Echocardiographic examination
All echocardiographic examinations were performed with an ultrasound platform equipped with a matrix-array transducer (X5-1, Philips Epiq 7, Philips Healthcare, Andover, MA, USA). Chamber quantification and other measurements were done according to the relevant international guidelines. For coronary flow measurements, distal part of the left anterior descending artery (LAD) was visualized using high ultrasound beam frequency (5-7 MHz). The color Doppler gain was optimized using conventional techniques and the Nyquist limit was set to 0.16-0.50 m/s. After visualization of the distal part of the LAD, pulse-wave Doppler cursor was placed to measure coronary flow velocity and measurements were done before and after dipyridamole infusion (0.84 mg/kg for 6 minutes). Patients were monitored during the procedure and heart rate and blood pressure data were recorded at baseline, during infusion and after the procedure. Coronary flow velocity reserve was calculated as the ratio of the hyperemic peak flow velocity to the resting peak flow velocity. We have previously reported interobserver and intraobserver variability values for our laboratory (15,16).
All echocardiographic examinations, including CFVR measurements were performed immediately after the stabilization of the patient. For patients that needed intubation or intensive unit care due to any cause, echocardiographic examinations were delayed until the patient was transferred to the ward.