Читать книгу Practical Cardiovascular Medicine - Elias B. Hanna - Страница 16

Type 1 or spontaneous MI is usually due to plaque rupture or erosion that promotes platelet aggregation, thrombus formation and microembolization of platelet aggregates.

NSTEMI is a type 1 MI without persistent ST-segment elevation. STEMI is a type 1 MI with persistent (> 20 min), ischemic ST-segment elevation.^1,4 For practical purposes, ischemic symptoms with ongoing ST-segment elevation of any duration are considered STEMI and treated as such. The diagnosis may be retrospectively changed to NSTEMI if ST elevation quickly resolves without reperfusion therapy, in < 20 minutes.

Figure 1.1 Diagnosis and types of myocardial infarction.

In NSTEMI, the thrombus is most often a platelet-rich non-occlusive thrombus. This contrasts with STEMI, which is due to an occlusive thrombus rich in platelets and fibrin. Also, NSTEMI usually has greater collateral flow to the infarct zone than STEMI.

As a result of the diffuse inflammation and alteration of platelet aggregability, multiple plaque ruptures are seen in ~30–80% of MIs, although only one is usually considered the culprit.⁵ This shows the importance of medical therapy to “cool down” the diffuse process, and explains the high risk of MI recurrence within the following year even if the culprit plaque is stented.⁵

Occasionally, a ruptured plaque or, more commonly, an eroded plaque may lead to microembolization of platelets and thrombi and impaired coronary flow without any residual, angiographically significant lesion or thrombus.