Two types of heart attack – but the same risk afterwards

The treatment of people undergoing heart attacks is changing. The results suggest that thousands of people could avoid unnecessary procedures – while also reducing their risk of another heart attack.

Now, a subanalysis from the large PROSPECT II study suggests that some groups of people might need to be treated differently than current European guidelines recommend.

This finding may be particularly important for treating people with heart attacks.

“There are two main types of heart attack: one in which the artery is completely blocked and one where a little blood can still flow through. Doctors call them ST-elevation myocardial infarction (STEMI) and non-STEMI. Both are caused by atherosclerosis – a kind of plaque inside the arteries that gradually narrows or completely blocks the passage. Our research shows that once the blood clot has been treated, atherosclerosis is just as dangerous in both types of heart attack – carrying the same risk of new blood clots in the heart,” says a researcher behind the PROSPECT II study, Clinical Professor and Senior Physician Michael Mæng from the Department of Cardiology at Aarhus University Hospital in Denmark.

The research has been published in Circulation.

Heart attacks are divided into two main types

The purpose of the PROSPECT II study was to investigate how to optimally identify people at greater risk of developing another blood clot when they have already had a heart attack.

The main study showed how two advanced technologies can map atherosclerosis: intravascular ultrasound, which measures the extent of the narrowing itself, and near-infrared spectroscopy, which reveals how much cholesterol and soft fatty deposits are present in the vessel wall. The combination provides an accurate picture of how unstable a narrowing is – helping doctors to predict who has the greatest risk of a new blood clot.

This main study was published in The Lancet.

With the new study, the researchers aimed to investigate whether people should be treated differently depending on whether their arteries are completely or almost completely blocked by a blood clot.

Doctors call it STEMI when the artery is completely blocked – like a pipe that is completely clogged. In non-STEMI, a little blood can still get through, so the person can first be stabilised with medication before the artery is opened.

In this context, people with STEMI must be treated urgently, whereas people with non-STEMI can usually wait two to three days before treatment.

Current treatment varies between groups

In the subanalysis, the researchers tested whether the risk of other narrowings – those that did not cause the current blood clot – differed between STEMI and non-STEMI people. They analysed the amount of atherosclerosis, cholesterol levels and the frequency of new blood clots over a four-year period.

Guidelines in this area in the United States and Europe dictate that, for people with STEMI, other narrowings can be treated with balloon angioplasty immediately without first measuring the pressure at the narrowing based on visual assessment of which vessels are narrowed.

The reason for this is based on the belief that other narrowings caused by atherosclerosis are more dangerous for people with STEMI and therefore carry an increased risk of another blood clot.

If the person has a non-STEMI, doctors first measure the pressure inside the narrowed artery – a bit like checking the water pressure in a pipe to decide whether it needs replacing.

“That is the question we are trying to answer with this study: is atherosclerosis more dangerous for people with STEMI, or is it just as dangerous for both STEMI and non-STEMI people?” explains Michael Mæng.

The study shows equal risk of new blood clots

The new subanalysis of the PROSPECT II study focused on this question.

The study included 898 patients with heart attacks.

A total of 199 patients with STEMI heart attacks had 849 other narrowings, and 699 patients with non-STEMI heart attacks had 2,784 other narrowings.

The results surprised researchers because earlier studies and guidelines assumed that patients with STEMI have more unstable and dangerous atherosclerosis than those with non-STEMI. But in this study, the amount of atherosclerosis and cholesterol deposits was similar in both groups once the blood clot had been treated.

The risk of a new blood clot was also the same, with an equal number of cases of another blood clot in the heart within the following four years.

According to Michael Mæng, this indicates that patients should be treated equally.

“We see some very small differences, but nothing of clinical significance. So it really does not make sense to treat these two groups differently – they should be treated the same,” he explains.

New studies will provide clear answers

Michael Mæng stresses that, based on this study, it is not yet possible to say whether pressure measurements should be taken on all narrowings regardless of STEMI status or whether visual assessment alone is enough.

This question is currently being addressed in a large international randomised study, COMPLETE II, in which hospitals in Denmark are helping to recruit patients. The study compares two strategies: treating all narrowings immediately or only the most critical ones – as assessed by pressure measurements. Experience from patients without blood clots has shown that pressure measurements can reduce the number of unnecessary balloon angioplasties without increasing the risk of new blood clots.

“COMPLETE II will now clarify whether all narrowings should be opened immediately or whether treating only the most critical ones is enough. The aim is to avoid unnecessary procedures – and reduce the risk of new blood clots. Pressure measurements have already reduced the number of balloon angioplasties among patients without heart attacks without increasing risk. If the same holds true for patients with heart attacks, thousands could be spared unnecessary procedures – without compromising safety,” concludes Michael Mæng.