Myocardial fibrosis assessed by late gadolinium enhancement cardiac magnetic resonance imaging is associated with cardiovascular events in patients with hypertrophic cardiomyopathy (HC), but few data are available regarding the utility of biomarkers for detecting late gadolinium enhancement. The aim of this study was to examine serum levels of myoglobin, cardiac myosin light chain I, high-sensitivity cardiac troponin T (hs-cTnT), and creatine kinase-MB isoenzyme and plasma levels of brain natriuretic peptide (BNP) in relation to late gadolinium enhancement in 53 patients with HC. Levels of hs-cTnT and BNP were higher in 23 patients with late gadolinium enhancement than in 30 patients without it (p <0.01 for both). An hs-cTnT level ≥0.007 ng/ml or a BNP level ≥70 pg/ml had good diagnostic value for detecting late gadolinium enhancement, with sensitivity of 96% or specificity of 90% with the combination of these 2 biomarkers. The extent of late gadolinium enhancement was correlated with BNP level (p <0.01) but not with hs-cTnT level in 23 patients with HC with late gadolinium enhancement. The increase in the extent of late gadolinium enhancement was related to hs-cTnT level in 8 patients during 22 months of follow-up (p = 0.02). In conclusion, the combination of hs-cTnT and BNP is useful in detecting myocardial fibrosis in patients with HC. The findings of this study indicate that hs-cTnT is a direct marker of ongoing myocardial fibrosis and that BNP is a marker of left ventricular overload partially associated with myocardial fibrosis.
Cardiac magnetic resonance imaging has been established for the morphologic and functional assessment of hypertrophic cardiomyopathy (HC). Late gadolinium enhancement cardiac magnetic resonance imaging is well known as the most reliable noninvasive imaging method for the detection of myocardial fibrosis. More recently, myocardial fibrosis as assessed by late gadolinium enhancement has been reported to be associated with adverse cardiovascular events in patients with HC. Blood-based biomarkers, such as cardiac troponin T (cTnT) in myocardial infarction and brain natriuretic peptide (BNP) in heart failure, have played important roles in the cardiovascular field for diagnosis, risk stratification, and treatment response. Biomarkers are expected to enhance daily clinical practice because of their simplicity and high reproducibility, but few data are available regarding the utility of biomarkers for the detection of myocardial fibrosis in patients with HC. The objective of the present study was to examine the relations of biomarkers with myocardial fibrosis as assessed by late gadolinium enhancement cardiac magnetic resonance imaging in patients with HC.
Methods
The present study consisted of consecutive patients with HC who were referred to our institute for gadolinium-enhanced myocardial resonance imaging from March 2010 to March 2013. The diagnosis of HC was based on the conventional echocardiographic demonstration of left ventricular end-diastolic thickness ≥15 mm and left ventricular end-diastolic diameter ≤55 mm in the absence of any cardiac or systemic disorder that could cause hypertrophy, such as severe hypertension or aortic stenosis. Furthermore, we excluded patients with HC with left ventricular outflow obstruction or systolic dysfunction because of the possible effect of hemodynamic overload on biomarkers independently of the presence or absence of myocardial fibrosis. Left ventricular outflow obstruction was considered present when the peak flow velocity was >2.5 m/s by the Doppler method under rest conditions or the Valsalva maneuver; systolic dysfunction was defined as a left ventricular ejection fraction <50% as measured using the modified Simpson’s method with echocardiographic equipment (Sonos 5500, Philips Medical Systems, Best, The Netherlands; or Vivid 9, GE Healthcare, Milwaukee, Wisconsin).
A total of 60 patients with HC met our inclusion criteria. Of these, 2 patients were excluded because of histories of myocardial infarction. We excluded 3 patients in whom magnetic resonance imaging was discontinued because of possible side effects of gadolinium, difficulty in holding breath, or claustrophobia. Because of missing biomarker data, a further 2 patients were excluded. Ultimately, the present study consisted of 53 patients with HC (15 women, mean age 62 years). All patients were in sinus rhythm and were clinically stable; none had clinically significant valvular heart disease or renal dysfunction, defined as an estimated glomerular filtration rate <60 ml/min/1.73 m 2 . There were no patients treated with permanent mechanical device implantation, septal myectomy, alcohol septal ablation, or heart transplantation. Coronary heart disease was ruled out in all patients on the basis of conventional coronary angiography, multidetector computed tomography, or exercise myocardial scintigraphy. Informed consent for this study was obtained from all patients with HC.
Cardiac magnetic resonance imaging was performed using a 1.5-T imaging system (Signa HDx; GE Medical Systems, Waukesha, Wisconsin). Steady-state free procession cine images were obtained in a long-axis view and in short-axis views at the basal, mid, and apical left ventricular levels (slice thickness 7 mm, slice gap 5 mm, field of view 360 × 360 mm). Approximately 10 minutes after an intravenous injection of 0.1 mmol/kg gadopentetate dimeglumine (Magnevist; Schering AG, Berlin, Germany), late gadolinium-enhanced images were obtained in a long-axis view and in short-axis views at the basal, mid, and apical left ventricular levels under serial breath holds using a 2-dimensional spoiled and segmented inversion recovery and gradient-echo sequence. Inversion time was selected using a standardized algorithm on the basis of myocardial and blood T1 values, heart rate, time of imaging from contrast injection, and dose of contrast. The following scan parameters were used: slice thickness 7 mm, slice gap 5 mm, field of view 270 × 270 mm, flip angle 20 ° , spatial resolution 1.6 × 2.3 mm, and number of averages 2.
The endocardial and epicardial borders and maximum wall thickness of the left ventricle were manually measured at the end-diastolic phase of cine short-axis views using commercially available software (Plissimo Ex version 1.0.4.5; Panasonic Medical Solutions Co., Ltd., Osaka, Japan). Left ventricular mass was calculated from the total volume multiplied by 1.05 g/ml and indexed to height in centimeters. Late gadolinium enhancement was defined as 2 SDs higher than the mean signal intensity of apparently normal myocardium. As shown in Figure 1 , the extent of late gadolinium enhancement was assessed by the sum of enhanced areas on all short-axis images (late gadolinium enhancement volume, expressed as grams per centimeter) and by the proportion of left ventricular mass (percentage late gadolinium enhancement). The location of late gadolinium enhancement was determined on the basis of a 17-segment model of the left ventricle, including 1 apical segment on a vertical long-axis view and 16 segments on 3 short-axis views. The areas of ventricular septum–free wall junctions were defined as located between the 2 radii, each making an angle of 30° with the junction line on the opposite side.
Serum levels of myoglobin, cardiac myosin light chain I, high-sensitivity cTnT (hs-cTnT), creatine kinase and its MB isoenzyme, and high-sensitivity C-reactive protein and plasma levels of atrial natriuretic peptide and BNP were measured before magnetic resonance imaging using commercially available kits : Myoglobin Daiichi III (TFB Inc., Tokyo, Japan) for myoglobin, Myosin LI kit Yamasa EIA II (Yamasa Co., Chiba, Japan) for cardiac myosin light chain I, Elecsys Troponin T hs (Roche Diagnostics GmbH, Mannheim, Germany) for hs-cTnT, CicaLiquid CK (Kanto Chemical Co., Inc., Tokyo, Japan) for creatine kinase, CicaLiquid CK-MB (Kanto Chemical Co., Inc., Tokyo, Japan) for creatine kinase-MB isoenzyme, CRP-Latex X2 Seiken (Denka Seiken Co., Ltd., Tokyo, Japan) for high-sensitivity C-reactive protein, MI02 Shionogi ANP (Shionogi & Co., Ltd., Osaka, Japan) for atrial natriuretic peptide, and MI02 Shionogi BNP (Shionogi & Co., Ltd.) for BNP. The analytic range and normal reference range, respectively, of the assays were as follows: 10 to 3,000 ng/ml and ≤60 ng/ml for myoglobin, 1.1 to 250.0 ng/ml and ≤2.5 ng/ml for cardiac myosin light chain I, 0.003 to 99,900,000.000 ng/ml and <0.014 ng/ml for hs-cTnT, 0 to 3,000 IU/L and 62 to 287 IU/L in men and 45 to 163 IU/L in women for creatine kinase, 3 to 2,500 IU/L and <25 IU/L in absolute value and ≤6.0% in relative index for creatine kinase-MB isoenzyme, 0.01 to 32.00 mg/dl and <0.30 mg/dl for high-sensitivity C-reactive protein, 5.1 to 1,290.0 pg/ml and <43.0 pg/ml for atrial natriuretic peptide, and 4.0 to 2,000.0 pg/ml and <18.4 pg/ml for BNP.
Categorical variables were compared using chi-square or Fisher’s exact tests as appropriate. Continuous variables were compared using Student’s t tests and are expressed as mean ± SD. Late gadolinium enhancement volume, percentage late gadolinium enhancement, and levels of biomarkers were compared using Mann-Whitney U tests or Wilcoxon’s signed-rank tests because of possibly skewed distributions and are expressed as mean ± SE. Spearman’s rank correlation coefficient was used to examine correlations among hs-cTnT levels, BNP levels, late gadolinium enhancement volume, and percentage late gadolinium enhancement. Receiver-operating characteristic curve analysis was applied to biomarkers tightly associated with late gadolinium enhancement, defined as p <0.01, to determine the optimal cut-off point. The reproducibility of hs-cTnT and BNP measurements was evaluated using mean absolute differences. Two-sided p values <0.05 were considered statistically significant. All calculations were performed using SPSS version 11.0 (SPSS, Inc., Chicago, Illinois) or StatView version 5.0 (SAS Institute Inc., Cary, North Carolina).
Results
Late gadolinium enhancement was detected in 23 of 53 patients (43%). The location of late gadolinium enhancement was the anterior ventricular septum–free wall junction in 12 patients (23%), the ventricular septum in 11 (21%), the apical area in 9 (17%), the posterior ventricular septum–free wall junction in 4 (8%), the anterior wall in 4 (8%), the posterior wall in 2 (4%), and the lateral wall in 1 (2%). Late gadolinium enhancement was associated with younger age, a lower left ventricular ejection fraction on echocardiography, and higher maximum wall thickness and higher left ventricular mass on magnetic resonance imaging ( Table 1 ).
| Variable | Late Gadolinium Enhancement | p Value | |
|---|---|---|---|
| Negative (n = 30) | Positive (n = 23) | ||
| Age (yrs) | 66 ± 10 | 58 ± 15 | 0.04 |
| Women | 7 (23%) | 8 (35%) | 0.36 |
| New York Heart Association functional class | 0.18 | ||
| I | 21 (70%) | 11 (48%) | |
| II | 9 (30%) | 11 (48%) | |
| III | 0 | 1 (4%) | |
| Family history of HC | 11 (37%) | 13 (57%) | 0.15 |
| Family history of sudden death | 5 (17%) | 7 (30%) | 0.20 |
| Echocardiography | |||
| Left ventricular end-diastolic diameter (mm) | 44 ± 6 | 45 ± 6 | 0.43 |
| Left ventricular ejection fraction (%) | 65 ± 7 | 60 ± 9 | 0.04 |
| Magnetic resonance imaging | |||
| Location of hypertrophy ∗ | |||
| Septum | 22 (73%) | 20 (87%) | 0.23 |
| Anterior wall | 7 (23%) | 8 (35%) | 0.36 |
| Apical area | 8 (27%) | 7 (30%) | 0.76 |
| Lateral wall | 8 (27%) | 6 (26%) | 0.96 |
| Posterior wall | 1 (3%) | 0 | 0.57 |
| Maximal wall thickness (mm) | 20 ± 5 | 24 ± 5 | <0.01 |
| Left ventricular mass (g/cm) | 61 ± 16 | 74 ± 17 | <0.01 |
| Late gadolinium enhancement volume (g/cm) † | 0 | 6.1 ± 1.2 | — |
| Percentage late gadolinium enhancement (%) † | 0 | 7.9 ± 1.3 | — |
∗ Some patients had ≥2 hypertrophic sites.
The mean levels of biomarkers in all patients were 42 ng/ml (range 13 to 99) for myoglobin, 1.9 ng/ml (range 1.0 to 8.8) for cardiac myosin light chain I, 0.012 ng/ml (range 0.003 to 0.073) for hs-cTnT, 106 IU/L (range 32 to 280) for creatine kinase, 10 IU/L (range 5 to 28) or 11% (range 4% to 28%) for creatine kinase-MB isoenzyme, 0.08 mg/dl (range 0.01 to 0.50) for high-sensitivity C-reactive protein, 67 pg/ml (range 8 to 195) for atrial natriuretic peptide, and 103 pg/ml (range 4 to 512) for BNP. Late gadolinium enhancement was associated with higher levels of hs-cTnT, BNP, and atrial natriuretic peptide ( Table 2 ).
| Variable | Late Gadolinium Enhancement | p Value | |
|---|---|---|---|
| Negative (n = 30) | Positive (n = 23) | ||
| Myoglobin (ng/ml) | 40 ± 3 | 45 ± 4 | 0.23 |
| Cardiac myosin light chain I (ng/ml) | 1.8 ± 0.3 | 2.1 ± 0.3 | 0.30 |
| Hs-cTnT (ng/ml) | 0.007 ± 0.001 | 0.020 ± 0.004 | <0.01 |
| Creatine kinase (IU/L) | 101 ± 9 | 113 ± 10 | 0.23 |
| Creatine kinase-MB isoenzyme | |||
| Absolute value (IU/L) | 9 ± 1 | 11 ± 1 | 0.27 |
| Relative index (%) | 11 ± 1 | 10 ± 1 | 0.57 |
| High-sensitivity C-reactive protein (mg/dl) | 0.09 ± 0.01 | 0.08 ± 0.02 | 0.09 |
| Atrial natriuretic peptide (pg/ml) | 53 ± 8 | 84 ± 12 | 0.02 |
| BNP (pg/ml) | 55 ± 12 | 166 ± 33 | <0.01 |
Receiver-operating characteristic curve analysis for the detection of late gadolinium enhancement showed an optimal cutoff of hs-cTnT of ≥0.007 ng/ml and of BNP of ≥70 pg/ml ( Figure 2 ). The combination of hs-cTnT ≥0.007 ng/ml and BNP ≥70 pg/ml had high specificity of 90%, whereas the combination of either hs-cTnT ≥0.007 ng/ml or BNP ≥70 pg/ml had excellent sensitivity of 96% ( Table 3 ).
