Scenario: A nurse in the intensive care unit (ICU) was reviewing an electrocardiogram (ECG) strip when he noted the couplet shown below. The patient is a 58-year-old woman admitted for pancreatitis due to alcoholism; she has no cardiac history and is hemodynamically stable. The nurse saw no other ectopy during his shift, and the patient is asymptomatic.

Normal sinus rhythm with a printer malfunction.

Three possibilities must be considered: (1) premature contraction (atrial versus ventricular), (2) pacemaker malfunction, or (3) printer malfunction. Premature beats should be evaluated to determine their origin, atrial or ventricular. Premature atrial contractions are among the most common premature beats and are characterized by a narrow QRS complex because conduction originates above the ventricles and proceeds down the normal pathway. Conversely, ventricular premature beats would result in a wide QRS complex. The second possibility can occur in the presence of a pacemaker. A malfunction should...

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