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Electrophysiology research includes MR Use of MR imaging is studied in atrial fibrillation and cardiac resynchronization therapy at Beth Israel Deaconess Medical Center. Electrophysiology (EP), the study, diagnosis and treatment of heart rhythm disorders, has replaced coronary stenoses as the fastest growing segment of invasive cardiology today. While the main tool of EP physicians is the electrocardiograph (ECG), the use of diagnostic imaging is increasing to help assess the causes and severity of EP conditions. Because MR offers high quality cardiac anatomical and functional imaging without the radiation or iodinated contrast exposure of interventional x-ray, Philips has dedicated a new Business Unit to EP. Philips supports MR-EP research at Beth Israel Deaconess Medical Center (BIDMC, Boston, Massachusetts, USA), where clinicians are using a Philips Achieva 1.5T to research in cardiovascular applications of MR since 1995,” says Warren J. Manning, M.D., Professor of Medicine and Radiology at Harvard Medical School and Section Chief of Non-Invasive Cardiac Imaging at BIDMC. “Most recently we are combining MR imaging with electrophysiology in two distinct areas: atrial fibrillation (AF) and cardiac resynchronization therapy (CRT).” MR imaging in two important cardiac procedures. “We have had a very strong relationship with Philips Mark Josephson, M.D. Reza Nezafat, Ph.D. 22 Warren Manning, M.D. Dana C. Peters, Ph.D. FieldStrength – Issue 34 – May 2008 MR aids in RF ablation research There are 2.5 million AF patients in the United States alone, and risk increases with age. In paroxysmal and some persistent forms of AF, abnormal electrical activity, often originating in the pulmonary veins, causes electrical and mechanical dysfunction of the atria. Blood pools in the atria, thereby promoting clot formation and raising the risk of stroke. One solution is to electrically isolate the pulmonary veins from the atria with radiofrequency (RF) ablation of the tissue surrounding the veins. MR imaging can benefit AF patients before, during and after treatment. “Pulmonary vein MR angiography helps identify the location of the pulmonary veins, their size and their orientation,” says Dr. Manning. “We send this information to the electrophysiologist, who can use it for planning before and during the RF ablation procedure.” Mark Josephson, M.D., chief of the Cardiovascular Division at BIDMC and author of the definitive text on cardiac electrophysiology (Clinical Cardiac Electrophysiology, Third Edition, Lippincott 2002), has a global reputation as a pioneer in arrhythmia research. He explains how a b c d “We have had a very strong relationship with Philips in cardiovascular applications of MR since 1995” post-ablation imaging with MR can be used to assess the results of RF ablation: “The biggest reason for failure of ablation is incomplete circumferential isolation of the pulmonary veins. The lesions don’t appear to be permanent; there is reconnection. If we can demonstrate scarring around the pulmonary vein, it is more likely that the vein is permanently isolated.” An additional area of research should focus on the use of MR imaging to delineate scar tissue in the left ventricle in order to optimize very complex VT ablation procedures. Pre- and post-ablation MRI MR angiography (a) and pre- and post-ablation MR imaging (b,c). On the reformatted image (d) ablation around the left inferior pulmonary vein is seen. Dana C. Peters, Ph.D., Assistant Professor of Medicine at Harvard and Scientific Director of the BIDMC Cardiac MR Center, has developed an MR protocol for research studies imaging post-RF ablation scars that has led to a better understanding of catheter ablation patterns. “MR, unique among modalities, can help identify post-RF ablation scars using a 3D navigator-gated method,” says Dr. Peters. “And MR does not give additional radiation to patients who otherwise would have repeated high doses of ionizing radiation in pre-procedure, postprocedure and follow-up CT imaging,” she adds. Dr. Josephson says preliminary study data suggests that the MR protocol, performed 30 days after RF ablation, may help to predict which patients will have clinical success and which will have a recurrence of atrial fibrillation. John Wylie, M.D., junior faculty member in electro physiology, has helped to create the bridge between imaging and electrophysiology at BIDMC. Dr. Wylie has established a collaboration between EP and the Cardiac MR Center that has resulted in important developments in imaging of AF patients, and CRT patients as well. Pre-CRT vein imaging using MR CRT is used to treat patients with impaired left ventricular contraction and ventricular dyssynchrony, which impairs the pump function of the heart and the Pre-CRT coronary vein MRI Example of pre-CRT coronary vein imaging with MRI, as performed to help identify dissimilarities in vein anatomy to help clinicians choose the most favorable veins for CRT leads. Dr Nezafat received the ISMRM Young investigator award 2007 for this work. FieldStrength 23 subsequent blood flow to the body. In CRT, a pacemaker or cardioverter defibrillator is implanted in the patient, with lead wires to effectuate electrical communication to the cardiac tissue. Typically, one lead is placed in the right atrium (RA), one in the right ventricle (RV) and one through the coronary veins to the left ventricle (LV). Reza Nezafat, Ph.D., Associate Scientific Director of the BIDMC Cardiac MR Center is researching innovative MR imaging protocols and techniques for patients undergoing CRT. Since one-third of CRT procedures in patients with congestive heart failure involve hemodynamic failure or implantation failure, Dr. Nezafat and his group have developed a novel MR imaging technique for assessing coronary vein anatomy, based on a free-breathing, non-contrast imaging sequence with magnetization transfer prepulse for improvement of tissue contrast. Studies have shown that the MR images may help to identify dissimilarities in vein anatomy so clinicians can choose the most favorable veins for CRT leads. EP research continues As the population ages and EP disorders become more common, MR will likely play a larger role in assisting EP clinicians. Philips continues to support MR research that will benefit both clinicians and patients with innovative diagnostic and treatment options. References ME Josephson Clinical Cardiac Electrophysiology, 3rd Edition, Lippincott 2002. R Nezafat, Y Han, DA Herzka, DC Peters, JV Wylie, B Goddu, KV Kissinger, SB Yeon, PJ Zimetbaum, WJ Manning. Magn Reson Med, 2007; 58:1196-206. JV Wylie, DC Peters, V Essebag, WJ Manning, ME Josephson, TH Hauser. Heart Rhythm, 2008 (in press) DC Peters, Wylie JV, TH Hauser, KV Kissinger, RM Botnar, V Essebag, ME Josephson, WJ Manning. Radiology, 2007; 243(3):690-695. EP-Navigator Ablation is usually done under x-ray fluoroscopic guidance, enabling doctors to see the catheters, but x-ray does not show the heart tissue well. For optimal navigation physicians need to see the left atrium outline, including the pulmonary veins. With Philips’ EP Navigator, a 3D roadmap CT image is superimposed on the live x-ray fluoroscopy. Philips is currently developing a similar procedure using MR. The 3D MR dataset acquired prior to the procedure is automatically segmented into the different chambers of the heart. After selecting the left atrium the doctor can immediately start navigation for the ablation process. The EP Navigator tool will facilitate more accurate assessment of 3D anatomy in relation to the electrical signals helping physicians to perform ablation procedures with more accuracy and more confidence. 24 FieldStrength – Issue 34 – May 2008 3D image data Automatic segmentation 3D images combined with x-ray of 3D data set fluoroscopy show the exact position of all catheters