Myocardial infarction with non-obstructive coronary arteries (MINOCA) is referred to as a syndrome characterised by the clinical characteristics of myocardial infarction but with normal coronary arteries or no significant coronary stenosis on coronary angiography.

Epidemiology

The suggested prevalence ranges from 1-14% ^1-4 with women being more commonly affected than men ^5,6.

Diagnosis

The entity MINOCA is a working diagnosis with the following diagnostic criteria ^1-4:

• universal criteria for acute myocardial infarction defined by

  • positive cardiac biomarker

  • confirmative clinical evidence

  • imaging evidence of new myocardial loss or myocardial ischaemia

• non-obstructive major epicardial coronary arteries on coronary angiography

• no clinically overt specific cause for the acute presentation

Clinical presentation

Patients present with features of acute myocardial infarction defined by the universal criteria ⁵ including a rise of cardiac troponin values above the 99^th percentile and one of the following ^1-4:

• typical clinical symptoms of myocardial ischaemia

• new ischaemic ECG changes as significant ST-T changes or left bundle branch block

• new pathological Q-waves

Complications

Complications of myocardial infarction with non-obstructive coronary arteries include major adverse cardiovascular events (MACE) and death ¹.

Pathology

Myocardial infarction with non-obstructive coronary arteries (MINOCA) is a heterogeneous clinical entity with many different possible pathologic causes ^1-4.

Once one of the aetiologies has become evident, the condition should be no longer termed this way.

Aetiology

Aetiologies include the following ^1-3:

• coronary plaque disruption when no thrombus can be found (due to plaque rupture, erosion or ulceration)

• coronary artery dissection or intramural haematoma

• coronary artery spasms (due to hyper-reactivity to endogenous substances or exogenous vasospastic agents e.g. drugs)

• endothelial dysfunction

• coronary embolism (due to hereditary or acquired thrombotic disorders, paradoxical embolism, valvular heart disease and/or vegetations, cardiac tumours etc.)

• supply-demand mismatch (tachyarrhythmia/bradyarrhythmia, anaemia, hypotension, shock, severe hypertension, cardiomyopathy etc.)

• uncertain aetiology

Radiographic features

Imaging features of myocardial infarction with non-obstructive coronary arteries (MINOCA) include the following ^1,5:

• new regional wall motion abnormality or a new loss of viable myocardium on imaging e.g. subendocardial late gadolinium enhancement

• non-obstructive coronary arteries on angiography, defined as the absence of any coronary artery stenosis ≥50% in any infarct-related artery

Echocardiography

Cardiac echo can show new regional or global wall motion abnormalities and has a role in the search for aetiology.

Intravascular ultrasound (IVUS) has an important role in the detection of plaque rupture and/or ulceration as well as the detection of coronary artery dissection.

Cardiac CT

To make the diagnosis of myocardial infarction with non-obstructive coronary arteries (MINOCA), cardiac CT should not show any significant coronary artery obstruction in any of the potential infarct-related arteries, even though the method is not part of the guidelines as yet ^1,5.

In the search of aetiology, it could help to demonstrate coronary dissection or intramural haematoma as well as the demonstration of coronary plaque burden ³.

Coronary angiography (DSA)

As per definition, myocardial infarction with non-obstructive coronary arteries features a normal coronary angiogram or at least no significant coronary artery stenosis in any of the potential infarct-related arteries.

Intravascular imaging as intravascular ultrasound (IVUS) or optical coherence tomography (OCT) has an important role in the workup, in particular in the detection of plaque rupture and/or ulceration as well as the detection of coronary artery dissection ^2,3.

Provocative spasm testing can detect and confirm coronary vasospasm. However, the procedure should not be conducted in the acute stage of a myocardial infarction ³.

MRI

Due to its cardiac tissue characterisation ability, cardiac MRI has an important role in the workup of myocardial infarction with non-obstructive coronary arteries (MINOCA) ^2,3. It can provide further clues in the search for the cause. The pattern of late gadolinium enhancement can suggest a typical infarct-related vascular pattern or might point towards a non-vascular or inflammatory type pattern or myocardial infiltrative disease ^2,3.

However, about 8-67% of patients with myocardial infarction with non-obstructive coronary arteries (MINOCA) do not show any cardiac wall motion abnormalities, myocardial oedema or late gadolinium enhancement ².

Radiology report

The radiological report should describe and suggest possible underlying causes of the above condition if this is evident on imaging.

Within the scope of this article is confined to the imaging methods besides coronary angiography and intravascular imaging:

Echocardiography

• wall motion abnormalities and/or hypertrophy

• valvular heart disease

• valvular vegetations if present

• cardiac thrombi

Cardiac CT

• coronary plaque burden

• coronary anomalies

• possible myocardial bridging especially in left ventricular hypertrophy

Cardiac MRI

• wall motion abnormalities

• presence myocardial oedema

• presence and characterisation of late gadolinium enhancement (vascular vs non-vascular patterns)

• findings are indicative of a possible source for coronary embolism as left ventricular thrombi cardiac valve disease, cardiac tumours, persistent foramen ovale (PFO) etc.

• indicate possible differential diagnosis e.g. myocarditis, takotsubo cardiomyopathy or other cardiomyopathies

Treatment and prognosis

The treatment of myocardial infarction with non-obstructive coronary arteries (MINOCA) varies with the underlying cause, which should be searched for.

Treatment options include the following ²:

• antiplatelet therapy, angiotensin receptor blocker and beta-blockers in case of coronary plaque disruption

• conservative treatment with antiplatelet therapy and beta-blockers in coronary artery dissection

• calcium antagonists and nitrates in coronary vasospasm

• PFO closure device, antiplatelet therapy, anticoagulation in case of a coronary embolism

• reversal of the underlying cause in an underlying oxygen supply-demand mismatch

• aspirin, statins and calcium antagonists in case of uncertain aetiology

The outcome of myocardial infarction with non-obstructive coronary arteries (MINOCA) is determined by the underlying aetiology, the overall prognosis is serious, though, with a 1-year mortality of about 3.5% ^1,6.

Differential diagnosis

Myocardial infarction with non-obstructive coronary arteries (MINOCA) is a working diagnosis and due to its quite serious prognosis, it warrants a meticulous search of the underlying causes ^1-3, which are part of the differential diagnosis of this entity. Others include

• takotsubo cardiomyopathy

• myocarditis

• cardiomyopathies

• valvular heart disease