BNP for Differentiating Constrictive Pericarditis vs Restrictive Cardiomyopathy
abstract & commentary
By Michael H. Crawford, MD
Synopsis: BNP levels are significantly elevated in RCM patients as compared to CP patients, and should be a useful noninvasive marker to distinguish the 2 conditions.
Source: Leya FS, et al. The Efficacy of Brain Natriuretic Peptide Levels in Differentiating Constrictive Pericarditis From Restrictive Cardiomyopathy. J Am Coll Cardiol. 2005;45:1900-1902.
Differentiating constrictive pericarditis (cp) from restrictive cardiomyopathy (RCM) is frequently challenging and often involves multiple imaging strategies and a full invasive hemodynamic
evaluation. Of course, the effort is worthwhile because CP is potentially curable, but an easier diagnostic marker
would be welcome. Leya and colleagues hypothesized that brain natriuretic peptide
(BNP) may not be elevated in CP since the myocardium is constrained from dilating, but would be in RCM due to increased filling
pressures in non restrained chambers. They studied 11
consecutive patients being invasively evaluated for these conditions and measured BNP at the time of the invasive evaluation. The hemodynamic evaluation was extensive and involved transseptal catheterization and fluid challenges when necessary. The diagnostic standard for CP was the presence of intracardiac and intrathoracic disassociation and right and left ventricular pressure discordance. Surgical findings were also considered.
Results: In 6 patients, CP was diagnosed (4 confirmed at surgery, 2 refused surgery); 5 had RCM. Right and left heart resting hemodynamics were not different between the 2 groups. However, BNP levels were higher in the RCM patients (826 vs 128 pg/mL, P < .001) and there was no overlap in each group’s range of values (639 to 1060 vs 50 to 186 pg/mL). Leya et al concluded that BNP levels are significantly elevated in RCM patients as compared to CP patients and should be a useful noninvasive marker to distinguish the 2 conditions.
Commentary
This is a new, novel use for BNP that promises to
be helpful to the clinician. In CP, BNP was < 200
pg/mL; in RCM it was > 600 pg/mL in this study. Although encouraging, there are a few caveats. First, this is a small study (n = 11) and highly select. They excluded patients with significant valvular disease, those suspected of having effusive constrictive disease, such as heart transplant patients, and radiation therapy patients. Second, all 11 patients had a definite diagnosis based upon invasive hemodynamics and some by surgical confirmation (4/6 with CP). One could argue that no patient should go to surgery without definite hemodynamic evidence of CP and a thickened pericardium by imaging. If imaging was done in this study, the results were not presented. So where would BNP be useful? I can think of a few scenarios. The patient with indeterminate hemodynamics and unclear imaging may be an example. In a patient with classic RCM on echocardiography, it may be reassuring to have a high BNP if you are not going to pursue an invasive evaluation. Only further experience will define the usefulness of BNP in this situation. Hopefully, its use will not lead to more unnecessary testing as troponins have in other hospitalized patients.
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