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Time course of coronary vasodilator response to intravenous adenosine in humans (1071.2)

Measurement of coronary flow velocity reserve (CFVR) has proven useful in assessing coronary vasodilator potential in humans. CFVR is frequently assessed by measuring coronary vasodilator responses to intravenous infusion of adenosine. Importantly, the time course of the coronary vasodilator response to intravenous adenosine infusion has not been well documented. We retrospectively studied this time course during 39 adenosine stress tests obtained in 21 adults (6 F; age range 22‐76 yrs.). Peak coronary blood velocity (CBV) in the left anterior descending artery was assessed non‐invasively in the distal left anterior descending artery using transthoracic Doppler echocardiography before (baseline) and continuously throughout a 6‐min adenosine infusion (0.14 mg/kg/min) in all subjects. CFVR was quantified as CBV peak adenosine/CBVbaseline. Overall, adenosine infusion increased CBV in all subjects (P<0.001) and peak CFVR was observed during the 4th minute in the group as a whole. However, marked variability in the timing of this response was observed. On an individual basis peak CFVR occurred during the 2nd (n=11), 3rd, (n=9), 4th (n=9,) 5th (n=7) and 6th min (n=3) of adenosine infusion. These data suggest that maximal coronary vasodilator responsiveness (i.e., CFVR) occurs variably between the 2nd and 6th minute of adenosine infusion. Based on these findings, we believe the current 6 min adenosine infusion protocol is appropriate. However, we suggest that CBV be monitored during each minute of the infusion so as to capture the true peak response in all subjects.