Is mitral valve prolapse due to cardiac entrapment in the chest Cavity? A CT view

Mitral valve prolapse (MVP) is the most frequently diagnosed valvular disease, but its pathophysiology remains elusive. Its complete absence in 1,734 neonatal echocardiographic studies suggests that this may be an acquired rather than a congenital disease. We observed several patients with distorted cardiac and valvular anatomies on electron beam CT (EBCT) images of the chest who reported symptoms reminiscent of MVP. In these patients, the heart is compressed between the spine and the anterior chest wall and it appears trapped in a chest cavity that is too small for its size.

We performed EBCT in 66 patients with echocardiographically proven MVP and no clinical pectus excavatum (group A; 80% were women; mean age, 48 +/- 12 years) and in 96 control patients without MVP by echocardiography (group B; 72% were women; mean age, 49 +/- 10 years). EBCT alone was also performed on 200 patients who had reported atypical chest discomfort and palpitations to their physicians (group C) and on 200 asymptomatic patients (group D). The EBCT measurements included the following: anteroposterior chest diameter (APD); the angle formed by the confluence of the mitral valve ring with the interatrial septum (ANGLE); and the contact area between the posterior surface of the anterior chest wall and the myocardium (CA). Entrapment was considered present if the individual patient's measurements varied by more than two SDs compared to measurements made in control subjects (group B).

EBCT images demonstrated cardiac entrapment in 82% of group A patients and in 4.2% of group B patients (p < 0.001). ANGLE and CA were significantly larger in MVP patients than in group B patients (114 +/- 9 degrees vs 91 +/- 5 degrees and 6,230 +/- 2,020 mm(2) vs 476 +/- 1,009 mm(2), respectively; p < 0.001 for both comparisons), while APD was significantly smaller (91 +/- 16 mm vs 128 +/- 17 mm, respectively; p < 0.001). The prevalence of entrapment was significantly greater in group C patients than in group D patients (22% vs 6.5%; p < 0. 001).

MVP may be an acquired condition caused by a growth disproportion between the heart and the chest cavity, with distortion of the mitral valve annulus and subsequent leaflet prolapse. A narrow APD, a wide ANGLE, and a large CA characterize this condition. Similar findings are found in a sizable proportion of patients with atypical chest pain symptoms and palpitations.