Enter Your Email Address to Receive a
Copy of MedicExhange Member Demograhpics

A new MRI protocol for patients with implantable devices allows for the early detection and response to potential complications and might make routine post- MRI defibrillation-threshold testing (DFTT) and defibrillator safety-margin testing (DSMT) of ICD patients unnecessary. The study results of the protocol in 38 patients, led by Dr Peter Thomas Burke (Providence Heart Institute, Southfield, MI) are published online January 29, 2010 in the Journal of Interventional Cardiac Electrophysiology.

Despite the risks of the MRI disrupting the device's function, imaging of patients with these devices can be done safely, according to Burke and colleagues. "With careful and strict supervision under an electrophysiologist-guided team, we have developed a protocol that allows us to provide the lowest possible risk to [cardiovascular implantable electronic device] patients in need of an MRI," the authors explain.

Burke et al say the study is the first to incorporate the 2007 American Heart Association recommendation that patients with an ICD undergo DFTT and DSMT after an MRI to ensure the powerful magnetic field did not damage the device or interfere with its programming. Defibrillation threshold is defined as the lowest amount of energy capable of terminating an episode of induced ventricular fibrillation. But because the success of defibrillation is probabilistic, the exact defibrillation threshold cannot be established with certainty, so the defibrillator safety margin is tested. The defibrillator safety margin is the energy level capable of terminating two episodes of induced ventricular fibrillation and low enough to be at least 10 joules less than the device's maximum output.

The authors argue that their protocol might obviate the need for DFTT and DSMT, which would be desirable because DFTT/DSMT is risky in some patients, such as those with intracavitary thrombus, persistent or permanent AF with unknown or inconsistent anticoagulation, suboptimal anticoagulation, or AF or left-ventricular thrombi or recent stroke.

The authors also point out that the European Society of Cardiology guidelines do not recommend DFTT/DSMT post- MRI because their committee determined that the risks outweigh the potential benefits.

Source: Journal of Interventional Cardiac Electrophysiology

Discuss more about MRI in the MRI user group.