tailieunhanh - Cardiovascular Emergencies - Part 2

Sự gián đoạn của các mảng bám dễ bị tổn thương xảy ra tương đối thường xuyên, 9 nhưng huyết khối không tích lũy trên bề mặt mảng bám và bệnh nhân vẫn không có triệu chứng với một điện tâm đồ bình thường, men tim, và troponi | Cardiovascular Emergencies Non-occlusive thrombus asymptomatic Disruption of vulnerable plaques occurs relatively frequently 9 but thrombus does not aCcumulate on the plaque surface and patients remain asymptomatic with a normal ECG cardiac enzymes and troponins. The relatively high frequency with which plaque fissuring occurs indicates the importance of the thrombotic response in determining subsequent clinical events. Figure Clinical syndromes associated with the presence of intracoronary thrombus. Modified from Abrupt reduction in luminal diameter unstable angina The next possibility is that the thrombus produces a reduction in luminal diameter that falls short of complete occlusion. Under these circumstances the luminal clot tends to be platelet rich10 and as such relatively resistant to thrombolysis11 . The release of vasoactive substances from these platelets produces spasm of the smooth muscle in the 30 Acute coronary syndromes I adjacent arterial wall which further contributes to luminal narrowing. Luminal obstruction may be sufficient to produce an abrupt reduction in flow or even intermittent 10-20 minutes occlusion resulting in unstable angina Figure . Several factors then determine the development of myocardial ischaemia. The degree of luminal obstruction caused by the plaque thombus complex This will vary due to the dynamic interplay between the innate thrombotic and thrombolytic factors active on the plaque s surface. These tend to produce cyclical variations in the thrombus load. Vascular tone of the adjacent arterial segment Forty per cent of non-stenotic plaques are eccentric and thus there will be segments of arterial wall adjacent to the plaque where vascular tone remains an important determinant of vessel diameter. Platelet aggregation results in intense vasoconstriction of the vessel wall which is not held rigid by the disrupted plaque. Myocardial oxygen demand For a given degree of arterial narrowing the amount of

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