Although the 12-lead ECG and response to vagal maneuvers or medical interventions are frequently helpful in distinguishing causes of PSVT, the exact mechanism may remain unclear, even in cases of overt preexcitation (Wolff-Parkinson-White syndrome). A diagnostic electrophysiologic study can be very accurate in reproducing the arrhythmia and elucidating the underlying pathophysiologic substrate. These studies employ three to four temporary transvenous pacing electrode catheters placed in the right atrium, right ventricle, His bundle region, and coronary sinus to pace and record local electrical signals.
Does the patient with PSVT require treatment once an episode is terminated?
Except for patients with the Wolff-Parkinson-White syndrome in whom there is very rapid conduction over their accessory connection (manifest during atrial fibrillation or electrophysiologic study), most episodes of PSVT are not life-threatening. The frequency of arrhythmia recurrence and the need for medical intervention to terminate episodes influence the decision to treat individual patients.
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Medical therapies (digoxin, calcium channel blockers, beta blockers, and antiarrhythmic agents) are all associated with relatively high failure rates (often 40% in the first year). Patients with frequent arrhythmia recurrence or patients at risk for a more serious arrhythmia should be evaluated by a cardiac electrophysiologist so that risk and treatment strategies can be discussed.
What is radiofrequency ablation?
Ablative therapies, either direct current (100-200 joules) or radiofrequency (400-500 Hz), use intracardiac electrode catheters to map and then permanently destroy the local tissue (atrial or ventricular) that plays a critical role in the maintenance of a reentrant circuit or automatic rhythm. The cardiac electrophysiologist first performs a diagnostic electrophysiologic study to uncover the underlying tachycardia mechanism. Then, at the same or a separate setting, specialized mapping catheters are used to locate precisely and destroy the patient's abnormal electrical connection (i.e. the accessory connection in patients with Wolff-Parkinson-White syndrome). Radiofrequency ablation is generally regarded as the safer of the two procedures because the lesions created are smaller and more discrete. Radiofrequency ablation can be used to cure patients with the Wolff-Parkinson-White syndrome (accessory connection ablation), AV node reentry tachycardia (slow‚ or fast‚ pathway ablation), primary atrial tachycardia (automatic or triggered‚ activity focus), as well as other, rarer forms of supraventricular tachycardia. The success rate in the first two conditions is 90% and the procedure can be used in the very young to the elderly.