100 QUESTIONS IN CARDIOLOGY

65 Which patients with SVT should be referred for

an intracardiac electrophysiological study (EP

study)? What are the success rates and risks of

radiofrequency (RF) ablation?

Roy M John

The management of supraventricular tachycardia (SVT) has

changed dramatically with the development of curative radiofre-

quency ablation (RF ablation). For most patients, the technique

offers a clear alternative to long term antiarrhythmic drug therapy

with its potential toxic side effects. Except for atrial fibrillation

and atypical atrial flutter, most SVTs are amenable to RF ablation

albeit with some variation in success rates depending on the

arrhythmia mechanism.

AV nodal re-entrant tachycardia and SVTs mediated via

accessory pathways are the easiest to treat with RF ablation with

success rates that exceed 90%.^1 Recurrence is rare occurring in less

than 10%. Focal atrial tachycardias and re-entrant atrial tachy-

cardias resulting from prior atrial surgical scars have lower success

rates of about 80%. Even for the rare but troublesome atrial tachy-

cardia that cannot be ablated, RF ablation of the AV node with

permanent cardiac pacing is effective in alleviating symptoms and

can reverse any tachycardia mediated cardiomyopathy. Atrial

flutter of the classical variety use a single re-entrant circuit in the

right atrium and typically require an isthmus of tissue between the

inferior vena cava and tricuspid valve for maintenance of the

arrhythmia. RF ablation to create conduction block in this isthmus

is effective in preventing recurrence of atrial flutter in 80% of

patients with negligible risks. Unfortunately some patients

develop atrial fibrillation because both arrhythmias share common

cardiac disease processes that act as substrates for the arrhythmia

mechanism. Nonetheless, fibrillation is easier to manage with

drugs and combination of flutter ablation and antiarrhythmic drug

therapy is often successful in maintaining sinus rhythm.

In the adult patient with the symptomatic Wolff Parkinson

White syndrome, it is now generally believed that RF ablation

should be the treatment of choice. Recurrent arrhythmias

associated with ventricular pre-excitation are difficult to treat

medically and often require the use of antiarrhythmic drugs with

potent pro-arrhythmic effects or organ toxicity (e.g. flecainide,