Entrainment with long postpacing intervals from within the flutter circuit: what is the mechanism?

Entrainment mapping is one of the most important tools in the localization of reentrant circuits and identifying critical sites for ablation. However, there are limitations to the use of this technique. This case report illustrates a pitfall of entrainment mapping. A 70-year-old gentleman with known ischemic heart disease was admitted with a 1-month history of exertional dyspnea (New York Heart Association class III) and presyncope. His 12-lead electrocardiograph showed atrial flutter, with 2:1 atrioventricular conduction resulting in a ventricular rate of 100 beats per minute (Figure 1). An echocardiogram showed a dilated left ventricle, with severe impairment of systolic function (estimated ejection fraction of 35%) and significant biatrial enlargement. He was referred for flutter ablation. Figure 1. Twelve-lead electrocardiogram showing atrial flutter. With the patient under conscious sedation, right femoral venous access was obtained. A deflectable decapolar catheter (Dynamic XT, Bard, Lowell, MA) was introduced into the coronary sinus (CS), and a 3.5-mm irrigated-tip catheter (Thermocool, Biosense Webster, Diamond Bar, CA) was introduced into the right atrium (RA). The tachycardia cycle length (TCL) was 274 ms, and CS activation was proximal to distal. Entrainment was initially performed at a cycle length of 250 ms from the proximal CS (CSp) and distal CS bipole pairs. The postpacing intervals (PPIs) were 341 and 405 ms, respectively. Further entrainment was performed in the RA at the lateral RA wall and cavotricuspid isthmus (CTI), showing PPIs of 343 and 345 ms, respectively (online-only Data Supplement Figure). Activation mapping showed that the majority of TCL was measured around the tricuspid valve annulus, activating in a counterclockwise fashion. Although PPIs from entrainment at sites around the tricuspid annulus were significantly >30 ms longer than TCL, the opinion was that this represented a CTI-dependent flutter. CTI ablation was performed at the typical position (6 o’clock in the left anterior …