br Conflict of interest br Acknowledgments br Introduction

Conflict of interest
Acknowledgments
Introduction Electroanatomical mapping is useful for locating a possible reentrant circuit, but it has limitations in terms of analyzing the functional property of the circuit [1,2]. Entrainment mapping using the postpacing interval (PPI) and the activation sequence of the last captured beat has been used for analyzing complex reentrant tachycardia circuits [3,4]. This article describes three cases of complex dual-loop reentrant atrial tachycardia analyzed by conventional entrainment mapping without using a three-dimensional PPI mapping system. Case 1 was dual-loop reentry consisting of the tricuspid annulus (TA) and a localized atrial reentry at the coronary sinus (CS) ostium with different atrial connection sites to the right and left atrium. Case 2 was dual-loop reentry around the TA and the superior trans-septal incision line. Case 3 was dual-loop reentry around the TA and longitudinal dissociation along the cavo-tricuspid isthmus. In these three cases, analysis of the activation sequence of the last captured beat was useful for clarifying the dynamic relation of reentrant circuits.
Materials and methods Electrophysiological study and radiofrequency catheter ablation was performed using standard methods after obtaining written informed consent. Entrainment mapping was performed from several atrial sites during tachycardia at a buy RG7112 length of 20–50ms shorter than the tachycardia cycle length (TCL). A shorter pacing cycle length was selected on purpose to demonstrate the deeper antidromic penetration to the reentrant circuit. The PPI from the pacing site and activation sequence of the last captured excitation from all available electrodes was analyzed to determine the composition of reentrant circuits. The last captured beat was defined as the last activation where the preceding cycle length was the same as the pacing cycle length after the termination of overdrive pacing. A radiofrequency catheter ablation was performed to achieve a target temperature of 55°C for a maximum power of 30–50W.
Results
Discussion Recent advances in three-dimensional electroanatomical mapping systems are useful for locating complex types of atrial reentrant circuits [1,2]. However, there have been limited data on the functional relation of these reentrant circuits. In the present study, entrainment mapping using the activation sequence of the last captured beats clearly demonstrated the complex dynamic relation of dual-loop reentrant circuits. In Case 1, dual-loop reentry consisted of the TA and the localized circuit at the CS ostium. The impulse propagated to the left lateral extent of the CS and in the counter-clockwise direction around the TA to the right atrium. Although the impulse simultaneously propagated in both the left and right atrium, the exit sites from the dominant localized reentrant circuit were anatomically different (Fig. 1, upper). A longer PPI from pacing at the cavo-tricuspid isthmus in a patient with the common type of atrial flutter was reported by Wong [5]. The decremental conduction within the reentrant circuit may contribute to the prolonged PPI; the degree of PPI prolongation from the TCL was 70ms in their case. In the present case, the difference between the PPI from pacing at the cavo-tricuspid isthmus and the TCL was 140ms, which was much longer than in reported cases, suggesting that the cavo-tricuspid isthmus was not on the dominant reentrant circuit (Fig. 8A). During entrainment from the cavo-tricuspid isthmus (site A), the long antidromic penetration through the right atrial free wall (n) collided with the orthodromic activation (n−1) through the slow conduction area (crosshatch) within the CS ostium from the septal isthmus. Entrainment from the cavo-tricuspid isthmus suggested the presence of counter-clockwise conduction through the septal isthmus, but the longer conduction time through the slow conduction area could not maintain reentry around TA and instead localized reentry at CS ostium.