Thousands of people with the most dangerous type of heart disease could suffer a fatal yet easily preventable heart attack due to ineffective tests, experts warn. 

Whilst any of the arteries in the heart can become dangerously blocked, blockages of the left main coronary artery (LMCA) are considered especially deadly as it increases the risk of a major, or what is known as a ‘widow-maker’, heart attack. 

Narrowing of the left artery is usually diagnosed by a doctor inserting a thin wire—called a catheter—through a blood vessel in the wrist or groin and into the heart. 

Here, doctors can monitor for a decrease in blood pressure, which indicates a blockage in the most critical artery of the heart.

But figures from charities suggest thousands of patients per year could have their potentially fatal heart condition missed because of outdated guidelines on how to read these test results. 

Previously, doctors have been taught to look out for a blood pressure ‘score’ below 0.8 in both major blood vessels of the LMCA, which supply most of the heart muscle with blood. 

However, researchers from King’s College London now say that just one low score below the 0.8 threshold in either of these branches of the LMCA could be a tell-tale warning sign of the disease. 

If missed by doctors and left untreated—as is the case with over a quarter of patients with the disease—this could result in sudden heart attack and even death. 

Researchers said more than a quarter of patients with a deadly form of heart disease that can result in a ‘widow-maker’ heart attack, so-called because of the extremely low survival rates, could be missed following current tests

While some warning signs are easy to spot — such as severe chest pain — others are more vague and hard to pinpoint

Professor Divaka Perera, senior author of the study and an expert in cardiology at KCL, said: ‘These findings are so important because they will guide doctors to accurately interpret seemingly conflicting test results.

‘That means doctors can correctly diagnose LMCA disease, and consider a stent or bypass surgery, or carry out further investigations of the LMCA, rather than ignoring potentially important disease in a major artery of the heart,’ he added. 

The experts, who published their findings in the journal Circulation: Cardiovascular Interventions, studied 80 patients undergoing tests on their heart—47 of which already had a LMCA disease diagnosis. 

This test—known as a coronary angiography—enables doctors to better visualise the structure and function of the heart, helping diagnose heart conditions and plan future treatments. 

All of the patients presented with ‘apparently conflicting results’.

This was the case even for patients who already had a confirmed diagnosis.

Researchers concluded that ruling out LMCA disease because of one ‘normal’ blood pressure reading, over 0.8 was insufficient.

The scientists estimated that the current methods could be leaving up to 28 per cent of patients without a diagnosis. 

NHS data shows a rise in the number of younger adults suffering from heart attacks over the past decade. The biggest increase (95 per cent) was recorded in the 25-29 year-old demographic, though as numbers of patients are low even small spikes can look dramatic 

They explained that a patient could have one normal reading, from the left circumflex artery, and still have the disease.

The experts said that because this branch is bigger, suppling more of the heart muscle with life-giving oxygen, it could have greater capacity to maintain a ‘healthy’ blood supply, providing a false sign that a person’s heart is healthy. 

The researchers are now calling for the current guidelines to be updated so that more people are diagnosed earlier and potentially save thousands of lives. 

When LMCA heart disease is caught early a heart attack can be easily avoided by providing a patient with either heart bypass surgery or a simple procedure in which a stent is fitted to widen the narrowed artery. 

However, the researchers acknowledged that further evidence is needed to better understand the issues as their study involved a relatively small number of patients. 

In the meantime, they are urging doctors to think twice before dismissing test results for the condition as normal and to conduct in-depth investigations of blood vessels when faced with potentially conflicting results. 

Dr Ozan Demir, an expert in cardiology and first author of the paper added: ‘These results will encourage doctors to do further evaluation before discounting LMCA disease. 

‘This could include important further investigations like the use of an ultrasound or near infra-red cameras to directly visualise the inside of the artery.’

Senior researchers at the British Heart Foundation welcomed the findings, as a ‘crucial step’ in preventing ‘major heart attacks’. 

Professor Bryan Williams, the charity’s chief scientific and medical officer, added that whilst more research is needed to confirm the results, the study may help doctors to ‘more accurately interpret their results in future.’

It comes as alarming data last year revealed that premature deaths from cardiovascular problems, such as heart attacks and strokes, had hit their highest level in more than a decade. 

MailOnline has previously highlighted how the number of young people, under 40, in England being treated for heart attacks by the NHS is on the rise with rising obesity rates, and its catalogue of associated health problems thought to be one of the major contributing factors.

In the UK, around 420 people of working age die of as a result of heart disease each week, totalling an alarming 21,975 a year. 

Cardiovascular disease is America’s number one killer and nearly 1million people die of it every year.