Lower loop reentry as a mechanism of clockwise right atrial flutter

Area of Science:

• Cardiology
• Electrophysiology
• Cardiac Arrhythmias

Background:

• Lower loop reentry (LLR) around the inferior vena cava (IVC) causes right atrial tachycardia.
• Previously reported LLR cases show negative flutter waves on inferior ECG leads, mimicking counterclockwise typical atrial flutter.
• Right atrial flutter with positive inferior ECG flutter waves was assumed to be a single reentrant wave around the tricuspid annulus (TA).

Purpose of the Study:

• To investigate the precise mechanism of right atrial flutters with positive flutter waves on surface ECG.
• To determine the role of LLR in patients with clockwise atrial flutter morphology.

Main Methods:

• Studied 12 patients with clockwise atrial flutter morphology on surface ECG.
• Utilized conventional multipolar electrode catheters for endocardial activation mapping.
• Performed entrainment pacing in all patients and 3D activation sequence mapping in 7 patients.

Main Results:

• Endocardial activation patterns confirmed clockwise atrial flutter around the TA.
• Entrainment and mapping revealed clockwise LLR around the IVC in 7 patients.
• Figure-of-8 double-loop reentry around both IVC and TA occurred in 4 patients; single loop around TA in 1.
• Radiofrequency ablation in the TA-IVC isthmus terminated tachycardia in all patients.

Conclusions:

• Surface ECG flutter wave morphology is insufficient to determine the mechanism of TA-IVC isthmus-dependent clockwise right atrial flutters.
• Most right atrial flutters with positive flutter waves are supported by LLR around the IVC or figure-of-8 reentry.
• Targeted ablation of the TA-IVC isthmus is effective in terminating these arrhythmias.