Introduction: Mapping and ablation of rhythm abnormalities in pediatric patients

It is estimated that every year approximately 30 000 children are either born with a cardiac arrhythmia or develop it 1 . The majority of them have tachyarrhythmias, such as supraventricular tachycardia, atrial flutter or ventricular arrhythmias. Survivors of congenital heart surgery, because of intracardiac surgical scars, are especially at risk for developing atrial and ventricular arrhythmias. The resources needed to care for this particular group of patients are great. Many patients have frequent recurrences that require either life-long medical therapy or a potentially curative interventional procedure. For many years, the only curative therapy available was surgical ablation requiring open-heart surgical techniques and intraoperative mapping. In the late 1980s, a transcatheter approach employing direct current energy was used to ablate the offending substrate. Although this approach had many advantages over the alternative of open-heart surgery, there were limitations. These include a high rate of recurrence, pericardial tamponade, heart block and an unexplained high incidence of sudden death after the procedure 2 4 . In the late 1980s an alternative energy source in the form of radiofrequency waves became available and allowed for discrete heating of the catheter to the myocardial interface. Radiofrequency ablation is now considered a safe and effective option for managing tachyarrhythmias in children. Over the last decade, advances in techniques have increased the success rate and lowered the incidence of complications. This issue of Progress in Pediatric Cardiology is devoted to the latest techniques used by pediatric electrophysiologists to manage infants, children and adolescents with tachyarrhythmias. The first three manuscripts deal with the three sub-categories of supraventricular tachycardia-atrioventricular node reentry tachycardia, atrial ventricular reentry tachyŽ . cardia AVRT involving left-sided accessory pathways and AVRT involving accessory pathways located along the tricuspid valve annulus. Then Dr Van Hare provides an eloquent review of intra-atrial reentry tachycardia. The last manuscript concerns ventricular arrhythmias. Although rare in children, ventricular tachycardia may be a source of significant morbidity and mortality and Drs Phillips and Case give us an update of the latest approaches to this difficult clinical problem. In each manuscript, the authors describe the demonstrated or likely mechanisms for each type of arrhythmia. Along with a detailed description of the state of the art approaches for mapping and ablation of each substrate, guidelines are offered for referral indications. The rate of success in ablative therapy is high in children 5 . However, it does vary with the substrate and location of the pathway. It is anticipated that advances in technology will allow for an even higher rate of success and wider inclusion of patients who have favorable characteristics for ablative therapy. Use of catheters as small as 2 Fr and delivery of multiple diagnostic catheters through a single vascular sheath may allow smaller patients to be successfully and safely ablated. Advances in catheter design also include multiple forms of ‘cool tip’ catheters capable of creating lesions of greater depth. This is important in dealing with epicardial pathways, ventricular tachycardia foci and with Fontan patients with intra-atrial reentry tachycardia who need full thickness lesions. An exciting area of evolving technology involves new mapping modalities.