Anatomy of the Tricuspid Cavo Isthmus

Abstract

The past decade has shown an almost explosive growth in electrophysiologic studies and catheter ablation procedures for cardiac arrhythmias. In the wake of this all a pressing need was felt to understand the underlying anatomy. Particularly so since some of the more frequent supraventricular tachyarrhythmias use reentrant circuits determined by preexistent anatomic pathways. One example, to be elaborated in this chapter, is atrial flutter. The typical situation is that of a counter clockwise reentrant circuit bordered on the one side by the tricuspid valve annulus and, on the other side, by the terminal crest.^1,2 Crucial for the genesis of a reentrant circuit is the presence of a delay-producing zone. The latter is generally accepted to be confined to the right atrial inferior wall between the entrance of the inferior caval vein, guarded by the Eustachian valve, and the tricuspid valve annulus immediately inferior to the os of the coronary sinus.^3,4 Cosio and coworkers⁵ used radiofrequency catheter ablation in this particular zone to treat patients with common atrial flutter. They introduced the term “inferior vena cava-tricuspid isthmus”. Since then the concept that this area serves as an electrophysiologic isthmus has been generally acknowledged and the term used often is shortened to either “tricuspid cavo isthmus”, “posterior isthmus” or “flutter isthmus”.