The endothelium injured during a therapeutic procedure releases free radicals and vasoactive substances, such as endothelin-1 (ET-1), a peptide derived from endothelial cells and cardiomyocytes, and platelet thromboxane. Microvasculature dysfunction hypothesis - This hypothesis is attractive and frequently mentioned in the literature. Arterial thrombosis as a cause of "no-reflow" is, therefore, unlikely. Often, however, as in acute myocardial infarction, "no-reflow" occurs despite the use of thrombolytic agents. Therefore, a fresh red thrombus would be dissolved by the anticoagulants. Anticoagulation therapy is an integral part of the therapeutic procedure when using a catheter. Although attractive, this explanation has no angiographic basis, which weakens this theory.Īrterial thrombosis hypothesis - Some 7 speculate that "no-reflow" results when a thrombosis due to a red thrombus occurs. ![]() The embolic hypothesis - Fragments of plaque and thrombi may detach from the plaque submitted to treatment and embolize to the distal portion of the circulation. The most accepted of these are: "no-reflow" due to embolism, arterial thrombosis, microvasculature dysfunction, platelet action, endothelial injury mediated by leukocytes, and regional myocardial contracture. With the description of the phenomenon in human beings, new hypotheses were formulated about the causes of "no-reflow". Initially, "no-reflow" was attributed to an obstruction of the microvasculature, resulting from neutrophil accumulation, endothelial edema and hemorrhage, and regional sustained contracture of myocytes 1. Several hypotheses have been suggested, but not all have experimental confirmation. Pathophysiology - The mechanisms of "no-reflow" are not completely understood, and many explanations are merely speculations. When coronary blood flow velocity is analyzed by Doppler flow-wire, retrograde systolic flow, reduction of anterograde systolic flow and fast deceleration of diastolic flow caused by the "no-reflow" phenomenon can be observed 6. "No-reflow," when visualized by angiography, appears as a column of contrast medium with slow back and forth movements inside a vessel usually close to the site of the treated lesion without progression of the contrast medium to the distal portion of the coronary artery. It is not to be confused with slow flow, which is a much less critical situation that is more frequently observed and usually reversible. The "no-reflow" phenomenon can be defined as an acute and severe reduction of coronary flow (TIMI 0 to 2) * *Īfter removal of an arterial occlusion, in the absence of spasm, thrombi, severe residual lesions, and arterial dissection. This phenomenon was also observed in other organs, such as the skin, kidneys and brain, where ischemia occurred 1. Later, "no-reflow" was observed in patients who experienced short periods of ischemia and coronary reperfusion with thrombolytic agents 2 and, more recently, in different types of coronary interventions with catheter 3-5. These investigators concluded that the absence of flow was an ischemic phenomenon, related to the duration of coronary occlusion, which resulted in muscle injury and death of myocardial cells 1. ![]() In the coronary arteries occluded for 40 minutes, there was uniform reperfusion of the ischemic myocardium however, in those occluded for 90 minutes, there was no reperfusion after removal of the coronary occlusion. The coronary arteries of these dogs were occluded for 40 or 90 minutes, and after that, they were reperfused and studied by means of contrast medium injection. Kloner and co-workers 1 first described the "no-reflow" phenomenon in 1974 in dogs with experimentally induced myocardial infarction. Its most intriguing clinical characteristic perhaps is its unpredictability. The "no-reflow" phenomenon, a side effect, is an uncommon and critical occurrence and, if not reversed, causes a high rate of morbidity and mortality. This therapeutic approach has had unexpected side effects, however, for which solutions must be found, particularly in the are of interventional cardiology. In the last twenty years, the treatment of coronary heart disease with cardiac catheterization has greatly advanced. The "No-Reflow" Phenomenon in the Coronary ArteriesĪntônio Esteves Fº, Donaldo Pereira Garcia, Eulógio Emílio Martinez Fº
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |