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.