The narrow band of muscle tissue between the inferior vena cava and the tricuspid valve is called what?

• A. Cavotricuspid isthmus
• B. Crista terminalis
• C. Eustachian ridge
• D. Chiari network

Answer: (A)

The main idea here is the specific right atrial region that forms a narrow band of muscle between the opening of the inferior vena cava and the tricuspid valve. This region is the cavotricuspid isthmus, a slender strip of myocardium that serves as a key part of the typical atrial flutter circuit. In many cases of flutter, the reentrant wavefront travels around the tricuspid annulus by passing through this isthmus, so creating a conduction block here with ablation can terminate or prevent the flutter. The other structures mentioned—crista terminalis, Eustachian ridge, and Chiari network—are distinct anatomical features in the right atrium and do not define this narrow isthmus between the IVC and the tricuspid valve.