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................................................................. • Antidromic AVRT due to an atriofascicular pathway usually produces a horizontal or superior QRS axis, but a normal axis may also occur, depending on the way of insertion into the right bundle and fusion over the left anterior fascicle. • Right bundle electrogram preceding His bundle activation during anterograde pre-excitation and SVT.

Mapping identifies the proximal and distal insertion of accessory fibres, and demonstrates pathway potentials in most cases that then guide ablation.409,411 Catheter ablation is associated with a high success rate and low recurrence rates, and is therefore recommended for all patients with recurrent symptomatic tachycardia, and especially incessant tachycardias due to concealed nodofascicular or nodoventricular pathways.418 Preventive ablation for prognostic reasons is not routinely recommended, not even in patients with preexcitation or BBB in the surface ECG, as fast conduction via the AP is unlikely due to decremental conduction properties.

11.3.10 Therapy 11.3.10.1 Acute therapy Adenosine should be used with caution for the treatment of AVRT because of potential induction of fast AF.119,120,272 AF with fast ventricular conduction could also induce ventricular fibrillation, therefore electrical cardioversion should always be available. During orthodromic and antidromic AVRT, drug therapy could be directed at one of the components of the circuit, the AVN (beta-blockers, diltiazem, verapamil, or etripamil),100,129,419,420 or the AP (ibutilide, procainamide, propafenone, or flecainide)421,422 (Figure 19). Antidromic AVRT is associated with malignant WPW syndrome due to a very fast-conducting AP,403 and drugs acting mainly on the AP should be preferred. In addition, in case of antidromic AVRT with APs representing both the anterograde and retrograde limb, drugs acting on the AVN are ineffective. In drug-refractory antidromic AVRT, amiodarone may also be considered.423425

In patients presenting with pre-excited AF, urgent cardioversion is usually required and the threshold for the use of electrical cardioversion is lower. Conduction of electrical impulses can occur preferentially via the AP due to its shorter RP compared with the AVN.426 Accordingly, any AVN-modulating agents (adenosine, verapamil, diltiazem, beta-blockers, or digoxin) should be avoided in pre-excited AF as they may contribute to a risk of ventricular fibrillation.427,428 Pharmacological cardioversion of pre-excited AF or delayed AP conduction can be achieved with ibutilide (Figure 20).421 Drugs such as procainamide, propafenone, or flecainide, which affect conduction

Recommendations for the therapy of atrioventricular re-entrant tachycardia due to manifest or concealed accessory pathways

Recommendation Classa Levelb

Acute therapy Haemodynamically unstable patients Synchronized DC cardioversion is recommended for haemodynamically unstable patients.8688 I B Haemodynamically stable patients Vagal manoeuvres, preferably in the supine position with leg elevation, are recommended.41,8991 I B In orthodromic AVRT, adenosine (618 mg i.v. bolus) is recommended if vagal manoeuvres fail and the tachycardia is orthodromic.9294 I B In orthodromic AVRT, i.v. verapamil or diltiazem should be considered if vagal manoeuvres and adenosine fail.92,9498 IIa B In orthodromic AVRT, i.v. beta-blockers (esmolol or metoprolol) should be considered in the absence of decompensated HF, if vagal manoeuvres and adenosine fail.97,99,100 IIa C In antidromic AVRT, i.v. ibutilide or procainamide or i.v. flecainide or profanenone or synchronized DC cardioversion should be considered if vagal manoeuvres and adenosine fail.421,422,429,437 IIa B In antidromic AVRT, i.v. amiodarone may be considered in refractory cases.423425,435 IIb B Synchronized DC cardioversion is recommended when drug therapy fails to convert or control the tachycardia.87,88 I B Chronic therapy Catheter ablation of AP(s) is recommended in patients with symptomatic, recurrent AVRT.391393,438441 I B Beta-blockers or non-dihydropyridine calcium-channel blockers (verapamil or diltiazem in the absence of HFrEF) should be considered if no signs of pre-excitation are present on resting ECG, if ablation is not desirable or feasible.340,341,442,443 IIa B Propafenone or flecainide may be considered in patients with AVRT and without ischaemic or structural heart disease, if ablation is not desirable or feasible.429,444,445 IIb B Digoxin, beta-blockers, diltiazem, verapamil, and amiodarone are not recommended and are potentially harmful in patients with pre-excited AF.427,428,432434,446 III B

i.v. verapamil and diltiazem are contraindicated in the presence of hypotension or HFrEF. i.v. beta-blockers are contraindicated in the presence of decompensated heart failure. i.v. ibutilide is contraindicated in patients with prolonged QTc interval. i.v. procainamide prolongs the QTc interval but much less than class III agents. i.v. flecainide and propafenone are contraindicated in patients with ischaemic or structural heart disease. They also prolong the QTc interval but much less than class III agents. i.v. amiodarone prolongs the QTc but torsades des pointes is rare. AF = atrial fibrillation; AP = accessory pathway; AVRT = atrioventricular re-entrant tachycardia; DC = direct-current; ECG = electrocardiogram; HFrEF = heart failure with reduced ejection fraction; i.v. = intravenous. aClass of recommendation. bLevel of evidence. Downloaded from academic.oup.com/eurheartj/article/41/5/655/5556821 by guest on 07 October 2026