Sources of QRS Couplets.

Abstract

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 be considered even though pacemaker spikes may be difficult to detect. Evaluating multiple leads for a pacer spike may be helpful. Importantly, the ECG feature in this example that helps differentiate the possible origin is that the couplet has a nonphysiologic look to it; that is, the complexes are too close together. The fouth QRS complex takes place during the absolute refractory period when depolarization cannot occur (between R wave and about halfway through the T wave). As the central stations in intensive care units age, the thermal or laser printers can malfunction. It appears that the paper either jammed right where the third QRS complex occurs or the movement of the paper was halted momentarily because the QRS complex looks identical to the sinus rhythm complex in both ECG leads.The Association for the Advancement of Medical Instrumentation guidelines permit up to ±5% variability in the motor speed of electrocardiographs. The printing speed in electrocardiographs includes both mechanical and digital controllers. In a hospital setting, it is expected that these ECG printers are routinely calibrated, as noncalibrated instruments may have greater variability in performance. Hospital engineering should be notified so that the central station can be serviced and calibrated. Importantly, unless the patient has a transient arrhythmia captured only by the bedside monitor (eg, ventricular tachycardia), electrocardiographic diagnosis should be based on resting 12-lead ECGs and not on rhythm strips.