Cardioversion of Pre-Excited Atrial Fibrillation Leading to Ventricular Fibrillation- Case Report and Review of Literature

Pre-excited, fast conducting atrial fibrillation (AF) is a serious condition that requires urgent termination of the AF. Often, class I AAD are successfully used but at times DC cardioversion is needed. Appropriate synchronization of the DC shock on the QRS is crucial, however not easily achieved. Since the QRS-T complexes in pre-excited AF are severely distorted, the diagnosis of inaccurate synchronization might be overlooked.

We present a case of a 19 year-old man who was admitted to the ER for pre-syncopal episode and palpitations. ECG on admission showed baseline rhythm of AF with pre-excitation pattern compatible with left anterolateral accessory pathway. The patient was stable hemodynamically however symptomatic, thus attempts to restore sinus rhythm were pursued. Administration of Procainamide did not terminate AF, and DC cardioversion was performed using a synchronized 100J shock, resulting in VF. It is apparent that inaccurate synchronization on the T-wave while the external defibrillator is set at "paddles" which showed a relatively small QRS complex with large positive T wave, led to "shock on T" and VF. The rhythm was diagnosed immediately and a second non-synchronized 200J were delivered, successfully restoring sinus rhythm. The patient underwent successful ablation of his AP.

Review of literature: six cases had been previously published; one was lethal. In all cases, the reason for post cardioversion VF was inaccurate synchronization on the T wave. Other notable observations include location of the pathway (left-sided in all cases) and gender (all man). Age and ventricular rate at presentation were quite variable. In all but one cases, the energy used was ≤100J or less. It had been suggested that lower shock energy predisposes to VF.

Conclusion: cardioversion of pre-excited AF may result in VF due to abnormal synchronization. Lead choice should take in to account the ability to accurately define the QRS complex.