Differentiation of the severity of rheumatic mitral stenosis using dimensionless index and its association with outcomes.

INTRODUCTION

The severity of mitral stenosis (MS) is commonly assessed using mitral valve area (MVA) measured with transthoracic echocardiography (TTE). The dimensionless index (DI) of mitral valve (MV) was recently studied in degenerative MS. We evaluated DI MV in rheumatic MS and studied its relationship with clinical outcomes.

METHODS

We studied 406 cases of rheumatic MS in a retrospective single centre cohort study, with 174 in a derivation cohort, 121 in a TTE validation cohort, and 111 in a transoesophageal echocardiography (TEE) validation cohort. DI MV was calculated by dividing the left ventricular outflow tract pulsed-wave Doppler time-velocity integral (TVI) by the MV continuous-wave Doppler TVI. DI MV was compared against MV area using the two-dimensional planimetry, pressure half-time and continuity equation methods, or, in the TEE validation cohort, TEE-derived three-dimensional planimetry. Severe MS was defined as an MV area ≤1.5 cm. Outcomes pertaining to all-cause death and mitral valve intervention were studied in the former two cohorts.

RESULTS

All-in-all, 231 patients (56.9 %) across the three cohorts had severe MS. In the derivation cohort, ROC analysis showed that DI MV could accurately classify MS severity (AUC = 0.838, 95 % CI, 0.780-0.897,  < 0.001). DI MV ≤ 0.25 and DI MV ≥ 0.40 had high specificity for identifying severe (93.7 %) and non-severe MS (93.7 %) respectively. In the validation cohorts, these respectively showed similar specificity for identifying severe (93.8 %) and non-severe MS (91.4 %). In the derivation and TTE validation cohorts, the median follow up duration was 6.32 years (interquartile range, 4.22-10.3 years) with 90 deaths (30.5 %) and 50 patients (17.0 %) undergoing MV intervention. DI MV was univariately significant (HR = 0.075, 95 % CI 0.0215-0.378,  = 0.002) in Cox regression for a composite outcome of death and MV intervention. DI MV remained independently associated with the composite outcome in multivariate analysis.

CONCLUSION

DI MV can help rule-in or rule-out severe MS with high specificity, and is independently associated with composite outcomes of death and MV intervention.