A deadly mix - rheumatic mitral stenosis, preexcited atrial fibrillation, left atrial appendage thrombus and left atrial appendage accessory pathway

A 38-year-old female with rheumatic mitral stenosis on medical management presented with palpitations and presyncope since 10 days. Electrocardiogram showed an irregular rhythm at a rate of 160 bpm with preexcitation suggestive of atrial fibrillation with a left free wall accessory pathway (Fig. 1). Transthoracic echocardiography showed severe rheumatic mitral stenosis with a valve area of 1 cm sq, moderate mitral regurgitation and a mobile clot within the left atrial appendage (LAA). She was not on anticoagulation. Ventricular rate was between 160 and 180 beats per minute on monitoring. Anticoagulation with heparin and warfarin was started immediately. Oral flecainide 50 mg bd was started along with oral metoprolol 25mg bd after two days in an attempt to slow accessory pathway conduction. However, after three doses she developed recurrent polymorphic ventricular tachycardia and ventricular fibrillation requiring defibrillation. With no other obvious cause for the recurrent arrhythmias with QT prolongation during sinus rhythm, the drugs were stopped considering possible proarrhythmia. She was taken up for electrophysiology study with a plan of ablating the accessory pathway. Diagnostic catheters were placed in the high right atrium,