Therapeutic advances in myocardial microvascular resistance: Unravelling the enigma

The coronary microcirculation regulates blood flow by responding to increased cardiac metabolic demands. Despite this important role, study of the microcirculation has been neglected for many years. This is because it is difficult to evaluate the function of this compartment, and doing so conflicts with the current clinical practice of many cardiologists, who are more familiar with dealing with the disease processes that affect the large epicardial arteries. The clinical importance of microvascular function is emerging because of attempts to develop techniques which allow for the objective assessment of microvascular function while in the catheter lab. In addition, there is a growing body of evidence to suggest that the microvascular compartment may show early changes in patients who are at risk of coronary artery disease. It is also possible that the microcirculation is responsible for the poor response to revascularisation in certain patients, potentially in the form of the no reflow phenomenon and peri-procedural myocardial infarction, which may be observed following percutaneous coronary intervention. Pathological microvascular changes could explain the significant midterm morbidity and mortality associated with these complications. The aim of this review is to provide an overview of the physiological mechanisms responsible for the regulation of the coronary microcirculation and to focus on the pathological processes which affect the microcirculation, particularly in relation to coronary angioplasty. We will also discuss potential mechanisms and therapeutic options which could improve microvascular perfusion in this group of patients.