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The newspaper of The Johns Hopkins University February 13, 2006 | Vol. 35 No. 21
Heart mapping technique guides catheter repair of arrhythmia

By David March
Johns Hopkins Medicine

In experiments with dogs, Johns Hopkins researchers successfully used a 3-D map of the heart and a sensor-guided catheter to perform cardiac ablation, a mainstay treatment that stops abnormally fast and potentially fatal heartbeats, or arrhythmias. The Johns Hopkins findings, presented in November at the American Heart Association's Scientific Sessions 2005 in Dallas, provided information and technology used by the U.S. Food and Drug Administration to approve the system for testing in humans, now under way.

The Johns Hopkins team created its own 3-D models of each heart from images obtained by integrating and superimposing CT and MRI scans. Using an upgraded computer software program known as electroanatomic mapping, the scientists were able to color code the heart models' structures.

The scientists safely ablated, or destroyed, tiny areas of diseased heart tissue that facilitate rhythm disturbances, guided only by these anatomically precise, reconstructed 3-D maps.

During the procedure, a catheter containing a magnetic sensor in its tip was inserted through a vein in the dog's leg, then guided to the heart, where it was used to burn off the small part of heart muscle that gives rise to the errant signaling responsible for the arrhythmia.

A magnetic location pad was placed under the operating table and situated directly beneath the animal's body to detect the position of the catheter and compare it to the computer-generated image of the heart displayed on a screen.

"This is a significant improvement for patient safety and the performance of minimally invasive procedures in the heart," said study senior investigator and cardiologist Timm Dickfeld, an adjunct assistant professor at the School of Medicine and its Heart Institute. Current methods for visualizing the heart, using X-rays and fluoroscopy, are potentially hazardous, Dickfeld said, because they involve radiation and produce only two-dimensional images, which are not as accurate as 3-D images.

"Our study proves the effectiveness of 3-D mapping in guiding and pinpointing the catheter's tip during a procedure, giving the electrophysiologist a more concrete awareness of the placement of lesions, and it eliminates the need for an X-ray, reducing the amount of radiation exposure for the patient," he said.

As part of the study, the Johns Hopkins scientists performed catheter ablation in nine dogs who had nearly 50 CT markers, small waferlike targets that could be seen by a scanner, surgically implanted on the outside of their heart's muscle wall. The placement of the wafers covered all regions of the heart, especially those where arrhythmias are known to occur. Three-dimensional maps of the heart, made shortly before the procedure, were then used to guide the catheter to its targets.

After the procedure, analysis of heart tissue showed that the 3-D maps worked very well and were extremely precise and safe, Dickfeld said. The range of errors in pinpointing therapy to a lesion was between 1.9 millimeters and 4.9 millimeters, and well within lesion boundaries, which average 6 millimeters in diameter.

"A physician really needs precise anatomical information during ablation because one move in the wrong direction could damage healthy heart tissue or puncture the organ," said study lead investigator Jun Dong, a postdoctoral research fellow. Previous research by Dong and colleagues showed that such complications occur in nearly 5 percent of catheter ablation procedures for atrial fibrillation.

Funding for this study was provided by Biosense Webster of Haifa, Israel, the manufacturer of the electro-anatomic mapping system.


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