Quantitative Assessment of the Coronary Microvasculature: New Tools for the Black Box
Epicardial coronary arteries are called conductance arteries1 (or "macrocirculation") as their normal intrinsic resistance is close to zero2 and their main function is to transport blood. They are visible at invasive coronary angiography with an unsurpassed spatial and temporal resolution. Coronary arteries smaller than 500 µm are usually referred to as resistance arteries (or "microvasculature") because, by continuously modifying their resistance, they match blood flow to the requirements of the myocytes.
At coronary angiography the microvasculature appear at best in the form of myocardial blush, a term which says something about its inaccuracy. The microvasculature consists of extramyocardial prearterioles ranging from 100 to 500 µm and intramural arterioles smaller than 100 µm where the largest pressure drop takes place. The resistance of the microvasculature - and thus myocardial blood flow - is controlled by mechanisms3 which are "multiple, interactive, cumulative and nonlinear"4. Changes to one factor will affect many others. This renders the study of the regulation of myocardial blood flow difficult, even in animal models. This also makes it obvious that - as in most biological systems - "resting" conditions is an elusive concept, especially in humans, not to mention in awake patients in a catheterization laboratory.
- microvascular dysfunction
- primary percutaneous coronary intervention
- Received May 14, 2013.
- Accepted May 15, 2013.