Augmented exercise plasma noradrenaline with impaired chronotropic responsiveness in patients with hypertrophic cardiomyopathy

Prognostic Value of Reduced Heart Rate Reserve during Exercise in Hypertrophic Cardiomyopathy

BACKGROUND

Sympathetic dysfunction can be evaluated by heart rate reserve (HRR) with exercise test.

OBJECTIVES

To determine the value of HRR in predicting outcome of patients with hypertrophic cardiomyopathy (HCM).

METHODS

We enrolled 917 HCM patients (age = 49 ± 15 years, 516 men) assessed with exercise stress echocardiography (ESE) in 11 centres. ESE modality was semi-supine bicycle in 51 patients (6%), upright bicycle in 476 (52%), and treadmill in 390 (42%). During ESE, we assessed left ventricular outflow tract obstruction (LVOTO), stress-induced new regional wall motion abnormalities (RWMA), and HRR (peak/rest heart rate, HR). By selection, all patients completed the follow-up. Mortality was the predetermined outcome measure Results: During ESE, RWMA occurred in 22 patients (2.4%) and LVOTO (≥50 mmHg) in 281 (30.4%). HRR was 1.90 ± 0.40 (lowest quartile ≤ 1.61, highest quartile > 2.13). Higher resting heart rate (odds ratio 1.027, 95% CI: 1.018-1.036, p < 0.001), older age (odds ratio 1.021, 95% CI: 1.009-1.033, p < 0.001), lower exercise tolerance (mets, odds ratio 0.761, 95% CI: 0.708-0.817, p < 0.001) and resting LVOTO (odds ratio 1.504, 95% CI: 1.043-2.170, p = 0.029) predicted a reduced HRR. During a median follow-up of 89 months (interquartile range: 36-145 months), 90 all-cause deaths occurred. At multivariable analysis, lowest quartile HRR (Hazard ratio 2.354, 95% CI 1.116-4.968 p = 0.025) and RWMA (Hazard ratio 3.279, 95% CI 1.441-7.461 p = 0.004) independently predicted death, in addition to age (Hazard ratio 1.064, 95% CI 1.043-1.085 p < 0.001) and maximal wall thickness (Hazard ratio 1.081, 95% CI 1.037-1.128, p < 0.001).

CONCLUSIONS

A blunted HRR during ESE predicts survival independently of RWMA in HCM patients.

Divergent effects of adrenaline in human induced pluripotent stem cell-derived cardiomyocytes obtained from hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is a common inherited cardiac disease that affects the heart muscle with diverse clinical outcomes. HCM can cause sudden cardiac death (SCD) during or immediately after mild to rigorous physical activity in young patients. However, the mechanism causing SCD as a result of exercise remains unknown, but exercise-induced ventricular arrhythmias are thought to be responsible for this fatal consequence. To understand the disease mechanism behind HCM in a better way, we generated patient-specific induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) from HCM patients carrying either the MYBPC3-Gln1061X or TPM1-Asp175Asn mutation. We extensively investigated the effects of low to high concentrations of adrenaline on action potential characteristics, and the occurrence of arrhythmias in the presence of various concentrations of adrenaline and in wash-out condition. We classified and quantified different types of arrhythmias observed in hiPSC-CMs, and found that the occurrence of arrhythmias was dependent on concentrations of adrenaline and positions of mutations in genes causing HCM. In addition, we observed ventricular tachycardia types of arrhythmias in hiPSC-CMs carrying the TPM1-Asp175Asn mutation. We additionally examined the antiarrhythmic potency of bisoprolol in HCM-specific hiPSC-CMs. However, bisoprolol could not reduce the occurrence of arrhythmias during administration or during the wash-out condition of adrenaline in HCM-specific hiPSC-CMs. Our study demonstrates hiPSC-CMs as a promising tool for studying HCM. The experimental design used in this study could be suitable and beneficial for studying other components and drugs related to cardiac disease in general.

Summary: Different concentrations of adrenaline have divergent effects during and immediately after administration in human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) obtained from hypertrophic cardiomyopathy (HCM) patients. Bisoprolol could not reduce the arrhythmias in HCM-specific hiPSC-CMs.

Metabolic crosstalk between the heart and liver impacts familial hypertrophic cardiomyopathy

Familial hypertrophic cardiomyopathy (HCM) is largely caused by dominant mutations in genes encoding cardiac sarcomeric proteins, and it is etiologically distinct from secondary cardiomyopathies resulting from pressure/volume overload and neurohormonal or inflammatory stimuli. Here, we demonstrate that decreased left ventricular contractile function in male, but not female, HCM mice is associated with reduced fatty acid translocase (CD36) and AMP-activated protein kinase (AMPK) activity. As a result, the levels of myocardial ATP and triglyceride (TG) content are reduced, while the levels of oleic acid and TG in circulating very low density lipoproteins (VLDLs) and liver are increased. With time, these metabolic changes culminate in enhanced glucose production in male HCM mice. Remarkably, restoration of ventricular TG and ATP deficits via AMPK agonism as well as inhibition of gluconeogenesis improves ventricular architecture and function. These data underscore the importance of the systemic effects of a primary genetic heart disease to other organs and provide insight into potentially novel therapeutic interventions for HCM.

Abnormal blood pressure response to exercise occurs more frequently in hypertrophic cardiomyopathy patients with the R92W troponin T mutation than in those with myosin mutations

Abnormal blood pressure response to exercise is reported to occur in up to a third of hypertrophic cardiomyopathy (HCM) cases and is associated with an increased risk of death, particularly in the young, but it is not known whether the HCM-causing mutation influences blood pressure response to exercise. The purpose of this article is to ascertain whether the blood pressure response to exercise differs among carriers of the R92W mutation in the cardiac troponin T gene (TNNT2), which has been associated with an increased risk of sudden cardiac death in young males; carriers of mutations in the cardiac β-myosin heavy chain gene (MYH7); and their noncarrier relatives. Thirty R92W_TNNT2 carriers, 51 MYH7 mutation carriers, and 68 of their noncarrier relatives were subjected to bicycle ergonometric exercise testing to assess blood pressure response to, as well as heart rate recovery after, exercise. Additional echocardiographic and demographic details were documented for all participants. R92W_TNNT2 carriers demonstrated significantly more abnormal blood pressure responses to exercise (P = .021; odds ratio 3.03; confidence interval 1.13–8.12) and smaller increases in systolic blood pressure than MYH7 mutation carriers or related noncarrier control individuals. Although abnormal blood pressure response occurred at similar frequencies in males in all groups (23%–26%), the percentage of R92W_TNNT2 females with abnormal blood pressure response was 64%, compared with 25% for MYH7 and 22% for noncarriers. Therefore, these results show that blood pressure response to exercise is influenced by genotype and gender in patients with HCM.