Predictive Values of N-Terminal Pro-B-Type Natriuretic Peptide and Cardiac Troponin I for Myocardial Fibrosis in Hypertrophic Obstructive Cardiomyopathy

Abstract

Background: Both high-sensitivity cardiac troponin T and B-type natriuretic peptide are useful in detecting myocardial fibrosis, as determined by late gadolinium enhancement (LGE) cardiovascular magnetic resonance (CMR), in patients with non-obstructive hypertrophic cardiomyopathy. However, their values to predict myocardial fibrosis in hypertrophic obstructive cardiomyopathy (HOCM) remain unclear. We investigated the role of N-Terminal Pro-B-Type Natriuretic Peptide (NT-proBNP) and cardiac troponin I (cTnI) to identify LGE-CMR in patients with HOCM.

Methods: Peripheral concentrations of NT-proBNP and cTnI were determined in patients with HOCM (n = 163; age = 47.2 ± 10.8 years; 38.7% females). Contrast-enhanced CMR was performed to identify and quantify myocardial fibrosis.

Results: LGE was detected in 120 of 163 patients (73.6%). Patients with LGE had significantly higher levels of NT-proBNP and cTnI than those without LGE (1386.2 [904.6-2340.8] vs. 866.6 [707.2-1875.2] pmol/L, P = 0.003; 0.024 [0.010-0.049] vs. 0.010 [0.005-0.021] ng/ml, P <0.001, respectively). The extent of LGE was positively correlated with log cTnI (r = 0.371, P <0.001) and log NT-proBNP (r = 0.211, P = 0.007). On multivariable analysis, both log cTnI and maximum wall thickness (MWT) were independent predictors of the presence of LGE (OR = 3.193, P = 0.033; OR = 1.410, P < 0.001, respectively), whereas log NT-proBNP was not. According to the ROC curve analysis, combined measurements of MWT ≥21 mm and/or cTnI ≥0.025 ng/ml indicated good diagnostic performance for the presence of LGE, with specificity of 95% or sensitivity of 88%.

Conclusions: Serum cTnI is an independent predictor useful for identifying myocardial fibrosis, while plasma NT-proBNP is only associated with myocardial fibrosis on univariate analysis. Combined measurements of serum cTnI with MWT further improve its value in detecting myocardial fibrosis in patients with HOCM.

Fig 1. A schematic diagram of the quantification of LGE by the visual scoring method based on the standard 17-segment model of the left ventricle.

The number in each segment represents the corresponding LGE score of that segment. By adding each individual segment score, the total LGE score was 13 for this patient. The extent of LGE (LGE %) was then calculated as 19.1% ([13/68]×100). Details of the scoring procedure are described in the Methods section. LGE indicates late gadolinium enhancement.

Fig 2. Correlations between the extent of LGE (LGE%) and MWT (A), LVMI (B), resting LVOTG (C), LVEF (D), Log cTnI (E) and log NT-proBNP (F) in the overall study patients.

cTnI indicates cardiac troponin I; LVEF, left ventricular ejection fraction; LVMI, left ventricular mass index; LVOTG, left ventricular outflow tract gradient; MWT, maximum wall thickness; NT-proBNP, N-terminal pro B-type natriuretic peptide. Other abbreviations as in Fig 1.

Fig 3. Concentrations (medians and interquartile ranges) of NT-proBNP (A) and cTnI (B) in patients with and without LGE.

Fig 4. Representative LGE images of patients with extensive and without LGE.

A 61-year-old woman with slightly elevated NT-proBNP plasma level (515.4pmol/L) and normal serum level of cTnI (0.006ng/ml), had no LGE detected in the 4-chamber view and end-diastolic short-axis views at basal, mid-ventricular and apical levels of left ventricle (A-D). A 47-year-old man with significantly elevated peripheral levels of NT-proBNP (2642.0pmol/L) and cTnI (0.321ng/ml), had extensive LGE (red arrows; LGE score, 46; LGE%, 67.6%) mainly involving the anterior, anteroseptal, septal, inferoseptal and inferior myocardium (E-H). Abbreviations as in Figs 1 and 2.

Fig 5. Receiver operating characteristic (ROC) curves of MWT (A) and cTnI (B) to predict the presence of LGE.

AUC indicates area under ROC curve. Other abbreviations as in Figs 1 and 2.