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Background: Microvascular dysfunction reflected by the decreased coronary flow reserve (CFR) in response to adenosine infusion is a common finding in hypertrophic cardiomyopathy (HCM). Decreased CFR is recognized as a major mechanism for ischemia which is related with unfavorable long term outcome. Its patophysiology is multifunctional, including reduced arteriolar density, fibrosis, myocyte disarray, elevated left ventricular end-diastolic pressure and structural abnormalities of small coronary vessels. Plasma levels of NT-pro-BNP in HCM correlates positively with cardiac filling pressures and is excellent marker for the abnormal LV wall stress and disease progression.Aims: 1. To examine relations between CFR, assessed in left anterior descending coronary artery (LAD) in HCM patients using transthoracic echocardiographic (TTE) techniques and morphological characteristics, LV mass and LVOT pressure gradient. 2. To explore relation between plasma levels of NT-pro-BNP and microvascular function.Methods: In 63 pts (mean age 48.6±16.4 yrs; 27male) with asymmetric HCM, 21 pts with LVOT obstruction and 42 pts without LVOT obstruction, transthoracic echocardiographic examination with measurement of CFR in LAD was done. CFR was defined as the ratio between maximal velocity of diastolic coronary blood flow during maximal hyperemia and in rest, induced by i.v. infusion of adenosine (140mcg/kg/min).Results: When HCM pts with LVOT obstruction were compared to HCM pts without LVOT obstruction, first group had strong trend for lower value of CFR-LAD (1.93±0.42 vs. 2.20±0.56, p=0.06). In the whole study group CFR-LAD was significantly inversely correlated with LVOT PG (r=-.392,p=0.024). CFR-LAD was also inversely correlated with LVmass (CFR-LAD: r=-.320, p=0.01) and with septal thickness (r=-.511, p<0.001). Levels of NT-pro-BNP were significantly inversely correlated with LAD-CFR in the whole study group (r=-.545, p<0.001).Conclusion: In patients with asymmetric HCM, coronary microvascular function determined as CFR is significantly inversely related to LV mass as well as to septal thickness. Coronary microvascular function is inversely correlated to gradient of LVOT obstruction showing that LVOT obstruction additionally aggravates microvascular dysfunction in LAD territory. In the whole study group, even in non-obstructive form of HCM coronary microvascular function is significantly related to left ventricular wall stress.