The mechanism may be that drugs that block atrioventricular nodal conduction force conduction over the accessory pathway and reduce retrograde concealed penetration of the accessory pathway, thereby further enhancing or releasing accessory pathway conduction capacity. Class Ic drugs and procainamide are the most effective IV but can provoke or aggravate hypotension by their negative inotropic action. Long-term oral antiarrhythmic therapy can be selected empirically, but, particularly for patients who have had intractable symptoms due either to reciprocating tachycardia or AF, RF ablation is the treatment of choice. Occasional deaths have been reported with RF ablation, principally through cardiac tamponade. Almost all accessory pathways can be located and ablated by RF techniques.
Septal variants demand considerably more technical skill than do left lateral pathways.
Catheter instability may make right-sided accessory pathways technically challenging. Even then it is probably preferable to deal with the accessory pathway by catheter techniques before surgery, which then can be restricted to nonarrhythmic goals. A rapid regular atrial rhythm due to intra-atrial reentry or to abnormal automaticity within atrial cells. Digoxin toxicity is relatively rare because of more consistent formulations and better prescribing. Because the arrhythmia source may be anywhere within the atria, the P-wave vector is inconsistent.