Noninvasive evaluation of flow reserve in the left anterior descending coronary artery in patients with cardiac syndrome X

Data on coronary flow reserve (CFR) in patients with syndrome X are still controversial. Furthermore, a non-invasive evaluation of epicardial and microvascular flow reserve in these patients has never been performed. In 17 patients with syndrome X and in 17 age and sex-matched controls, CFR in the mid left anterior descending (LAD) coronary artery was evaluated by transthoracic color and pulse wave Doppler, using a 7 mHz probe (Sequoia, Siemens). Peak diastolic LAD flow was calculated at rest and at peak adenosine (140 µg/kg/min i.v. in 90 sec). Myocardial contrast echo (MCE) was performed at rest and during adenosine by real time Cadence Pulse Sequencing (CPS) and i.v. Sonovue® (Bracco) (5 ml at 1 ml/min) and microvascular blood volume (A), velocity (β) and flow (Axβ) by replenishing curves (y=A(1-eβt)). CFR was measured both by Doppler echo as adenosine/rest velocity ratio, and by MCE as microvascular volume (A), velocity (β) and flow (Axβ) adenosine/rest ratio. Compared to controls, patients with syndrome X demonstrated lower LAD CFR, β MFR and Axβ MFR (p<0.01, p<0.005 and p<0.005 respectively). Among syndrome X patients, those with angina and ST-segment depression during adenosine test had even lower LAD CFR, β MFR and Axβ MFR compared with those with no-symptoms (p<0.0001, p<0.0001, p<0.005 respectively). LAD CFR demonstrated a significant linear correlation with β MFR (r=.92, p<.0001) and Axβ MFR (r=.77, p<.0001). In conclusion, CFR in the LAD, successfully evaluated by transthoracic Doppler echo and MCE, is significantly reduced in syndrome X patients and even more in those with angina pectoris and ST-segment depression during adenosine test. Thus, non-invasive evaluation of CFR by echo is feasible and it provides information on the severity of the microvascular impairment.