Friday, February 8, 2008
Imaging potentially increases precision and shortens treatment time
Cardiologists at the University of Maryland Medical Center in Baltimore are among the first in the world to combine advanced three-dimensional PET/CT imaging with standard techniques to treat ventricular tachycardia, a life-threatening electrical disorder that causes the heart to beat too fast. The imaging component offers the potential to improve precision and patient safety, reduce treatment time and boost the success rate of ablation therapy, which uses high-energy radio waves to redirect the heart’s electrical pathway to prevent abnormal heart rhythms.
The usefulness of this sophisticated technology is confirmed in a University of Maryland School of Medicine study that was published in the January 2008 issue of the Journal of the American College of Cardiology’s Cardiovascular Imaging. The study is the first to compare the combination of advanced high-resolution PET (positron emission tomography) and CT (computed tomography) images with traditional catheter-based electrical mapping of the heart to guide the ablation treatment.
“With this advanced imaging, before patients come for treatment, I know where the scar tissue causing the abnormal rhythms is located,” says principal investigator Timm-Michael L. Dickfeld, M.D., Ph.D., a cardiologist with expertise in image-guided electrophysiological procedures at the University of Maryland Medical Center. “The PET/CT imaging has the potential to reduce the time patients spend in the electrophysiology lab by several hours,” says Dr. Dickfeld, who is also an assistant professor of medicine at the University of Maryland School of Medicine. “Additionally, the imaging should make the procedures more precise and more successful.”
Medications are typically the first-line therapy for ventricular tachycardia, but their use is often limited by side effects and a reduction in effectiveness over the long term. Most patients diagnosed with ventricular tachycardia are given internal cardiac defibrillators that shock the heart to correct electrical abnormalities. Dr. Dickfeld says that while the electrical jolt does restore normal heart rhythm, some of these patients, who may require multiple shocks each day, live in fear of the next shock. He says radiofrequency ablation is an appropriate treatment for many of these patients. The goal is to reduce or eliminate the need for the defibrillator’s jolts.
Scars, which often form in the heart muscle after a heart attack, cause most of the spiraling electrical signals characteristic of ventricular tachycardia. The current “gold standard” method to determine scar location is called electrical or voltage mapping. A catheter with an electrode is inserted into an artery through the groin and guided to the beating heart. The probe detects variations in electrical signals as it is moved a few millimeters at a time. High voltage indicates normal cardiac tissue. Low or no voltage is associated with dead scar tissue. A computer compiles the data into a map which shows where to apply ablation to eliminate cardiac tissue in and near the scars.
CT imaging shows the heart’s anatomy while PET imaging distinguishes between healthy and abnormal cardiac tissue by keying in on cellular function and metabolism. The combined result is revealed in 3-D images of both the inner and outer surfaces of the heart muscle and the coronary arteries. The imaging is currently used in combination with electrical mapping. Once the scars are defined, the imaging also helps improve the accuracy and efficiency of the ablation process.
The study looked at 14 patients who had PET/CT imaging prior to ablation for ventricular tachycardia. The goal was to determine its accuracy and feasibility compared to the traditional electrical mapping.
The study concluded that PET/CT imaging can accurately predict the location and extent of left ventricular scar tissue and the border between scarred and normal heart tissue. It also found that integration of a 3-D scar map into a clinical mapping system is feasible and shows additional scar data not available from voltage maps alone.
“Electrical mapping is a technique that helps us figure out what is going on with the heart’s electrical system,” says the study’s senior author, Stephen R. Shorofsky, M.D., Ph.D., director of the medical center’s electrophysiology laboratory and professor of medicine at the University of Maryland School of Medicine. “The heart is a rather big place when you’re down at the millimeter level and trying to measure the electricity. The clarity and accuracy of PET/CT imaging may one day replace a major part of electrical mapping,” says Dr. Shorofsky.