A Take on the Radiology Community
|Nassir Marrouche, MD|
The federal laws that regulate certain economics of imaging seem to mirror the topsy-turvy world of Lewis Carroll’s Through the Looking Glass. Because of the flawed methodology of the sustainable growth rate (SGR) formula for determining physician Medicare payments, the more we improve technologies (thus increasing their utilization), the less they are worth. This perverse logic fails to recognize the overall cost benefits of these technological advances, not to mention their inestimable value to patients.
Fortunately, these economic disincentives will not deter our efforts to develop game-changing scientific and clinical breakthroughs. At the University of Utah School of Medicine, our atrial fibrillation (AF) program is pioneering the use of MRI instead of fluoroscopy for AF ablation techniques. Over the last decade, the need to find safe, effective AF treatment options has grown in importance, and MRI shows tremendous promise as a tool for improving curative rates and decreasing complications.
AF is a heart rhythm disorder that is the country’s most common cardiac malfunction. It afflicts more than 3.5 million people and accounts for one-third of hospital admissions.
The treatment of AF has been challenging, due in part to the irregular, generalized pervasiveness of electrical abnormalities throughout much of the left and right upper heart chambers. Since the pulmonary veins have been identified as one of the primary sources of AF, a variety of treatment strategies have been developed to minimize their electrical effects. These procedures often use a mapping catheter under fluoroscopic guidance to electrically isolate the pulmonary veins from the rest of the left atrium. An electrode that emits radiofrequency (RF) energy also is placed into the heart through a catheter to ablate the responsible tissue.
One ablation technique in particular, Circumferential Pulmonary Vein Isolation (CPVI), has been shown to be effective for both the paroxysmal (episodic) and persistent forms of AF. Studies report that CPVI has helped return the majority of patients to normal rhythm independent of the effects of anti-arrhythmic-drug therapy, cardioversion, or both. However, despite years of investment and extensive research, the overall curative rate and complication rate for AF treatment have not changed since the turn of the millennium.
In order to maximize efficacy and safety on a more consistent basis, electrophysiologists require more detailed information about the physiology of the cardiac chambers and the effects of ablation. Of all the imaging modalities, MRI offers the most detailed anatomic and physiologic information about normal and damaged myocardial tissue. In comparison to fluoroscopy and CT scans, MRI has vastly superior soft tissue contrast and does not expose the patient to ionizing radiation.
Our research at the University of Utah, which we recently presented at the American College of Cardiology meeting, has shown MRI to be a powerful tool before, during, and after AF ablation procedures. For example, in patient screening and procedure planning, MRI can be used as a diagnostic tool for measuring the progression and precise location of AF. Our findings from experimental studies indicate that images created utilizing MRI can be used efficiently to monitor the effect of RF ablation on heart tissue during an ablation procedure. These images also can improve anatomical maps, which are used in conjunction with other imaging modalities to determine appropriate sites for ablation.
As real-time 3D MRI becomes available, it will become more important in providing real-time information regarding structure and function during CPVI procedures. Electroanatomic mapping systems that allow for high-resolution MRI images to be merged with electrophysiological data can help the physician performing the procedure to guide the catheter manipulation near pulmonary vein ostia and to ascertain potential complications. MRI scans will also help to determine appropriate power delivery settings for the RF energy needed for effective lesion formation without causing unnecessary damage to other structures.
Lastly, MRI has applications in postprocedural assessment and follow-up. Using delayed enhancement MRI, it is possible to visualize the scar utilizing clinical scanners, which will likely prove valuable in diagnosing postprocedural complications and determining their relation to the RF parameters.
MRI has the potential to be an extremely important—and cost-effective—modality for the treatment of AF. As we build on the success of other groups that have successfully applied MRI technology in interventional procedures targeting the ventricle, we may soon be able to assess lesion size and change in tissue pathology in real time. These and the other aforementioned MRI applications will help electrophysiologists improve AF curative rates and decrease complications. That’s good news for our aging population, since the risk of contracting AF increases significantly for people in their 60s, 70s, and 80s. We can only hope that government officials realize that such outcomes are also economically beneficial, since they will reduce the need for costly AF follow-up procedures and expensive medications.
Nassir Marrouche, MD, is director of the Cardiac Electrophysiology Laboratories and the Atrial Fibrillation Program at the University of Utah School of Medicine, Salt Lake City.