Cardiac rhythm disturbances are relatively common in the pediatric age group, occurring in about 1 of 1,000 children. Although most of these arrhythmias tend to be benign, some can be debilitating or life-threatening. In the past, the options to treat young patients with arrhythmias were few, including a limited number of medications or open-heart surgery.
"Technology has rapidly advanced so that now almost all children with arrhythmias can be successfully treated or completely cured with percutaneous ablation," according to Bryan C. Cannon, M.D., director of pediatric electrophysiology at Mayo Clinic in Rochester, Minn.
The most common arrhythmia in children is paroxysmal supraventricular tachycardia (PSVT). Children with PSVT can achieve heart rates higher than 300 beats per minute. Although this high heart rate is not often life-threatening, children are typically symptomatic, with palpitations, dizziness or even syncope when PSVT occurs. Some children learn techniques to terminate their tachycardia, but many children require some type of medical intervention, particularly when their symptoms occur during school or sports.
The most common mechanism of PSVT in pediatrics involves an accessory pathway. Prior to 1990, the only way to ablate these accessory pathways was via open-heart surgery. In the early 1990s, however, percutaneous radiofrequency ablation (RFA) technology was developed.
RFA lesions are very small (on the order of 4-6 millimeters), and they do not typically affect the overall structure or function of the heart. More than 20 years of follow-up has confirmed that there are no major negative long-term consequences as a result of performing this procedure in children.
The success rate for affecting a complete cure in ablation procedures is greater than 95 percent. The complication rate is very low (approximately 2 percent); the most common complication is ecchymosis at the catheter entry site.
Once a child is over the age of 5 years or weighs more than 33 pounds, the risk of complications is no greater than that for adult patients undergoing the same procedure. Ablations can be performed in smaller children (even neonates) who have medically refractory or life-threatening arrhythmias. The most severe complication that can occur in younger patients is damage to the atrioventricular (AV) node; if this complication occurs, the patient requires lifetime pacing therapy.
Some of the original open-heart surgical ablations were performed using cryoablation, but until several years ago, this technology was too large and bulky to be introduced percutaneously. Today, this technology can be delivered through a catheter that is similar in size to a traditional RFA catheter. The advantage to cryoablation is that cooling the tissue creates a temporary effect on the electrical tissues in the heart that becomes permanent only after several minutes of freezing.
"Use of percutaneous cryoablation in children therefore allows monitoring of the normal cardiac conduction system during lesion formation," says Dr. Cannon. "Cryoablation is especially valuable because it allows ablation of accessory pathways that are very close to critical structures such as the AV node and the His-Purkinje system." There has not been an incidence of permanent damage to normal conducting tissue when this system is used properly.
Another challenge that complicates ablation procedures in children involves the manipulation of the catheters. Since catheters are typically placed into the heart from the femoral vein, precise manipulation and location can be challenging.
Stereotactic technology has been developed to direct the tip of the catheter using a strong magnetic field, eliminating the need for the physician to move the catheter manually. This magnetic field can be manipulated in any direction, allowing an almost limitless number of catheter positions. This approach is useful particularly in patients with complex congenital heart disease.
An important breakthrough in the field involves advanced computer technology that is reducing radiation exposure in pediatric patients. Until recently, manipulating the catheters for the ablation was performed exclusively using fluoroscopy. New technology, however, is now making it possible to create 3-D computer models of the entire heart to be used as a map to perform ablation procedures. The computer images can be rotated in any direction to allow visualization of all parts of the heart. "In some cases, ablations are performed without any radiation exposure to the patient, which is particularly important in growing children," says Dr. Cannon.
The pediatric electrophysiologists at Mayo Clinic collaborate with colleagues in adult electrophysiology and cardiovascular surgery to plan the most appropriate treatment for each individual child. "New technology has made it possible to both safely and effectively eliminate most arrhythmias in the pediatric population," says Dr. Cannon.