Interventional cardiology

MRI safe in people with ICDs say US clinicians

Most patients who are currently denied an MRI due to an implanted cardiac device could safely undergo the scan if a simple protocol was followed say US researchers.

Concerns about myocardial thermal injury and potentially harmful changes to pacing settings have meant that patients with older implanted cardiac devices (ICDs) who require an MRI are forced to forgo the scan – even when it would otherwise have been considered the most appropriate diagnostic imaging method for the patient’s clinical care.

But a group of cardiologists and radiologists in the US who have been performing thousands of scans in device-contraindicated patients say they have deciphered a safety protocol that could open up a range of diagnostic opportunities for patients.

The authors say it’s a significant problem, estimating that some 8 million people will have non-MRI-conditional implanted cardiac devices, half of whom are predicted to have an indication for MRI during their lifetime.

The magnasafe registry study  set out to determine the risks of MRI in people with non-MRI-conditional devices who have ‘highly compelling’ circumstances for non-thoracic MRI.

Some 1500 patients were involved in the study – 75% of whom were scheduled for an MRI on their brain or spine because their treating physician believed the potential diagnostic benefits would outweigh any risk of harm, the authors said.

Before undergoing MRI (set at 1.5 tesla) patients had their device interrogated, and in some cases, reprogrammed.

For example patients with a pacemaker who were not pacing dependent had their device programed to a no-pacing mode.

Whereas those who were pacing-dependent had their device programmed to an asynchronous pacing mode at the previously programmed lower rate limit.

For patients with an ICD who were not pacing-dependent, the device was programmed with all bradycardia and tachycardia functions in an inactive mode.

Pacing dependent patients with an ICD were excluded because not all patients had a device that was capable of providing pacing function while allowing for inactivation of tachycardia therapy, the authors noted.

Next, patients were hooked up to an MRI compatible cardiac monitor overseen by a cardiologist.

According to the study authors, no patient who was appropriately screened and who had their device reprogrammed according to the protocol had a device or lead failure.

One ICD generator could not be interrogated after MRI and required immediate replacement but that device had not been appropriately programmed per protocol before the MRI, the authors said.

There were also six cases of atrial arrhythmias, each lasting less than 49 hours. Six partial electrical resets occurred that were detected and corrected during post-MRI reprogramming and while changes in device settings were common the authors said relatively few exceeded their pre-specified threshold criteria for a clinically important change.

According to the researchers, nonthoracic MRI is safe for patients with a pacemaker or an ICD provided a protocol similar to the one used in their study is followed.

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