Introduction: Maximal hyperemia is a key element of invasive physiological studies and intravenous (IV) infusion of adenosine is the most commonly used method. However, hyperemic efficacy of IV adenosine under low cardiac output state has never been elucidated. Given that adenosine’s plasma half life is extremely short, the plasma accumulation of adenosine by IV infusion may be hampered by the reduced cardiac output. The aim of this pilot study was to evaluate the hyperemic efficacy of IV adenosine in comparison with intracoronary (IC) nicorandil in patients with both intermediate coronary stenosis and reduced ejection fraction.
Methods: Patients with left ventricle ejection fraction (LVEF) of 40% or less who had intermediate coronary stenosis was prospectively enrolled. Hyperemic efficacy of IV infusion of adenosine (140 μg/kg/min) and IC bolus of nicorandil (2 mg) was compared with FFR. LVEF was measured by biplane Simpson’s method. Cardiac index (CI) was calculated using continuity equation.
Results: Seven patients were enrolled for this pilot study. Mean value of LVEF was 30.9% (range 18-40%). Hyperemic efficacy of IV adenosine 140 μg/kg/min was numerically inferior to that of IC nicorandil (FFR: 0.90±0.05 vs. 0.85±0.06, respectively)(Figure 1). Three patients (43%) failed to induce maximal hyperemia with IV adenosine; Cardiac index of these patients were numerically lower (CI: 2.6±0.3 vs. 3.5±0.5 L/min/m2, respectively). One patient showed oscillating hyperemic curve with IV adenosine 140 μg/kg/min, which was resolved with IV adenosine 180 μg/kg/min.
Conclusion: This pilot study suggests that hyperemic efficacy of IV adenosine is not reliable in patients with reduced cardiac index. Therefore, IC administration of hyperemic agent is recommended for invasive physiological evaluations in these settings.