Cardiovascular disease is the leading cause of death according to WHO.  Coronary artery
disease can lead to stenosis and occlusion of the vessel leading to inadequate coronary
perfusion. This could lead to diseases like stabile angina, acute myocardial infarction or death.
Coronary angiography is used to visualize these changes to the coronary arteries. Stenosis and occlusion can be treated with percutaneous coronary intervention. The decision to do so is based on the angiographic morphology and the patient's symptoms. Though is the visual
assessment subjective and not always in accordance with the physiological importance of the stenosis.  
Fractional flow reserve (FFR) is a more objective measurement of the significance of the stenosis. It represents the maximal flow with the presence of the stenosis compared to the hypothetical maximal flow without the stenosis. It is measured during medically induced maximal hyperemia with adenosine  Due to the need for maximal hyperemia to measure FFR, it has been developed measurement without the need for adenosine like instantaneous wave free ratio(iFR), that can be calculated without the need for medication. 
The existence of disease in the microcirculation is likely to influence the measurement and importance of a stenosis or occlusion. It can be determined using Index of microcirculatory resistance (IMR) which also is measured using maximal hyperemia. A Value of less than 0.24 is considered to be normal. 
There have been studies regarding the FFR and IMR. IMR was found to be an independent predictor of FFR, and patient with a high IMR was found to have a higher FFR. Such studies have not been conducted for iFR. 
The aim of the project is to investigate the influence of microcirculatory disease on the cut off value for IFR.
Patient referred to supplementary flow and pressure measurements and that have either stabil angina or an non-ST elevation myocardial infarction will be included. During the produce FFR, IFR and IMR will be measured by conventional standards.
The project is a pilot study and 200 patients will be enrolled.
There will be calculated a receiver-operator curve (ROC) to predict FFR <= 0.80 for the groups with normal microcirculation and for the group with microcirculatory disease defined as having a IMR >= 0.24.
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