Invasive measurement of coronary microvascular resistance in patients with acute myocardial infarction treated by primary PCI.

Up to 40% of patients with acute myocardial infarction develop microvascular obstruction (MVO) despite successful treatment with primary percutaneous coronary intervention (PCI). The presence of MVO is linked to negative remodelling and left ventricular dysfunction, leading to decreased long-term survival, increased morbidity and reduced quality of life. The acute obstruction and dysfunction of the microvasculature can potentially be reversed by pharmacological treatment in addition to the standard PCI treatment. Identifying patients with post-PCI occurrence of MVO is essential in assessing which patients could benefit from additional treatment. However, at present there is no validated method to identify these patients. Angiographic parameters like myocardial blush grade or corrected Thrombolysis In Myocardial Infarction (TIMI) flow do not accurately predict the occurrence of MVO as visualised by MRI in the days after the acute event. Theoretically, acute MVO can be detected by intracoronary measurements of flow and resistance directly following the PCI procedure. In MVO the microvasculature is obstructed or destructed and will therefore display a higher coronary microvascular resistance (CMVR). The methods for intracoronary assessment of CMVR are based on either thermodilution or Doppler-flow measurements. The aim of this review is to present an overview of the currently available methods and parameters for assessing CMVR, with special attention given to their use in clinical practice and information provided by clinical studies performed in patients with acute myocardial infarction.