Abstract 15572: Hypertrophic Cardiomyopathy With Borderline Septal Hypertrophy is Characterised by Impaired Myocardial Blood Flow Reserve Predominantly Due to Attenuated Capillary Recruitment: A Quantitative Myocardial Contrast Echocardiography Study
Background: Hypertrophic cardiomyopathy (HCM) is the commonest cause of sudden death in the young. Left ventricular hypertrophy (LVH) which is the hallmark of HCM may fall in the gray zone area (12-15mm) where present diagnostic techniques are suboptimal for distinguishing between physiological vs pathological LVH. LVH of HCM is characterized by increased fibrosis and microvascular abnormalities. We hypothesised that HCM subjects with gray zone LVH will not only have reduced capillary volume but also reduced myocardial blood flow reserve (MBFR) due to impaired capillary recruitment.
Methods: 25 HCM subjects (age:32±8 yrs,males:21) with gray zone LVH and 10 age and sex matched control subjects underwent 2D echocardiography and tissue Doppler imaging followed by rest and stress vasodilator myocardial contrast echocardiography (MCE). Capillary blood volume [CBV (dβ)], blood velocity (dβ/s), myocardial blood flow [MBF(db/s2)] and MBFR (stress MBF/rest MBF) of the septum and apex were quantified.
Results: HCM had thicker interventricular septum (13.7mm ±1.03 vs 10.67mm±0.05, p=0.01) and larger left atrium (LA) (46mm ± 0.3 vs 3.3mm±0.3, p=0.02) but no difference in LV systolic (left ventricular ejection fraction or septal longitudinal function) or diastolic (E/A ratio,e prime or E/e prime) functions vs controls . At rest HCM had lower CBV (13.56±12.4 vs 14.60±2.3, p=0.04), lower MBF(14.1±15 vs 30.75±5, p=0.032) with no significant difference(1.03±0.3 vs 1.70±1.01, p=0.19) in MBV vs controls. At stress, the CBV increase was lower in HCM compared to controls (14.60±2.3 vs 30.35±7.4 p=0.01) with no significant difference in the increase in MBV(2.8±2.0 vs 2.5±1.2 p=0.21) with resultant attenuated rise in MBF(36.1±2.4 vs 85.0±36.1, p=0.01) in HCM vs control. Consequently, MBFR was significantly lower in HCM vs controls (2.4 vs 2.8, p=0.04). Multivariate logistic regression analysis showed that LA size (p=0.045), stress CBV(p<0.01) and MBFR (p=0.04) were the only independent predictors of HCM.
Conclusion: HCM with borderline LVH is characterised by reduced MBFR predominantly due to attenuated capillary recruitment. It has implications for use of vasodilator MCE to distinguish between pathological vs physiological gray zone LVH in athletes.
- © 2013 by American Heart Association, Inc.