A new tool for assessing the narrowing of the heart's arteries was found to be as effective as current methods and less painful for patients.

The tool is similar to current techniques in telling surgeons whether a patient needs a stent – a type of mesh tube used to hold open clogged arteries and increase blood flow. However, this new technique, known as instantaneous wave–free ratio (iFR), is much more pleasant for the patient, and could be cheaper and less time–consuming for healthcare providers.

Now, Dr Justin Davies and his team from the National Heart and Lung Institute at Imperial College London have developed iFR to measure the pressure loss caused by the narrowing in these important blood vessels without the need for drugs with sometimes unpleasant side effects. This novel technology was licensed to Volcano–Philips by Imperial Innovations, the College's technology transfer partner.

The technique received FDA approval in 2013 and is already used in 4,500 labs worldwide, but the latest study is the biggest yet to prove its effectiveness compared with the current most widely established technique.

Measuring pressure in the coronary artery is important when deciding whether patients need to have a stent fitted – a procedure known as angioplasty. This helps to improve the blood supply to the heart muscle by widening the narrowed coronary arteries. However, before patients can undergo angioplasty, cardiologists must test the pressure of the artery to make sure it is narrow enough for a stent to be useful.

The first line technique in current guidelines, known as fractional flow reserve (FFR), requires using powerful drugs such as adenosine to open the blood vessels for easier measurement. However, it can cause severe crushing pain, low blood pressure and breathing difficulties, and adds more time and costs on to the procedure.

The latest study has shown that using the new technique (iFR) is just as accurate, causes less discomfort, is less time–consuming, and might be cheaper, than FFR. Click here for a live case demonstration of iFR, courtesy of Imperial College Healthcare NHS Trust.

Like FFR, iFR measures pressure using a thin wire in the coronary artery, but unlike FFR, it uses a mathematical algorithm to take measurements only when the heart is relaxed and the coronary blood flow is high, negating the need for adenosine.

In this study, the researchers enrolled 2,492 patients in 17 countries who suffered with chest pain or acute coronary syndrome (heart attack). They randomly assigned participants to undergo iFR or FFR, and either inserted a stent or not, depending on the measurements. Patients were followed up for 12 months after the procedure.

Although there were no significant differences in rates of death or subsequent heart attack between the two techniques, patient experience was much improved with the iFR technique.

The researchers found that adverse events occurred in 31 per cent of FFR patients and three per cent of iFR patients overall.

FFR was also associated with a higher rate of shortness of breath (reported in one per cent of iFR patients and 20 per cent of FFR patients); chest pain (nearly two percent in iFR and seven per cent in FFR); heart rhythm disturbances (nearly zero per cent in iFR and nearly five per cent in FFR); abnormally low blood pressure (nearly zero per cent in iFR and one per cent in FFR); and serious adverse events, which included severe shortness of breath or disturbance of normal heart rhythm (nearly zero per cent in iFR and nearly one per cent in FFR).

They also found that iFR reduced the overall length of the procedure, from an average of 45 minutes for FFR to 40 minutes for iFR.

The results from this trial, known as DEFINE–FLAIR, were published in the New England Journal of Medicine, and were presented at the ACC 17.