The achievement of maximal vasodilatation is mandatory for obtaining valid measurements of the coronary flow reserve (CFR) and the fractional flow reserve (FFR). Recent studies have indicated that an incremental dose or a high dose of adenosine is necessary to achieve maximal hyperemia. We performed this study to examine the response of the physiologic parameters to different doses and to different methods of administration of adenosine in Koreans.

CFR: The CFR was measured in 25 consecutive patients with angiographically normal coronary arteries by using a Doppler wire. Three different doses (9, 18 and 36 µg in the left coronary artery (LCA), and 6, 12 and 24 µg in the right coronary artery (RCA)) of adenosine were used. FFR: In a phase I study, 102 consecutive patients with 188 intermediate lesions (160 LCA and 28 RCA lesions) underwent FFR measurements with using a pressure wire. Three different bolus doses (20, 40 and 80 µg) were administered in an incremental fashion. In a phase II study, the hyperemic efficacy of 3 different doses of intracoronary (IC) infusion (180, 240 and 300 µg/min) and of 3 methods of administration (IC infusion, intravenous infusion and IC bolus) were compared.

CFR: The higher 2^nd dose of adenosine had a tendency to achieve a higher CFR than the lower 1st dose. But when we increased the adenosine to more than 20 µg (LCA 36 and RCA 24 µg), there was a tendency towards obtaining a lower CFR than that obtained after the 2^nd dose of adenosine (LCA: 2.78±0.71 vs. 2.66±0.60, p=0.055, RCA: 3.19±0.88 vs. 3.04±0.80, p=0.86). FFR: Phase I: The dose of adenosine that achieved maximal hyperemia was 51±16 µg in the LCA and 35±20 µg in the RCA. In 73 (46%) of the LCA lesions and 12 (42%) of the RCA lesions, a further reduction of the FFR occurred when a higher dose of adenosine was used (LCA>40 ug, RCA>20 µg). Phase II: The FFR obtained after an IC bolus injection (0.83±0.06) was significantly higher than obtained with an IV infusion (0.79±0.07) and an IC (0.78±0.09) infusion (p<0.01). However, no difference in the FFR was observed for the IC and IV infusions.

This study suggests that more than 20 µg adenosine does not have an additive effect on measuring the CFR. Adenosine 40 µg for the LAD and 20 µg for the RCA seems to be optimal as a intracoronary bolus injection for measuring the FFR in most cases. However, for the patients with borderline FFR, a higher bolus adenosine dose or an adenosine continuous infusion may be necessary.