Page 120 - Coronary hemodynamics in acute myocardial infarction - Matthijs Bax

Chapter 7
Intracoronary doppler flow measurements and data analysis
A bolus of 0.1 mg nitroglycerine was administered intracoronary prior to Doppler flow measurements. Intracoronary flow was measured with a 0.014- inch Doppler-tipped guidewire (FloWire®; Volcano Corporation, San Diego, CA, USA) that was positioned distal to the previously implanted stent in the IRA. Following optimization of the Doppler signal, the average peak flow velocity recordings were obtained before and after induction of hyperaemia by an intracoronary bolus administration of 20 to 40 μg adenosine. Also, intracoronary flow was assessed in the non-IRA (reference artery), if there was <30% stenosis. The position of the Doppler-tipped guidewire in both arteries was documented on angiography at baseline in order to obtain a similar guidewire position at four months.
Doppler flow velocity was recorded continuously and analyzed offline by an independent investigator10. The following parameters were assessed: systolic and diastolic mean aortic pressure and average peak flow velocity at baseline and hyperaemia. CFR was determined as the ratio of hyperaemic to baseline average peak flow velocity. An impaired CFR was defined at the cut-off value of <2.0, according to the mean of the current study population. The relative CFR was calculated as the absolute CFR in the IRA divided by the absolute CFR in the reference vessel. HMRI was calculated by dividing the mean aortic pressure by the average peak flow velocity during maximum hyperaemia. Improvement of microvascular function could be assessed by calculating the difference (∆) between CFR and HMRI at four months and baseline. Both the absolute (∆) and relative (%) differences of both indices were assessed.
Cardiac magnetic resonance and data analysis
CMR was performed on a clinical MRI scanner at 4±2 days following PPCI (baseline) and at four and 24 months, as previously described8. In short, both cine and delayed contrast-enhanced CMR was performed to measure LVF, infarct size, transmurality and the presence of microvascular obstruction. The changes (∆) in left ventricular ejection fraction (LVEF), left ventricular end-diastolic volume (LVEDV) and left ventricular end-systolic volume (LVESV) index were evaluated as the absolute and percentage increases or decreases from baseline to four months and baseline to two years. Total infarct size was determined as previously described using a predefined and standardized definition of
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