Читать книгу Practical Cardiovascular Medicine - Elias B. Hanna - Страница 20

About 6-10% of patients presenting with a picture of type 1 MI have normal coronary arteries or insignificant CAD (<50% obstructive; 50% being considered obstructive in MI, unlike the 70% cutoff in stable CAD). This prevalence is higher among women and younger patients; up to 15% of women presenting with a type 1 MI picture have no CAD.^19-27 The picture is mostly a NSTEMI picture, but up to a third of cases are STEMI, and half of the patients have completely normal angiographic appearance of the coronary arteries.¹⁹ This phenomenon is coined MINOCA and may be due to any of the following processes:^19,23

1 True type 1 infarction from:plaque rupture or plaque erosion that has embolized distally without leaving any significant stenosis; or thrombosed then recanalized with antithrombotic therapy (or spontaneously). As such, intracoronary imaging often needs to be performed to assess moderate or hazy irregular stenoses in ACS.overlooked occlusion of a branch vessel, such as a diagonal or OM, particularly when it is a flush occlusioncoronary embolus (in patients with AF or severe LV dysfunction) or spontaneous coronary thrombosis from thrombophilia

2 Infarction from isolated coronary spasm or microvascular disease17-19

3 Myopericarditis

4 Takotsubo cardiomyopathy

5 Overlooked type 2 MI mechanisms:Hypertension with diastolic dysfunction and elevated LVEDPPulmonary embolismTachyarrhythmia, or unsuspected hyperthyroidism

Troponin elevation is generally mild, <1 ng/ml, in overlooked type 2 MI, but may be severe in the other processes 1-4.

Work-up with cardiac MRI - Cardiac MRI is a central investigation in MINOCA. In an analysis of all comers with MINOCA, MRI established the diagnosis in most patients (three main diagnoses: myocarditis 33%, infarction 24%, and takotsubo 16%);¹⁹ ~25% did not have significant MRI abnormality (myocardial injury too small, <1 gram?). In two studies of patients with severely elevated troponin (up to 27 ng/ml, mean 9 ng/ml) and unobstructed coronary arteries, cardiac MRI established the diagnosis in 90% of patients (myocarditis 60%, infarction 15%, and takotsubo ~14%).^{26,27 **}

Other work-up- In a cohort of 145 women with MINOCA (median angiographic stenosis 30%), OCT showed plaque disruption in 46% of the cases, at times in an angiographically normal coronary segment and even in some patients with a fully normal coronary angiogram.²⁰ An even higher prevalence of plaque disruption, >50%, was seen in another OCT study of men and women with MINOCA.²¹ MRI showed an ischemic pattern in most (75%) but not all of these plaque disruption cases. Yet MRI detected an ischemic pattern in an additional 25% of patients, missed by OCT, coronary vasospasm being the likely culprit in this subset. Half the time, ischemic edema was seen with no LGE.

Regarding coronary artery vasospasm, one meta-analysis showed that vasospasm, macro- or microvascular, was inducible in 27% of patients with MINOCA, suggesting that it is a common pathogenetic mechanism in MINOCA.¹⁹ In a contemporary study of MINOCA patients, coronary vasospasm was induced in 46% of them.¹⁸

Beware of microvascular dysfunction diagnosis in MINOCA: microvascular dysfunction may be a consequence of the myocardial injury, not the cause of it.

Thrombophilia was detected in 14% of MINOCA patients¹⁹ (but beware that factor V Leiden and factor II mutation are also prevalent in normal subjects, 5% and 2%, respectively).

Prognosis- Most studies suggest that MI patients without significant CAD have good long-term outcomes,^22-25 particularly if the coronary arteries are angiographically normal,^22,24 with a 6-month risk of death of < 1% and death/MI of ~2%. One review suggests a more guarded prognosis, albeit better than MI with obstructive CAD with half of its 12-month mortality.¹⁹ The finding of plaque disruption on OCT does not dictate stenting if stenosis <50%, but rather aggressive antiplatelet and statin therapy.

Consider the diagnosis of coronary embolus in patients with AF or severe LV dysfunction who present with a large troponin rise yet no obstructive CAD.

Beware of the misuse of the term MINOCA. The term MINOCA does not apply to patients with type 2 MI context or non-MI troponin elevation. It only applies to those with type 1 MI presentation.