Answer

Bifascicular block with a new onset of atrial fibrillation: The ECG reveals an irregular rhythm of 150 beats per minute and no clear P waves. The QRS complex lasts 128 milliseconds with an RR^ wave in leads V1 and V2 and a wide S wave in the lateral leads I, V5, and V6. The axis is deviated to the right.

This patient has severe ischemic heart disease that produces a bifascicular block with a new onset of atrial fibrillation (ie, irregular rhythm with no clear P waves). The right bundle branch block is associated with a left posterior hemiblock. This hemiblock is characterized by a right axis deviation of +120°, small R waves and deep S waves in lead I, a qR wave in lead III, and no evidence of other causes of right axis deviation (eg, lateral myocardial infarction, cor pulmonale, right ventricular hypertrophy). In the setting of acute myocardial infarction, this type of block carries a poor prognosis and mortality rate of 71%. Reference: Conover MB. Understanding Electrocardiography. 7th ed. Mosby-Year Book; 1996:362-386.

BACKGROUND

An 83-year-old man with a history of ischemic congestive heart failure presents with intermittent lightheadedness that has lasted 1 week.

Hint

Review the ECG systematically for rate, rhythm, and axis. Count at least 3 disturbances.

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