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October 2007
Children's Research Institute News Brief
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Bernard L. Maria, MD, MBA
Executive Director
Darby Children's
Research Inst. |
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Inderjit Singh, PhD
Scientific Director
Darby Children's
Research Inst. |
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Safer, more effective cardiac ablation for kids
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| Dr. Dieter Haemmerich |
For children with heart rhythm abnormalities, Dr. Dieter Haemmerich's research aims to make treatment safer and more effective.
Kids with arrhythmia benefit from cardiac catheter ablation, during which an electrophysiologist locates the tissue responsible for the abnormal heart beat and then destroys it using either heat (radiofrequency ablation) or cold (cryo ablation), via a catheter inserted into the heart.
"Though heating is the most effective method, coronary vessel shrinkage is a considerable concern," says Dr. Haemmerich, PhD, assistant professor in pediatric cardiology.
"This is especially risky for kids, who have smaller coronary arteries than adults. When you perform this treatment in children, the chance of coronary stenosis is higher because there is less blood flow to protect the vessel from heat-induced shrinkage."
Freezing offers a much larger safety margin.
"The safety window is wider because during cryo, when heart tissue stops working, you have time to stop treatment before it's destroyed, and tissue function resumes. With heating, when the tissue stops working there's no way of bringing it back," he explains.
This is particularly problematic when treating close to the AV-node, because if it's destroyed the child will need a permanent pacemaker.
Because of these hazards, the preferred treatment for children is cryo-ablation. But while freezing avoids the danger of vessel shrinkage and damage, it's not as effective as heat.
That's where Dr. Haemmerich's work comes in.
"We're working to improve cryo ablation because, although there are fewer dangers than with radiofrequency ablation, the downside is you're not able to kill as large an area," he explains.
To optimize the effectiveness of this safer treatment, Dr. Haemmerich is collaborating with Dr. Phil Saul and pediatric cardiology fellows Drs. Kelly Gajewski and Tom Pilcher to characterize parameters that affect the tissue destruction zone during ablation.
"We're using computer models to determine temperature distribution and treatment parameters. For instance, is it advantageous to treat the area for a longer amount of time? How is blood flow affecting the size of the treatment zone? Can we shield the catheter from blood flow to create a larger zone?"
Using computational models and experimental work, Dr. Haemmerich Ð whose work has already resulted in clinically available ablation devices for the treatment of large tumors Ð is developing devices that improve upon the current ablation technology.
A recently funded NIH grant is powering another of his improvements on ablation: possible ways to reduce burns caused by grounding pads.
Burns from the electric current concentration below the gel pads, which are used as a return path for electrical currents, are becoming increasingly common during ablation and other procedures requiring high power.
"This is particularly a problem in children, whose skin area is limited and the heat, therefore, much more concentrated," explains Dr. Haemmerich.
Working with Dr. Michael Swindle of the department of comparative medicine, Dr. Haemmerich is testing prototype devices in animals, which he hopes will result in commercial devices.
"This has applications beyond cardiac ablation to many other procedures that use electrical currents, including electro-surgery, tumor ablation and more," he notes.
Drs. Singh and Maria who direct the DCRI are especially proud of programs like Dr. Haemmerich's that bridge basic science laboratory research and clinical care in the Children's Hospital.
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