Angiographic assessment of myocardial perfusion: TIMI myocardial perfusion (TMP) grading system.

Since the introduction of reperfusion therapy in the early 1980s, cardiologists have largely focused on coronary artery flow and diameter, with the goal being to restore normal epicardial artery perfusion and large lumens. For many years, epicardial coronary flow has been simply assessed by the TIMI (thrombolysis in myocardial infarction) flow grade. This semiquantitative coronary angiographic tool places a patient’s coronary flow into one of four diVerent categories and has been shown to be associated with mortality. The corrected TIMI frame count provides a more objective quantitative index of coronary flow and has been shown to segregate even TIMI grade 3 flow into lower and higher risk subgroups. It is becoming increasingly clear that tissue perfusion, not just an open artery, is critical to myocardial salvage. For instance, among all patients with “open arteries” (TIMI grade 2 or 3), those with TIMI 2 flow have a higher mortality, probably as a result of impaired microcirculation. Myocardial contrast echocardiography demonstrates impaired microvascular flow among TIMI grade 2 patients, and even those with TIMI 3 flow after primary percutaneous transluminal coronary angioplasty (PTCA) have a poor recovery if there is no perfusion by this method. Impaired microvascular perfusion in the presence of open epicardial coronary arteries is thought to be caused by downstream microvascular obstruction, á adrenergic neural reflexes, spasm or thrombotic occlusions of microvessels. Establishing a perfusion grading system Just as the TIMI flow grades are important to studies of coronary artery flow, establishing a myocardial perfusion grading system is important to standardise studies of myocardial perfusion. A number of methods have been used to assess myocardial perfusion such as myocardial contrast echocardiography, thallium/sestamibi myocardial perfusion imaging, and coronary flow reserve measurement. Recently, coronary angiography has been used to assess myocardial perfusion by the measurement of dye passing into and out of the myocardium which is evident as a ground glass appearance, or “blush.” Adequacy of tissue perfusion can be graded by quantifying this blush using conventional dye and angiographic techniques. Perfusion of the myocardium can be categorised using the TIMI myocardial perfusion (TMP) classification system. In TMP grade 3, there is the normal diVuse ground glass appearance of myocardial blush. At the end of the washout phase, dye is only mildly persistent or gone. The washout phase is the time after the end of dye injection during which dye would normally be expected to clear from the epicardial vessels during opacification of the myocardium, followed by clearing from the myocardium. In TMP grade 2, dye enters the myocardium, but accumulates and exits more slowly, so that at the end of the washout phase dye in the myocardium is strongly persistent; however, dye totally clears by the next injection. In TMP