Right Atrial Cavotricuspid Isthmus: Anatomic Characterization with Multi–Detector Row CT

Abstract

To retrospectively evaluate the anatomic characteristics of the right atrial cavotricuspid isthmus (CTI) by using 64-section multi-detector row computed tomography (CT). Institutional review board approval and waiver of informed consent were obtained for this HIPAA-compliant study. The anatomic region of the CTI was evaluated in 201 patients (116 men and 85 women; mean age, 58 years +/- 11 [standard deviation]) who underwent coronary multi-detector row CT. CTI length was assessed along three parallel isthmic levels (paraseptal, central, and inferolateral). Central isthmus depth was classified as straight (3 mm), concave (>3 to </=5 mm), or pouchlike (>5 mm). Measurements were obtained during three cardiac phases: midsystole, middiastole, and atrial contraction. Subthebesian recess dimensions and eustachian ridge width were measured. Distances from the atrioventricular node artery to the coronary sinus, from the right coronary artery (RCA) to the inferior vena cava, and from the RCA to the tricuspid valve annulus were measured. Software was used for statistical analysis. At middiastole, the paraseptal isthmus (mean length, 20 mm +/- 3.5; range, 11-34 mm) was significantly shorter than the central isthmus (24 mm +/- 4.3; range, 12-43 mm) and the central isthmus was shorter than the inferolateral isthmus (27 mm +/- 4.8; range, 13-45 mm) (P < .001). The longest CTI measurements were obtained during midsystole, and the shortest were obtained during atrial contraction (40% variation per cardiac cycle). Isthmus contraction occurred primarily in the posterior segment of the central isthmus (RCA to inferior vena cava distance). At middiastole, the central isthmus was straight in 8% of patients, concave in 47% of patients, and pouchlike (>5 mm) in 45% of patients. The mean depth was greater during atrial contraction (6.3 mm +/- 2.1) than in midsystole (4.3 mm +/- 1.5) and middiastole (5.1 mm +/- 1.8) (32% variation during cardiac cycle). A subthebesian recess greater than 5 mm deep was identified in 45% of patients. In 24% of patients, a thick eustachian ridge greater than 4 mm was seen. The atrioventricular node artery passed close to the coronary sinus wall (mean distance, 2.1 mm +/- 0.7; range, 1-6 mm). Cardiac multi-detector row CT provides extensive information regarding the size and morphology of the CTI and its related structures.