Which region is defined as the narrow strip of myocardium between the inferior vena cava inlet and the tricuspid valve?

Which region is defined as the narrow strip of myocardium between the inferior vena cava inlet and the tricuspid valve?

• A. Cavotricuspid isthmus
• B. Crista terminalis
• C. Eustachian ridge
• D. Fossa ovalis

Answer: (A)

The region described is the cavotricuspid isthmus, a narrow strip of myocardium in the right atrium between the inferior vena cava inlet and the tricuspid valve annulus. This area is central in typical atrial flutter because it serves as the main conduction pathway around which the re-entrant circuit travels; ablation here often disrupts the circuit and terminates the flutter. The other landmarks are located elsewhere in the right atrium: the Crista terminalis is a muscular ridge that marks the boundary between the smooth sinus venarum and the trabeculated atrial appendage; the Eustachian ridge sits near the IVC ostium but isn’t the whole conduction pathway used in flutter; and the fossa ovalis lies in the interatrial septum, not between the IVC and the tricuspid valve.

The region described is the cavotricuspid isthmus, a narrow strip of myocardium in the right atrium between the inferior vena cava inlet and the tricuspid valve annulus. This area is central in typical atrial flutter because it serves as the main conduction pathway around which the re-entrant circuit travels; ablation here often disrupts the circuit and terminates the flutter. The other landmarks are located elsewhere in the right atrium: the Crista terminalis is a muscular ridge that marks the boundary between the smooth sinus venarum and the trabeculated atrial appendage; the Eustachian ridge sits near the IVC ostium but isn’t the whole conduction pathway used in flutter; and the fossa ovalis lies in the interatrial septum, not between the IVC and the tricuspid valve.