A 64-year-old man with a history of congestive heart failure secondary to nonischemic cardiomyopathy, mitral and aortic valve replacements, and biventricular cardioverter-defibrillator placement, developed a tachycardia. The tachycardia exhibited a biventricular paced rhythm with a short R-P interval and concentric atrial activation sequence within the coronary sinus, suggesting that the tachycardia might be a pacemaker-mediated tachycardia (PMT). However, the tachycardia was diagnosed as counterclockwise cavotricuspid isthmus (CTI)-dependent atrial flutter (AFL), and linear ablation of the CTI eliminated the tachycardia. This case illustrated that typical AFL can mimic a PMT when there is a severe conduction delay through the CTI.
