Updates in EP: 2006

The official advice has always been, no MRI if your patient has an implantable pacemaker or defibrillator. Although it is still recommended that such patients not undergo MRI, two recent studies have suggested that MRI could be possible, if the scan is absolutely necessary. Nazarian et al looked at 68 MRI studies in 55 patients with a device.¹ They excluded patients with older devices that might be more prone to failure with an MRI. The authors found no significant changes in the device with the MRI (including 29 thoracic MRI studies right over the device). Sommer et al looked at 82 patients with fairly new Medtronic pacemakers who underwent MRI scans (most were brain MRIs), and none had long-term damage to the pacemaker.² In both studies, the authors carefully monitored the patients during MRI and tried to limit the MRI scanning time. Another concern in EP right now is that patients with defibrillators frequently develop atrial fibrillation and are started on antiarrhythmic drugs. The question has been, should there be repeat DFT (defibrillation testing) once drug therapy has been initiated? Hohnloser et al evaluated this issue in the Optimal Pharmacological Therapy in Cardioverter Defibrillator Patients (OPTIC) trials.³ Patients were randomized to amiodarone plus beta-blocker versus sotalol plus beta-blocker (n = 94 patients). After 8 to 12 weeks of drug therapy, the mean DFT in the sotalol group dropped from 8.09 to 7.20 J and increased in the amiodarone group from 8.53 to 9.82 J. It was also striking how low the baseline DFTs were in these patients. The authors concluded that it was likely not necessary to retest DFTs after initiating antiarrhythmic drug therapy. Leadless technology is also a new area in EP that will grow and develop over the coming years. Certainly complications like lead fracture or need for lead extraction are fairly common. Echt et al and colleagues from EBR Systems, Inc. in California have described an investigational pacing system.⁴ They implanted a pacemaker receiver-electrode catheter transvenously via the femoral vein or artery directly into the myocardium in 11 Yorkshire pigs. They were able to pace the heart using externally applied ultrasound transmitters. On another note, the risk of thromboembolism after ablation for atrial fibrillation is highest in the first two weeks post ablation, according to Oral et al.⁵ The authors looked retrospectively at 755 patients upon whom atrial fibrillation ablation was performed. They found that only 1.2% suffered a thromboembolic event due to high-dose anticoagulation; this is an extremely low event rate. Their recommendation was to discontinue anticoagulation after successful pulmonary vein ablation (probably three to six months later) unless patients were over age 65 years or had a previous history of stroke.⁶ Lastly, more than 130,000 ICDs were recalled in 2005 for defects that could affect function of the device. The Multicenter Registry is a database funded through the Minneapolis Heart Institute Foundation. The authors looked at ICD recalls and failures at nine participating centers between 1998-2005.⁷ They found 1,220 ICD pulse generators that failed (defined as not functioning according to the manufacturer's specifications, usually due to premature battery depletion), and 135 devices that were recalled and replaced. Twenty patients experienced major device-related adverse events, including one death associated with a change-out of a recalled device.