Right atrial flutter due to lower loop reentry: mechanism and anatomic substrates

Area of Science:

• Cardiology
• Electrophysiology
• Cardiac Arrhythmias

Background:

• Mechanisms of rapid and irregular atrial flutter (AFL) distinct from typical AFL remain unclear.
• Understanding these mechanisms is crucial for effective arrhythmia management.

Purpose of the Study:

• To investigate the mechanisms of a distinct, rapid atrial flutter.
• To identify the anatomical substrate and electrophysiological properties of this AFL subtype.

Main Methods:

• Electrophysiological recordings using multi-electrode catheters in 29 patients with AFL.
• Atrial extrastimuli delivered to the tricuspid annulus-eustachian ridge isthmus.
• Linear ablation targeting the tricuspid annulus-eustachian ridge isthmus.

Main Results:

• Identified a new AFL subtype, lower-loop reentry (LLR), involving the lower right atrium.
• LLR demonstrated shorter cycle lengths than typical AFL (217±32 ms vs. 272±40 ms).
• Bidirectional block in the tricuspid annulus-eustachian ridge isthmus terminated spontaneous LLR and prevented induction.

Conclusions:

• Lower-loop reentry (LLR) is a distinct subtype of right atrial flutter.
• LLR is critically dependent on conduction through the tricuspid annulus-eustachian ridge isthmus.
• Targeting this isthmus with ablation is effective in managing LLR.