Mechanism of coronary flow reserve reduction in systemic sclerosis: insight from intracoronary pressure wire studies.

OBJECTIVE Functional impairment of coronary microcirculation is thought to be a major pathway in the development of primary cardiac involvement in SSc; however, the underlying mechanism is not fully understood. We aimed to investigate the mechanisms of coronary flow reserve (CFR) reduction in patients with SSc. METHODS Seventeen SSc patients and 17 gender- and age-matched controls were enrolled. Coronary angiography and determination of coronary flow parameters including index of myocardial resistance (IMR) using intracoronary pressure wire at basal conditions and during vasodilator-induced maximal hyperaemia were performed. Transit times of repeated intracoronary saline injection were measured to evaluate the role of cold exposure. RESULTS SSc patients with decreased CFR had accelerated basal coronary flow velocity (P < 0.05), and their IMR in hyperaemia (IMR(hyp)) did not differ from either SSc patients with normal CFR or from the controls (P = 0.292 and P =  0.308). The coronary flow velocity of SSc patients correlated with the IMR at baseline (IMR(bas)) (r  = 0.56, P  = 0.019). Injection of room temperature saline did not provoke changes in coronary transit times. CONCLUSIONS The lack of decrease in the maximal vasodilatation response indicates that there is no irreversible functional damage at the level of the coronary arterioles. In patients with reduced CFR, the decreased basal IMR and higher velocity reflect compensatory vasodilatory mechanisms probably triggered by ischaemic signals deriving from abnormal myocardial microcirculation.