Electrocardiographic Diagnosis of Myocardial Infarction in the Presence of Left Bundle-Branch Block

Abstract

It is generally accepted that most myocardial infarctions are obscured on the electrocardiogram by left bundle-branch block. The number of published cases in which this could be evaluated, however, is small, and the case reports are scattered. We have studied 30 cases of myocardial infarction with left bundle-branch block in which the location of the infarction could be determined with certainty, by autopsy, or by a previous electrocardiogram with normal intraventricular conduction. Twenty such published cases have also been collected. Electrocardiographic abnormalities have been correlated with infarctions in different locations. The possible specificity of these abnormalities is discussed.T HE observation of Wilson and associates' that "in the presence of left bundle branch block it is seldom possible to make a diagnosis of myocardial infarction on the basis of electrocardiographic findings alone" is still widely accepted. A number of cases in which a myocardial infarction could be recognized in the presence of left bundle-branch block (LBBB) have been reported, but these usually have been single case reports, with the exception of the groups of cases reported by Dressler et al.2 and by Sodi-Pallares and co-workers.3' Most of these have been diagnosed by Q waves in lead V6, by S-T segment or T-wave abnormalities, or by fortuitous normally conducted complexes.Our review of 50 cases of myocardial infarction with LBBB leads us to believe that a myocardial infarction produces electrocardiographic changes almost as often in the presence of LBBB as it does with normal intraventricular conduction. In most instances the presence of the myocardial infarction is indicated by changes in the QRS complex. As would be expected, the abnormalities of the QRS complex indicating the presence of a myocardial infarction are not always the same in the presence of LBBB as they are with normal intraventricular conduction. QRS configurations similar to those seen in our cases in association with myocardial infarction are also present in published cases. Several of these QRS abnormalities have not previously been described as being associated with myocardial infarction in the presence of LBBB. MATERIALS AND METHODSWe have studied all cases with complete LBBB in our files from 1953 through June 1956. Complete LBBB was diagnosed by the usual criteria. The QRS complex should be of 0.12 second duration or longer, of sinus origin, and associated with a P-R interval of at least 0.12 second. The left precordial leads should have a broad, slurred, or notched R wave with an abnormally delayed "intrinsicoid" deflection, similar complexes usually being present in lead I. There should be rS or QS complexes in lead V, with a normal "intrinsicoid" deflection. Cases in which the diagnosis of LBBB was questionable were excluded from this study, as were all cases of incomplete LBBB.

The pathologic correlates of the electrocardiogram: complete left bundle branch block.

“…Each of these areas was further subdivided into two basal, two central and one apical zone, for a total of 15 zones ( fig. 1) [6][7][8][9][10], between the anterior septal attachment and the lateral border of the anterior papillary muscle (and usually the circumflex artery); and posteroinferior (zones [11][12][13][14][15], from the lateral border of the anterior papillary muscle (and circumflex artery) to the posteroinferior septal attachment (and posterior descending artery). These regions were each divided into one apical, two central and two basal portions, for a total of 15 zones.…”

M-mode and cross-sectional echocardiographic study of the left ventricular wall motions in complete left bundle-branch block.

“…Electrocardiographic and vectorcardiographic ab- normalities, which were consistent with extensive septal infarction with complete left bundle-branch block (Chapman and Pearce, 1957;Scott, 1962;Doucet et al, 1966), were observed in 75 per cent and 89 per cent of patients with abnormal septal motion of type C, respectively, contrasting with type A (20%, 33%), and type B (15%, 23%) (Table). These abnormal findings consisted of abnormal Q waves in leads I, aVL, or anterior chest leads, with complete left bundle-branch block.…”

Left Bundle Branch Block Eliminates Q Waves of Inferior Infarction: Confirmation by Ventriculography

“…This problem is compounded by the recognition that the development of the conduction dis order may eliminate specific Q waves. The rSr 'notched' morphology in leads III and aVF has been stated to be a Q wave equivalent in left bundle branch block [ 12] and reportedly never observed in the absence of prior infarc…”