Advances in CMR

Advances in Cardiovascular Magnetic Resonance
Magnetic resonance angiography (MRA) is a magnetic resonance imaging (MRI) exam that takes pictures of the blood vessels

SEQ looks at some of the research presented at CMR 2018, illustrating advances in the field of cardiovascular magnetic resonance.

In February, the international cardiovascular magnetic resonance (CMR) community gathered in Barcelona, Spain, for CMR 2018, a joint EuroCMR*/SCMR meeting organised by the European Association of Cardiovascular Imaging (EACVI), a registered branch of the European Society of Cardiology, and the Society for Cardiovascular Magnetic Resonance (SCMR).

Research presented at the event during Focus Session Two: CMR in Acute Coronary Syndromes on 2 February revealed that standard medical tests miss nearly two-thirds of heart attack diagnoses.

Unrecognised heart attacks (myocardial infarction; MI) refer to sub-clinical events that are missed in routine medical care but are picked up by electrocardiogram (ECG) or by cardiovascular magnetic resonance (CMR) imaging, which is more accurate.

According to the presented paper, undiagnosed patients do not receive as many medications to reduce the risk of death and other adverse outcomes as patients with known heart attacks.

Long-term outcomes

Lead author Dr Tushar Acharya, a cardiologist at the National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, USA, said: “Unrecognised MI has a poor short-term prognosis but until now the long-term outlook was unknown. This study investigated long-term outcomes.”

The study included 935 community dwelling participants of ICELAND MI, a sub-study of the AGES-Reykjavik epidemiology study. At the start of the study, participants underwent an ECG and CMR and were categorised into one of three groups:

  • Unrecognised MI (sub-clinical events, missed on routine medical care, but picked up by CMR);
  • Recognised MI (clinical events, also picked up by CMR); and
  • No MI (verified by CMR).

52% of the participants were females, and the average age of participants was 76 years. At the beginning of the study, 91 participants (10%) had recognised MI, 156 (17%) had unrecognised MI, and 688 (74%) had no MI. According to Acharya, this means that “63% (156 out of 247) of the myocardial infarctions identified by cardiovascular magnetic resonance were missed in routine medical care. Unrecognised MI may be more common than recognised MI.”

Mortality rates

The study found that mortality rates were similar in patients with unrecognised and recognised MI (49% and 51%, respectively) and significantly higher than in those with no MI (30%) (p<0.001) at ten years. This compares to rates at five years, where the mortality rate of patients with unrecognised MI (13%) was higher than in those with no MI (8%) but was lower than in those with recognised MI (19%).

Acharya said: “This shows that with time, the mortality rate of patients with sub-clinical MI increases and is the same as those with diagnosed MI,” adding: “Patients with unrecognised MI do not receive medications commonly prescribed to heart attack patients to reduce the risks of death or another heart attack. These include aspirin, high intensity statins, angiotensin converting enzyme (ACE) inhibitors and beta blockers. They should also be advised to control risk factors such as hypertension and diabetes, and may be candidates for revascularisation to open blocked arteries.

“Knowing that they had a heart attack may also persuade some people to adopt a healthier lifestyle with adequate physical exercise and no smoking.”

Increased detection

While population screening to identify MI using cardiovascular magnetic resonance is not likely to be cost-effective or practical, Acharya said shifting a proportion of cardiac evaluation from traditional tests to CMR could diagnose more unrecognised MI.

He said: “Using CMR in patients with cardiac symptoms would likely detect many more heart attacks than traditional diagnostic tests. There are good therapies to treat survivors of MI so finding them early should improve prognosis.”

Five-minute imaging

Also at the CMR 2018 event, a new five-minute procedure to scan the blood vessels and which offers hope for claustrophobic patients unable to tolerate the conventional longer test was unveiled.

Magnetic resonance angiography (MRA) is a magnetic resonance imaging (MRI) exam that takes pictures of the blood vessels. Physicians use the images to diagnose diseases of the blood vessels, such as aneurysms or blockages, with an MRA typically taking 30 minutes to one hour, from start to finish.

Dr Puja Shahrouki, research fellow, David Geffen School of Medicine at UCLA, Los Angeles, USA, said: “Lengthy scans can be problematic for patients with even modest levels of claustrophobia who may refuse the test or ask for it to be stopped early. They also limit the number of patients that can be scanned each day. In addition, the usual gadolinium-based contrast agents can be an issue for patients with kidney problems.”

This study that developed the new test therefore aimed to shorten the scan time and still produce high quality images. The researchers used ferumoxytol as the contrast agent as it stays within the vascular system for much longer than the gadolinium-based dyes used in an MRA, which only offer a short time window for the images to be taken, meaning that patients have to wait in the scanner while the clinician watches the dye move through the body in order to capture the images when the dye enters the blood vessels.

The UCLA study included seven claustrophobic patients aged 11 to 63 years with kidney failure (four men and three women), all of whom had said they were reluctant to undergo MRA due to claustrophobia, but agreed to a trial of up to ten minutes in the scanner bore.

All eight MRA scans – taking an average of 6.27 minutes (range four to ten minutes – using ferumoxytol were successfully completed in the study, with no adverse events. All scans were high quality and allowed full visualisation of the arterial and venous anatomy from the neck to the thighs.

Shahrouki said: “Despite being claustrophobic, all patients completed the MRA and the images could be used for diagnosis of the entire vascular system. Some of the scans were done in less than five minutes once the procedure started, making it much shorter than the tests currently used in medical practice.”

The researchers have demonstrated that the test can be used to diagnose venous and arterial diseases, such as central venous occlusion and aneurysms, and to aid pre-procedural planning, for example in transcatheter aortic valve replacement. In principle, the researchers have argued, it is possible to scan several patients in an hour as opposed to just one or two, raising promising possibilities for workflow and efficiency.

Shahrouki concluded: “This method could enable claustrophobic patients to receive lifesaving diagnoses and procedures. For appropriate types of studies, it could also shorten waiting lists and improve the cost-benefit ratio for hospitals.”

The new protocol should be technically easier than current practice because there is no time pressure for taking images. Ferumoxytol is increasingly recognised as an alternate contrast agent in patients with poor kidney function, but is not marketed outside the USA, however, where it is approved by the US Food and Drug Administration (FDA) only for the treatment of iron deficiency anaemia in adults with chronic kidney disease (the FDA has warned against ferumoxytol because hypersensitivity reactions have occurred in patients receiving a high dose for therapy in a short period of time).

The new MRA protocol administers the dye by slow infusion outside the MRI machine while monitoring the patient’s vital signs, in compliance with FDA guidelines, and a preliminary study has shown this was safe, while a larger registry is generating a safety profile of slow infusion under close monitoring. However, additional safety data is required before any conclusions can be drawn about the true rate of hypersensitivity reactions and in the meantime close monitoring is the rule.

Shahrouki concluded: “The protocol could have huge implications for claustrophobic patients and efficient use of scanners. We envisage it being used very widely in patients with a clear clinical indication.”

This article will appear in SciTech Europa issue 26, which will be published in March, 2018

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