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ECG Challenge: A 75-year-old man with a previous history of complete heart block for which he received a dual-chamber pacemaker presents to his cardiologist for a routine follow-up and pacemaker check. He denies all symptoms. Physical examination is unremarkable, although an irregular pulse is found. An ECG is obtained.
The rhythm is irregular, but there is repeating pattern of equivalent long and equivalent short intervals (grouped beating). Hence, the rhythm is regularly irregular with an average rate of 84 beats per minute. The first QRS complex of the pair is preceded by both an atrial (+) and ventricular (^) pacing …