Primary, atrial secondary, and ventricular secondary mitral regurgitation in the general population

While primary mitral valve regurgitation (PMR) results from structural abnormalities of the mitral valve leaflets, secondary mitral valve regurgitation (SMR) arises from either mitral annular dilatation (atrial type, aSMR) or left ventricle remodelling (ventricular type, vSMR) in the absence of intrinsic leaflet disease. Although SMR is considered the most common cause of clinically relevant mitral regurgitation (MR), population-based data on its prevalence, subtype distribution, and clinical profiles are lacking. We aimed to determine the prevalence of PMR and SMR and to characterize PMR, aSMR, and vSMR in the general population.

We analyzed the first 10,000 participants of the population-based Hamburg City Health Study enrolled 2016-2019; 8543 echocardiographic examinations were available. Mitral valve morphology and function were independently assessed by two investigators. PMR was defined by the presence of intrinsic leaflet pathology, whereas SMR was classified as ventricular when left ventricular ejection fraction was less than 50% or less than 55% in the presence of geometric distortion (tenting area ≥ 150 mm² or coaptation depth ≥ 10 mm) and cases with left ventricular ejection fraction equal to or above 50% were classified as aSMR.

A total of 216 participants had moderate or severe MR (2.53% of the total cohort, 95% confidence interval (CI): 2.20%-2.89%, see Fig. 3). Of these, 148 were classified as SMR (68.5%, 95% CI: 61.8%-74.7%), the remaining were mainly of primary etiology (31.5%, 95% CI: 25.3%-38.2%). Among SMR cases, aSMR was predominant (84.5%, 95% CI: 77.5%-89.9%), whereas vSMR accounted for 15.5% (95% CI: 10.1%-22.4%). Compared with aSMR, individuals with vSMR were older, more symptomatic, and more frequently had atrial fibrillation and hypertension. Echocardiographic parameters indicated more advanced cardiac remodelling and dysfunction in vSMR. Compared with SMR, participants with PMR had greater MR severity, while age and the proportion of women were numerically higher without reaching statistical significance. During a median follow-up of 4.56 years, 10 participants had died, with all-cause mortality being significantly higher among participants with PMR than among those with aSMR.

In this population-based cohort, SMR accounted for two-thirds of relevant MR, with aSMR being the predominant subtype. MR severity was higher in PMR as compared to SMR. Distinct echocardiographic and clinical profiles suggest more advanced disease in vSMR. Multivariate analysis revealed that atrial fibrillation was significantly more present in the vSMR cohort. These findings highlight the need for refined SMR subclassification and longitudinal studies to define prognostic implications and clinically meaningful definitions. All-cause mortality was highest in participants with PMR than in those with aSMR.