ECHOCARDIOGRAPHIC CHARACTERISTICS AND CAUSAL MECHANISM OF PHYSIOLOGICAL MITRAL REGURGITATION IN YOUNG NORMAL SUBJECTS

Background: It has become evident that mitral regurgitation (MR) is no t uncommon in healthy subjects, and Doppler color flow mapping is a te chnique that imparts important information relevant to its detection. Hypothesis: Using transthoracic echocardiography, this study evaluated the mechanism of physiologic MR in young normal subjects using transt horacic echocardiography. Methods: The study population consisted of 4 8 young normal subjects (mean 21 +/- 5 years) with MR (physiologic MR group), 40 age-matched young normal subjects (mean 20 +/- 5 years) wit hout MR (control group), 45 patients (mean 41 +/- 15 years) with mitra l valve prolapse with MR (MVP group), and 27 patients (mean 59 +/- 13 years) with ruptured chordae tendineae (rupture group). Results: Men w ere predominant in the rupture group, whereas there were no significan t gender differences in the other three groups. Left ventricular end-d iastolic dimension and left atrial systolic dimension were slightly sm aller in the physiologic MR group than in the control group, but were significantly smaller than those in the MVP and rupture groups. The ra tio of the maximum anteroposterior diameter to the maximum transverse diameter on chest radiography and the ratio of the short- to long-axis diameter of the left ventricular cavity at end diastole, determined f rom two-dimensional short-axis echocardiogram, were significantly lowe r in the physiologic MR group than in the other three groups. Mitral r egurgitation occurred more frequently at the posteromedial commissural site in the physiologic MR and MVP groups, whereas there was no prefe rence for location in the rupture group. Early systolic MR was often o bserved in the physiologic MR group, whereas pansystolic MR was common in the MVP and rupture groups. Conclusion: As a causal mechanism for physiologic MR detected in young normal subjects, ''flattening'' of th e thorax during growth may cause morphologic abnormalities of the left atrial and ventricular cavities, resulting in spatial imbalance of th e mitral complex and resulting in malcoaptation of the valve.