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BNP and Survival in Degenerative Mitral Regurgitation
Study Questions:
Is there an association between B-type natriuretic peptide (BNP) activation and mortality among patients with degenerative mitral regurgitation (MR)?
Methods:
A cohort of 1,331 patients with MR due to mitral valve prolapse or flail at one of four tertiary medical centers (68% at one center; and 14%, 9%, and 9%, respectively, at the three others) during 2001 through 2013 were followed if the patient also had BNP assessed at the time of echocardiography. MR was assessed semi-quantitatively (on a scale of 1-4) using echocardiography/Doppler. BNP was expressed as a BNP ratio (the ratio of the BNP value to an upper-limit-of-normal based on patient age, sex, and the specific assay used). Patients were considered to have undergone initial mitral surgery if surgery was performed within 3 months of the echocardiogram. Patients who did not undergo surgery within 3 months of the echocardiogram were classified as having undergone initial medical therapy. Clinicians caring for the patients were not blinded to BNP results. The primary endpoint was all-cause mortality; secondary endpoints were mortality under medical therapy and mortality after surgery.
Results:
Mean patient age was 64 ± 15 years, 66% were male, mean ejection fraction was 64 ± 9%, mean regurgitant volume was 67 ± 31 ml, and mean Charlson comorbidity index was 1.09 ± 1.76. Median BNP ratio was 1.01 (interquartile range [IQR], 0.42-2.36). Overall, BNP ratio was an independent predictor of mortality (hazard ratio [HR], 1.33 [1.15-1.54]; p < 0.0001), although absolute BNP was not (p = 0.43). Among 770 patients (58%) initially treated medically (of whom 52% had severe MR), BNP ratio was an independent and incremental predictor of mortality after diagnosis (HR, 1.61 [1.34-1.93]; p < 0.0001); higher BNP activation was associated with higher mortality (p < 0.0001). All subgroups, particularly severe MR, incurred similar excess mortality with BNP activation. Among 561 patients (42%) who underwent initial surgical treatment (of whom 82% had severe MR), BNP activation was not associated with excess long-term mortality (p = 0.23).
Conclusions:
The authors concluded that BNP ratio is a powerful, independent, and incremental predictor of long-term mortality among patients with degenerative MR who do not undergo surgery within 3 months. They suggest that BNP ratio should be incorporated into the routine clinical assessment of patients with degenerative MR.
Perspective:
Although BNP has been associated with worse outcomes among patients with aortic stenosis or with MR, prospective, randomized studies are lacking. Apart from a lack of methodologic detail in this manuscript, limitations associated with this retrospective, observational study raise concern. Severe (4+) or even moderate-to-severe (3+) MR were not inclusion criteria; clinicians were not blinded to BNP results; adequacy of medical follow-up was not defined; and conservatively managed patients included 51% with dyspnea and 19% with atrial fibrillation, respectively, Class I and potentially Class IIa indications for intervention. As with prior studies, this study fails to provide a compelling argument for including BNP in timing intervention for MR.
Keywords: Aortic Valve Stenosis, Biomarkers, Cardiac Surgical Procedures, Diagnostic Imaging, Echocardiography, Heart Valve Diseases, Mitral Valve Insufficiency, Mitral Valve Prolapse, Mortality, Natriuretic Peptide, Brain
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