Arterial compliance and ambulatory stiffness index in hypertrophic cardiomyopathy: should them be normalized for dynamic gradient?

Purpose. We sought to recognize total arterial compliance (AC) and ambulatory arterial stiffness index (AASI) in patients (pts) with hypertrophic cardiomyopathy with (HOCM) or without (HCM) obstruction, and whether such indices should be normalized for left ventricular (LV) dynamic gradients. Methods. 81 pts (mean aged 60±16 years) with no evidence of previous myocardial infarction or depressed systolic function were studied by echocardiography. LV outflow tract obstruction was established for peak gradient >30mmHg. Total AC and AASI were measured as suggested by Westerhof et al.(Hypertension 2007), as follows: AC=ratio of stroke volume (SV) over pulse pressure (PP); systemic vascular resistance (R)=ratio of mean pressure (Pm) and cardiac output (Q). With SV times heart rate (HR), being Q, Pm=QxR=SV×HR×R or SV×R/T, with T=R-R interval. Thus PP/Pm=T/RxAC=T/τ, with τ=RxAC, the decay time of aortic pressure in diastole. We approximated Pm as by (Ps+2Pd)/3, and PP=Psist−Pdiast. Thus, AASI was calculated as 1-(3-T/τ)/(3+2T/τ)=(T/τ)/(1+2T/3τ). Also, both indices were normalized for LV peak dynamic gradient (nAC and nAASI). Results. 33 pts (41%) had HOCM and 48 (59%) HCM. There were no between-group differences in LV mass and ejection fraction at baseline, whereas ejective gradient was 72±47 and 11±7 mm Hg, respectively (<0.0001). Crude AC and AASI values were similar. On the contrary, lower nAC and higher nAASI were shown in HOCM pts (Fig). Conclusions. Basal AC and AASI values were not different between HOCM and HCM pts. However, being dynamic obstruction a potential determinant of ventriculo-arterial coupling in HCM, these markers should be normalized for dynamic pulse pressure, if applicable. It is reasonable that new-technologies like e-tracking overcome this methodological limitation.