In recent years, imaging techniques such as the most commonly used single-photon emission computed tomography (SPECT), have gradually replaced exercise treadmill tests for diagnosing heart disease. Now a five-year trial of over 750 heart disease patients conducted by the University of Leeds in the UK suggests that a more modern scanning method based on magnetic resonance imaging (MRI) is better for diagnosing coronary heart disease than SPECT and should be more widely adopted.
The findings could change the way patients with suspected heart disease are tested, not least because the MRI approach, called multiparametric cardiovascular magnetic resonance (CMR), does not involve invasive procedures or ionizing radiation.
In a paper published online on 23 December in The Lancet, lead author Dr John Greenwood, senior lecturer and consultant cardiologist at Leeds, and colleagues, conclude that CMR is superior to SPECT, which varies in accuracy and exposes patients to ionizing radiation. They conclude that CMR should form part of all evidence-based clinical management guidelines for the diagnosis of coronary heart disease (CHD).
CHD is a leading cause of death and disability. There are around 2.6 million people living with the disease in the UK, costing the National Health Service (NHS) £9 billion a year.
The disease develops when fatty substances in the bloodstream build up in vital arteries serving the heart. These vessels narrow and become blocked, causing severe chest pain, a condition known as angina, which, if untreated, can worsen and lead to heart attack.
Patients with chest pain who are suspected of having angina are usually sent to hospital for tests to confirm the presence of CHD. Once CHD is confirmed, treatment options include “stretch and stent”, a procedure where a balloon opens the narrowed artery and props it open; drug therapy; or heart bypass.
At present, there are two types of test to confirm if patients have angina: angiogram and SPECT. In the angiogram, the specialist uses a catheter guided by x-ray, to inject a dye directly through blood vessels and into the heart. The dye shows up any narrowed areas or blockages in the arteries on the x-ray.
SPECT is a type of nuclear imaging test where a radioactive tracer that emits gamma rays in injected into the bloodstream. A scanner traces the gamma rays and feeds the traces to a computer that translates them into two-dimensional cross-sections and then assembles them into three-dimensional images. From these images you can see how blood is flowing, or impeded, in the vessels around and in the heart.
In CMR, the patient undergoes an MRI scan that focuses on the area around the heart. The test takes a bit longer than SPECT, but it unlike SPECT it does not involve ionizing radiation. CMR is considered very safe and is becoming more widely available. However, it is unsuited for patients with claustrophobia or who have implanted devices like pacemakers.
For their study, Greenwood and colleagues compared the diagnostic accuracy of the CMR approach with SPECT, using x-ray coronary angiography as the reference standard in a group of 752 patients with suspected coronary heart disease.
All the patients had suspected angina pectoris and at least one cardiovascular risk factor, and underwent all three procedures.
The researchers calculated four measures for each of the two tests: sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV).
The findings show that:
- According to the x-ray angiography results, 39% of the patients had significant CHD.
- CMR sensitivity was 86·5% (95% CI 81·8 to 90·1), specificity 83·4% (79·5 to 86·7), positive predictive value 77·2%, (72·1 to 81·6) and negative predictive value 90·5% (87·1 to 93·0).
- SPECT sensitivity was 66·5% (95% CI 60·4 to 72·1), specificity 82·6% (78·5 to 86·1), positive predictive value 71·4% (65·3 to 76·9), and negative predictive value 79·1% (74·8 to 82·8).
- The sensitivity and negative predictive value of CMR and SPECT differed significantly (p
The authors conclude that their study, which is called CE-MARC, is the “largest, prospective, real world evaluation of CMR and has established CMR’s high diagnostic accuracy in coronary heart disease and CMR’s superiority over SPECT.”
They recommend CMR “should be adopted more widely than at present for the investigation of coronary heart disease”.
In a separate press release, the University of Leeds note this is “the first time that MRI has been compared head-to-head against the ‘gold standard’ tests for CHD in such a large group of patients”.
“We have shown convincingly that of the options available to doctors in diagnosing coronary heart disease, MRI is better than the more commonly-used SPECT imaging test. As well as being more accurate, it has the advantage of not using any ionising radiation, sparing patients and health professionals from unnecessary exposure.”
He explains that CMR could be used more widely, not just in the UK.
“The scans were all carried out on a standard 1.5 Tesla scanner – exactly the type of MRI scanner that you would find in most hospitals today,” he adds.
Professor Peter Weissberg is Medical Director at the British Heart Foundation, whose £1.3 million grant helped pay for the study. He told the press that:
“For patients suffering with chest pains, there are a number of tests that can be used to decide whether their symptoms are due to coronary heart disease or not. This research shows that a full MRI scan is better than the most commonly used alternative – a SPECT scan using a radioactive tracer.”
“MRI has the additional advantage that it doesn’t involve radiation. At present, not all hospitals have the expertise to undertake such scans but these findings provide clear evidence that MRI should be more widely used in the future,” he added.
But in an accompanying comment in The Lancet, Robert Bonow of the Center for Cardiovascular Innovation at the Northwestern University Feinberg School of Medicine in Chicago, USA, suggests that the future role of CMR is not quite so clear. Its “enhanced diagnostic accuracy” has to be “balanced against availability and cost-effectiveness”, he writes, explaining that there is also a need to show more “evidence of measurable improvements in patient outcomes”.
“Diagnosis of coronary artery disease alone is not sufficient to determine the need for revascularisation,” notes Bonow, explaining that if they are to add value, advances in imaging techniques “must be coupled with enhanced patient well-being or a reduction in unnecessary downstream testing and procedures”.
Written by Catharine Paddock PhD