Prognostic significance of myocardial fibrosis in hypertrophic cardiomyopathy

Quantifying late gadolinium enhancement on CMR provides additional prognostic information in early risk-stratification of nonischemic cardiomyopathy: a cohort study

Background

Suspected nonischemic cardiomyopathy (NICM) is a common clinical setting with highly variable prognosis. Early noninvasive risk-stratification is important for justification of invasive examinations, specific treatment and patient surveillance. We studied the additional prognostic value of late gadolinium enhancement (LGE) and segmental wall motion abnormality (SWMA) extent on cardiovascular magnetic resonance (CMR) compared to traditional risk factors in suspected NICM.

Methods

In this observational cohort study, we enrolled 86 consecutive patients referred for CMR due to suspected NICM. Patients with ischemic cardiomyopathy were excluded. CMR images were analysed for left ventricular LGE and SWMA extents and patients were followed-up for major adverse cardiac events (MACE), including cardiovascular death, aborted sudden death and cardiac transplantation.

Results

Of 86 patients (median age: 53 years, 45% female), mainly presenting with ventricular arrhythmias (40%) and congestive heart failure (44%), 76% were finally diagnosed with NICM, 17% with left ventricle hypertrophy and 7% with idiopathic arrhythmia. On CMR, 61 patients (71%) had LGE and 56 (65%) SWMA. During median follow-up of 835 days, 15 patients (17%) reached MACE. In univariant analysis, LGE volume (hazard ratio [HR] 1.028 per 1% increase in LGE, p < 0.001), left ventricular ejection fraction (LVEF) (HR 0.959, p = 0.009) and SWMA score (HR 1.067, p = 0.012) had strongest associations with MACE. In multivariate analysis, the best overall model for event prediction included LGE volume (HR 1.027, p = 0.003), sustained ventricular tachycardia (HR 4.7, p = 0.011) and LVEF (HR 0.962, p = 0.034). Among patients with LGE, there was an event rate of 26% (14 of 61) versus 4% (1 of 25) in patients without LGE (p = 0.041, Log-rank). The highest event rate was observed in patients with LGE volume of ≥17%. Patients without SWMA did not experience MACE (p = 0.002, Log-rank), giving additional information in the subgroup of patients with preserved LVEF (≥50%).

Conclusions

In suspected NICM, presenting with ventricular arrhythmias or heart failure, LGE extent gives additional prognostic information compared to traditional risk factors, while the absence of SWMA may give prognostic information beyond normal LVEF. Even though the final diagnosis is uncertain in NICM, extensive amount of LGE should be considered as a sign of poor prognosis.

Coronary microvascular ischemia in hypertrophic cardiomyopathy - a pixel-wise quantitative cardiovascular magnetic resonance perfusion study

BACKGROUND

Microvascular dysfunction in HCM has been associated with adverse clinical outcomes. Advances in quantitative cardiovascular magnetic resonance (CMR) perfusion imaging now allow myocardial blood flow to be quantified at the pixel level. We applied these techniques to investigate the spectrum of microvascular dysfunction in hypertrophic cardiomyopathy (HCM) and to explore its relationship with fibrosis and wall thickness.

METHODS

CMR perfusion imaging was undertaken during adenosine-induced hyperemia and again at rest in 35 patients together with late gadolinium enhancement (LGE) imaging. Myocardial blood flow (MBF) was quantified on a pixel-by-pixel basis from CMR perfusion images using a Fermi-constrained deconvolution algorithm. Regions-of-interest (ROI) in hypoperfused and hyperemic myocardium were identified from the MBF pixel maps. The myocardium was also divided into 16 AHA segments.

RESULTS

Resting MBF was significantly higher in the endocardium than in the epicardium (mean ± SD: 1.25 ± 0.35 ml/g/min versus 1.20 ± 0.35 ml/g/min, P<0.001), a pattern that reversed with stress (2.00 ± 0.76 ml/g/min versus 2.36 ± 0.83 ml/g/min, P<0.001). ROI analysis revealed 11 (31%) patients with stress MBF lower than resting values (1.05 ± 0.39 ml/g/min versus 1.22 ± 0.36 ml/g/min, P=0.021). There was a significant negative association between hyperemic MBF and wall thickness (β=-0.047 ml/g/min per mm, 95% CI: -0.057 to -0.038, P<0.001) and a significantly lower probability of fibrosis in a segment with increasing hyperemic MBF (odds ratio per ml/g/min: 0.086, 95% CI: 0.078 to 0.095, P=0.003).

CONCLUSIONS

Pixel-wise quantitative CMR perfusion imaging identifies a subgroup of patients with HCM that have localised severe microvascular dysfunction which may give rise to myocardial ischemia.

Patterns of late gadolinium enhancement in Duchenne muscular dystrophy carriers

BACKGROUND

This study was designed to assess whether cardiovascular magnetic resonance imaging (CMR) in Duchenne muscular dystrophy carriers (DMDc) may index any cell milieu elements of LV dysfunction and whether this cardiac phenotype may be related to genotype. The null hypothesis was that myocardial fibrosis, assessed by late gadolinium enhancement (LGE), might be similarly accounted for in DMDc and gender and age-matched controls.

METHODS

Thirty DMDc patients had CMR and genotyping with 37 gender and age-matched controls. Systolic and diastolic LV function was assessed by 2D-echocardiography.

RESULTS

Absolute and percent LGE were higher in muscular symptomatic (sym) than asymptomatic (asy) DMDc (1.77 ± 0.27 vs 0.76 ± 0.17 ml; F = 19.6, p < 0.0001 and 1.86 ± 0.26% vs 0.68 ± 0.17%, F = 22.1, p < 0.0001, respectively). There was no correlation between LGE and age. LGE was seen most frequently in segments 5 and 6; segment 5 was involved in all asy-DMDc. Subepicardial LGE predominated, compared to the mid-myocardial one (11 out of 14 DMDc). LGE was absent in the subendocardium. No correlations were seen between genotyping (type of mutation, gene region and protein domain), confined to the exon's study, and cardiac phenotype.

CONCLUSIONS

A typical myocardial LGE-pattern location (LV segments 5 and 6) was a common finding in DMDc. LGE was more frequently subepicardial plus midmyocardial in sym-DMDc, with normal LV systolic and diastolic function. No genotype-phenothype correlation was found.

High sensitivity of late gadolinium enhancement for predicting microscopic myocardial scarring in biopsied specimens in hypertrophic cardiomyopathy

BACKGROUND

Myocardial scarring can be assessed by cardiac magnetic resonance imaging with late gadolinium enhancement and by endomyocardial biopsy. However, accuracy of late gadolinium enhancement for predicting microscopic myocardial scarring in biopsied specimens remains unknown in hypertrophic cardiomyopathy. We investigated whether late gadolinium enhancement in the whole heart reflects microscopic myocardial scarring in the small biopsied specimens in hypertrophic cardiomyopathy.

METHODS AND RESULTS

Twenty-one consecutive patients with hypertrophic cardiomyopathy who were examined both by cardiac magnetic resonance imaging and by endomyocardial biopsy were retrospectively studied. The right interventricular septum was the target site for endomyocardial biopsy in all patients. Late gadolinium enhancement in the ventricular septum had an excellent sensitivity (100%) with a low specificity (40%) for predicting microscopic myocardial scarring in biopsied specimens. The sensitivity of late gadolinium enhancement in the whole heart remained 100% with a specificity of 27% for predicting microscopic myocardial scarring in biopsied specimens. Quantitative assessments of fibrosis revealed that the extent of late gadolinium enhancement in the whole heart was the only independent variable related to the microscopic collagen fraction in biopsied specimens (β  =  0.59, 95% confident interval: 0.15 - 1.0, p  =  0.012).

CONCLUSIONS

Although there was a compromise in the specificity, the sensitivity of late gadolinium enhancement was excellent for prediction of microscopic myocardial scarring in hypertrophic cardiomyopathy. Moreover, the severity of late gadolinium enhancement was independently associated with the quantitative collagen fraction in biopsied specimens in hypertrophic cardiomyopathy. These findings indicate that late gadolinium enhancement can reflect both the presence and the extent of microscopic myocardial scarring in the small biopsied specimens in hypertrophic cardiomyopathy.

Role of late gadolinium enhancement cardiovascular magnetic resonance in the risk stratification of hypertrophic cardiomyopathy

OBJECTIVE

Myocardial fibrosis identified by late gadolinium enhancement (LGE) cardiovascular magnetic resonance (CMR) in patients with hypertrophic cardiomyopathy (HCM) is associated with adverse cardiovascular events, but its value as an independent risk factor for sudden cardiac death (SCD) is unknown. We investigated the role of LGE-CMR in the risk stratification of HCM.

METHODS

We conducted a prospective cohort study in a tertiary referral centre. Consecutive patients with HCM (n=711, median age 56.3 years, IQR 46.7-66.6; 70.0% male) underwent LGE-CMR and were followed for a median 3.5 years. The primary end point was SCD or aborted SCD.

RESULTS

Overall, 471 patients (66.2%) had myocardial fibrosis (median 5.9% of left ventricular mass, IQR: 2.2-13.3). Twenty-two (3.1%) reached the primary end point. The extent but not the presence of fibrosis was a significant univariable predictor of the primary end point (HR per 5% LGE: 1.24, 95% CI 1.06 to 1.45; p=0.007 and HR for LGE: 2.69, 95% CI 0.91 to 7.97; p=0.073, respectively). However, on multivariable analysis, only LV-EF remained statistically significant (HR: 0.92, 95% CI 0.89 to 0.95; p<0.001). For the secondary outcome of cardiovascular mortality/aborted SCD, the presence and the amount of fibrosis were significant predictors on univariable but not multivariable analysis after adjusting for LV-EF and non-sustained ventricular tachycardia.

CONCLUSIONS

The amount of myocardial fibrosis was a strong univariable predictor of SCD risk. However, this effect was not maintained after adjusting for LV-EF. Further work is required to elucidate the interrelationship between fibrosis and traditional predictors of outcome in HCM.

Phenotypic expression in hypertrophic cardiomyopathy and late gadolinium enhancement on cardiac magnetic resonance

INTRODUCTION AND AIM

The prognostic value of late gadolinium enhancement (LGE) for risk stratification of hypertrophic cardiomyopathy (HCM) patients is the subject of disagreement. We set out to examine the association between clinical and morphological variables, risk factors for sudden cardiac death and LGE in HCM patients.

METHODS

From a population of 78 patients with HCM, we studied 53 who underwent cardiac magnetic resonance. They were divided into two groups according to the presence or absence of LGE. Ventricular arrhythmias and morbidity and mortality during follow-up were analyzed.

RESULTS

Patients with LGE were younger at the time of diagnosis (p=0.046) and more often had a family history of sudden death (p=0.008) and known coronary artery disease (p=0.086). On echocardiography they had greater maximum wall thickness (p=0.007) and left atrial area (p=0.037) and volume (p=0.035), and more often presented a restrictive pattern of diastolic dysfunction (p=0.011) with a higher E/É ratio (p=0.003) and left ventricular systolic dysfunction (p=0.038). Cardiac magnetic resonance supported the association between LGE and previous echocardiographic findings: greater left atrial area (p=0.029) and maximum wall thickness (p<0.001) and lower left ventricular ejection fraction (p=0.056). Patients with LGE more often had an implantable cardioverter-defibrillator (ICD) (p=0.015). At follow-up, no differences were found in the frequency of ventricular arrhythmias, appropriate ICD therapies or mortality.

CONCLUSIONS

The presence of LGE emerges as a risk marker, associated with the classical predictors of sudden cardiac death in this population. However, larger studies are required to confirm its independent association with clinical events.

Ex-vivo Assessment of Coronary Artery Atherosclerosis by Magnetic Resonance Imaging: Correlation with Histopathology

Introduction: In recent years, high-resolution magnetic resonance imaging (MRI) has emerged as a very promising technique for studying atherosclerotic disease in humans. Aim: In the present study we sought to determine whether MRI allowed for the morphological characterization of the coronary vessel wall and atherosclerotic plaques using histopathological assessment as the reference standard. Methods: The study population consisted of 13 patients who died of acute myocardial infarction and underwent autopsy. The proximal portions of the coronary arteries were excised and were evaluated both by MRI and by histopathology. For each arterial segment, the following parameters were calculated through manual planimetry: 1. total vessel area (TVA); 2. luminal area (LA) and 3. plaque area (PA). Results: A total of 207 coronary artery cross-sections were found to be suitable for analysis by both MRI and histopathology and were included in the final analyses. Both methods demonstrated moderate to good agreement for the quantification of TVA (mean difference = 2.4±2.4 mm², 95‰ limits of agreement from -2.4 to +7.2 mm²; CCC = 0.69, 95‰ CI from 0.63 to 0.75), LA (mean difference = 0.0±1.7 mm², 95‰ limits of agreement from -3.3 to + 3.3 mm²; CCC = 0.84, 95‰ CI from 0.80 to 0.88) and PA (mean difference = 2.4±2.4 mm², 95‰ limits of agreement from -2.3 to + 7.1 mm²; CCC = 0.64, 95‰ CI from 0.58 to 0.71). Conclusion: In this ex vivo experimental model we demonstrated good agreement between coronary artery morphometrical measurements obtained by high-resolution MRI and by histopathology.

Extensive late gadolinium enhancement on cardiovascular magnetic resonance predicts adverse outcomes and lack of improvement in LV function after steroid therapy in cardiac sarcoidosis

BACKGROUND

Gadolinium-enhanced cardiovascular magnetic resonance is an emerging tool for the diagnosis of cardiac sarcoidosis (CS); however, the correlations between extent of late gadolinium enhancement (LGE) and efficacy of steroid therapy and adverse outcomes in patients with CS remain unclear.

OBJECTIVE

We aimed to clarify the prognostic impact of extent of LGE in patients with CS.

METHODS

Before the start of steroid therapy, 43 consecutive LGE-positive patients with CS were divided into two groups based on the extent of LGE by a median value: small-extent LGE (LGE mass <20% of LV mass; n=21) and large-extent LGE (LGE mass ≥20% of LV mass; n=22). We examined the correlations between extent of LGE and outcomes after steroid therapy.

RESULTS

Among the 6 patients who died from heart disorders, 11 patients who were hospitalised because of heart failure and 6 patients who suffered life-threatening arrhythmia during the follow-up period, large-extent LGE predicted higher incidences of cardiac mortality and hospitalisation for heart failure. Multivariate Cox regression analysis showed that large-extent LGE was independently associated with combined adverse outcomes including cardiac death, hospitalisation for heart failure, and life-threatening arrhythmias. In the small-extent LGE group, LV end-diastolic volume index significantly decreased and LVEF significantly increased after steroid therapy, whereas in the large-extent LGE group, neither LV volume nor LVEF changed substantially.

CONCLUSIONS

Large-extent LGE correlates with absence of LV functional improvement and high incidence of adverse outcomes in patients with CS after steroid therapy.

Role of cardiac MRI in the assessment of nonischemic cardiomyopathies

In this review, we will highlight the role of late gadolinium enhancement, along with other strengths available by cardiac MRI, in determining the underlying etiology of various nonischemic cardiomyopathies. Furthermore, we will also emphasize how late gadolinium enhancement may serve as a novel risk stratification tool to further impact patient care.

A comprehensive evaluation of myocardial fibrosis in hypertrophic cardiomyopathy with cardiac magnetic resonance imaging: linking genotype with fibrotic phenotype

AIMS

In hypertrophic cardiomyopathy (HCM), attempts to associate genotype with phenotype have largely been unsuccessful. More recently, cardiac magnetic resonance (CMR) imaging has enhanced myocardial fibrosis characterization, while next-generation sequencing (NGS) can identify pathogenic HCM mutations. We used CMR and NGS to explore the link between genotype and fibrotic phenotype in HCM.

METHODS AND RESULTS

One hundred and thirty-nine patients with HCM and 25 healthy controls underwent CMR to quantify regional myocardial fibrosis with late gadolinium enhancement (LGE) and diffuse myocardial fibrosis with post-contrast T1 mapping. Collagen content of myectomy specimens from nine HCM patients was determined. Fifty-six HCM patients underwent NGS for 65 cardiomyopathy genes, including 36 HCM-associated genes. Post-contrast myocardial T1 time correlated histologically with myocardial collagen content (r = -0.70, P = 0.03). Compared with controls, HCM patients had more LGE (4.6 ± 6.1 vs. 0%, P < 0.001) and lower post-contrast T1 time (483 ± 83 vs. 545 ± 49 ms, P < 0.001). LGE negatively correlated with left-ventricular (LV) ejection fraction and outflow tract obstruction, whereas lower post-contrast T1 time, suggestive of more diffuse myocardial fibrosis, was associated with LV diastolic impairment and dyspnoea. Patients with identifiable HCM mutations had more LGE (7.9 ± 8.6 vs. 3.1 ± 4.3%, P = 0.03), but higher post-contrast T1 time (498 ± 81 vs. 451 ± 70 ms, P = 0.03) than patients without.

CONCLUSION

In HCM, contrast-enhanced CMR with T1 mapping can non-invasively evaluate regional and diffuse patterns of myocardial fibrosis. These patterns of fibrosis occur independently of each other and exhibit distinct clinical associations. HCM patients with recognized genetic mutations have significantly more regional, but less diffuse myocardial fibrosis than those without.

Significance of left ventricular apical-basal muscle bundle identified by cardiovascular magnetic resonance imaging in patients with hypertrophic cardiomyopathy

AIMS

Cardiovascular magnetic resonance (CMR) has improved diagnostic and management strategies in hypertrophic cardiomyopathy (HCM) by expanding our appreciation for the diverse phenotypic expression. We sought to characterize the prevalence and clinical significance of a recently identified accessory left ventricular (LV) muscle bundle extending from the apex to the basal septum or anterior wall (i.e. apical-basal).

METHODS AND RESULTS

CMR was performed in 230 genotyped HCM patients (48 ± 15 years, 69% male), 30 genotype-positive/phenotype-negative (G+/P-) family members (32 ± 15 years, 30% male), and 126 controls. Left ventricular apical-basal muscle bundle was identified in 145 of 230 (63%) HCM patients, 18 of 30 (60%) G+/P- family members, and 12 of 126 (10%) controls (G+/P- vs. controls; P < 0.01). In HCM patients, the prevalence of an apical-basal muscle bundle was similar among those with disease-causing sarcomere mutations compared with patients without mutation (64 vs. 62%; P = 0.88). The presence of an LV apical-basal muscle bundle was not associated with LV outflow tract obstruction (P = 0.61). In follow-up, 33 patients underwent surgical myectomy of whom 22 (67%) were identified to have an accessory LV apical-basal muscle bundle, which was resected in all patients.

CONCLUSION

Apical-basal muscle bundles are a unique myocardial structure commonly present in HCM patients as well as in G+/P- family members and may represent an additional morphologic marker for HCM diagnosis in genotype-positive status.

The relationship between electrocardiographic changes and CMR features in asymptomatic or mildly symptomatic patients with hypertrophic cardiomyopathy

To investigate the relationship between electrocardiographic (ECG) abnormalities and left ventricular (LV) segmental hypertrophy and myocardial fibrosis assessed by cardiovascular magnetic resonance (CMR) in asymptomatic or mildly symptomatic patients with hypertrophic cardiomyopathy (HCM). 118 asymptomatic or mildly symptomatic patients with HCM were examined with late gadolinium enhancement (LGE) CMR, 12-lead ECG, and echocardiography. The distribution and magnitude of LV segmental hypertrophy and LGE were assessed and analyzed in relation to ECG abnormalities. Abnormal electrocardiograms were found in 113 of 118 (95%) patients. Negative T waves were associated with greater apical septal thickness (P = 0.009) and an increased ratio of LV septum to free wall thickness (P = 0.01). Giant negative T waves (GNT) were found in 19 patients (16%), and were associated with apical HCM (P < 0.001), greater apical thickness (P = 0.004), and increased ratio of LV apical to basal wall thickness (P < 0.001). However, no significant association was demonstrated between GNT and apical LGE (P = 0.71). Abnormal Q waves were associated with greater basal anteroseptal thickness (P = 0.001), maximal basal thickness (P = 0.004), and more segments with extensive LGE (>75% wall thickness involved) (P = 0.001). LV hypertrophy was related to greater LV mass (P = 0.002) and LV end diastolic volume (P = 0.002). In addition, a modest but significant correlation was observed between maximum LV wall thickness and the Romhilt-Estes score (r = 0.41, P < 0.001). GNT were associated with apical HCM and an increased ratio of LV apical to basal wall thickness. Abnormal Q waves were related to basal anteroseptal hypertrophy and segmental extensive LGE.

Clinical significance of late gadolinium enhancement in patients<20 years of age with hypertrophic cardiomyopathy

Late gadolinium enhancement (LGE) on cardiovascular magnetic resonance imaging is associated with adverse events in adults with hypertrophic cardiomyopathy (HC). However, limited data exist on the extent and clinical significance of LGE in the pediatric population. In 30 patients (aged 14.1±3.2 years) with clinically diagnosed HC who underwent cardiovascular magnetic resonance imaging from 2007 to 2012, segments with hypertrophy and LGE were identified by 2 experienced readers blinded to outcome. Radial, circumferential, and longitudinal strains were evaluated using feature tracking software. The composite outcome was defined as cardiac death, nonsustained ventricular tachycardia, ventricular fibrillation, or appropriate implantable cardioverter-defibrillator discharge. LGE was present in 17 of 30 patients (57%), all in a midmyocardial pattern, with median 3 segments per patient (interquartile range [IQR] 2 to 5). No LGE was detected in patients without phenotypic hypertrophy. Segments with LGE had decreased radial (basal segments 20.7% vs 70.9%, p=0.01), circumferential (basal segments -23.2% vs -29.3%, p=0.04), and longitudinal strains (basal segments -13.8% vs -20.9%, p=0.04). After median follow-up of 26.9 months (IQR 7.5 to 34.3), 7 patients who had an adverse outcome (5 ventricular tachycardia, 1 appropriate implantable cardioverter-defibrillator discharge, and 1 death) had more segments of LGE (median 4, IQR 2 to 7 vs 0, IQR 0 to 2, p=0.01). One patient without LGE had ventricular tachycardia on exercise test. In conclusion, LGE occurs in a similar pattern in pediatric patients with HC as in adults, associated with hypertrophy, decreased myocardial strain, and adverse clinical outcomes. Further longitudinal studies are necessary to evaluate the rate of development of LGE and relation to outcomes in a larger cohort.

Myocardial fibrosis imaging based on T1-mapping and extracellular volume fraction (ECV) measurement in muscular dystrophy patients: diagnostic value compared with conventional late gadolinium enhancement (LGE) imaging

AIM

Cardiac involvement with progressive myocardial fibrosis leading to dilated cardiomyopathy is a major cause of death in muscular dystrophy patients. Extracellular volume fraction (ECV) measurement based on T1-mapping pre- and post-contrast promises the detection of early 'diffuse' myocardial fibrosis that cannot be depicted by conventional contrast-imaging based on late gadolinium enhancement (LGE). With this study, we evaluated the presence of diffuse myocardial fibrosis in regions of 'normal' (LGE-negative) and 'diseased' (LGE-positive) appearing myocardium as well as its relation to the extent of left ventricular (LV) dysfunction and the occurrence of arrhythmias in Becker muscular dystrophy (BMD) patients.

METHODS AND RESULTS

Twenty-seven BMD patients (35 ± 12 years) and 17 matched male healthy controls (33 ± 8 years) underwent cardiovascular magnetic resonance (CMR) studies including ECV measurement and LGE-imaging. Ambulatory monitoring of arrhythmic events was performed by means of an external event loop recorder. Twenty BMD patients (74%) demonstrated cardiac involvement as detected by typical inferolateral presence of LGE. Twelve patients (44%) had an impaired LV ejection fraction-all being LGE-positive. Global myocardial ECV was significantly higher in the BMD group (29 ± 6%) compared with the control group (24 ± 2%, P = 0.001). Patients with cardiac involvement demonstrated higher global ECV (31 ± 6%) as well as significantly increased regional ECV not only in LGE-positive segments (34 ± 6%), but also in LGE-negative segments (28 ± 6%) compared with BMD patients without cardiac involvement and to controls, respectively (24 ± 3 and 24 ± 2%, P = 0.005). Global ECV in patients with cardiac involvement substantially correlated to LV ejection fraction (r = -0.629, P = 0.003) and to the number of LGE-positive segments (r = 0.783, P < 0.001). On univariable analysis, global ECV-but not the categorical presence of LGE per se--was significantly associated with arrhythmic events (OR: 1.97, CI: 32.22-1.21, P = 0.032).

CONCLUSION

ECV measurement by CMR is a useful tool in assessing the total extent of myocardial fibrosis as well as in depicting subtle diffuse fibrosis in areas of normal appearing myocardium on LGE-images. Thus, myocardial ECV is a potential additional quantitative tool for accurate detection of cardiac involvement and risk stratification in muscular dystrophy patients.

Cardiovascular Magnetic Resonance Imaging of Myocardial Interstitial Expansion in Hypertrophic Cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is a cardiovascular genetic disease with a varied clinical presentation and phenotype. Although mutations are typically found in genes coding for sarcomeric proteins, phenotypic derangements extend beyond the myocyte to include the extracellular compartment. Myocardial fibrosis is commonly detected by histology, and is associated with clinical vulnerability to adverse outcomes. Over the past decade, the noninvasive visualization of myocardial fibrosis by cardiovascular magnetic resonance (CMR) techniques has garnered much interest given the potential applications toward improving our understanding of pathophysiologic mechanisms of disease, as well as diagnosis and prognosis. Late gadolinium enhancement (LGE) imaging techniques are able to detect focal (typically replacement) fibrosis. Newer CMR techniques that measure absolute T1 relaxation time allow the quantification of the entire range of focal to diffuse (interstitial) fibrosis and may overcome potential limitations of LGE. This review will discuss the methodology and current status of these novel techniques, with a focus on extracellular volume fraction (ECV). Recent findings describing ECV measurement in HCM will be summarized.

Evaluating the Utility of Circulating Biomarkers of Collagen Synthesis in Hypertrophic Cardiomyopathy

Background—

In hypertrophic cardiomyopathy (HCM), accumulation of myocardial collagen may play a central role in the pathogenesis of diastolic dysfunction and arrhythmia. Previous studies have suggested that peripheral levels of byproducts of collagen synthesis are reflective of myocardial extracellular matrix metabolism, although this has not been validated in detail. Given the potential clinical utility of such biomarkers, we sought to validate the assumed relationship between peripheral markers and myocardial fibrosis in HCM.

Methods and Results—

Fifty patients with HCM and 25 healthy controls underwent peripheral venous sampling to determine plasma concentrations of key collagen precursors (procollagen I and III N-terminal propeptides [PINP, PIIINP]). Contrast-enhanced cardiac magnetic resonance imaging was performed to quantify regional (by late-gadolinium enhancement) and diffuse (by T 1 mapping) myocardial fibrosis. Nineteen subjects also underwent simultaneous arterial and coronary sinus blood sampling (to derive transcardiac concentration gradients of PINP, PIIINP, and C-terminal telopeptide of type I collagen) and right heart catheterization. Despite cardiac magnetic resonance evidence of regional (late-gadolinium enhancement quantity, 6.4±8.0%) and diffuse (T 1 time, 478±79 ms) myocardial fibrosis in patients with HCM, peripheral levels of collagen precursors were similar compared with control subjects (PINP, 45.9±22.9 versus 53.4±25.9 μg/L; P =0.21; PIIINP, 4.8±1.7 versus 4.4±1.1 μg/L; P =0.26). No significant net positive transcardiac concentration gradient was detected for either biomarker of collagen synthesis.

Conclusions—

The cardiac contribution to peripheral levels of byproducts of collagen synthesis in patients with HCM is insignificant. Furthermore, peripheral levels of these biomarkers do not accurately reflect myocardial collagen content in these patients.

T₁ mapping detects pharmacological retardation of diffuse cardiac fibrosis in mouse pressure-overload hypertrophy

BACKGROUND

Diffuse interstitial fibrosis is present in diverse cardiomyopathies and associated with poor prognosis. We investigated whether magnetic resonance imaging-based T1 mapping could quantify the induction and pharmacological suppression of diffuse cardiac fibrosis in murine pressure-overload hypertrophy.

METHODS AND RESULTS

Mice were subjected to transverse aortic constriction or sham surgery. The angiotensin receptor blocker losartan was given to half the animals. Cine-magnetic resonance imaging performed at 7 and 28 days showed hypertrophy and remodeling and systolic and diastolic dysfunction in transverse aortic constriction groups as expected. Late gadolinium-enhanced magnetic resonance imaging revealed focal signal enhancement at the inferior right ventricular insertion point of transverse aortic constriction mice concordant with the foci of fibrosis in histology. The extracellular volume fraction, calculated from pre- and postcontrast T1 measurements, was elevated by transverse aortic constriction and showed direct linear correlation with picrosirius red collagen volume fraction, thus confirming the suitability of extracellular volume fraction as an in vivo measure of diffuse fibrosis. Treatment with losartan reduced left ventricular dysfunction and prevented increased extracellular volume fraction, indicating that T1 mapping is sensitive to pharmacological prevention of fibrosis.

CONCLUSIONS

Magnetic resonance imaging can detect diffuse and focal cardiac fibrosis in a clinically relevant animal model of pressure overload and is sensitive to pharmacological reduction of fibrosis by angiotensin receptor blockade. Thus, T1 mapping can be used to assess antifibrotic therapeutic strategies.

Cardiac magnetic resonance imaging for the investigation of cardiovascular disorders. Part 1: current applications

Cardiac magnetic resonance imaging is a robust noninvasive technique for investigating cardiovascular disorders. The evolution of cardiac magnetic resonance and its widening span of diagnostic and prognostic applications have generated excitement as well as uncertainty regarding its potential clinical use and its role vis-à-vis conventional imaging techniques. The purpose of this evidence-based review is to discuss some of these issues by highlighting the current (Part 1) and emerging (Part 2) applications of cardiac magnetic resonance. Familiarity with the versatility and usefulness of cardiac magnetic resonance will facilitate its wider clinical acceptance for improving the management of cardiovascular disorders.

Ventricular structure, function, and focal fibrosis in anabolic steroid users: a CMR study

PURPOSE

Anabolic steroid (AS) misuse is widespread amongst recreational bodybuilders; however, their effects on the cardiovascular system are uncertain. Our aim was to document the impact of AS use on cardiac structure, function and the presence of focal fibrosis using the gold standard cardiovascular magnetic resonance imaging (CMR).

METHODS

A cross-sectional cohort design was utilised with 21 strength-trained participants who underwent CMR imaging of the heart and speckle-tracking echocardiography. Thirteen participants (30 ± 5 years) taking AS for at least 2 years and currently on a "using"-cycle were compared with age and training-matched controls (n = 8; 29 ± 6 years) who self-reported never having taken AS (NAS).

RESULTS

AS users had higher absolute left ventricular (LV) mass (220 ± 45 g) compared to NAS (163 ± 27 g; p < 0.05) but this difference was removed when indexed to fat-free mass. AS had a reduced right ventricular (RV) ejection fraction (AS 51 ± 4 % vs. NAS 59 ± 5 %; p < 0.05) and a significantly lower left ventricular E':A' myocardial tissue velocity ratio [AS 0.99(0.54) vs. NAS 1.78(0.46) p < 0.05] predominantly due to greater tissue velocities with atrial contraction. Peak LV longitudinal strain was lower in AS users (AS -14.2 ± 2.7 % vs. NAS -16.6 ± 1.9 %; p < 0.05). There was no evidence of focal fibrosis in any participant.

CONCLUSIONS

AS use was associated with significant LV hypertrophy, albeit in-line with greater fat-free mass, reduced LV strain, diastolic function, and reduced RV ejection fraction in male bodybuilders. There was, however, no evidence of focal fibrosis in any AS user.

ECG characteristics according to the presence of late gadolinium enhancement on cardiac MRI in hypertrophic cardiomyopathy

BACKGROUND

Late gadolinium enhancement (LGE) on cardiac MRI (CMR) has been described as an independent predictive factor of cardiovascular events among patients with hypertrophic cardiomyopathy (HCM). LGE and Q waves are considered as myocardial scar markers but their relation in the context of HCM is poorly established and has to be more supported. The objective of the study was to compare ECG findings in the presence or absence of LGE.

METHODS

42 patients with HCM confirmed by CMR were included in the study. ECG abnormalities including abnormal Q waves and five ECG scores of left ventricular hypertrophy were assessed and compared according to LGE presence and its extension. Some CMR features, such as septal to posterior wall thickness ratio, were also studied according to the presence of LGE and the presence of abnormal Q waves.

RESULTS

Abnormal Q waves were more prevalent in the LGE (+) group (60% vs 12%; p=0.002), but there was no correlation between location of Q waves on ECG and territory of LGE on CMR. Among patients with LGE, quantitative analysis of LGE was not different in the presence or absence of Q waves. In contrast to the LGE mass, septal to posterior wall thickness was higher in patients with abnormal Q waves (2.3±0.7 vs 1.6±0.5; p=0.012).

CONCLUSIONS

Although abnormal Q waves were more prevalent in the presence of LGE, no correlation was found with the LGE location and extent. These data suggest that abnormal electrical activation of the hypertrophied ventricular septum represented by a high septal to posterior wall thickness ratio seems to be an important mechanism of abnormal Q waves in HCM.

Noninvasive assessment of myocardial fibrosis in patients with obstructive hypertrophic cardiomyopathy

Objective

Late gadolinium enhancement cardiac magnetic resonance (LGE-CMR) imaging is the reference standard for non-invasive assessment of fibrosis. In hypertrophic cardiomyopathy (HCM) patients the histological substrate for LGE is still unknown. The aim of this study was to assess the ability of LGE and strain echocardiography to detect type and extent of myocardial fibrosis in obstructive HCM patients undergoing septal myectomy.

Methods

Thirty-two HCM patients (age 60±10) were included in this cross-sectional study and preoperatively examined by speckle-tracking strain echocardiography and LGE-CMR (n=21). Histological fibrosis was classified as interstitial, replacement and total.

Results

Histological fibrosis was present in 31 patients. The percentage of total, interstitial and replacement fibrosis was 15(7, 31)%, 11(5, 24)% and 3(1, 6)%, respectively. Reduced longitudinal septal strain correlated with total (r=0.50, p=0.01) and interstitial (r=0.40, p=0.03), but not with replacement fibrosis (r=0.28, p=0.14). Septal LGE was detected in 13/21 (62%), but percentage LGE did not correlate with total fibrosis (r=0.25, p=0.28). Extent of fibrosis did not differ between patients with and without septal LGE (20(9, 58)% versus 14(5, 19)% p=0.41). Patients with ventricular arrhythmias (n=8) had lower septal longitudinal strain and increased extent total and interstitial fibrosis in myectomy specimens, but no differences were demonstrated in LGE. Reduced longitudinal septal strain and increased extent of interstitial fibrosis predicted ventricular arrhythmias independently of age and gender.

Conclusions

In myectomised HCM patients, reduced longitudinal septal strain correlated better with interstitial and total fibrosis in myectomy specimens, and was a more powerful tool to predict arrhythmias than LGE.

Prevalence and distribution of late gadolinium enhancement in a large population of patients with Duchenne muscular dystrophy: effect of age and left ventricular systolic function

BACKGROUND

Duchenne muscular dystrophy (DMD), an X-linked disorder affects approximately 1 in 5000 males, is universally associated with heart disease. We previously identified myocardial disease by late gadolinium enhancement (LGE) in DMD subjects at various stages of disease, but the true prevalence is unclear. Cardiovascular magnetic resonance (CMR) is well established for both assessment of ventricular function and myocardial fibrosis by LGE. We sought to establish i) prevalence and distribution of LGE in a large DMD population and ii) relationship among LGE, age, LVEF by CMR and current living status.

METHODS

Current living status, demographic and CMR data including ventricular volumes, LVEF and LGE from 314 DMD patients undergoing evaluation at a single large tertiary referral center were analyzed.

RESULTS

113 of 314 (36%) of DMD subjects showed LGE positivity with prevalence increasing from 17% of patients <10 years to 34% of those aged 10-15 years and 59% of those >15 years-old. Patients with LVEF ≥55% were LGE positive in 30% of cases; this increased to 84% for LVEF <55%. LGE was more prevalent in the free wall (531/1243, 42.7%) vs. septal segments (30/565, 5.3%). Patients with septal involvement were significantly older and had lower LVEF than those with isolated free wall LGE. Ten percent (11/113) patients who had LGE died 10.8 months after CMR. Only one patient from the LGE negative group died. Patients who died had higher heart rate, larger left ventricular volume and mass, greater number of positive LGE segment and increase incident of septal LGE compared to those who remained alive.

CONCLUSION

In DMD patients, LGE occurs early, is progressive and increases with both age and decreasing LVEF. Segmentally, the incidence of the number of positive LGE segments increase with age and lower LVEF. Older patients and those who died during the study period had more septal LGE involvement. The current studies suggest that the time course and distribution of LGE-positivity may be an important clinical biomarker to aid in the management of DMD-associated cardiac disease.

Emerging roles for cardiovascular magnetic resonance

Cardiovascular magnetic resonance (CMR) is a noninvasive imaging tool with high spatial resolution in the absence of ionising radiation. CMR imaging is routine in the functional assessment of coronary lesions and is widely held as the gold standard in myocardial viability imaging. Its unique tissue characterisation capabilities have revolutionised the assessment of the cardiomyopathies and it is the investigation of choice for cardiovascular surveillance imaging. To date its greatest success has been in the management of thalassaemia major, where the ability to detect myocardial iron loading has significantly improved patient survival. In the near future, CMR fibrosis imaging may serve as a risk stratification tool for the cardiomyopathies; and the ability to assess interstitial fibrosis may advance this role into other disease processes. Novel methods of tissue characterisation and emerging technical advances present new avenues for this modality, securing its place as the noninvasive imaging tool of the future.

Effect of sleep apnea and continuous positive airway pressure on cardiac structure and recurrence of atrial fibrillation

BACKGROUND

Sleep apnea (SA) is associated with an increased risk of atrial fibrillation (AF). We sought to determine the effect of SA on cardiac structure in patients with AF, whether therapy for SA was associated with beneficial cardiac structural remodelling, and whether beneficial cardiac structural remodelling translated into a reduced risk of recurrence of AF after pulmonary venous isolation (PVI).

METHODS AND RESULTS

A consecutive group of 720 patients underwent a cardiac magnetic resonance study before PVI. Patients with SA (n=142, 20%) were more likely to be male, diabetic, and hypertensive and have an increased pulmonary artery pressure, right ventricular volume, atrial dimensions, and left ventricular mass. Treated SA was defined as duration of continuous positive airway pressure therapy of >4 hours per night. Treated SA patients (n=71, 50%) were more likely to have paroxysmal AF, a lower blood pressure, lower ventricular mass, and smaller left atrium. During a follow-up of 42 months, AF recurred in 245 patients. The cumulative incidence of AF recurrence was 51% in patients with SA, 30% in patients without SA, 68% in patients with untreated SA, and 35% in patients with treated SA. In a multivariable model, the presence of SA (hazard ratio 2.79, CI 1.97 to 3.94, P<0.0001) and untreated SA (hazard ratio 1.61, CI 1.35 to 1.92, P<0.0001) were highly associated with AF recurrence.

CONCLUSIONS

Patients with SA have an increased blood pressure, pulmonary artery pressure, right ventricular volume, left atrial size, and left ventricular mass. Therapy with continuous positive airway pressure is associated with lower blood pressure, atrial size, and ventricular mass, and a lower risk of AF recurrence after PVI.

Myofibroblasts: trust your heart and let fate decide

Cardiac fibrosis is a substantial problem in managing multiple forms of heart disease. Fibrosis results from an unrestrained tissue repair process orchestrated predominantly by the myofibroblast. These are highly specialized cells characterized by their ability to secrete extracellular matrix (ECM) components and remodel tissue due to their contractile properties. This contractile activity of the myofibroblast is ascribed, in part, to the expression of smooth muscle α-actin (αSMA) and other tension-associated structural genes. Myofibroblasts are a newly generated cell type derived largely from residing mesenchymal cells in response to both mechanical and neurohumoral stimuli. Several cytokines, chemokines, and growth factors are induced in the injured heart, and in conjunction with elevated wall tension, specific signaling pathways and downstream effectors are mobilized to initiate myofibroblast differentiation. Here we will review the cell fates that contribute to the myofibroblast as well as nodal molecular signaling effectors that promote their differentiation and activity. We will discuss canonical versus non-canonical transforming growth factor-β (TGFβ), angiotensin II (AngII), endothelin-1 (ET-1), serum response factor (SRF), transient receptor potential (TRP) channels, mitogen-activated protein kinases (MAPKs) and mechanical signaling pathways that are required for myofibroblast transformation and fibrotic disease. This article is part of a Special Issue entitled "Myocyte-Fibroblast Signalling in Myocardium ".

MR, CT, and PET imaging in pericardial disease

Although echocardiography remains the standard diagnostic tool for identifying pericardial diseases, procedures with better delineation of morphology and heart function are often required. The pericardium consists of an inner visceral (epicardium) and outer parietal layer (pericardium), which constitute for the pericardial cavity. Pericardial effusion can occur as transudate, exudate, pyopneumopericardium, or hemopericardium. Potential causes are inflammatory processes, that is, pericarditis due to autoimmune or infective reasons, neoplasms, irradiation, or systemic disorders, chronic renal failure, endocrine, or metabolic diseases. Pericardial fat can mimic pericardial effusion. Using various image-acquisition sequences, MRI allows identifying and separating fluid and solid structures. Fast spin-echo T1-weighted sequences with black-blood preparation are favourably used for morphological evaluation. Fast spin-echo T2-weighted sequences, particularly with fat saturation, and short-tau inversion-recovery sequences are useful to visualize oedema and inflammation. For further tissue characterization, delayed inversion-recovery imaging is used. Therefore, image acquisition is performed at 5-20 min subsequent to contrast agent administration, the so-called technique of late gadolinium enhancement. Ventricular volumes and myocardial mass can be assessed accurately by steady-state free-precession sequences, which is required to measure cardiac function and ventricular wall stress. Constrictive pericarditis usually results from chronic inflammatory processes leading to increased stiffness, which impedes the slippage of both pericardial layers and thereby the normal cardiac filling. CT imaging can favourably assess pericardial calcification. Thus, MR and CT imaging allow a comprehensive delineation of the pericardium. Superior to echocardiography, both methods provide a larger field of view and depiction of the complete chest including abnormalities of the surrounding mediastinum and lungs. PET provides unique information on the in vivo metabolism of 18-fluorodeoxyglucose that can be superimposed on CT findings and is useful for identifying inflammatory processes or masses, for example neoplasms. These imaging techniques provide advanced information of anatomy and cardiac function to optimize the pericardial access, for example by the AttachLifter system, for diagnosis and treatment.

Effects of losartan on left ventricular hypertrophy and fibrosis in patients with nonobstructive hypertrophic cardiomyopathy

OBJECTIVES

The aim of this study was to evaluate the effects of losartan on left ventricular (LV) hypertrophy and fibrosis in patients with nonobstructive hypertrophic cardiomyopathy (HCM).

BACKGROUND

Despite evidence that myocardial hypertrophy and fibrosis are mediated by angiotensin II and are important determinants of morbidity and mortality in patients with HCM, no prior studies have evaluated the effects of angiotensin receptor blockers on LV hypertrophy and fibrosis with cardiac magnetic resonance imaging.

METHODS

In double-blind fashion, 20 patients (3 women, 17 men; age: 51 ± 13 years) with HCM were randomly assigned to receive placebo (n = 9) or losartan 50 mg twice a day (n = 11) for 1 year. Cardiac magnetic resonance imaging was performed at baseline and 1 year to measure LV mass and extent of fibrosis as assessed by late gadolinium enhancement.

RESULTS

There was a trend toward a significant difference in the percent change in LV mass (median [interquartile range]: +5% [-4% to +21%] with placebo vs. -5% [-11% to -0.9%] with losartan; p = 0.06). There was a significant difference in the percent change in extent of late gadolinium enhancement, with the placebo group experiencing a larger increase (+31% ± 26% with placebo vs. -23% ± 45% with losartan; p = 0.03).

CONCLUSIONS

This pilot study suggests attenuation of progression of myocardial hypertrophy and fibrosis with losartan in patients with nonobstructive HCM. Confirmation of these results in a larger trial is required to confirm a place for angiotensin receptor blockers in the management of patients with HCM. (Effect of Losartan in Patients With Nonobstructive Hypertrophic Cardiomyopathy; NCT01150461).