In a presentation at the American Heart Association's Scientific Sessions meeting, members of the Michigan Congenital Heart Center will present new data from a study of a treatment called RF catheter ablation in children using a three-dimensional computer assisted navigation system.
They show that by adding the 3-D navigation system to a conventional X-ray based method to visualize electrophysiological catheters inside the heart, they were able to successfully treat 99.1 percent of 113 patients included in the study.
While the procedural success rate was very high, the most significant finding was that the patients who were treated using the 3-D computer navigation system were spared almost half the radiation dose received by 108 comparable patients treated immediately before the new system was available.
"The goal of reducing radiation dose is especially important in children, because of the risk it can pose to their health and fertility later in life," says Peter Fischbach, M.D., M.A.., senior author of the new study. "Radiation exposure is very different for children and adults due to their small body mass as well as their longer life expectancy, which allows for a greater likelihood of the radiation to cause adverse effects. This system allows us to see multiple catheters in real time and guide their movements in three dimensions. We can record electrical activity in specific locations to help plan and deliver RF treatment."
RF (radiofrequency) catheter ablation treatment uses electrical current transmitted at very high frequencies through a tiny thin probe called a catheter that is steered through the blood vessels and into the heart. The electricity is passed through the tip of the catheter, cauterizing a small piece of muscle on the inside of a child's heart. Prior to delivering the electrical energy, doctors test the targeted area to determine if it is critical for supporting abnormal electrical activity in the heart that leads to fast heart rates, also known as tachycardia. Both the X-ray and 3-D systems allow doctors to see exactly where the catheter is positioned during testing and treatment.
The data are being presented by Mohamed Al-Ahdab, M.D., a former member of the U-M team now at Children's Hospital in Boston. Fischbach, an assistant professor at the U-M Medical School, directs the pediatric electrophysiology laboratory at C.S. Mott Children's Hospital, where children with abnormal heart rhythms are treated.
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.
In children, rapid heartbeats and other rhythm problems can cause palpitations, nervousness, anxiety, lightheadedness, fatigue, neck and chest discomfort, coughs and fainting. The rhythm problems can come and go, or be persistent. Medications are often used, but for children with chronic or severe problems, RF ablation is becoming more commonly used.
In addition to Fischbach and Al-Adhdab, the study's authors are Andrew Papez, M.D., a pediatric electrophysiology fellow at U-M, and Macdonald Dick II, M.D., professor of pediatric cardiology. The authors have no financial connection with Medtronic, which formerly sold the LocaLisa system, nor with the company now producing a similar system, Endocardial Solutions, part of St. Jude Medical.
The U-M Cardiovascular Center is a leader in RF ablation for both adults and children, attracting patients from throughout the nation for specialized care. U-M doctors have treated children as young as a few days with RF ablation, and perform dozens of the procedures a year. For details on heart-rhythm diagnosis and treatment at the U-M Cardiovascular Center, call 1-888-287-1082.