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ECG Review-Does LBBB Prevent Diagnosis?

Clinical Scenario: The ECG shown in the figure was obtained from a 69-year-old man who was known to have complete left bundle branch block (LBBB). Is it possible to draw any other conclusions from evaluation of his ECG?

Interpretation: The rhythm is sinus at a rate of 80 beats/min. As noted above, the patient has complete LBBB. Despite opinion to the contrary, myocardial infarction can sometimes be diagnosed despite the presence of complete LBBB. Prior infarction is suggested in the above tracing by the presence of the wide and deep Q wave in lead aVL, late notching of the upslope of the S wave in two or more mid-precordial leads (in this case, leads V4 and V5), and primary ST-T wave changes (unexpected ST segment elevation in lead aVL, and the presence of an upright T wave in leads I and aVL). Q waves should not normally be present in lateral leads with typical LBBB. ST segments and T waves are normally directed opposite to the last QRS deflection in the three key leads (I, V1, V6) with typical bundle branch block. Thus, although one often will not be able to comment on the likelihood of past or present infarction in the setting of LBBB, the tracing shown here illustrates an example in which acute infarction should nevertheless be strongly suspected.

Suggested Reading

1. Hands ME, Cook EF, Stone PH. ECG diagnosis of myocardial infarction in the presence of complete LBBB. Am Heart J 1988;116:23-31.

2. Sgarbossa EB, et al for the GUSTO Investigators. ECG diagnosis of evolving acute myocardial infarction in the presence of LBBB. N Engl J Med 1996;334:481-487.

3. Grauer K. 12-Lead ECGs: A 'Pocket Brain' for Easy Interpretation. Gainesville, FL: KG/EKG Press; 1998:23, 26.