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 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. Would you say there is typical LBBB (left bundle branch block)? Would you interpret this tracing as suggestive of LVH (left ventricular hypertrophy)? of acute MI (myocardial infarction)?
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 near 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 should really 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. This is because the conduction defect dramatically alters the usual sequence (and therefore QRS morphology) of ventricular activation. However, several relevant points relating to LBBB can still 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 are statistically 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, V3 makes it highly likely that the patient also has LVH. On the other hand, 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, Assistant Director, Family Practice Residency Program, University of Florida, is Associate Editor of Internal Medicine Alert.
The ECG in the Figure was obtained from a 63-year-old woman with a history of hypertension, heart failure, and atypical chest pain. Would you say there is typical LBBB (left bundle branch block)? Would you interpret this tracing as suggestive of LVH (left ventricular hypertrophy)? of acute MI (myocardial infarction)?
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