Otavio R. Coelho-Filho

Myocardial Fibrosis as an Early Manifestation of Hypertrophic Cardiomyopathy

BACKGROUND Myocardial fibrosis is a hallmark of hypertrophic cardiomyopathy and a proposed substrate for arrhythmias and heart failure. In animal models, profibrotic genetic pathways are activated early, before hypertrophic remodeling. Data showing early profibrotic responses to sarcomere-gene mutations in patients with hypertrophic cardiomyopathy are lacking. METHODS We used echocardiography, cardiac magnetic resonance imaging (MRI), and serum biomarkers of collagen metabolism, hemodynamic stress, and myocardial injury to evaluate subjects with hypertrophic cardiomyopathy and a confirmed genotype. RESULTS The study involved 38 subjects with pathogenic sarcomere mutations and overt hypertrophic cardiomyopathy, 39 subjects with mutations but no left ventricular hypertrophy, and 30 controls who did not have mutations. Levels of serum C-terminal propeptide of type I procollagen (PICP) were significantly higher in mutation carriers without left ventricular hypertrophy and in subjects with overt hypertrophic cardiomyopathy than in controls (31% and 69% higher, respectively; P<0.001). The ratio of PICP to C-terminal telopeptide of type I collagen was increased only in subjects with overt hypertrophic cardiomyopathy, suggesting that collagen synthesis exceeds degradation. Cardiac MRI studies showed late gadolinium enhancement, indicating myocardial fibrosis, in 71% of subjects with overt hypertrophic cardiomyopathy but in none of the mutation carriers without left ventricular hypertrophy. CONCLUSIONS Elevated levels of serum PICP indicated increased myocardial collagen synthesis in sarcomere-mutation carriers without overt disease. This profibrotic state preceded the development of left ventricular hypertrophy or fibrosis visible on MRI. (Funded by the National Institutes of Health and others.)

CMR Quantification of Myocardial Scar Provides Additive Prognostic Information in Nonischemic Cardiomyopathy

OBJECTIVES This study sought to determine whether the extent of late gadolinium enhancement (LGE) can provide additive prognostic information in patients with a nonischemic dilated cardiomyopathy (NIDC) with an indication for implantable cardioverter-defibrillator (ICD) therapy for the primary prevention of sudden cardiac death (SCD). BACKGROUND Data suggest that the presence of LGE is a strong discriminator of events in patients with NIDC. Limited data exist on the role of LGE quantification. METHODS The extent of LGE and clinical follow-up were assessed in 162 patients with NIDC prior to ICD insertion for primary prevention of SCD. LGE extent was quantified using both the standard deviation-based (2-SD) method and the full-width half-maximum (FWHM) method. RESULTS We studied 162 patients with NIDC (65% male; mean age: 55 years; left ventricular ejection fraction [LVEF]: 26 ± 8%) and followed up for major adverse cardiac events (MACE), including cardiovascular death and appropriate ICD therapy, for a mean of 29 ± 18 months. Annual MACE rates were substantially higher in patients with LGE (24%) than in those without LGE (2%). By univariate association, the presence and the extent of LGE demonstrated the strongest associations with MACE (LGE presence, hazard ratio [HR]: 14.5 [95% confidence interval (CI): 6.1 to 32.6; p < 0.001]; LGE extent, HR: 1.15 per 1% increase in volume of LGE [95% CI: 1.12 to 1.18; p < 0.0001]). Multivariate analyses showed that LGE extent was the strongest predictor in the best overall model for MACE, and a 7-fold hazard was observed per 10% LGE extent after adjustments for patient age, sex, and LVEF (adjusted HR: 7.61; p < 0.0001). LGE quantitation by 2-SD and FWHM both demonstrated robust prognostic association, with the highest MACE rate observed in patients with LGE involving >6.1% of LV myocardium. CONCLUSIONS LGE extent may provide further risk stratification in patients with NIDC with a current indication for ICD implantation for the primary prevention of SCD. Strategic guidance on ICD therapy by cardiac magnetic resonance in patients with NIDC warrants further study.

Quantification of extracellular matrix expansion by CMR in infiltrative heart disease.

OBJECTIVES The aim of this study was to perform direct quantification of myocardial extracellular volume fraction (ECF) with T1-weighted cardiac magnetic resonance (CMR) imaging in patients suspected to have infiltrative heart disease. BACKGROUND Infiltrative heart disease refers to accumulation of abnormal substances within the myocardium. Qualitative assessment of late gadolinium enhancement (LGE) remains the most commonly used method for CMR evaluation of patients suspected with myocardial infiltration. This technique is widely available and can be performed in a reproducible and standardized manner. However, the degree of extracellular matrix expansion due to myocardial infiltration in the intercellular space has, to date, not been amenable to noninvasive quantification with LGE. METHODS We performed 3-T CMR in 38 patients (mean age 68 ± 15 years) who were referred for assessment of infiltrative heart disease and also in 9 healthy volunteers as control subjects. The T1 quantification by Look-Locker gradient-echo before and after contrast determined segmental myocardial partition coefficients. The ECF was obtained by referencing the tissue partition coefficient for gadolinium to the plasma volume fraction in blood, derived from serum hematocrit. Cine CMR and LGE imaging in matching locations were also performed. RESULTS Seventeen patients (45%) had cardiac amyloidosis (CA) (biopsy-confirmed or clinically highly probable), 20 (53%) had a non-amyloid cardiomyopathy, and 1 had lysosomal storage disease. Median global ECF was substantially higher in CA patients (0.49) compared with non-amyloid cardiomyopathy patients (0.33, p < 0.0001) and volunteers (0.24, p = 0.0001). The ECF strongly correlated with visually assessed segmental LGE (r = 0.80, p < 0.0001) and LV mass index (r = 0.69, p < 0.0001), reflecting severity of myocardial infiltration. In patients with CA, ECF was highest in segments with LGE, although it remained elevated in segments without qualitative LGE. CONCLUSIONS The CMR ECF quantification identified substantial expansion of the interstitial space in patients with CA compared with volunteers. Further studies using this technique for diagnosis and assessment of the severity of myocardial infiltration are warranted.

Left Ventricular Mass in Patients With a Cardiomyopathy After Treatment With Anthracyclines

We aimed to describe the cardiac magnetic resonance (CMR) findings and determine the prognostic variables in patients with a cardiomyopathy after treatment with anthracyclines. CMR imaging was performed in 91 patients (58% men, mean age 43 ± 18 years, and mean anthracycline dose of 276 ± 82 mg/m(2)) with a reduced ejection fraction after anthracycline-based chemotherapy. Major adverse cardiovascular events were defined as cardiovascular death, appropriate implantable cardioverter-defibrillator therapy, and admission for decompensated heart failure. Patients presented a median of 88 months (interquartile range 37 to 138) after chemotherapy and were followed for 27 months (interquartile range 22 to 38). Late gadolinium enhancement was an uncommon finding (5 patients, 6%) despite a reduced ejection fraction (36 ± 8%). An inverse association was found between the anthracycline dose and the indexed left ventricular (LV) mass by CMR (r = -0.67, p <0.001). A total of 52 adverse cardiac events occurred (event rate of 22%/year). When the patients were grouped according to the presence or absence of a major adverse cardiovascular event, the indexed LV mass and glomerular filtration rate were lower and the anthracycline dose was greater among the patients who experienced an adverse event. In a multivariate model, the indexed LV mass demonstrated the strongest association with major adverse cardiovascular events (hazard ratio 0.89, chi-square 26, p <0.001). In conclusion, myocardial scar by late gadolinium enhancement-CMR is infrequent in patients with anthracycline-cardiomyopathy despite a reduced ejection fraction, the event rate in patients with established anthracycline-cardiotoxicity is high, and indexed LV mass by CMR imaging is a predictor of adverse cardiovascular events.

Stress myocardial perfusion imaging by CMR provides strong prognostic value to cardiac events regardless of patient's sex.

OBJECTIVES The major aim of this study is to test the hypothesis that stress cardiac magnetic resonance (CMR) imaging can provide robust prognostic value in women presenting with suspected ischemia, to the same extent as in men. BACKGROUND Compelling evidence indicates that women with coronary artery disease (CAD) experience worse outcomes than men owing to a lack of early diagnosis and management. Numerous clinical studies have shown that stress CMR detects evidence of myocardial ischemia and infarction at high accuracy. Compared to nuclear scintigraphy, CMR is free of ionizing radiation, has high spatial resolution for imaging small hearts, and overcomes breast attenuation artifacts, which are substantial advantages when imaging women for CAD. METHODS We performed stress CMR in 405 patients (168 women, mean age 58 ± 14 years) referred for ischemia assessment. CMR techniques included cine cardiac function, perfusion imaging during vasodilating stress, and late gadolinium enhancement imaging. All patients were followed for major adverse cardiac events (MACE). RESULTS At a median follow-up of 30 months, MACE occurred in 36 patients (9%) including 21 cardiac deaths and 15 acute myocardial infarctions. In women, CMR evidence of ischemia (ISCHEMIA) demonstrated strong association with MACE (unadjusted hazard ratio: 49.9, p < 0.0001). While women with ISCHEMIA(+) had an annual MACE rate of 15%, women with ISCHEMIA(-) had very low annual MACE rate (0.3%), which was not statistically different from the low annual MACE rate in men with ISCHEMIA(-) (1.1%). CMR myocardial ischemia score was the strongest multivariable predictor of MACE in this cohort, for both women and men, indicating robust cardiac prognostication regardless of sex. CONCLUSIONS In addition to avoiding exposure to ionizing radiation, stress CMR myocardial perfusion imaging is an effective and robust risk-stratifying tool for patients of either sex presenting with possible ischemia.

Role of Transcytolemmal Water-Exchange in Magnetic Resonance Measurements of Diffuse Myocardial Fibrosis in Hypertensive Heart Disease

Background—The myocardial extracellular volume fraction (MECVF) has been used to detect diffuse fibrosis. Estimation of MECVF relies on quantification of the T1 relaxation time after contrast enhancement, which can be sensitive to equilibrium transcytolemmal water-exchange. We hypothesized that MECVF, quantified with a parsimonious 2-space water-exchange model, correlates positively with the connective tissue volume fraction in a rodent model of hypertensive heart disease, whereas the widely used analysis based on assuming fast transcytolemmal water-exchange could result in a significant underestimate of MECVF. Methods and Results—N&ohgr;–nitro-L-arginine-methyl-ester (L-NAME) or placebo was administered to 22 and 15 wild-type mice, respectively. MECVF was measured at baseline and 7-week follow-up by pre- and postcontrast T1 cardiac magnetic resonance imaging at 4.7 T, using a 2-space water-exchange model. Connective tissue volume fraction was quantified, using Masson trichrome stain. L-NAME induced hypertrophy (weight-indexed left-ventricular mass 2.2±0.3 versus 4.1±0.4 &mgr;g/g, P<0.001), and increased connective tissue volume fraction (8.6%±1.5 versus 2.58%±0.6, P<0.001), were compared with controls. MECVF was higher in L-NAME-treated animals (0.43±0.09 versus 0.26±0.03, P<0.001), and correlated with connective tissue volume fraction and weight-indexed left-ventricular mass (r=0.842 and r=0.737, respectively, both P<0.0001). Neglecting transcytolemmal water-exchange caused a significant underestimate of MECVF changes. Ten patients with history of hypertension had significantly higher MECVF (0.446±0.063) compared with healthy controls (0.307±0.030, P<0.001). Conclusions—Cardiac magnetic resonance allowed detection of myocardial extracellular matrix expansion in a mouse model and in patients with a history of hypertension. Accounting for the effects of transcytolemmal water-exchange can result in a substantial difference of MECVF, compared with assuming fast transcytolemmal water-exchange.

Quantification of Cardiomyocyte Hypertrophy by Cardiac Magnetic Resonance Implications for Early Cardiac Remodeling

Background— Cardiomyocyte hypertrophy is a critical precursor to the development of heart failure. Methods to phenotype cellular hypertrophy noninvasively are limited. The goal was to validate a cardiac magnetic resonance–based approach for the combined assessment of extracellular matrix expansion and cardiomyocyte hypertrophy. Methods and Results— Two murine models of hypertension (n=18, with n=15 controls) induced by L-NG-nitroarginine methyl ester (L-NAME) and pressure overload (n=11) from transaortic constriction (TAC) were imaged by cardiac magnetic resonance at baseline and 7 weeks after L-NAME treatment or up to 7 weeks after TAC. T1 relaxation times were measured before and after gadolinium contrast. The intracellular lifetime of water (&tgr;ic), a cell size–dependent parameter, and extracellular volume fraction, a marker of interstitial fibrosis, were determined with a model for transcytolemmal water exchange. Cardiomyocyte diameter and length were measured on FITC–wheat germ agglutinin–stained sections. The &tgr;ic correlated strongly with histological cardiomyocyte volume-to-surface ratio (r=0.78, P<0.001) and cell volume (r=0.75, P<0.001). Histological cardiomyocyte diameters and cell volumes were higher in mice treated with L-NAME compared with controls (P<0.001). In the TAC model, cardiac magnetic resonance and histology showed cell hypertrophy at 2 weeks after TAC without significant fibrosis at this early time point. Mice exposed to TAC demonstrated a significant, longitudinal, and parallel increase in histological cell volume, volume-to-surface ratio, and &tgr;ic between 2 and 7 weeks after TAC. Conclusion— The &tgr;ic measured by contrast-enhanced cardiac magnetic resonance provides a noninvasive measure of cardiomyocyte hypertrophy. Extracellular volume fraction and &tgr;ic can track myocardial tissue remodeling from pressure overload.

MR myocardial perfusion imaging

Contrast material-enhanced myocardial perfusion imaging by using cardiac magnetic resonance (MR) imaging has, during the past decade, evolved into an accurate technique for diagnosing coronary artery disease, with excellent prognostic value. Advantages such as high spatial resolution; absence of ionizing radiation; and the ease of routine integration with an assessment of viability, wall motion, and cardiac anatomy are readily recognized. The need for training and technical expertise and the regulatory hurdles, which might prevent vendors from marketing cardiac MR perfusion imaging, may have hampered its progress. The current review considers both the technical developments and the clinical experience with cardiac MR perfusion imaging, which hopefully demonstrates that it has long passed the stage of a research technique. In fact, cardiac MR perfusion imaging is moving beyond traditional indications such as diagnosis of coronary disease to novel applications such as in congenital heart disease, where the imperatives of avoidance of ionizing radiation and achievement of high spatial resolution are of high priority. More wide use of cardiac MR perfusion imaging, and novel applications thereof, are aided by the progress in parallel imaging, high-field-strength cardiac MR imaging, and other technical advances discussed in this review.

The Incidence, Pattern, and Prognostic value of Left Ventricular Myocardial Scar by Late Gadolinium Enhancement in Patients with Atrial Fibrillation

OBJECTIVES This study sought to identify the frequency, pattern, and prognostic significance of left ventricular (LV) late gadolinium enhancement (LGE) in patients with atrial fibrillation (AF). BACKGROUND There are limited data on the presence, pattern, and prognostic significance of LV myocardial fibrosis in patients with AF. LGE during cardiac magnetic resonance imaging is a marker for myocardial fibrosis. METHODS A group of 664 consecutive patients without known prior myocardial infarction who were referred for radiofrequency ablation of AF were studied. Cardiac magnetic resonance imaging was requested to assess pulmonary venous anatomy. RESULTS Overall, 73% were men, with a mean age of 56 years and a mean LV ejection fraction of 56 ± 10%. LV LGE was found in 88 patients (13%). The endpoint was all-cause mortality, and in this cohort, 68 deaths were observed over a median follow-up period of 42 months. On univariate analysis, age (hazard ratio [HR]: 1.05; 95% confidence interval [CI]: 1.03 to 1.08; chi-square likelihood ratio [LRχ(2)]: 15.2; p = 0.0001), diabetes (HR: 2.39; 95% CI: 1.41 to 4.09; LRχ(2): 10.3; p = 0.001), a history of heart failure (HR: 1.78; 95% CI: 1.09 to 2.91; LRχ(2): 5.37; p = 0.02), left atrial dimension (HR: 1.04; 95% CI: 1.01 to 1.08; LRχ(2): 6.47; p = 0.01), presence of LGE (HR: 5.08; 95% CI: 3.08 to 8.36; LRχ(2): 28.8; p < 0.0001), and LGE extent (HR: 1.15; 95% CI: 1.10 to 1.21; LRχ(2): 35.6; p < 0.0001) provided the strongest associations with mortality. The mortality rate was 8.1% per patient-year in patients with LGE compared with 2.3% patients without LGE. In the best overall multivariate model for mortality, age and the extent of LGE were independent predictors of mortality. Indeed, each 1% increase in the extent of LGE was associated with a 15% increased risk for death. CONCLUSIONS In patients with AF, LV LGE is a frequent finding and is a powerful predictor of mortality.

Cardiac Magnetic Resonance Assessment of Interstitial Myocardial Fibrosis and Cardiomyocyte Hypertrophy in Hypertensive Mice Treated With Spironolactone

Background Nearly 50% of patients with heart failure (HF) have preserved LV ejection fraction, with interstitial fibrosis and cardiomyocyte hypertrophy as early manifestations of pressure overload. However, methods to assess both tissue characteristics dynamically and noninvasively with therapy are lacking. We measured the effects of mineralocorticoid receptor blockade on tissue phenotypes in LV pressure overload using cardiac magnetic resonance (CMR). Methods and Results Mice were randomized to l‐nitro‐ω‐methyl ester (l‐NAME, 3 mg/mL in water; n=22), or l‐NAME with spironolactone (50 mg/kg/day in subcutaneous pellets; n=21). Myocardial extracellular volume (ECV; marker of diffuse interstitial fibrosis) and the intracellular lifetime of water (τic; marker of cardiomyocyte hypertrophy) were determined by CMR T1 imaging at baseline and after 7 weeks of therapy alongside histological assessments. Administration of l‐NAME induced hypertensive heart disease in mice, with increases in mean arterial pressure, LV mass, ECV, and τic compared with placebo‐treated controls, while LV ejection fraction was preserved (>50%). In comparison, animals receiving both spironolactone and l‐NAME (“l‐NAME+S”) showed less concentric remodeling, and a lower myocardial ECV and τic, indicating decreased interstitial fibrosis and cardiomyocyte hypertrophy (ECV: 0.43±0.09 for l‐NAME versus 0.25±0.03 for l‐NAME+S, P<0.001; τic: 0.42±0.11 for l‐NAME groups versus 0.12±0.05 for l‐NAME+S group). Mice treated with a combination of l‐NAME and spironolactone were similar to placebo‐treated controls at 7 weeks. Conclusions Spironolactone attenuates interstitial fibrosis and cardiomyocyte hypertrophy in hypertensive heart disease. CMR can phenotype myocardial tissue remodeling in pressure‐overload, furthering our understanding of HF progression.