Radiofrequency Ablation Target for Right Atrial Macroreentrant Tachycardia
The cavotricuspid isthmus should be targeted for radiofrequency ablation in this patient with typical atrial flutter at 300 bpm and confirmed macroreentrant circuit in the right atrium. 1
Rationale for Cavotricuspid Isthmus Targeting
The clinical presentation—regular tachycardia at 300 bpm with a macroreentrant circuit confined to the right atrium—is pathognomonic for typical (cavotricuspid isthmus-dependent) atrial flutter. 1 The cavotricuspid isthmus (CTI) is the critical anatomical pathway located between the tricuspid valve annulus and the inferior vena cava, through which the reentrant wavefront must pass to sustain typical atrial flutter. 1
Why This Is the Definitive Target
The CTI represents the obligatory pathway in typical atrial flutter circuits, making it the ideal ablation target because interrupting conduction through this narrow isthmus terminates the arrhythmia permanently. 1, 2
Entrainment mapping has confirmed macroreentry, which in the context of right atrial flutter at 300 bpm virtually always indicates CTI-dependent flutter (also called "common" or "typical" atrial flutter). 1
Ablation success rates are exceptionally high when bidirectional conduction block across the CTI is achieved, with chronic success rates of 90-100% and superior outcomes compared to antiarrhythmic drug therapy. 1
Clinical Evidence Supporting CTI Ablation
A prospective randomized trial demonstrated that CTI ablation resulted in 80% of patients remaining in sinus rhythm at 21-month follow-up, compared to only 36% with chronic antiarrhythmic drug therapy. 1 Additionally, patients treated with ablation required significantly fewer hospitalizations (22% versus 63%) and experienced substantially improved quality of life. 1
Technical Considerations
The ablation line extends from the tricuspid annulus to the inferior vena cava, creating a linear lesion that blocks the reentrant circuit. 1, 3
Confirmation of bidirectional conduction block across the CTI is the critical endpoint—simply terminating the arrhythmia is insufficient for optimal long-term success. 1
Modern techniques using irrigated-tip or large-tip catheters achieve complete CTI block more efficiently, with mean ablation times of 7-12 minutes and success rates approaching 90-100%. 3, 4
Why Other Anatomical Sites Are Incorrect
Crista terminalis: This structure can serve as a lateral boundary for the flutter circuit but is not the critical isthmus requiring ablation. 1
Coronary sinus ostium: While the coronary sinus musculature can rarely participate in atypical flutter circuits, this is uncommon and would not be the primary target in typical right atrial flutter at 300 bpm. 5
Atrioventricular node: Ablating the AV node would only control ventricular rate, not cure the atrial arrhythmia, and would necessitate permanent pacemaker implantation—an unacceptable outcome when curative ablation is available. 1
Right atrial appendage: This structure is not involved in typical atrial flutter circuits and would not be an appropriate ablation target. 1
Important Caveats
In patients with prior cardiac surgery or congenital heart disease, non-CTI-dependent macroreentrant circuits can occur around surgical scars, patches, or atriotomy incisions. 1 However, even in these complex cases, CTI-dependent flutter remains common and often coexists with atypical circuits. 1 The clinical scenario presented—a 62-year-old man without mention of prior surgery and with classic 300 bpm atrial rate—strongly indicates typical CTI-dependent flutter. 1
Complications are rare (1-2%) and include cardiac perforation, phrenic nerve injury, and thromboembolism, but the risk-benefit ratio strongly favors ablation over chronic medical therapy. 1