Lower Loop Reentry as a Mechanism of Clockwise Right Atrial Flutter

Abstract

Background-Right atrial reentrant tachycardia resulting from lower loop reentry (LLR) around the inferior vena cava (IVC) has been described recently. However, all reported cases of LLR in the literature have negative flutter waves on the inferior surface ECG leads similar to that of counterclockwise typical atrial flutter around the tricuspid annulus (TA). Right atrial flutter with positive flutter waves in the inferior ECG leads has been assumed to rotate as a single reentrant activation wave front around the TA, and the role of LLR in those patients is not known. Methods and Results-Twelve consecutive patients with flutter wave morphology on surface ECG consistent with clockwise atrial flutter were studied. The endocardial activation pattern recorded from conventional multipolar electrode catheters was characteristic of clockwise atrial flutter around the TA. Entrainment pacing in all 12 patients and 3D activation sequence mapping in 7 patients, however, revealed clockwise LLR involving the lower right atrium around the IVC in 7 patients, figure-of-8 double-loop reentry around both the IVC and TA in 4, and single reentrant loop around the TA in 1. Linear radiofrequency ablation in the isthmus between the TA and IVC (TI isthmus) terminated the tachycardia in all patients. Conclusions-Surface ECG flutter wave morphology and limited recording intracardiac sites proved insufficient to delineate the precise mechanism of the TI isthmus-dependent clockwise right atrial flutters. Most right atrial flutters with positive flutter wave on surface ECG may be supported by a reentrant circuit around the IVC or a figure-of-8 double-loop reentry involving both the IVC and TA.

Three Dimensional Electroanatomical Mapping of Lower Loop Reentry in Patients with Intracardiac Operation

“…On the other hand, as Zhang et al showed, 3D activation sequence mapping in patients with CCW LLR revealed an activation wavefront circulating around the IVC with evidence of slow conduction and wavefront collision on the septal side. 8) In our study, all patients with CW LLR had a collision of the wavefronts over the high RA. The higher collision site than that of the previous report could be explained by the conduction delay created by the RA incisional scar.…”

“…In contrast, Zhang and Scheinman et al previously confirmed that the LLR circuit propagated CCW around the IVC (caudal view). 8) We assumed that the clockwise direction of conduction around IVC may have better conductivity than the CCW direction. Scar around lower posterior RA may contribute to the different direction of conductivity.…”

“…7) LLR is defined as a macroreentrant tachycardia maintained by circus movement of the activation wavefront around the inferior vena cava (IVC) instead of around the tricuspid annulus as in typical right AFL. 8) However few reports have been published regarding the mechanism and electrocardiographic characteristics of LLR. [7][8][9] The purpose of this study was to clarify the mechanism and electrocardiographic characteristics of LLR and the differences from that of typical counterclockwise (CCW) AFL using a 3D electroanatomical mapping system.…”

Development of Lower Loop Reentrant Atrial Tachycardia in a Patient Late after Surgical Operation of Multiple Right‐sided Accessory Pathways

“…Zhang et al also reported patients whose tachycardia on surface ECG was consistent with clockwise atrial flutter, and in whom they found figure-of-8 double-loop reentry around both the IVC and TA. 9) They hypothesized that the flutter circuit was determined by the Oginosawa Y Lower loop reentry after WPW surgery revolution or conduction times around the IVC and TA; i.e., a shorter revolution time around the IVC compared with that around the TA caused LLR, whereas a shorter revolution time around the TA caused typical AFL. Similar revolution times around the IVC and TA resulted in figure-of-8 double loop reentry.…”

Sudden Change From Counterclockwise to Clockwise Flutter During Cavotricuspid Isthmus Ablation

“…The likely mechanism in this case appears to be conduction of the last counterclockwise flutter beat across the crista terminalis breaking into the midseptal area and activating the septum, upward and downward, a clockwise lower loop re-entry. 3,4 Manifest conduction of the last beat of counterclockwise flutter across the crista terminalis with minimal delay (255 versus 245 ms measured at the bipole RA 19,20) likely becomes possible because of the absence of a competing wavefront of activation after the development of unidirectional block in the cavotricuspid isthmus. The upward wavefront subsequently travels up to the high right atrium and then down the lateral wall of the right atrium.…”