Introduction.

Ventricular tachyarrhythmia is a term used to describe a spectrum of cardiac arrhythmias arising from the ventricular myocardium. It comprises monomorphic ventricular tachycardia (VT), polymorphic VT, ventricular fibrillation (VF) and ventricular flutter1. Sustained ventricular tachyarrhythmia is a highly lethal arrhythmia and is implicated in an estimated 95% of cases of arrhythmic sudden cardiac death2.
In the majority of cases, ventricular tachyarrhythmias are secondary to either an identifiable structural heart abnormality (e.g., coronary artery disease, non-ischaemic cardiomyopathy) or a primary electrophysiological disease evident on baseline electrocardiography (e.g., long QT syndrome, Brugada syndrome). However, an estimated 6-10% of patients who present with ventricular tachyarrhythmias have no clear aetiology suggested by ECG, transthoracic echocardiography (TTE) or coronary assessment3,4. While data in these patients with unexplained ventricular arrhythmia (UVA) is sparse, small case series have shown that these patients are often younger5 and have a higher risk of recurrent cardiac arrest in the future6.
Management of patients with UVA represents a clinical challenge, with the diagnostic workup for these patients being poorly standardised and often incomplete. Consensus guidelines published by the American College of Cardiology/American Heart Association/Heart Rhythm Society (ACC/AHA/HRS) on the evaluation of patients with ventricular tachyarrhythmias provides a Class I recommendation for the use of a baseline ECG, resting TTE and coronary angiography in the workup of patients presenting with ventricular tachyarrhythmia7. Other investigations, such as cardiac magnetic resonance imaging (CMR), electrophysiology study (EPS) and genetic testing, carry a Class II recommendation. Exercise stress testing, provocative testing for Brugada Syndrome (flecainide/ajmaline challenges) are not referenced in this guideline. The relative yield of each of these modalities of testing in the evaluation of UVA is uncertain.

Aims.

The present study had three aims. First, we aimed to evaluate the clinical characteristics of younger adults presenting with unexplained ventricular arrhythmia (UVA), as compared with patients who have an identifiable aetiology of ventricular tachyarrhythmia. Second, we aim to examine the variability in diagnostic evaluation undertaken in this UVA cohort. In particular, we will evaluate the adoption rate of five ‘second-line’ investigations: CMR, exercise stress ECG, flecainide challenge, EP study and genetic testing. Third, we aimed to assess differences in management and subsequent outcomes in patients with unexplained ventricular arrhythmia compared to their counterparts with an identified aetiological mechanism.
We hypothesised that the diagnostic workup in patients with UVA will be heterogeneous and incomplete. We also hypothesised that these patients with UVA will have lower rates of prescribed anti-arrhythmic drugs and a higher rate of recurrent ventricular tachyarrhythmia, as failure to identify a specific underlying aetiology may preclude appropriate targeted therapy.