3. RESULTS
The baseline characteristics and pre-operative TTE data, including MR etiologies, are listed in Table 1. The mean age was 62 ± 13 years, and 105 (61%) patients were men. The mean value of the LV ejection fraction was 64.6 ± 8.7%. A large proportion (87%) had a prolapse of the anterior and/or posterior mitral leaflets due to fibroelastic deficiency as the main etiology of MR. Fifteen patients experienced new onset AA events, including paroxysmal or persistent AF and AT during the post-operative follow-up period, with a median of 35.7 months (range, 0.5 to 132 months). No significant difference was found in baseline characteristics between patients who experienced post-operative AA events and those who didn’t. Table 2 shows the data for the surgical procedure. There were no significant differences in any pre-operative TTE parameter between the two groups, including the MR etiology, extent of mitral valve lesions and aorto-mitral angle (135 ± 11 degrees vs. 131 ± 12 degrees, P = 0.29). The cardiopulmonary bypass (CPB) time was longer in patients who had post-operative AA events than in patients who didn’t (195 ± 69 min vs. 168 ± 53 min, P = 0.035). The post-operative TTE data are listed in Table 3. The patients who experienced post-operative AA events had a smaller aorto-mitral angle at the post-operative TTE than the patients who didn’t (119 ± 6 degrees vs. 125 ± 10 degrees, P = 0.003). There was no significant difference in the grading of residual MR or the mean TMPG between the two groups.
The univariate Cox proportional hazards analyses revealed that the CPB time and the aorto-mitral angle at the post-operative TTE were significant predictors of the post-operative AA events among all demographic, procedural and echocardiographic parameters. A multivariate Cox proportional hazards analysis revealed that the CPB time (odds ratio 1.12 per 10 minutes; 95% CI 1.03-1.21; P = 0.008) and the aorto-mitral angle at the post-operative TTE (odds ratio 0.92; 95% CI 0.86-0.98; P = 0.014) were the independent predictors of the new onset AA events (Table 4). The area under the ROC curve of the aorto-mitral angle to predict the new onset AA event was 0.717 (Figure 2). One-hundred and seventeen degrees was the optimal cutoff value of the post-operative aorto-mitral angle for predicting the post-operative AA events with a sensitivity of 57% (95% CI, 29-82%) and a specificity of 80% (95% CI, 73-86%). Figure 3 shows the Kaplan-Meier event-free curves in patients stratified based on the post-operative aorto-mitral angle. The post-operative AA event-free rate was higher in patients with the post-operative aorto-mitral angle > 117 degrees than in patients with the post-operative aorto-mitral angle ≤ 117 degrees.
We additionally analyzed the determinants of the small post-operative aorto-mitral angle (≤ 117 degrees). TMPG > 3mmHg (odds ratio 2.53; 95% CI, 1.19-5.37, P = 0.016) was the only determinant of the small post-operative aorto-mitral angle among the post-operative echocardiographic parameters.