The gold standard to induce coronary hyperemia for measurement of fractional flow reserve (FFR), coronary flow reserve (CFR) and index of microcirculatory resistance (IMR) is adenosine, but it exerts several side effects due to its unspecific action on adenosine receptors. The specific A2a-receptor agonist, regadenoson, has been shown to dilate coronary arteries and enables FFR measurements. The aim of the study was to evaluate whether simultaneous measurement of FFR, CFR and IMR is feasible, safe and effective within regadenoson-induced hyperemia.

Fractional flow reserve (FFR), coronary flow reserve (CFR) and the index of microcirculatory resistance (IMR) provide significant information on the conductance of coronary macro- and microcirculation.

FFR-based functional assessment of coronary artery disease has proven to be superior to purely morphologic assessment and thereby guides therapy decision. IMR is a pressure-temperature derived parameter for quantifying microcirculatory resistance, which has been proven to be relatively independent of epicardial stenosis severity when taking collateral flow into account. IMR is increased in patients with acute myocardial infarction and microvascular obstruction (MVO) as assessed by contrast-enhanced CMR and predicts left ventricular function and enddiastolic volumes at 6 month independently of initial infarct size.

Most interestingly, even in the absence of obstructive coronary artery disease, IMR is elevated in more than 20% of patients presenting with chest pain. The clinical meaning for this finding has to be elucidated.

FFR, CFR and IMR can only be measured under conditions of minimal coronary resistance with the need for coronary hyperemia. The current "gold standard" to induce hyperemia in the assessment of coronary conductance is adenosine. However, adenosine is known to cause side effects (bronchospasm and disturbances in atrioventricular conduction) due to its unselective action on all adenosine receptors. Besides that, adenosine requires a body weight adapted dosing and continuous infusion. However, alternative routes like intracoronary injection show good correlation compared with the intravenous route and side effects can be reduced. In contrast, regadenoson, a specific A2A receptor agonist, exhibits negligible side effects. It can be administered intravenously as a non-body weight adapted bolus via peripheral vein without the need for transfemoral delivery. Thus, patients with a transradial access for cardiac catheterization might benefit the most from inducing hypermedia via peripheral vein. It has already been shown that regadenoson increases coronary blood flow yielding comparable values for FFR and indexes of perfusion in SPECT. However, the duration and stability of regadenoson-induced hyperemia might be insufficient for a simultaneous measurement of FFR, CFR and IMR, which has not been tested so far.

The aim of the present study is to evaluate whether simultaneous measurement of the parameters FFR, CFR and IMR under regadenoson-induced hyperemia is feasible, safe and effective in patients with stable coronary artery disease undergoing a transradial procedure

Inclusion Criteria:

Coronary angiography with indication of FFR measurement

• angiography without pathological results explaining the patients' symptoms
• intermediate stenosis (50-70%)

Exclusion Criteria:

• <18 years
• Hypersensitivity towards regadenoson
• hemodynamic instability
• severe hypotension
• acute myocardial ischemia
• AV block II-III

Patients with indication for FFR measurement due to a coronary artery stenosis of unclear hemodynamic relevance