Electrophysiology Procedures Without Radiation in the Pediatric Population

Background

Cardiac rhythm disturbances are relatively common in the pediatric age group, occurring in about 1 in 1,000 children. Although most of these arrhythmias tend to be benign, some can be debilitating or life-threatening. These arrhythmias may cause significant problems in the lives of young people, including visits to the emergency room or the need for daily medications that may have significant side effects. The most common arrhythmia in the pediatric age group is supraventricular tachycardia (SVT).

Children with SVT can have a sudden increase in their heart rate to over 300 beats per minute. Although this is not often life-threatening, children are typically symptomatic with palpitations, dizziness, or even syncope when it occurs. The most common form of SVT in pediatrics involves an accessory pathway or AV node reentry tachycardia. Fortunately, in many of these pediatric patients, the tachycardia is the only abnormality in their heart and elimination of their underlying cause of tachycardia results in a permanent cure with no limitations.

Prior to 1990, the only way to remove these accessory pathways was to perform open-heart surgery to eliminate conduction in the pathway. With the advent of catheter-based technology in adults in the early 1990s, adaptations to perform this procedure in young patients were utilized to cure pediatric patients as well. The success rate for affecting a complete cure in ablation procedures in the pediatric population is greater than 95 percent.¹ The complication rate is very low (around two percent) — the most common being a bruise at the catheter entry site.² Once a child is over the age of five or weighs more than 33 pounds, there is no increased risk of complications when compared to adult patients who have undergone the same procedure.³ Ablations can also be performed in children younger than this (even neonates) who have medically refractory or life-threatening arrhythmias. In addition, there have been no major negative long-term consequences as a result of performing this procedure with over 20 years of follow up.

Despite the safety in the pediatric population, one concern that has arisen from these procedures is the fluoroscopy exposure to the patient as well as to the lab staff. Radiation exposure from multiple medical sources (X-ray, CT, nuclear medicine, and interventional fluoroscopy) elevate the lifetime risk of patients, physicians, and allied staff developing cancer. As the dose increases, the probability that cancer or a genetic effect will occur also escalates. It is estimated that approximately 20 percent of a typical citizen’s radiation exposure comes from medical exposure (Figure 1). Fluoroscopy is used to visualize the position of the electrophysiology catheters within the heart and determine the correct anatomic position to perform an ablation. Although the amount of radiation from fluoroscopy is comparable to a CT scan, there is still some concern in developing children about exposure to ionizing radiation (Figure 2).

Nonfluoroscopic Mapping and Catheter Navigation

However, with recent advancements in technology, imaging of catheters in the heart is now possible with limited or no use of fluoroscopy (Figure 3). Both St. Jude Medical (EnSite Velocity^™ Cardiac Mapping System) and Biosense Webster, Inc. (Carto RMT^™ Electroanatomical Mapping System) have a nonfluoroscopic mapping and catheter navigation system. These systems create a three-dimensional (3D) model of the heart that is based on the actual structure of the patient’s cardiac anatomy. Cardiac electrical activity within the heart can then be displayed as waveform tracings or as dynamic activation sequences, which are superimposed on the 3D models. The navigation systems can display the real-time position of conventional electrophysiology catheters in relation to the 3D model. In this manner, it is possible to perform the ablation with minimal fluoroscopy exposure.

The Carto mapping system uses proprietary deflectable catheters. These catheters have a locator sensor at the distal end that transmits signals using a hybrid magnetic and electrical current-based processing unit. A 3D electroanatomic map of any cardiac chamber of interest can be created with these catheters using point-by-point mapping.

The EnSite system uses an impedance-based technology. This mapping system is based on localization of multiple electrodes using an electrical field generated by three pairs of surface electrodes placed on the patient’s body along the x, y, and z axes. The patches emit a low-current electrical field across the chest using different frequencies for each of the three orthogonal axes to create a three-dimensional area. Any catheter can be localized by measuring the electrical potential received by the catheter. Using this technology, it is possible to quickly create a 3D geometric map of the cardiac chamber of interest by moving the catheter within a chamber within the heart. Catheters can then be moved within this created model to perform the ablation.

Case Presentation

We present the case of a 16-year-old female with supraventricular tachycardia. She initially presented at age 12 with palpitations. Her episodes were initially less than one minute and occurred about every three months. Over the next several years, her episodes began occurring more frequently and also lasted longer, although she was able to terminate the episodes by leaning forward or by using the Valsalva maneuver. She was evaluated in the pediatric cardiology clinic and given an event monitor. A narrow complex tachycardia was documented at a rate of 220 beats per minute. She initially chose to begin medical therapy rather than undergoing an electrophysiology study and ablation. Six months after her cardiology evaluation, she presented with fatigue, dyspnea, and a cough. She was subsequently diagnosed with Hodgkin’s lymphoma. She underwent both chemotherapy as well as radiation therapy. Her therapy was complicated by multiple episodes of supraventricular tachycardia. Despite medical therapy, she had multiple episodes of SVT, particularly following the placement of a port-a-cath. In order to try to eliminate her mechanism of tachycardia, the decision was made that she would undergo an electrophysiology study and ablation. Because of her recent chest radiation required for treatment of her Hodgkin’s lymphoma, there was concern about any additional radiation exposure to the chest. For this reason, she underwent an electrophysiology study with mapping performed solely with the EnSite Velocity Cardiac Mapping System. She was found to have AV node reentry tachycardia and underwent a successful cryoablation with no radiation exposure at all. She was discharged home after the procedure, and has done well with no evidence of tachycardia recurrence and no recurrence of her Hodgkin’s lymphoma.

Discussion

he advent of technology to allow electrophysiology studies and ablations with minimal radiation exposure has special utility in at-risk patients, including young patients and patients who have had other radiation exposure. Although the long-term risk for development of a complication such as malignancy from radiation exposure during an EP study in a pediatric patient is likely low, the possibility of performing these procedures with no radiation exposure is certainly an appealing one. The minimization of ionizing radiation to patients as well as operators may reduce the long-term complications that occur as a result of ablation procedures.

The use of nonfluoroscopic-based mapping systems has been shown to be very effective⁴ and safe⁵ in the pediatric population. In experienced hands, there is little difference in success or recurrence when compared to traditional fluoroscopy-based ablations. In addition, these systems may offer physicians the ability to perform ablations in patients who would not otherwise be candidates, such as those who have recently undergone chest radiation therapy or pregnant patients.⁶ In addition, ablation points can be marked on the map, which allows the physician to know exactly where ablation lesions were placed. This permits the operator to quickly return to a spot if the catheter is dislodged by inadvertent catheter movement during an ablation lesion or if there is a recurrence of the tachycardia mechanism in the waiting period following an ablation. The expansion of this technology and its basic techniques has been expanded to allow implantation of both pacemakers and ICDs with no radiation exposure, and there are currently multicenter studies occurring to determine the efficacy of this procedure within the pediatric population.⁷ 

Summary

In summary, it is currently possible and practical to perform safe and effective electrophysiology studies and ablations in the pediatric and adult population with potentially no fluoroscopy exposure. Advances in the technology available will only add to the ease and success of this procedure in the future.

Disclosures: Bryan Cannon is a consultant for St. Jude Medical and Medtronic.

References

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