After primary PCI was completed, intracoronary nitroglycerin (100-200 micrograms) was administered and a coronary pressure wire (St. Jude Medical) was calibrated, equalized to the guide catheter pressure with the pressure wire sensor positioned at the tip of the catheter, and then advanced to the distal two-thirds of the culprit vessel. Three milliliters of room temperature saline were briskly injected through the guide catheter and the mean transit time was measured using a previously described thermodilution technique.11 (link),12 (link) Three measurements were made and averaged. Maximal hyperemia was then induced by infusing intravenous adenosine at 140 μg/kg/min or by injecting intracoronary papaverine (10-20 mg). During maximal hyperemia, the mean transit time was measured again as described above. The mean distal coronary pressure measured with the pressure wire and mean proximal coronary pressure measured with the guide catheter were recorded during maximal hyperemia.
IMR was defined as the mean distal pressure multiplied by the mean hyperemic transit time, as previously described.5 (link) CFR was calculated by dividing the mean resting transit time by the mean hyperemic transit time and fractional flow reserve (FFR) was defined as the mean distal pressure divided by the mean proximal pressure during maximal hyperemia.11 (link),12 (link) The coefficient of variation for the IMR and CFR were previously reported to be 6.9 ± 6.5% and 18.6 ± 9.6% respectively.6 (link)