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Editorial Indian Pediatrics 1999;36: 1091-1096 |
Treatment of Tachycardia in Infants and Children |
Diagnosis and Natural History of Tachycardia Precise diagnosis is of fundamental importance to management of tachycardias. The term "supraventricular tachycardia" is an inadequate description of a group of 10 or 12 different tachycardia mechanisms. Analysis of a 12 lead electrocardiogram recorded in sinus rhythm and in tachycardia, coupled with knowledge of the age of onset of symptoms will often lead to a precise diagnosis. Knowing the diagnosis, one can define the natural history and plan treatment. Most infants with "supraventricular tachy-cardia" have atrioventricular reentry via an accessory connection. The connection some-times conducts anterogradely in sinus rhythm producing ventricular pre-excitation (Woff- Parkinson-White syndrome) but more often conduction only occurs retrogradely and the connection is known as "concealed". Most infants with atrioventricular reentry tachycardia will have no problems beyond the age of six or 12 months whereas in a minority the problem will persist or recur(1). Other tachycardias encountered in infancy include atrial ectopic tachycardia and atrial flutter, both of which will usually resolve, and permanent junctional reciprocating tachycardia and junctional ectopic tachycardia, both of which are persistent(2). Ventricular tachycardia in infancy is rare. Specialist evaluation is required to define the prognosis and treatment(3,4). Atrioventricular reentry is also the commonest tachycardia encountered in children of school age. In this age group the problem will usually persist(1), so a long term treatment strategy is required. In later childhood atrioventricular nodal re-entry tachycardia becomes progressively more common and becomes the main differential diagnosis(5). Other arrhythmias are less common at this age but they require precise diagnosis. They include atrial ectopic tachycardia, permanent junctional reciprocating tachycardia and atrial flutter, all of which are likely to persist(2). Our under-standing of the mechanisms of ventricular tachycardia in childhood has changed signifi-cantly in recent years so that drug treatment or catheter ablation can be employed more precisely(6). Choice of Treatment Most tachycardias in childhood are not life threatening. Decisions about treatment are based on symptoms, taking account of the frequency, duration and severity of episodes. In infants in particular, it is important to be aware of the natural history as a long term strategy is not required for a tachycardia with a high chance of spontaneous resolution. In childhood it is important also to take account of the disruption to school and family life by attacks of tachycardia and of anxiety produced in children and their families by each episode. The three options for long term management are no prophylactic treatment, prophylactic antiarrhythmic drugs, and radiofrequency ablation. The choice should be made by balancing the risks, inconvenience, cost and benefit of each option. Patient choice (and parental choice) is also important and is now the commonest indication for radiofrequency catheter ablation(7). A recent cost effectiveness assessment compared the cost, morbidity, mortality and efficacy of drug treatment, surgery and radio frequency ablation for a five year old child with symptomatic tachycardia in Wolff-Parkinson-White syndrome(8). It concluded that catheter ablation had a lower cost, mortality and morbidity than drug treatment or surgery and should be the treatment of choice in that situation. The analysis and conclusions can be extrapolated to other forms of persistent tachycardia in childhood. Treatment of Tachycardia in Infancy Once the diagnosis of atrioventricular tachycardia in infancy has been made, the main priority is restoration of sinus rhythm. Acute termination of tachycardia is most easily achieved by intravenous administration of adenosine in a dose of 150-300 mg/kg given by rapid bolus injection(9). The drug is metabolized very quickly and can be repeated as necessary. Facial immersion in iced water is also usually effective but is only appropriate in early infancy(10). Other drugs are rarely required for termination of tachycardia. The dangers of verapamil in early infancy are well recognized and this drug is no longer recommended(11). Synchronized electrical cardioversion is effective but is not easily repeated. Once sinus rhythm is restored the baby's condition will improve. Early recurrence of tachycardia is quite likely in the short term so prophylactic drug treatment is usually advised. There are no controlled trials of drug treatment in this situation but it does seem that digoxin probably has a relatively weak antiarrhythmic affect(12). Treatment with a beta-blocker, a class IC drug, such as propafenone or flecainide, or amiodarone will usually achieve arrhythmia suppression(12-14). The majority of babies will not be prone to episodes of tachycardia by the end of infancy so drug treatment can usually be withdrawn after six or 12 months if there has been good control(15). In a few cases there will be a recurrence later in childhood(1). Other tachycardias in infancy require a specific management plan. Atrial flutter can usually be terminated by electrical cardioversion or transoesophageal overdrive pacing. Recurr-ence is rare and prophylactic treatment is usually not necessary. Atrial ectopic tachycardia is usually incessant and will not respond to adenosine. Short term treatment may be required but in most cases the problem resolves by six months of age(16). Permanent junctional reciprocating tachycardia will respond to treatment with a betablocker, class IC drug or amiodarone in the short term. It is unlikely to resolve and a longer term strategy will be required(2). Incessant idiopathic infant ventricular tachycardia usually presents in later infancy, often with incessant tachycardia and poor ventricular function(17). Drug treatment with flecainide or amiodarone, sometimes in combination or with the addition of a beta-blocker, has proved most effective. Treatment can usually be withdrawn by the age of five years without recurrence(3,4). Management of Tachycardia in Childhood Acute termination of atrioventricular reentry or atrioventricular nodal reentry tachycardia in childhood is usually straightforward. Adenosine is probably the drug most often used but verapamil is also safe and effective in this age group(14). Long term treatment involves a choice between antiarrhythmic drug treatment and catheter ablation, as mentioned above(8). Many drugs can be used to suppress atrioventricular reentry tachycardia. The literature relating to their use is mainly a series of retrospective reports of clinical experience(14). There are no placebo-controlled or blinded trials and very few comparisons between one drug and another. Most antiarrhythmic drugs have been used at some time for control of atrioventricular reentry tachycardia(18). Those most likely to be effective include beta-blockers, propafenone, flecainide, amiodarone and sotalol(14). Radiofrequency ablation has become the standard treatment for atrioventricular reentry tachycardia despite its fairly recent introduc-tion(18,19). The procedure involves trans-catheter deliver of a high frequency electric current to induce a small burn at the point of contact of the catheter with the heart(19,20). If the catheter is accurately targeted at the accessory pathway, the arrhythmia substrate will be destroyed. The Pediatric Electrophysiology Society has the largest register of ablation procedures and reports immediate success rates for ablation of accessory pathways of around 85-90% with 74% freedom from recurrence at three years(7). Other large series report similar results(19,21,22). Significant complications of catheter ablation are rare. The main concern is production of atrioventricular block from ablation of pathways close to the normal conduction axis. Damage to the mitral and aortic valves is rare. The mortality is low, particularly if ablation in infancy and early childhood is avoided(7). Atrioventricular nodal reentry tachycardia becomes an increasing common arrhythmia during later childhood. The arrhythmia circuit involves the atrioventricular node and the adjacent low right atrium(5,19) and has become much better understood since the development of radiofrequency ablation. Drug treatment is often relatively ineffective or poorly tolerated. Radiofrequency modification aims to destroy the posterior slowly conducting fibers while leaving the anterior fibers and the atrio-ventricular node unaffected. The Pediatric Electrophysiology Society report an acute success rate of 96%(7). The reported risk of producing complete atrioventricular block is 1-5%(5,19,23). The management plan for other types of "supraventricular tachycardia" depends on the precise diagnosis. Atrial ectopic tachycardia in childhood will respond to drug treatment but spontaneous resolution in the long term is not very likely. The arrhythmia is particularly amenable to catheter ablation with a high success rate and low complication rate(2,19). Permanent junctional reciprocating tachycardia will also respond to drugs but is almost always a long term problem and the success rate from catheter ablation is high(2,19). Congenital junctional ectopic tachycardia is rare but is best treated by drugs because of the high risk of complete atrioventricular block associated with catheter ablation. Ventricular tachycardia in childhood is not a single entity and the prognosis and treatment plan depends on the particular type(4). Monomorphic ventricular tachycardia may arise in the left or right ventricle. With a structurally normal heart, some tachycardias of left ventricular origin are now known to be amenable to catheter ablation which provides an alternative to long term drug treat-ment(6,19,24). Idiopathic right ventricular tachycardia often arises from the outflow and is most often seen in older children or teenagers(24,25). Many are asymptomatic and the prognosis is benign so it is debatable whether any treatment is required(4). Catheter ablation has been employed but its use is controversial(26). Polymorphic ventricular tachycardia is rare but often dangerous. It most often occurs in congenital long QT syndrome in which life-threatening tachycardia is associated with underlying prolongation of the QT interval(27,28). Because of the high risk of sudden death, treatment is required even in the absence of symptoms during childhood(27). Treatment with a beta-blocker, most often nadolol, has been shown to produce a dramatic reduction in mortality. Patients who remain symptomatic despite treatment with beta-blocking drugs may require pacemaker or defibrillator implantation. Other rare varieties of polymorphic ventricular tachycardia and their management have been described by Coumel(29) and Brugada(30). Arrhythmias in Other Situations One of the remaining difficult challenges in management of tachycardias involves treatment of atrial and ventricular arrhythmias late after repair of structural heart disease(14,31). The most common clinical problem is treatment of atrial flutter after atrial repair of transposition of the great arteries (Senning or Mustard operations) or after atriopulmonary bypass for complex congenital heart disease with a functional single ventricle (Fontan operations and variants). Atrial tachycardias in repaired transposition are particularly difficult to control with drugs and are associated with an increased risk of sudden death(32). The published results of catheter ablation are also relatively disappointing when compared with simpler arrhythmias. This is due both to the frequent presence of more than one tachycardia circuit and the physical difficulties of intracardiac mapping. Recently introduced computerized mapping techniques may lead to improved results from ablation in the near future. Ventricular tachycardia after repair of tetralogy of Fallot or other operations requiring a right ventricular outflow conduit also presents a formidable challenge(2). Treatment options include drugs, surgical revision, catheter ablation and defibrillator implantation and require expert assessment. Future Developments As is the case with most newly introduced techniques, there was a significant learning curve in early experience with radiofrequency ablation(33,34). The results of catheter ablation of common arrhythmias are likely to continue to improve and recurrence rates are likely to fall. Increasing experience will define the role of ablation compared with drug treatment in rarer types of tachycardia. Technical developments will widen the indications for catheter based techniques in postoperative tachycardias. Drugs will remain fundamental to acute management but the advances in catheter treatment are likely to discourage development of newer drugs and those currently available will probably assume a smaller role in long term management. Christopher Wren, References 1. 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