ECG Challenge: Beating at a Fast Clip

Philip J. Podrid, MD


June 03, 2019

The correct diagnosis is atrial flutter with variable block.

Figure 2. Courtesy of Dr Podrid.


The rhythm is regular at a rate of 150 beats/min; however, there are two long RR intervals (↔). The QRS complex is narrow (0.08 sec) and has a normal morphology and normal axis between 0° and 90° (positive QRS complex in leads I and aVF). The QT/QTc intervals are slightly prolonged (300/470 msec). There is nonspecific T-wave flattening. Evidence of atrial activity (+) is best seen in leads V1 and V3, although atrial waveforms can be seen in other leads (v). The RP interval (0.28 sec) is longer than the PR interval (0.18 sec). Hence, this is a long RP tachycardia. The possible etiologies for a long RP tachycardia include:

Of note, during the two long RR intervals, there is evidence of atrial activity (*) and the PP interval is constant (└┘) with a rate of 300 beats/min. The only regular atrial rhythm at a rate > 260 beats/min is atrial flutter. Therefore, the underlying rhythm in this case is atrial flutter with primarily 2:1 AV conduction. The long RR intervals are the result of a higher degree of AV block (ie, 3:1 and 4:1).


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