All that is irregular is not AF!

Abstract

A 64-year-old man with no signifi cant past medical history presented to a district hospital in June 2012 with a 3-week history of palpitations and breathlessness. The electrocardiogram (ECG) showed an irregularly irregular wide complex tachycardia at a rate of 150 beats/min with right bundle branch block-like morphology (Box 1). A transthoracic echocardiogram showed moderate segmental left ventricular dysfunction. Coronary angiography showed no evidence of signifi cant coronary artery disease to account for his left ventricular impairment. A diagnosis of atrial fi brillation (AF) with a rapid ventricular response and tachycardia-mediated cardiomyopathy was made.Therapy with diuretics and antiarrhythmic medications was commenced. Despite substantial doses of amiodarone (600 mg daily), metoprolol (200 mg daily), verapamil (240 mg daily) and digoxin (250 μg daily) over 2 weeks, his heart rate remained uncontrolled at between 100 and 200 beats/min. A transoesophageal echocardiogram-guided cardioversion was performed, but failed to restore normal rhythm. He was subsequently referred to our tertiary cardiac centre for further management. , and normal fi ndings on thyroid function tests. Although his ECG showed an irregularly irregular broad complex tachycardia suggestive of AF, closer inspection of the ECG showed P waves of probable sinus bradycardia with atrioventricular dissociation (Box 1, red arrows) indicative of ventricular tachycardia (VT). A repeat echocardiogram showed moderately impaired left ventricular function (ejection fraction, 35%-40% [RI, 55%-75%]) due to global hypokinesis. The patient had incessant VT throughout an electrophysiology study that was performed. Three-dimensional electro-anatomical mapping (Ensite NavX, St Jude Medical) identifi ed a VT focus emanating from the base of the posteromedial papillary muscle of the left ventricle. Ablation at this focus terminated the VT with no further ectopic activity. His ECG after the ablation showed sinus rhythm (Box 2). He has remained well since discharge, taking only a low daily dose of bisoprolol (1.25 mg). Six months after the ablation, a 24-hour Holter monitor has not detected any recurrence of VT, and a repeat echocardiogram showed normalisation of left ventricular function.All that is irregular is not AF! T he differential diagnoses of broad complex tachycardia include ventricular tachycardia (VT), supraventricular tachycardia with aberrancy and a ventricular paced rhythm. The diagnosis of broad complex tachycardia remains challenging despite various criteria having been established to differentiate VT from supraventricular tachycardia with aberrancy. 1,2 1,2 The patient's initial presenting electrocardiogram (ECG) was misdiagnosed as atrial fi brillation (AF) because of the irregularly irregular rhythm.In VT, the rhythm is usually regular or almost regular but beat-to-beat variations can occur in the presence of captured beats (when an atrial impulse causes depolarisation via the normal conduction system, resulting in a narrow QRS complex oc...