The three-dimensional geometric relationship between the mitral valvar annulus and the coronary arteries as seen from the perspective of the cardiac surgeon using cardiac computed tomography.

OBJECTIVES: Mitral annuloplasty involves sewing a prosthetic ring to the mitral annulus. This involves a risk of damaging the surrounding structures in the left atrioventricular (AV) groove, particularly the left circumflex artery, which may be inadvertently sutured, causing an arterial occlusion. We have used cardiac computed tomography (CT) scans to study the three-dimensional relationship between the mitral valvar annulus and the neighbouring coronary arteries in the AV groove, and to map the distance between the arteries and the annulus.

METHODS: We examined cardiac CT scans of two groups of patient: 40 normal subjects, and 30 patients with left ventricular dysfunction and/or mitral regurgitation. The hinge line of the mitral valve, as well as the location of the coronary arteries within the left AV groove, was manually marked on a workstation and three-dimensional coordinates saved in digital format. Dedicated software was developed to calculate the plane of the mitral annulus, and the smallest distance between each point on the annulus and each of the left circumflex and right coronary arteries, called local minima. The global minimum for each heart is defined as the minimum of all local minima.

RESULTS: The global minimum for the left circumflex averaged 6.4 ± 2.1 mm, usually involving the proximal portion, just laterally to the left trigone. In three-tenths of patients, the global minimum was <5 mm. This was more common in patients with left dominance, and in the normal subjects. The major component of the line vector between the annulus and circumflex is parallel to the plane of the mitral annulus, while the perpendicular component is usually in an atrial direction. For the dominant right coronary artery (RCA), the global minimum distance to the annulus is 14.7 ± 5.7 mm. In no patient did the RCA approach to within 5 mm with respect to the mitral annulus, albeit that 13% were <10 mm.

CONCLUSIONS: In a significant proportion of patients, the left circumflex is in very close proximity to the annulus of the mitral valve. Knowledge of the precise three-dimensional relationships between the structures can be expected to minimize iatrogenic complications.