By Ken Grauer, MD
Figure: 12-lead ECG obtained from a 63-year-old woman with a history
of hypertension, heart failure, and atypical chest pain.
Clinical Scenario: The electrocardiogram (ECG) in the figure was obtained from a 63-year-old woman with a history of hypertension, heart failure, and atypical chest pain. The ECG shows normal sinus rhythm at a rate of 85 beats/minute. The QRS complex is widened. Does it indicate a typical left bundle-branch block (LBBB)? Would you interpret this tracing as suggestive of left ventricular hypertrophy (LVH) or acute myocardial infarction (MI)?
Interpretation: The first point to make about this 12-lead ECG relates to the bizarre progression of QRS morphology in the precordial leads. It makes no anatomic (or physiologic) sense for the QRS complex to alternate from almost total negativity (in leads V1, V2, V3)—to total positivity (in leads V4, V5)—and then abruptly back to near total negativity in lead V6. Instead, we strongly suspect misplacement of several precordial leads. Most likely the QRS complex seen in lead V6 really should appear in lead V4 — and the complex in lead V4 should appear in lead V6. Were this the case, then this patient would manifest the typical pattern of complete LBBB (predominantly negative QRS in lead V1; monophasic R wave with or without a notch in leads I and V6). A repeat ECG is, of course, needed to verify our suspicion.
The diagnosis of LVH cannot be made by the usual criteria in the presence of complete LBBB because the conduction defect dramatically alters the usual sequence (and therefore QRS morphology) of ventricular activation. However, several relevant points relating to LBBB still can be made. First, most patients with complete LBBB have underlying heart disease. Simply the presence of LBBB identifies a high prevalence group of individuals who statistically are likely to have heart disease predisposing to ventricular hypertrophy (note the history of the 63-year-old woman in this case). In the presence of underlying heart disease and complete LBBB, the ECG finding of very deep S waves (of more than 25-30 mm) in leads V1, V2, and V3 makes it highly likely that the patient also has LVH. However, nothing can be said about the presence or absence of myocardial infarction (old or acute) from interpretation of the typical LBBB pattern seen here.
Dr. Grauer, Professor and Associate Director, Family Practice Residency Program, Department of Community Health and Family Medicine, College of Medicine, University of Florida, Gainesville, is on the Editorial Board of Emergency Medicine Alert.