The
Cardiomyopathy
Association

Low strength MRI scans of non-chest areas appear to be safe for patients with pacemakers and internal defibrillators (ICDs), says a multi-centre study in America.

Among 500 patients undergoing scans at the lower field strength of 1.5 Tesla, there were no deaths, device failures, generator-lead replacements, losses of capture, or ventricular arrhythmias, said Dr Debra Doud, of the Scripps Clinic in La Jolla, California.

In addition, the rate of clinically relevant changes in various device parameters was low, she reported at the Heart Rhythm Society meeting in Boston.

MRI (magnetic resonance imaging) uses strong magnetic fields and radio waves to take pictures of various parts of the body. Because of the strong magnets used, the test is not thought to be suitable for people with metal implants, including pacemakers and ICDs. 

Considering the large number of patients with cardiac devices, the aging of the population, the increasing indications for cardiac devices, and the strengths of MRI in examining soft tissue, the availability of being able to perform these exams in this patient population is extremely important, Dr Doud said in an interview.

Current guidelines state that MRI is not suitable for patients with cardiac devices, and health insurer Medicare has not reimbursed for MRI scans performed in patients who have a device. But Dr Doud said that Medicare has since begun reimbursing for such scans as long as the patient is enrolled in the MagnaSafe Registry which is determining the risks of MRI in pacemakers and ICDs.  

The registry is expected to enrol 1,500 adult patients with pacemakers and ICDs who have a clinical indication for non-chest imaging. The study is being conducted at 12 centres under an investigational device exemption from the FDA.

Patients with ICDs who were pacemaker dependent were excluded. Pacemaker-dependent patients had their devices programmed to an asynchronous pacing mode, and those who were not dependent had pacing functions deactivated. Tachyarrhythmia therapies were disabled in patients with ICDs who were not pacemaker dependent.

The researchers examined the devices before and after MRI. The current analysis included the first 500 patients included in the registry -- 378 with pacemakers and 122 with ICDs. The devices used a total of 964 leads. MRIs were performed an average of 2.9 years after device implant. The average length of the scan was 42 minutes.

There were no major complications from the MRI scans.

An issue not addressed in the current analysis is whether the images obtained in these patients are usable. Dr Doud said that she and her colleagues are in the process of preparing those data for presentation, but that out of more than 500 images she has seen, only one was uninterpretable. That came in a left shoulder scan of a patient with a left-sided ICD, although Dr Doud noted that other such scans have been clear. Further research will be needed to identify factors that can affect image quality, she said.