Embolus and Thrombosis

Pathogenesis

Acute leg ischemia is caused by a sudden deterioration of perfusion to the distal parts of the leg. While the abrupt inhibition of blood flow causes the ischemia, its consequences are variable because acute leg ischemia is multifactorial in origin. Hypercoagulable states, cardiac failure, and dehydration predispose the blood for thrombosis and make the tissue more vulnerable to decreased perfusion. Besides the fact that a healthy leg is more vulnerable than one accustomed to low perfusion, it is unknown what determines the viability of the tissue. The most important factor is probably the duration of ischemia. The type of tissue affected also influences viability. In the leg, the skin is more ischemia-tolerant than skeletal muscle.

The etiology of the occlusion is not what determines the management process. It is, however, of importance when choosing therapy. Embolus is usually best treated by embolectomy, whereas arterial thrombosis is preferably resolved by thrombolysis, percutaneous transluminal angioplasty (PTA), or a vascular reconstruction. The reason for this difference is that emboli often obstruct a relatively healthy vascular bed, whereas thrombosis occurs in an already diseased atherosclerotic artery. Consequently, emboli more often cause immediate threatening ischemia and require urgent restoration of blood flow. Thrombosis, on the other hand, occurs in a leg with previous arterial insufficiency with well-developed collaterals. In the latter case it is important not only to solve the acute thrombosis but also to get rid of the cause. It must be kept in mind that emboli can be lodged in atherosclerotic arteries as well, which then makes embolectomy more difficult.

Table 3 summarizes typical findings in the medical history and physical examination that suggest thrombosis or embolism. Many risk factors, such as cardiac disease, are common for both embolization and thrombosis. Atrial fibrillation and a recent (less than 4 weeks) myocardial infarction with intramural thrombus are the two dominating sources for emboli (80–90%). Other possible origins are aneurysms and atherosclerotic plaques located proximal to the occluded vessel. The latter are often associated with microembolization (discussed later) but may also cause larger emboli.

Table 3. History and clinical indings diferentiating the etiology of acute ischemia

Plaque rupture, immobilization, and hypercoagulability are the main causes of acute thrombosis. Severe cardiac failure, dehydration, and bleeding are less common causes. Hypoperfusion due to such conditions can easily turn an extremity with longstanding slightly compromised perfusion into acute ischemia.

Location of embolic obstruction

Дата добавления: 2014-12-23