limb lead pattern was not characteristic. In only 5% of the cases were the chest leads not characteristic of infarction and the limb leads diagnostic. It was found that in chest leads CF2 and CF4 the QRS contours most diagnostic of anterior wall infarction were the diphasic QRS with a deeply inverted initial phase, its equivalent, the triphasic QRS with a deeply inverted initial phase, and the entirely inverted QRS with notching on its downstroke. The QRS which is almost entirely inverted with a small initial upright phase is not pathognomonic since it occurs in other conditions besides myocardial infarction. The value of viewing the entire QRST pattern of the chest leads as a unit in diagnosis is emphasized. The QRS pattern is of value in the differential diagnosis in the Ecg of myocardial infarction, and in doubtful cases it may point to the true cause of the contour seen in the record. This fact in no way depreciates the value of the S-T-T patterns in the diagnosis of myocardial infarction and the utility of the S-T-T evolution in determining whether the infarct is very recent, healing, almost healed, or old. The information obtained by the S-T-T evolution is not replaced by the QRS patterns since these do not undergo such characteristic changes while the infarct is healing.