The Rancher, the Roof, and the Rogue Heart

ANSWER

The correct interpretation of this ECG includes atrial fibrillation with variable atrioventricular (AV) block and a left-axis deviation.

Atrial fibrillation is evidenced by the absence of P waves, a consistent PR interval, and an irregularly irregular rhythm. The ventricular rate in atrial fibrillation is due to variable conduction through the AV node, and the 1.6-second pause prior to the last beat on this ECG is due to variable block in the conduction system below the AV node. Pauses such as these may result in clinical symptoms; when seen, the clinician should exercise caution in determining which method (six-second rule, 300/150/100 method) to use to measure the overall heart rate. Note that a pause of undetermined time also exists prior to the first QRS complex seen on the rhythm strip.

Finally, a left-axis deviation is evidenced by an R-wave axis between –30 and –120°.