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Abstract & Commentary
Synopsis: BNP levels could identify patients with abnormal diastolic dysfunction among patients with normal systolic function.
Source: Lubian E, et al. Circulation. 2002;105:595-601.
B-natriuretic peptide (bnp) has shown promise for the diagnosis of heart failure in acute care settings. However, the relationship of BNP to diastolic left ventricular (LV) function is not clear. Thus, Lubien and colleagues measured BNP and echo-Doppler diastolic function in 294 patients referred for echocardiography to evaluate LV function, who had normal systolic LV function. Without knowledge of the BNP levels, patients were classified as normal, impaired relaxation, psuedonormal or restrictive pattern by standard echo-Doppler parameters. In the 119 patients with abnormal diastolic function, mean BNP was 286 pg/mL vs. 33 pg/mL in the normal diastolic function group (P < .001). Also, mean BNP was progressively higher as the severity of diastolic dysfunction category increased, with the highest BNP levels observed in the restrictive filling group. Receiver operating curves identified a BNP cut-off value of 62 pg/mL, which provided a sensitivity of 85%, specificity of 83%, and an accuracy of 84%, for detecting diastolic dysfunction. A clinical history of overt heart failure raised mean BNP levels in all diastolic dysfunction categories. Lubian and associates concluded that BNP levels could identify patients with abnormal diastolic dysfunction among patients with normal systolic function.
BNP is a cardiac neurohormone excreted by the LV in response to pressure or volume load. In patients with symptoms suggestive of heart failure, it can distinguish heart failure from other entities that can cause dyspnea, but do not impair left or right heart function. For example, acute pulmonary embolism with right ventricular dysfunction would have a high BNP level, but COPD exacerbation without acute pulmonary hypertension and right ventricular dysfunction would not. Some studies suggest that BNP can detect systolic dysfunction as a cause of heart failure symptoms as well. In this study, Lubien et al show that BNP levels predict diastolic dysfunction in a nonacute care setting of patients with normal systolic function. Since echocardiography is usually done to identify LV systolic dysfunction, what would be the point of measuring BNP, when diastolic dysfunction can be evaluated on the same echo? There would be no reason to measure BNP if an echo is being done. However, since BNP can detect systolic dysfunction as well, it could be used to screen for who needs an echo. Patients with a low BNP are unlikely to have systolic or diastolic dysfunction and may not need an echo Patients with an elevated BNP would benefit from an echo.
The major limitation of this paper is the selection bias of referral for an echo. In a nonselected sample, especially of older patients, BNP may not be as predictive of diastolic dysfunction. Also, BNP was more predictive as diastolic abnormalities were more severe. Those with the most severe diastolic dysfunction also have systolic dysfunction. Systolic dysfunction was excluded in this paper so data on this interrelationship is not available. Finally, the relationship of BNP to acute ischemic LV dysfunction that is usually systolic and diastolic may explain the specificity of 83% in this study. Some patients with elevated BNP and normal systolic and diastolic function may have had transients myocardial ischemia and need to be evaluated for this possibility if appropriate.
Dr. Crawford is Professor of Medicine, Mayo Medical School, Consultant in Cardiovascular Diseases and Director of Research, Mayo Clinic, Scottsdale, AZ.