BNP in Mitral Regurgitation
abstract & commentary
By Michael H. Crawford, MD
Synopsis: Higher BNP levels predict worse outcomes under medical management and may be useful for decisions regarding surgery.
Source: Detaint D, et al. B-Type Natriuretic Peptide in Organic Mitral Regurgitation. Circulation. 2005;111:2391-2397.
The assessment of the severity of mitral regurgitation (MR) and the timing of mitral valve surgery are challenging. Thus, this group from the Mayo Clinic, Rochester, MN, prospectively analyzed the value of BNP levels for predicting severity of MR and its outcome. Consecutive patients with isolated chronic organic mitral regurgitation underwent a comprehensive echo/Doppler evaluation and a BNP level. A total of 124 patients were enrolled and followed for an average of 4 years. Causes of MR included prolapse in 94, degenerative in 22, rheumatic in 5, and healed endocarditis in 3. Regurgitant fraction (RF) by echo/Doppler identified mild MR (RF < 30%) in 30%, moderate MR in 34% (RF 30-49%), and severe MR (RF 50%) in 35%. Multivariate analysis showed that BNP was independently determined by age, female sex, left ventricular (LV) end-systolic volume index, left atrial (LA) volume, atrial fibrillation, and presence of symptoms. The degree of MR was not associated with BNP. Splitting patients into those above and below the median BNP level (31 pg/mL) showed that patients with high BNP (> 31 pg/mL) had a lower survival rate (72 vs 95% at 5 years, P = .03) and a higher incidence of achieving the combined end point of death or heart failure (42 vs 16% at 5 years, P = .03). Also, BNP was independently predictive of mortality (hazard ratio 1.23, CI 1.07-1.48, P = .004). Detaint and colleagues concluded that BNP elevation in chronic organic MR represents the LV and LA adaptation to the lesion rather than the severity of MR per se. Thus, higher BNP levels predict worse outcomes under medical management and may be useful for decisions regarding surgery.
Commentary
This is an interesting study that addresses 2 challenges in the management of chronic organic MR: determining regurgitation severity and timing of surgery. BNP was not useful for confirming the severity of MR, and so we are left with doing a careful quantitative echo/Doppler analysis and correlating it with clinical findings. BNP did predict overall outcomes suggesting that high levels represent patients in whom surgery should be considered. Detaint et al seem ready to embrace it and state that BNP is an "emerging biomarker of severe consequences and poor clinical outcomes under conservative management." However, time will tell if measuring BNP is valuable for clinical decision making or adds more to the confusion.
Of note, BNP was related to symptoms (NYHA functional class), LV end systolic volume, LA size, and atrial fibrillation; all 4 of which have been proposed as useful for predicting who should be considered for surgery. However, it was only weakly related to LV ejection fraction (EF) and not in the multivariate analysis; yet, LVEF < 60% is believed to be a strong indicator of need for surgery. Recognizing this discrepancy, Detaint et al conjecture that EF is a late marker of patients who do poorly with surgery and that we need earlier markers, especially in patients who are candidates for valve repair. Thus, they believe that BNP is a "promising clinical tool for risk stratification." Whether BNP can be used effectively in individual patients remains to be proven in a prospective trial designed to test this concept. Given the multiple causes of positive BNPs, such as age and gender (noted in this study) and controversy over the best assay (eg, pro BNP). I doubt that it will be as straight forward as Detaint et al hope. On the other hand, this test is now readily available and would seem worth ordering in patients with moderate to severe MR (3-4/4) who may be candidates for valve repair. I agree with Detaint et al that a high BNP should occasion a closer look at the patient and more intense follow-up. Perhaps a high BNP should occasion a quantitative echo/Doppler evaluation if only a qualitative one has been done. Clearly, the clinical utility of BNP continues to evolve.
By Michael H. Crawford, MD Synopsis: Higher BNP levels predict worse outcomes under medical management and may be useful for decisions regarding surgery. Source: Detaint D, et al. B-Type Natriuretic Peptide in Organic Mitral Regurgitation. Circulation. 2005;111:2391-2397.You have reached your article limit for the month. Subscribe now to access this article plus other member-only content.
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