An 80-year-old man presents to the emergency department with a three-hour history of left arm pain. He describes the pain as constant, aching, and cramping, involving the entire left arm without radiation.

The onset was sudden, occurring at rest, and the condition did not become noticeably worse with exertion. The intensity is described as 4 or 5 on a scale of 10, and there are no associated symptoms of chest pain or tightness, shortness of breath, or back pain.

Medical history includes hypertension, hyperlipidemia, atrial fibrillation, diabetes mellitus, and chronic obstructive pulmonary disease. Family history is remarkable for diabetes.

The patient is retired and has a remote history of smoking and heavy alcohol consumption, both of which he stopped approximately 15 years ago. He does not use recreational or homeopathic drugs.

He is allergic to penicillin and sulfa. Current medications include enalapril, hydrochlorothiazide, lovastatin, metformin, and warfarin.

A review of systems is unremarkable for recent or current cardiovascular, pulmonary, neurologic, gastrointestinal, urologic, or endocrine symptoms. Physical examination reveals a mildly distressed man with a height of 172 cm and a weight of 84 kg. Vital statistics include a blood pressure of 148/70 mm Hg; pulse, 53 beats/min and irregular; respiratory rate, 18 breaths/min; oxygen saturation, 96% on room air; and temperature, 36.9°C.

The chest is clear without wheezes or rales; the cardiac exam reveals an irregularly irregular rhythm, no murmurs, and a jugular venous pressure of 7 cm. Upper and lower extremities are warm with good pulses bilaterally and no evidence of ischemia or paresthesias. The neurologic exam is normal.

Before the patient undergoes a blood draw and a chest x-ray, an ECG is obtained, which reveals the following: a ventricular rate of 53 beats/min; PR interval, not measurable; QRS duration, 106 ms; QT/QTc interval, 438/410 ms; R axis, –67°; and T axis, 75°. What is your interpretation of this ECG?

ANSWER

The correct interpretation of this ECG includes atrial fibrillation with a slow ventricular response, left anterior fascicular block, poor R-wave progression, and left-axis deviation.

Electrocardiographic evidence of atrial fibrillation includes absent P waves with fibrillatory (f) waves present at a rate between 350 and 600 beats/min, irregularly irregular R-R intervals, a normal QRS interval, and ventricular rates ranging from 60 to 170 beats/min.

Ventricular rates of less than 60 beats/min may occur in the presence of atrioventricular (AV) nodal disease or AV nodal blocking agents. Left anterior fascicular block is evidenced by the presence of an upright QRS complex in lead I with a negative QRS complex in lead aVF with a normal QRS duration.

The late transition of R waves in lead V₄ is indicative of poor R-wave progression. Finally, left-axis deviation is evidenced by an R-wave axis between 0° and –90°.