Making Peace Between Heart Devices and MRI
After electrophysiologist Henry Halperin decided to challenge the dogma that magnetic resonance imaging can’t be done in patients with pacemakers or implanted cardioverter defibrillators, he wasn’t exactly surprised when the positive results his team reported two years ago ignited fierce debate. Yet by combining carefully worked-out adjustments to both the MR scanner and the heart devices, Halperin and his group now have scanned more than 100 patients who had no imaging alternatives. 
To prevent misfires, they reprogram each device so that its electronics won’t mistake the MR radiofrequency for an arrhythmia. They also turn off a defibrillator’s shocking function for the 30 to 60 minutes needed to do an MR scan. In addition, they halve the amount of energy used at peak scanning, reducing the strength of the electromagnetic field from as much as 4 watts per kilogram to 2 watts per kilogram per patient. And during the scan, they closely monitor every patient using electrocardiography and pulse oximetry.
To be eligible, patients must have one of the 24 modern heart devices the Hopkins physicians have already tested—pacemakers made after 1996 and defibrillators manufactured after 2000—which are made of titanium and thus better protected from radiofrequency energy. Halperin says they also found in earlier research that device leads on the surface of the heart or those capped with metal are prone to overheating, so only patients with leads embedded in blood vessels or connected to the device battery have been allowed to undergo MR imaging. Among the patients who’ve been scanned at Hopkins, lead sensing didn’t fluctuate or change during the MRIs, the scans didn’t alter battery charges, and the devices performed successfully after the scans without any premature firing or false alarms.
The overarching goal, of course, is to gather needed clinical information, and Halperin reports that physicians here have been able to make definitive diagnoses in all the patients they’ve scanned who had nonthoracic conditions and in 93 percent of those with problems involving the heart and upper body. They’ve planned artery-opening procedures, measured tumor growth, detected strokes and a brain mass, and diagnosed a blood clot in the spine that had been missed by CT scanning.
Halperin cautions that there are still risks. “But,” he adds, “our results show that with appropriate precautions, MRI is a safe and effective diagnostic tool in patients with modern implanted heart devices. We’ve turned a once exceptional procedure into one that’s now routine at Hopkins.”
