DROPPING to the bathroom floor with crushing pains in her chest, Irene Birtwhistle was convinced she was having a heart attack.
"I was in agony," recalls Irene (53), who lives in Turriff, Aberdeenshire, with husband Simon, a retired council road worker and their children, Christopher (18) and Sophie (13).
"The stabbing pains in my chest had woken me early at 6am, my skin was clammy and sweaty, and I was breathless and nauseous. I rushed to the bathroom and vomited, and then I shouted to Simon to call for an ambulance. I was terrified as my symptoms ticked all the boxes for a heart attack."
The ambulance arrived within 10 minutes, yet before the crew had time to take an ECG reading to check the activity and rhythm of her heart, Irene's pains had mysteriously vanished.
"It was like a switch had been flicked off," she recalls. "By the time we got to our local hospital, all my symptoms had died down and my ECG reading was completely normal."
Irene, a retired water company sampler, was transferred to a larger hospital, where a nurse initially diagnosed indigestion.
Yet further blood tests showed Irene had raised levels of a chemical called troponin - high levels indicate the heart has been damaged and can be a sign of a heart attack.
However, a consultant cardiologist ruled out a heart attack because an angiogram (X-ray of the blood vessels) performed six weeks earlier had revealed her blood vessels looked clear.
The consultant instead diagnosed a coronary artery spasm, which affects the muscles of the artery wall, temporarily reducing blood flow to the heart - this can happen spontaneously or be triggered by stress, exercise, cold weather or even the menstrual cycle.
So Irene was sent home the next day, and told to 'forget about it'.
She was to suffer two further terrifying episodes - in October 2016 and October 2017 - again experiencing agonising chest pains, sweats and vomiting.
Ambulances were called and each time her symptoms vanished within around 15 minutes and her ECG readings were normal.
"I felt they thought I was a hypochondriac or neurotic and was having a panic attack," she says.
On a third occasion a consultant again concluded her attacks were due to coronary artery spasms - and again reassured her they were nothing to worry about.
Sceptical, Irene began her own research online and came across support groups for those affected by spasms and a lesser-known type of heart attack called a MINOCA (myocardial infarction with non-obstructed arteries).
While a traditional heart attack is brought on by a blockage to an artery, a MINOCA is triggered by a temporary blockage - including as a result of coronary artery spasms - and so angiograms will show the blood vessels are clear.
MINOCA symptoms can be similar to a classic heart attack. "But they may also wax and wane over several days, because the artery is open and any blockage is only temporary," says Colin Berry, a professor of cardiology and imaging at Glasgow University.
According to research published in June, MINOCAs account for between 5 and 15 per cent of all heart attacks.
More common in women and those under 55, they can be hereditary and can occur for a number of reasons, including a build-up of fatty deposits rupturing and breaking away from the lining of the artery, causing a temporary blockage that clears as the plaque disperses. Other causes include coronary artery spasms.
Diagnosing a MINOCA is complex: it involves a blood test to measure troponin levels and an immediate follow-up with an angiogram, as well as functional tests and a cardiac MRI, which will show up any damage suffered by the heart.
Despite being a recognised medical event, MINOCAs are underdiagnosed in the UK, says Professor Berry.
"This is partly to do with how heart attacks are taught in medical school - students are told that they are caused by blocked arteries," he says.
"They're not told you can have heart attacks with non-blocked arteries, which is actually sex bias because more women than men suffer MINOCAs."
Someone is much less likely to die suddenly from a MINOCA heart attack than from one arising from a blocked coronary artery - fewer than 5 per cent died within 12 months of a MINOCA compared with a death rate of around 10 per cent for heart attacks from blocked arteries, according to a review published in the journal Circulation in 2015.
However, in a study published in the International Journal of Cardiology in 2018, one in four of the 9,000 MINOCA patients studied experienced a major adverse cardiac event such as heart attack, hospitalisation with heart failure or stroke, or death, within four years.
Professor Berry says: "When patients are followed up in the weeks and months after their attack they are at risk of complications such as atrial fibrillation [an irregular heartbeat that raises the risk of stroke], heart failure or another heart attack which can be fatal."
Professor Berry, one of the authors of a paper published in June in the journal International Cardiology: Reviews, Research and Resources, said MINOCAs are not "rare".
"There are at least 100,000 heart attacks a year in the UK - if MINOCAs make up 10 per cent, that's at least 10,000," he says.
He fears some of these patients will have died of the consequences of having an unrecognised heart attack.
"What's happening is that some patients with heart attack symptoms are being given angiograms rather than the tests they need, and if the angiograms are clear it's presented to them as good news," he says.
"By then, MINOCA patients are often stable and well enough to go home. But with a suspected MINOCA, a patient should be offered a cardiac MRI scan when an angiogram is clear," he adds.
"It may be then that they need additional functional tests for coronary artery spasms and they should be offered a specific treatment for this."
However, access to cardiac MRI varies greatly across the UK "with scant provision in Wales and Scotland", according to research published in the journal Heart.
Waiting times vary, too, from 25 days in London to 180 days in Northern Ireland.
Professor Berry says that as well as better access to cardiac MRIs, more research is needed to find treatments for MINOCAs.
"At the moment we're just transferring treatments for classic coronary heart attacks to MINOCAs," he says.
"Cardiologists will recognise a MINOCA, but the issues unfold thereafter in the management of what happens next."
Irene has been suffering from daily chest pain since 2017 and is sometimes so breathless she struggles to walk up stairs and has to drive everywhere.
Frustratingly, her medical records still state that she hasn't had a heart attack. She would like to have a more specialist functional test done at a regional centre, but can't get a referral.
"It's always at the back of my mind that I could have another heart attack and this one could be fatal," she says.
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