Background Intravenous adenosine is used to minimise the coronary micro-resistance to achieve maximal hyperaemia along with nitrates for optimal fractional flow reserve (FFR) measurements. We hypothesise that caffeine, being a competitive inhibitor of adenosine, would influence adenosine-mediated FFR readings.

Methods Consecutive patients undergoing angiogram and FFR measurements were enrolled after abstaining from caffeine for 24 h. Patients with any contraindications to intravenous adenosine or caffeine were excluded. FFR measurements were taken using nitrates and adenosine pre and post 4 mg/kg intravenous caffeine administration and results were compared.

Results 10 patients were analysed (80% men, age 59.9±9.4, weight 87.5±15.6). Baseline caffeine levels were undetectable in all patients and increased significantly postintravenous caffeine administration (16.4±5.5 μg/mL). Baseline preadenosine FFR values were similar before and after caffeine administration (0.91±0.06 vs 0.91±0.07; p=0.41). Postadenosine FFR readings were 0.79±0.07, which increased non-significantly to 0.82±0.11 postcaffeine (p=0.15). Two significant FFR readings (≤0.8) changed to non-significant after caffeine administration (0.77–0.93 and 0.8–0.91).

Conclusions Caffeine may affect FFR results in some patients. Larger studies are warranted to clarify the extent and magnitude of caffeine/adenosine interaction particularly due to ubiquitous nature of caffeine and increasing importance of FFR in clinical practice.