By Ken Grauer, MD
Figure. Rhythm strip obtained from a patient in atrial flutter. What is unusual about this example of atrial flutter?
Clinical Scenario: The lead II rhythm strip shown in the Figure was taken from a patient in atrial flutter. Although difficult to see due to artifact in the baseline, an underlying sawtooth pattern is nevertheless present. In addition, there is something distinctly unusual about this example of atrial flutter. What is it? What clinical diagnosis is suggested as a possible cause of this ECG finding?
Interpretation/Answer: As noted above, despite the presence of significant baseline artifact, there is still suggestion of the underlying sawtooth pattern of atrial flutter. The unusual aspect of this example of atrial flutter is patterned beating of ventricular response, which regularly occurs with alternating short-long cycles. This presence of grouped beating suggests Wenckebach conduction, which is a highly characteristic finding of digitalis toxicity. Since the underlying rhythm is atrial flutter, the only place that Wenckebach conduction can be occurring in this supraventricular (narrow QRS complex) rhythm is at the lower level of the AV node. A distinct pattern of group beating in a patient with either atrial fibrillation or atrial flutter is therefore indicative of Wenckebach conduction out of the AV node, and should strongly suggest digitalis toxicity if the patient is taking this medication.
Dr. Grauer, Professor, Assistant Director, Family Practice Residency Program, University of Florida, is Associate Editor of Internal Medicine Alert.