Reply: Caffeine and fractional flow reserve overestimation: a word of caution

The letter by Siig et al1 raises a question about caffeine's antagonism to adenosine-induced coronary hyperaemia, in connection with our recent publication2, by quoting a paper by Kasumi et al3. They showed no relationship between adenosine triphosphate-induced hyperaemia and caffeine intake before fractional flow reserve (FFR) measurements. The paper, however, has critical limitations. First, they evaluated the time from the last caffeine intake alone and did not measure serum caffeine levels, which precluded any conclusion on the effect of caffeine on adenosine-induced FFR (FFRADN). Other than the time from the last caffeine intake, several factors influence serum caffeine levels, including ...