Hypertrophic Cardiomyopathy, Fibrosis, and Aortic Stiffness

Prevalence and Clinical Correlates of Aortic Dilation in Hypertrophic Cardiomyopathy

BACKGROUND

Aortic dilation has been associated with various cardiac conditions, although its prevalence and clinical correlates in hypertrophic cardiomyopathy (HCM) remain unclear.

OBJECTIVES

The purposes of this study were to define the prevalence of ascending aortic dilation in a large referral population of patients with HCM and to determine clinical and echocardiographic correlates of aortic dilation.

METHODS

A total of 1,698 patients with HCM underwent echocardiographic measurement of the tubular ascending aorta (proximal and midlevel) during index evaluation at a tertiary HCM referral center. End-diastolic ascending aorta dimension was indexed to body surface area, with dilation defined for the tubular ascending aorta as 2 SD above the mean (>19 mm/m²) and independently as greater than published age-, sex-, and body surface area- adjusted norms (for the sinus of Valsalva and midlevel). Aortic size and presence of aortic enlargement were correlated with clinical and echocardiographic parameters.

RESULTS

Tubular ascending aortic dilation >19 mm/m² was present in 303 patients with HCM (18%), and dilation above adjusted norms was present in 210 patients with HCM (13%). The median indexed tubular ascending thoracic aortic dimension was 16.5 (interquartile range, 14.8-18.2) mm/m². Indexed dimension increased linearly with age (R = 0.53, P < .0001). Women and patients with a history of systemic hypertension were more likely to have tubular aortic enlargement >19 mm/m² (29.8% vs 9.9% and 24.1% vs 10.5%, respectively, P < .0001 for both). Patients with obstructive physiology were more likely to have tubular aortic enlargement >19 mm/m² than those without resting or provocable obstruction (19.6% vs 14.4%, P = .007). Using adjusted norms, aortic enlargement was more frequent at the midlevel compared with the sinus of Valsalva (71% vs 29%), more common in patients with hypertension (15.4% vs 10.6%, P = .009), and more common in patients with paroxysmal atrial fibrillation (16.3% vs 11.5%, P = .036), but no other relationships remained statistically significant.

CONCLUSIONS

In this large cohort of patients with HCM, aortic dilation was common. The key correlate of tubular aortic enlargement >19 mm/m², and aortic enlargement greater than adjusted norms included a history of systemic hypertension. Given an increased prevalence of aortic dilation in HCM, further study is needed on the clinical impact of aortic dilation.

Aortic Stiffness in Youth with Hypertrophic Cardiomyopathy Genotype

Clinical events in hypertrophic cardiomyopathy (HCM) patients are related to the degree of hypertrophy. Aortic stiffness in adult HCM patients has been reported to be higher than control patients. Increased stiffness may cause more LV hypertrophy and thus lead to more clinical events. We sought to (a) noninvasively compare aortic structure and function between youth with sarcomeric HCM genotype versus control youth and (b) explore the relation between aortic function and degree of left ventricular (LV) hypertrophy. In a prospective study from a single referral center, clinical, anthropometric, and hemodynamic data were acquired on 28 consecutive pathogenic HCM gene mutation carriers and 26 unrelated controls (mean age 16.3, 50 % girls). Hemodynamic data included applanation tonometry measured central pulse pressure, carotid-femoral pulse wave velocity (CFPWV), reflected wave augmentation index (AIx). In the HCM gene carriers, LV mass-to-volume ratio was extracted from clinically indicated echocardiograms as an index of hypertrophy. Associations were assessed using multivariable adjusted linear regression. The HCM group was comprised of 14 myosin binding protein C3 carriers, 13 myosin heavy chain 7 carriers, and 1 child with both. HCM and control groups did not differ by age, sex, height, body mass index, heart rate, or blood pressure. HCM carriers had significantly lower CFPWV than controls (4.46 ± 0.88 vs. 4.97 ± 0.44 m/s, p = 0.01) and higher AIx magnitude (27 ± 19 vs. 18 ± 7 %, p = 0.04). These associations persisted after adjustment for age, sex, height, heart rate, mean pressure, and medication use. Within the HCM group, LV hypertrophy was related to AIx but not CFPWV. CFPWV nor AIx differed by genotype. Aortic stiffness appears lower, but wave reflection appears higher in youth carrying HCM gene mutations. The degree of wave reflection appears correlated with LV hypertrophy in this high-risk cohort, suggesting that mitigation of wave reflection may possibly attenuate LV hypertrophy.

Endothelial progenitor cells as markers of severity in hypertrophic cardiomyopathy

AIMS

Endothelial progenitor cells (EPCs) are bone marrow-derived cells that are mobilized into the circulation to migrate and differentiate into mature endothelial cells contributing to post-natal physiological and pathological neovascularization. In this study, we evaluated circulating EPCs in patients with hypertrophic cardiomyopathy (HCM) and examined a potential association with clinical parameters of the disease.

METHODS AND RESULTS

We included 40 HCM patients and 23 healthy individuals. Using flow cytometry we measured EPCs in peripheral blood as two subpopulations of CD45-/CD34+/VEGFR2+ and CD45-/CD34+/CD133+ cells. Circulating CD45-/CD34+/VEGFR2+ cells were significantly increased in HCM patients in comparison with the controls (0.000238 ± 0.0003136 vs. 0.000057 ± 0.0001316, respectively, P = 0.002). However, there was no significant difference in the number of circulating CD45-/CD34+/CD133+ cells (0.003079 ± 0.0033288 vs. 0.002065 ± 0.0022173, respectively, P = 0.153). The CD45-/CD34+/VEGFR2+ subpopulation revealed a moderate correlation with LV mass index (r = 0.35, P = 0.026), while both EPC subpopulation levels showed strong positive correlations with th E/e' ratio (r = 0.423, P = 0.007 for CD45-/CD34+/VEGFR2+ and r = 0.572, P < 0.001 for CD45-/CD34+/CD133+).

CONCLUSION

HCM patients showed an increased mobilization of EPCs compared with healthy individuals that correlated with diastolic dysfunction. Our findings may open up new dimensions in the pathophysiology, prognostication, and treatment of HCM.

[Vascular functional alterations in hypertrophic cardiomyopathy]

Hypertrophic cardiomyopathy is a hereditary, not uncommon cardiac disease, which is associated with asymmetric thickening and hypertrophy of the interventricular septum unrelated to hemodynamic reasons. Despite hypertrophic cardiomyopathy is considered to be a disorder of the heart muscle, several associated vascular alterations have been described. The aim of the present review is to summarize vascular functional alterations in hypertrophic cardiomyopathy.

Hypertrophic cardiomyopathy is associated with abnormal echocardiographic aortic elastic properties and arteriograph-derived pulse-wave velocity

OBJECTIVE

Hypertrophic cardiomyopathy (HCM) is a genetic cardiac disease and defined by the presence of unexplained left ventricular hypertrophy (LVH). Vascular alterations are frequently associated with HCM including microvascular and/or peripherial endothelial dysfunction. This study was designed to evaluate echocardiographic ascending aortic elastic properties and arteriograph-derived pulse-wave velocity (PWV) and augmentation index (Aix) in HCM.

METHODS

This study comprised 38 patients with typical features of HCM. Their results were compared to 20 hypertensive patients with LVH and 23 controls. Systolic and diastolic ascending aortic diameters were recorded in M-mode at a level of 3 cm above the aortic valve from a parasternal long-axis view. The following echocardiographic aortic elastic properties were measured from aortic data and forearm blood pressure values: aortic strain, distensibility, and stiffness index. Arteriograph-derived PWV and AIx were also measured.

RESULTS

Aortic stiffness index (18.4 ± 17.6 vs. 6.88 ± 3.63, P < 0.05), PWV (9.44 ± 4.08 vs. 7.97 ± 1.20 m/sec, P < 0.05) and Aix (-24.9 ± 32.6 vs. -41.4 ± 24.3, P < 0.05) were increased, while aortic strain (0.061 ± 0.053 vs. 0.100 ± 0.059, P < 0.05) and aortic distensibility (1.94 ± 1.68 cm(2) /dynes 10(-6) vs. 3.08 ± 1.77 cm(2) /dynes 10(-6) , P < 0.05) were decreased in HCM patients compared to controls. Aortic elastic properties of hypertensive patients with LVH showed similar alterations to HCM patients.

CONCLUSIONS

Abnormal echocardiographic aortic elastic properties and arteriograph-derived PWV and Aix could be demonstrated in HCM patients compared to matched controls.

Arterial stiffness, its assessment, prognostic value, and implications for treatment

Arterial stiffness has been known as a sign of cardiovascular risk since the 19th century. Despite this, accurate measurement and clinical utility have only emerged in recent times. Arterial stiffness and its hemodynamic consequences are now established as predictors of adverse cardiovascular outcome. They are easily and reliably measured using a range of noninvasive techniques, which can be used readily by risk assessment facilities or individual practitioners. The techniques described in this review are based on the pulsatility of the cardiovascular system, utilizing the timing of pulse travel along major arteries and the magnitude of wave reflection. These have enabled better understanding of the ill effects of arterial stiffening, not only on large arteries and the left ventricle, but also on tiny arteries in highly perfused organs such as brain and kidneys. Treatment options, which directly target the consequences of arterial stiffening, as opposed to arbitrary reduction of brachial blood pressure, have proved clinical superiority; optimal therapy entails use of angiotensin-converting enzyme inhibitors, angiotensin-receptor blockers, and calcium-channel blockers, as well as vasodilating β-blockers. Arterial stiffness will undoubtedly contribute to cardiovascular assessment and management in future clinical practice. Reviews such as this will hopefully increase awareness of the mounting evidence underlying this transition, and the relevant theory and methodology. As we begin the second decade of the 21st century, we are finally collectively coming to realize what pioneers such as Osler, Roy, Bramwell and Hill foresaw in the 19th and 20th centuries.