The research study involved a mapping system known as LocaLisa, which uses a law of physics known as Ohm's law to localize a catheter in 3-dimensional space and tell doctors where in the heart thier catheters are located. The catheters are inserted into the child's body through a small incision in the leg, and threaded up into the heart through the blood vessels.

Once inside the heart, the catheter can be steered by doctors to measure electrical activity and pinpoint the source or sources of the child's heart-rhythm problem. Conventionally, doctors have steered the catheters using fluoroscopy, or X-rays beamed from below the patient that show the probe as a solid object. U-M cardiologists were among the first to use this technique in children, and reported successful results from a large study in 1991.
The LocaLisa system reveals the probe's location by passing electrical current through the child's chest and measuring the interruption to that current created when the probe moves. That information is translated by a computer into a colorful three-dimensional map that is displayed on a monitor in front of the doctor.
Although X-rays are still needed for part of the procedure, the new study shows that the dose can be greatly reduced with the 3-D mapping system. Children treated before LocaLisa was available were exposed to an average of 37 minutes of X-rays throughout their procedure, compared with an average of 17 minutes with LocaLisa.

Interestingly, the 3-D mapping system also allowed doctors to reduce the number of RF applications they used to treat patients. LocaLisa patients had an average of 8.5 applications of RF energy, compared with an average of 12.1 for patients treated before the system was available. This difference, the authors say, is probably due to the increased accuracy in finding and treating specific locations made possible by the 3-D navigation.

In all, the treatment success rates from the two groups were statistically identical: 99.1 percent of LocaLisa patients were completely free from their rhythm problem after treatment, as were 97.2 percent of patients treated without the system. Neither group had major complications.

Fischbach also notes that the while the system lacks many of the features of other mapping systems, it is much less expensive to use and equally effective for treating routine tachycardias in children.

The patients in the study had an average age of 13 to 14 years, and about half were boys. Two-thirds of the patients had heart rhythm irregularities caused by accessory pathways -- an additional electrical connection between the top and bottom chambers of the heart. One-third had atrioventricular nodal reentry tachycardia (AVNRT), a form of the most common rapid-heartbeat rhythm problem in adults . All patients were treated between August 2001 and April 2005.

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