State-of-the-Art Treatment of Pediatric Abnormal Cardiac Rhythm
Kathryn K. Collins, MD
Associate Professor of Pediatrics, University of Colorado Denver
Director, Pediatric Arrhythmia Center , Children's Hospital Colorado
Director, Adult Congenital Electrophysiology
Supraventricular tachycardia (SVT) is an abnormal cardiac rhythm that occurs in pediatric patients with an otherwise normal heart structure. Figure 1. This condition is usually not life-threatening, but can cause significant symptoms such as palpitations, dizziness, lightheadedness and occasional syncope. The first step is making the diagnosis by obtaining a cardiac rhythm strip when the patient is having symptoms and is in the supraventricular tachycardia. This can be accomplished by several different methods: obtaining a cardiac rhythm strip in the Emergency Department or Clinic, a 24-hour ambulatory monitor, or an event monitor which the patient has at home for a one-month period. Wolff-Parkinson-White (WPW) syndrome is a specific type of cardiac abnormality that can cause supraventricular tachycardia. Figure 2. In patients with Wolff-Parkinson-White syndrome, the abnormality can be seen on surface electrocardiogram and one does not need to wait for documentation of tachycardia. For Wolff-Parkinson-White patients, the recommendation is for an invasive electrophysiology study and ablation to risk-stratify the extra pathway regardless of patient symptoms.
Once the diagnosis of SVT and/or WPW is confirmed by an electrocardiogram or rhythm strip, the next step is for the patient to be seen and evaluated by a pediatric cardiologist or electrophysiologist. Depending on the age of the patient, the family will be offered a choice among clinical monitoring (if the episodes are brief, associated with only minor symptoms, and occur infrequently), antiarrhythmic medications (which make it less likely that the child will have supraventricular tachycardia, but does not cure the problem), or an invasive electrophysiology study and ablation procedure. Electrophysiology studies and ablation procedures have been available since the early 1990s and have been significantly improved upon since that time. Ablation technology is now often utilized as first-line therapy for the treatment of supraventricular tachycardia in the pediatric population. The purpose of this report is to provide an update on the state-of-the-art technology in ablation procedures.
Mechanisms of supraventricular tachycardia
The two most common mechanisms of supraventricular tachycardia are accessory pathway mediated tachycardia and atrioventricular nodal reentry tachycardia. What both mechanisms have in common are that there are two connections between the atria and the ventricles instead of one. Whenever there are two paths, there is a potential for a reentrant loop to occur. Both of these mechanisms are easily and safely treated with ablation technology.
Invasive electrophysiology studies are conducted under general anesthesia by pediatric cardiac anesthesiologists at Children's Hospital Colorado. Once the child is asleep, percutaneous vascular access is obtained to the femoral vein(s) and possibly the internal jugular vein. Four electrode catheters are then advanced into the heart using intermittent fluoroscopy to show where they are in the heart. Figure 3. The first step of the electrophysiology study is to complete a standard pacing protocol where the heart is stimulated with pacing through the catheters. With the pacing, we evaluate the normal electric conduction as well as the abnormal electric conduction. We discern the arrhythmia mechanism and determine the location of the abnormality within the heart.
Once the electrophysiology study is completed, we move to the ablation. We remove one of the prior catheters and then advance an ablation catheter in the heart. The ablation catheter is a special catheter that we manipulate to specific locations within the heart to give us an electrical ‘map’ of the patient’s heart. From this electrical map, we can then precisely locate the group of cells that are causing the tachycardia. In the Pediatric Electrophysiology Laboratory at Children's Hospital Colorado, we have the most up-to-date technology available. We utilize a combination of a traditional 2-dimensional mapping system as well as a newer 3-dimensional mapping system.
Once the location of the abnormal fast heart rhythm is determined, the ablation catheter is placed directly on that spot. The ablation catheter can be one of two types: heat energy with radio frequency or cold energy with cryoablation. Both energies effectively rid the conduction pathway of those electrical cells, which cause the problem and cure the patient of their supraventricular tachycardia. The heat energy (radio frequency) has been utilized since the 1990s and has excellent long-term cure rates. The cryoablation (freezing) energy has been utilized since 2003 and was developed because it is safer at locations close to the patient’s atrioventricular node (the patient’s normal electrical conduction). It does, however, have higher arrhythmia recurrence rates after a successful procedure.
For invasive electrophysiology studies and ablation procedures in patients with normal heart structure, the cure rate is high and the risks of the procedure are extremely low. The ablation procedure can be done electively on children as young as three years of age (and even younger if necessary). It takes approximately three hours for the procedure and then an in-hospital recovery time of four to six hours following the procedure. Depending on the precise mechanism and location of the SVT, the success rate from the procedure is > 95 percent. The risks of major complications are < 1 percent and the risks of minor complications are < 4 percent. Following a successful ablation procedure, patients are followed for one year to monitor for arrhythmia recurrence. The risk of a recurrence depends on the location of the supraventricular tachycardia and on the details of the specific procedure. Fortunately, the majority of patients remain arrhythmia-free.
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2. Chanani NK, Chiesa NA, Dubin AM, Avasarala K, Van Hare GF, Collins KK. Cryoablation for atrioventricular nodal reentrant tachycardia in young patients: predictors of recurrence. Pacing Clin Electrophysiol. 2008 Sep;31(9):1152-9
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5. Van Hare GF, Javitz H, Carmelli D, Saul JP, Tanel RE, Fischbach PS, Kanter RJ, Schaffer M, Dunnigan A, Colan S, Serwer G; Pediatric Electrophysiology Society. Prospective assessment after pediatric cardiac ablation: demographics, medical profiles, and initial outcomes. J Cardiovasc Electrophysiol. 2004 Jul;15(7):759-70.