The term MINOCA stands for Myocardial infarction with non-obstructive coronary arteries.
I’ll try and explain this a bit better by using a case study.
A 50-year-old lady was admitted to my hospital with crushing chest tightness. She had an ECG which suggested changes in keeping with a lack of blood getting to the heart. She had a blood test to measure Troponin. Troponins are enzymes released from the heart when the heart has been damaged. In this lady the troponin was found to be elevated. On the basis of these findings we told her that she had suffered a heart attack. She asked me why I felt she had had a heart attack and I explained to her that she had had chest pains and the blood test indicating damage to the heart was elevated and that was all we needed to say that she had had a heart attack. Clearly quite upset, she asked me what would happen next and i said to her that the heart attack was probably caused by a very severe narrowing or even a blockage of one or more of the blood vessels (the coronary vessels) that supplied blood to the heart and the next step would be to do a test called an angiogram to look at her coronary vessels, identify exactly where the narrowings were and fix them. She agreed and we performed an angiogram and we were fully expecting a blockage but interestingly there weren’t any. She had some very minor plaque but certainly nothing that could explain the heart attack and therefore she was discharged with a diagnosis of MINOCA i.e to all intents and purposes she had a heart attack but without significant obstructive disease in her coronaries.
We have known that patients can present with heart attacks in the absence of obstructive coronary disease for over 80 years but the term MINOCA has been adopted for about the past 7-8 years.
MINOCA is not an uncommon diagnosis. Up to 5-15% of all patients who present with heart attacks are found to have unobstructed coronary vessels and therefore diagnosed with MINOCA. The big problem is that as nothing major is found, there is nothing to fix and this leaves the poor patient feeling very perplexed and uncertain about their future.
Whilst traditional heart attacks are seen in older patients and more men than women, MINOCA is seen more often in younger women (<55y). Genetics and physiological stress are also risk factors.
Whilst it is reassuring to find that the heart arteries are not obstructed, MINOCA should not be considered a benign diagnosis because the heart has still suffered damage and the areas of damage can cause the heart to become irritable and cause dangerous heart rhythm disturbances. In addition, the heart can still be left weak and of course, the underlying problem can still manifest with another ‘heart attack’ and more damage in the future.
It is important for me to stress that MINOCA is not a complete diagnosis in itself but rather an umbrella term for patients who present like the lady I mentioned earlier did. There are lots of underlying causes that could explain MINOCA and this is why the diagnosis of MINOCA should prompt more detailed and more sophisticated investigation.
The causes can be divided into 3 groups:
- Coronary causes
- Cardiac Causes
- Non-Cardiac Causes
Coronary causes include:
- Coronary artery spasm – In this scenario, for some reason the coronary vessel goes into spasm, the blood does not get through, the heart gets damaged but by the time we look, the spasm has resolved and the coronaries look unobstructed.
- Coronary artery embolism – In this scenario, a blood clot which forms elsewhere goes down a coronary artery, causing a blockage but by the time we do the angiogram, the clot has dissipated and we see unobstructed vessels.
- Coronary artery dissection – a tear happens in the wall of the coronary artery creating a flap which obstructs the coronary transiently and causes the chest pain and the damage
- Coronary artery plaque rupture – Not uncommonly, a minor plaque may rupture, causing blood clots to form around the area and the blood clots stop the blood from getting through and by the time you come to look the clots have dissipated.
- Micro vascular disease – the blockages occur in tiny blood vessels which are not visualized on the angiogram.
- Myocarditis – an infection of the heart may cause damage to the heart muscle and cause chest pain.
- Takotsubo Cardiomyopathy – a huge surge of stress hormones causes part of the heart to become paralysed and this leads to release of troponins and chest pain
- Other forms of cardiomyopathy
- Heart rhythm disorders
- Blood clots in the lung can present with chest pain and a rise in troponins
- Strokes or intracranial catastrophes
- Blood clotting disorders
Given the fact that so many conditions could cause a MINOCA presentation, it is vital that doctors look further than just sending the patient home with a diagnosis of MINOCA because some of these conditions, if identified, can be treated.
Firstly I think the angiogram needs to be carefully reappraised to ensure that nothing has been missed and any narrowings have not been under-egged.
Then I think it is important that patient has an assessment of the function of the heart by means of an ultrasound to look for cardiomyopathies, Takotsubo etc.
It is also very important to exclude blood clots in the lung and look for evidence of heart rhythm disorders, infections (e.g. myocarditis), and blood clotting disorders.
Finally if nothing is found, the patient should undergo an MRI scan. The advantage of MRI is that it is very good at identifying scar in the heart and the pattern of scar can sometimes help identify the etiology. As the coronaries sit on the surface of the heart and send tributaries into the heart muscle, anything that even transiently blocks the coronaries will cause the innermost layers of the heart to become damaged first and therefore the scar will always affect the innermost layer first. However with conditions such as myocarditis, scar will not follow this distribution and will be more random. Some conditions such as Takotsubo are not associated with the finding of any scar whatsoever.
Studies that have looked at this group of patients have shown that up to 30% of MINOCA patients are actually confirmed as having had myocarditis by the MRI, 25% of patient have no scar, 20% have a traditional heart attack scar (suggesting a coronary cause) and 20% are confirmed as having a Takotsubo process.
MINOCA, as i mentioned is not a benign diagnosis and the all-cause mortality is up to 3.5% at one year and this is why it is important to look hard and correct the correctible. At present we still do not have enough data on what medications to discharge these patients on so they still go on the same medications as people with a traditional heart attack go on but I suspect that in the next few years we should have more data on which medications offer protection to MINOCA patients and which don’t.
I hope you found this useful. I appreciate you more than you can imagine.
Here is a video I have done on this subject.
Keywords: MINOCA; MI with normal coronary arteries; Coronary vasospasm; Microvascular angina; Syndrome X; Prinzmetal angina.