Risk factors for systolic dysfunction and ventricular dilatation in hypertrophic cardiomyopathy

ELAC2/RNaseZ-linked cardiac hypertrophy in Drosophila melanogaster

A severe form of infantile cardiomyopathy (CM) has been linked to mutations in ELAC2, a highly conserved human gene. It encodes Zinc phosphodiesterase ELAC protein 2 (ELAC2), which plays an essential role in the production of mature tRNAs. To establish a causal connection between ELAC2 variants and CM, here we used the Drosophila melanogaster model organism, which carries the ELAC2 homolog RNaseZ. Even though RNaseZ and ELAC2 have diverged in some of their biological functions, our study demonstrates the use of the fly model to study the mechanism of ELAC2-related pathology. We established transgenic lines harboring RNaseZ with CM-linked mutations in the background of endogenous RNaseZ knockout. Importantly, we found that the phenotype of these flies is consistent with the pathological features in human patients. Specifically, expression of CM-linked variants in flies caused heart hypertrophy and led to reduction in cardiac contractility associated with a rare form of CM. This study provides first experimental evidence for the pathogenicity of CM-causing mutations in the ELAC2 protein, and the foundation to improve our understanding and diagnosis of this rare infantile disease.

This article has an associated First Person interview with the first author of the paper.

Summary: A newly established Drosophila model recapitulates key features of human heart pathology linked to mutations in ELAC2, thus providing experimental evidence of the pathogenicity of ELAC2 variants.

Clinical characteristics and outcomes of dilated phase of hypertrophic cardiomyopathy: report from the registry data in Japan

BACKGROUND

A subset of patients with hypertrophic cardiomyopathy (HCM) has been reported to progress into dilated-HCM (D-HCM), characterized by left ventricular (LV) systolic dysfunction and cavity dilatation, resembling idiopathic dilated cardiomyopathy (DCM). We compared the characteristics, treatments, and outcomes in patients with heart failure (HF) due to D-HCM vs. DCM by using national registry data in Japan.

METHODS AND RESULTS

The Japanese Cardiac Registry of Heart Failure in Cardiology (JCARE-CARD) is a prospective observational study of patients hospitalized due to worsening HF with an average of 2.2 years of follow-up. Patients with D-HCM (n=41) were more likely to be male, have prior stroke, atrial fibrillation, and sustained ventricular tachycardia or ventricular fibrillation compared with DCM (n=486). Echocardiography demonstrated that D-HCM patients had smaller LV end-systolic diameter, higher ejection fraction, and greater wall thickness. Treatments for HF including angiotensin-converting enzyme inhibitor or angiotensin receptor blocker, β-blocker, and spironolactone were similar between groups except for higher use of amiodarone, warfarin, and implantable cardioverter-defibrillator for D-HCM. Mortality was significantly higher in patients with D-HCM (29.7% vs. 14.4%; p<0.05). Sudden death tended to be higher also in D-HCM (8.1% vs. 2.6%; p=0.06), which, however, did not reach statistical significance.

CONCLUSIONS

HF patients with D-HCM had higher mortality risk than those with DCM. Effective management strategies are critically needed to be established for D-HCM.

Prevalence, clinical profile, and significance of left ventricular remodeling in the end-stage phase of hypertrophic cardiomyopathy

BACKGROUND

End stage (ES) is a recognized part of the hypertrophic cardiomyopathy (HCM) disease spectrum. Frequency, clinical profile and course, and treatment strategies in these patients remain incompletely defined.

METHODS AND RESULTS

Three HCM cohorts comprised 1259 patients, including 44 (3.5%) characterized as ES with systolic dysfunction (ejection fraction <50% at rest; range 15% to 49%). ES developed at a wide age range (14 to 74 years), with 45% of patients < or = 40 years old. Although 29 patients (66%) died of progressive heart failure, had sudden death events, or underwent heart transplantation, 15 (34%) survived with medical management over 3+/-3 years. Duration from onset of HCM symptoms to ES identification was considerable (14+/-10 years), but ES onset to death/transplantation was brief (2.7+/-2 years). ES occurred with similar frequency in patients with or without prior myectomy (P=0.84). Appropriate defibrillator interventions were 10% per year in patients awaiting donor hearts. Most ES patients (n=23; 52%) showed substantial left ventricular (LV) remodeling with cavity dilatation. Less complete remodeling occurred in 21 patients (48%), including 5 with persistence of a nondilated and markedly hypertrophied LV. Pathology and magnetic resonance imaging showed extensive (transmural) fibrosis in 9 of 11 ES patients. At initial evaluation, patients who developed ES were younger with more severe symptoms, had a larger LV cavity, and more frequently had a family history of ES than other HCM patients.

CONCLUSIONS

ES of nonobstructive HCM has an expanded and more diverse clinical expression than previously appreciated, including occurrence in young patients, heterogeneous patterns of remodeling, frequent association with atrial fibrillation, and impaired LV contractility that precedes cavity dilatation, wall thinning, and heart failure symptoms. ES is an unfavorable complication (mortality rate 11% per year) and a sudden death risk factor; it requires vigilance to permit timely recognition and the necessity for defibrillator implantation and heart transplantation.

Is I-123-beta-methyl-p-iodophenyl-methylpentadecanoic acid imaging useful to evaluate asymptomatic patients with hypertrophic cardiomyopathy? I-123 BMIPP imaging to evaluate asymptomatic hypertrophic cardiomyopathy

PURPOSE

Myocardial imaging with I-123-beta-methyl-p-iodophenyl-methylpentadecanoic acid (BMIPP) is useful for predicting the outcome of patients with hypertrophic cardiomyopathy (HCM). But its usefulness in asymptomatic patients is unclear.

MATERIALS AND METHODS

Eighteen patients with asymptomatic HCM were examined with BMIPP and exercise stress perfusion imaging and then followed for 4.0 +/- 0.8 years. Extent of the defect (total defect score, TDS) and myocardial uptake of BMIPP (%uptake) were calculated to evaluate the BMIPP images.

RESULTS

In the first study abnormal findings in the BMIPP and perfusion images were detected of 67 and 22% of the patients, respectively. In the second BMIPP study, the TDS had increased (2.1 +/- 2.7 to 4.1 +/- 4.9, p < 0.005) and the %uptake had decreased (5.67 +/- 0.88% to 4.81 +/- 0.91%, p < 0.001), but there were no differences in myocardial perfusion between the first and second study. Exertional dyspnea developed in 17% of the patients, and they were among the one third of the patients with the greatest reduction of %uptake. This group also showed deterioration of left ventricular (LV) %fractional shortening and LV volume in the second study.

CONCLUSIONS

Abnormal findings on BMIPP images were frequently observed in patients with asymptomatic HCM, and these abnormal findings progressed with time. The greater reduction of %uptake during the follow-up period reflects the deterioration of the LV function.

Myocardial metabolic abnormalities in hypertrophic cardiomyopathy assessed by iodine-123-labeled beta-methyl-branched fatty acid myocardial scintigraphy and its relation to exercise-induced ischemia

Reversible thallium-201 (201Tl) abnormalities during exercise stress have been used as markers of myocardial ischemia in hypertrophic cardiomyopathy (HCM) and are most likely to identify relatively underperfused myocardium. Although metabolic abnormalities in HCM were reported, the relationship between impaired energy metabolism and exercise-induced ischemia has not been fully elucidated as yet. To assess the relationship between myocardial perfusion abnormalities and fatty acid metabolic abnormalities, 28 patients with HCM underwent exercise 201Tl and rest 123I-15-(p-iodophenyl)-3-methyl pentadecanoic acid (BMIPP) scintigraphy. Perfusion abnormalities were observed by exercise 201Tl in 19/28 patients with HCM. 123I-BMIPP uptake was decreased compared with delayed 201Tl in 106/364 (29%) of the total myocardial segments (p<0.01, McNemar symmetry test). Such disparity between 123I-BMIPP and 201Tl was observed more often in the 49/75 (65%) segments with reversible exercise 201Tl defects (p<0.001). Our results indicate that exercise-induced myocardial ischemia exists in HCM, resulting in metabolic abnormalities. The combination of 123I BMIPP and 201Tl suggests that myocardial ischemia may play an important role in metabolic abnormalities in HCM.