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Q1: What is the differential diagnosis?
The important differential diagnosis for a irregular broad complex QRS tachycardia is:
Atrial fibrillation with aberrant conduction
Atrial fibrillation with pre-excitation
Atrial fibrillation with pre-existing bundle branch block
Polymorphic ventricular tachycardia
Q2: What is the most likely diagnosis?
The rapid ventricular rates and the absence of cardiovascular risk factors should make one suspect atrial fibrillation with pre-excitation (conduction via the accessory pathway). Wolff-Parkinson-White syndrome was confirmed in this patient in the electrocardiogram taken during sinus rhythm after treatment.
Q3: How will you manage this patient acutely?
In view of the hypotension DC cardioversion is the best choice.
Q4: What is the long term management?
Patients with Wolff-Parkinson-White syndrome with symptomatic arrhythmias, particularly life threatening ones like atrial fibrillation, should be referred for radiofrequency ablation for elimination of the accessory pathway. Flecainide, propafenone, and sotalol are prophylactic antiarrhythmic drugs of choice while the patient is awaiting the procedure.
Atrial fibrillation is the second commonest (10%–30%) arrhythmia in patients with Wolff-Parkinson-White syndrome after orthodromic atrioventricular (AV) re-entrant tachycardia (AVRT) which is a narrow QRS regular tachycardia almost identical to AV nodal re-entrant tachycardia. The cardinal features of atrial fibrillation in Wolff-Parkinson-White syndrome are the irregularity and the rapid ventricular rates as well as the varying QRS configuration. Ventricular rate is an aggregate of conduction over the normal AV node and accessory pathways and it can approach 300 to 350 beats/min. QRS configuration is determined by the route of atrial impulses which is dependent mainly upon the refractory period of the accessory pathway.
If the refractory period of the accessory pathway is short, the antegrade conduction occurs via the accessory pathway to produce an irregular wide QRS tachycardia as in this case, while it is no different from usual atrial fibrillation if conduction takes place via the AV node. Varying degrees of fusion beats can also be found. Short effective refractory period of accessory pathway1 and short R-R interval between consecutive pre-excited complexes2 are associated with rapid ventricular rates that can degenerate into ventricular fibrillation3 and sudden death.
The pathogenesis of atrial fibrillation in Wolff-Parkinson-White syndrome is poorly understood.4 5 It is more common in patients with multiple accessory pathways. Though the accessory pathway is important in the pathogenesis of atrial fibrillation, it is probably not required for the initiation of atrial fibrillation6and the accessory pathway is usually a passive bystander. However some reports suggest that accessory pathways are branched and can support microre-entry.
Atrial fibrillation is almost always associated with concomitant inducible AVRT, and spontaneous degeneration of AVRT into atrial fibrillation has been reported to represent the most frequent mode of initiation. It is unclear why all patients with AVRT do not develop atrial fibrillation.7 Intrinsic atrial electrophysiological abnormalities5 8 and exaggerated sympathoadrenal discharge have all been blamed in the pathogenesis of atrial fibrillation. Associated abnormalities like mitral valve prolapse and Ebstein's anomaly9 can be found.
Electrical cardioversion is the treatment of choice in pre-excited atrial fibrillation as it can degenerate into ventricular fibrillation. However if haemodynamically well tolerated, chemical cardioversion can be tried. Though intravenous flecainide, propafenone, procainamide, sotalol, and amiodarone have all been shown to be effective in cardioverting pre-excited atrial fibrillation or reducing the ventricular rate, class Ic drugs (flecainide and propafenone) are popular choices. Verapamil and digoxin are contraindicated as they block conduction via the AV node enhancing conduction via the accessory pathway thereby actually increasing the ventricular rate. Intravenous amiodarone should be used with caution in pre-excited atrial fibrillation as increase in the ventricular rates and ventricular fibrillation have been reported. Radiofrequency ablation is the treatment of choice in patients with symptomatic arrhythmias. It is usually but not always successful in preventing atrial fibrillation. However it will eliminate the life threatening rapid ventricular rates which can be associated with it.