Cardiomyopathy
Usefulness of N-Terminal Pro-B-Type Natriuretic Peptide Levels to Predict Exercise Capacity in Hypertrophic Cardiomyopathy

https://doi.org/10.1016/j.amjcard.2006.02.057Get rights and content

Most patients with hypertrophic cardiomyopathy (HC) have reduced maximal oxygen consumption (VO2max) during exercise. The degree of impairment is poorly predicted by the magnitude of hypertrophy, left ventricular (LV) outflow tract obstruction, and other conventional markers of disease severity. The aim of this study was to determine the usefulness of N-terminal–pro-B-type natriuretic peptide (NT–pro-BNP) as a marker of exercise performance in HC. Plasma NT–pro-BNP was measured in 171 consecutive patients (mean age 46 ± 18 years) who underwent echocardiography and cardiopulmonary exercise testing. The mean log NT–pro-BNP was 2.79 ± 0.5; log NT–pro-BNP levels were higher in women patients (p = 0.001) and patients with chest pain (p = 0.010), in New York Heart Association class ≥II (p = 0.009), with atrial fibrillation (p <0.001), with systolic impairment (p = 0.025), and with LV outflow tract obstructions (p <0.0001). NT–pro-BNP levels were also correlated with maximal wall thickness (r = 0.335, p <0.0001), left atrial size (r = 0.206, p = 0.007), and the mitral Doppler E/A ratio (r = 0.197, p = 0.012). The mean percent VO2max achieved was 73.8 ± 22.6%; percent VO2max was smaller in patients with systolic impairment (p = 0.044) and LV outflow tract obstructions (p = 0.025). There were inverse correlations between percent VO2max and NT–pro-BNP (r = −0.352, p = 0.001), LV end-systolic cavity size (r = −0.182, p = 0.031), and left atrial size (r = −0.251, p = 0.003). On multivariate analysis, only NT–pro-BNP was correlated with percent VO2max. A NT–pro-BNP level of 316 ng/L had 78% sensitivity and 44% specificity (area under the curve 0.616) for predicting percent VO2max <80%. In conclusion, NT–pro-BNP levels correlate with peak oxygen consumption in HC and are more predictive of functional impairment than other conventional markers of disease severity.

Section snippets

Patient selection

One hundred seventy-one consecutive patients (63 male patients; mean age 46 ± 18 years, range 15 to 89) from the HC clinic at St. George’s Hospital, London, United Kingdom, underwent histories, examinations, 12-lead electrocardiography, echocardiography, and cardiopulmonary exercise testing. The diagnosis of HC was based on the echocardiographic demonstration of LV hypertrophy >2 SD for age and gender or on published criteria for the diagnosis of disease in relatives.23, 24 Patients unable to

Baseline characteristics of patients studied

Clinical characteristics are listed in Table 1. The mean maximal LV wall thickness of patients studied was 20 ± 5 mm (range 13 to 40). Ten patients (6.5%) had LV hypertrophy at initial presentation but at the time of study had evidence of wall thinning, cavity enlargement, and systolic impairment (fractional shortening <25%). All were in NYHA class III. One patient had severe restrictive physiology, with a maximal LV wall thickness of 23 mm, bi-atrial dilation, atrial fibrillation, and normal

Discussion

This study demonstrates that there is an inverse relation between peak oxygen consumption during upright exercise and NT–pro-BNP levels. Although percent VO2max was related to other commonly used markers of disease severity, such as LV outflow tract obstruction, fractional shortening, left atrial size, and NYHA class, only NT–pro-BNP levels retained a correlation (albeit weak) with percent VO2max in the multivariate analysis. Therefore, NT–pro-BNP level may be a more useful marker of disease

References (30)

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    Currently, N-terminal prohormone of B-type natriuretic peptide (NT-proBNP) and high-sensitivity cardiac troponin I (hs-cTnI) facilitate diagnosis, improve clinical and therapeutic management, both early and late in the course of the disease, and show a potential role for risk stratification. Elevated NT-proBNP is significantly associated with more severe disease, independent of LVEF, New York Heart Association (NYHA) class and left ventricular outflow tract (LVOT) obstruction [6–8]. An integrated approach combining laboratory assays with imaging could lead to better identification of patients with worse outcome.

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    Atrial fibrillation is a common complication of HCM occurring in about 25% of patients and is a marker of poor prognosis [24,40]. Six of seven studies, summarized in Table S2d, demonstrate that atrial fibrillation is more common among HCM patients with elevated natriuretic peptides [8,23,32,33,35,41,42]. The prevalence of atrial fibrillation among patients with elevated BNP ≥ 200 pg/mL was 42% in one cohort, compared to 8% in patients without elevated BNP [23], and the prevalence varies with natriuretic peptide levels [35].

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Drs. Thaman and Tome were supported by the British Heart Foundation, London, United Kingdom.

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