Study of 256 Patients with Intermittent Left Bundle Branch Block

In an attempt to elucidate the specificity and sensitivity of atypical findings during left bundle branch block (LBBB) with respect to myocardial infarction (MI), we analyzed ECGs from patients with intermittent LBBB obtained by mail solicitation of cardiologists. The group consisted of 256 patient files fulfilling the following criteria: 1) complete LBIIB present on one or more 12.. lead ECGs, and 2) at least one 12-lead ECG taken subsequent to a LBBB tracing exhibiting absence of �he electrocardiographic diagnosis of myocardial infarction in the presence of left bundle branch block (LBBB) has been the subject of many, often conflicting, articles. These reports have presented atypical characteristics of the QRS complex such as Q waves or S waves in V6 during LBBB, that support the diagnosis of myocardial infarction.�4 Since by definition patients with intermittent LBBB have electrocardiograms with LBBB as well as electro- cardiograms with "normal conduction," this group allows determination of whether various patterns of atypical LBBB predict the presence of myocardial infarction as diagnosed by standard electrocardio- graphic criteria. In this study, we attempted to eluci- date the specificity and sensitivity of atypical find- ings during LBBB by analyzing a large number of electrocardiograms from patients with intermittent LBBB, comparing findings during LBBB (with re- spect to atypicality) with those during "normal con- duction" (with respect to infarction).