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............................................................................................................................................................................. sinus node dysfunction may occur as a consequence of the atrial redirection procedure.495 As tachycardia is not well tolerated in patients with asystemic right ventricular and diastolic dysfunction, maintaining long-term sinus rhythm is highly desirable in this setting. Use of antiarrhythmic drugs is limited due to ventricular and sinus node dysfunction, and pro-arrhythmic risk. Ablation procedures in patients with a Mustard or Senning repair have a high acute success rate; however, recurrence rates approach 30% during long-term follow-up.500,514516

12.3.4 Tetralogy of Fallot SVTs are not uncommon in patients with tetralogy of Fallot. In addition to being related to symptoms, the occurrence of supraventricular arrhythmias has been linked to a statistically higher risk of sudden cardiac death in this population.517 As catheter ablation has a high procedural success rate, it should be considered as a first-line option in this setting.518 In addition, patients with new-onset atrial arrhythmias should be thoroughly evaluated to exclude addressable haemodynamic lesions such as severe pulmonary valve regurgitation, which may be amenable to surgical or interventional therapy leading indirectly to reduced arrhythmia burden.

12.3.5 Fontan repairs AT is common in patients post-Fontan palliation. Patients with a classic (atriopulmonary) Fontan procedure are at especially high risk for AT, with <_60% developing SVTs after 15 years of follow-up.519 In addition to symptoms and the risk of cardiac thromboembolism, AT is poorly tolerated haemodynamically in patients with univentricular hearts, and may lead to acute deterioration and overt HF in this setting.520 Catheter ablation is often effective but challenging, due to the nature of the arrhythmia circuits as well as issues with cardiac access.514,515 Various surgical modifications, such as the conversion to total cavopulmonary connection, have evolved and can ameliorate the risk of atrial arrhythmias.521

13 Supraventricular tachycardia in

the paediatric population

Specific detailed recommendations for paediatric patients are published elsewhere522,523 and are beyond the scope of this document. In general, certain aspects are different in the paediatric population and should be taken into account. Immaturity of the cardiac structures, including conduction tissue, may lead to modifications in the electrophysiology of the heart. Therefore, some APs present in the first months of life (even those associated with tachycardias) may disappear before the first year of age.522 Actually, AVRT due to WPW that begins in infancy may resolve in 90% of patients, but may recur in later childhood in 30- 50% of patients; however, if the tachycardia is present after the age of 5, it persists in >75% of patients.524 It is clear that small children may not complain of symptoms, so indirect signs have to be assessed when SVT is suspected, i.e. irritability, failure to thrive, and even flat growing curves. It is not uncommon to discover an incessant SVT in a patient presenting with cardiogenic shock due to TCM. This most frequently occurs in relatively slow SVTs, such as PJRT and focal AT.525,526 Pharmacokinetics and pharmacodynamics in children are different to those in adults; therefore, special attention has to be given when prescribing drugs.527 This is particularly important in newborns as milk can substantially modify the absorption of the drug and, as feeding schedules tend to be erratic, can affect effective drug availability. Furthermore, many drugs have to be prepared at specialized pharmacies, adding to the risk of incorrect dosing, and drug solutions may also need to be stored under special conditions to maintain their stability. This can be inconvenient when long-term treatment is required as, for example, a portable cooler bag must be carried. In addition, the long-term effects of some drugs, as they accumulate, are especially dangerous in growing bodies. This is of special interest regarding amiodarone, which can chronically provoke the same secondary effects as it does in adults. Verapamil has to be avoided whenever possible or given very carefully to small patients as it can provoke severe hypotension.522 A decreased response of adenosine in younger children has also been suggested.528

Invasive techniques are possible and effective even in very small children, when indicated, but there are several limiting factors. First, radiofrequency lesion formation in immature sheep myocardium is similar to that in adult sheep myocardium acutely, but is associated with late lesion enlargement and fibrous tissue invasion of normal myocardium. These observations may have implications for clinical radiofrequency ablation procedures in infants529 and avoidance of radiofrequency ablation, if at all possible, in the first 2 years of life is prudent. Second, no specific catheters and tools exist for the paediatric population. Currently, available catheters (minimum 5 French for non-irrigated radiofrequency tips) and curves are, in general, too large. This is particularly limiting in small children needing an ablation to resolve incessant tachycardia. Finally, the experience of the operator and the centre is crucial. Small patients requiring ablation should be referred to experienced reference centres for treatment. The number of catheters used, and procedural and radiation times, should be minimized in these growing bodies.530 Electroanatomical mapping systems are most valuable in this setting.

13.1 Foetal arrhythmias

Foetal arrhythmias can be detected at an early gestational age, with incessant, rapid SVTs associated with foetal death due to hydrops. Therefore, a special effort has to be made to detect and control foetal arrhythmias. A strong correlation between post-natal SVT and later gestational age at foetal SVT diagnosis has been reported.531 Diagnosis relies on echocardiography as foetal ECGs are not available in most clinics (it is used in just a few centres worldwide and primarily for research purposes).532 When sustained foetal tachycardia is observed, treatment is mandated. There are several protocols for this purpose, and they are mostly based on digoxin, flecainide, and sotalol alone or in combination depending on the type of tachycardia. These drugs have to be given to the mother, with a fraction reaching the foetus. This means that the secondary effects of these drugs can manifest in both the foetus and mother. Close follow-up is therefore needed.522,533,534

14 Supraventricular tachycardia in

pregnancy

Sustained SVT becomes more frequent during pregnancy, occurring in 2224/100000 pregnancies. It may even manifest for the first time, particularly in the third trimester or peri-partum, according to comprehensive discharge data from hospitals.535 The overall Downloaded from academic.oup.com/eurheartj/article/41/5/655/5556821 by guest on 07 October 2026