Methodology.
The study was approved by our institutional ethics committee (Alfred
Health Ethics Research Administration) as a low-risk project. Records
were reviewed for all patients under the age of 60 who underwent
implantation of a secondary prevention implantable cardiac defibrillator
(ICD) between January 2010 and July 2021 at a single quaternary
cardiology centre in Melbourne, Australia. Secondary prevention ICD was
defined in our study as a device implanted after a clinical presentation
with either 1) ventricular tachyarrhythmias resulting in syncope and/or
cardiac arrest, or 2) conscious sustained ventricular tachycardia. We
included patients receiving both subcutaneous ICDs and transvenous
devices, with the transvenous devices comprising single chamber ICDs,
dual chamber ICDs and biventricular ICDs.
Records were reviewed for all cardiac investigations performed as part
of the diagnostic evaluation in these device recipients, defined as
investigations performed either within 3 months prior to device implant
or within 6 months following device implant. Baseline ECGs were accessed
to record rhythm, cardiac axis, QT interval and the presence or absence
of the early repolarisation pattern. Transthoracic echocardiography
(TTE) records were accessed to collect both qualitative parameters
(overall left and right ventricular function, presence of segmental
hypokinesis, degree of valvular dysfunction) and quantitative parameters
(LV diastolic diameter and left ventricular ejection fraction).
Investigations for coronary artery disease, including invasive coronary
angiography and computerised tomographic coronary angiography (CTCA),
were accessed to record the presence of obstructive coronary artery
disease, defined as >70% luminal stenosis, and requirement
for follow-on coronary revascularisation.
We then identified a cohort of patients with unexplained ventricular
arrhythmias (UVA, Group 1) in whom the aetiology for ventricular
arrhythmia remained unexplained after three ‘first-line’ cardiac
investigations: TTE, ECG and coronary assessment (Table 1). More
specifically, patients with UVA were defined as those structurally
normal heart on TTE, absence of obstructive disease on coronary
assessment and no clear diagnostic features on ECG. Examples of clear
diagnostic features on ECG included long or short QT intervals, features
of arrhythmogenic right ventricular cardiomyopathy (ARVC), features of
Brugada syndrome or manifest pre-excitation.
We compared this UVA cohort of patients with patients having a confirmed
or strongly suspected aetiology of their ventricular arrhythmia on the
basis of 12-lead ECG, TTE and coronary assessment. This group was
labelled was labelled VA with clear aetiology (Group 2).
We then evaluated the adoption rate of five modalities of ‘second-line’
investigations for ventricular arrhythmia in both groups. These
second-line investigations included cardiac magnetic resonance imaging
(CMR), exercise stress ECG, flecainide challenge, electrophysiology
studies (EP) and genetic testing. Where these investigations were
available, we recorded whether the result elucidated the underlying
aetiology of the presenting ventricular arrhythmia.
Clinical discharge summaries were reviewed to determine which
antiarrhythmic drugs were prescribed to patients following presentation
with a ventricular arrhythmia. We recorded rates of prescription of beta
blockers, amiodarone, flecainide and sotalol.
Finally, we sought to evaluate outcome data for patients with respect to
future burden of ventricular arrhythmia and all-cause mortality. We
reviewed all available records from subsequent device interrogations for
the first five years following device implantation. In order to be
included for this phase of the analysis, patients were required to have
documentation of at least two device interrogation reports over this
five-year period. We assessed for the frequency of device-detected NSVT
and requirement for tachycardia therapies, including anti-tachycardia
pacing (ATP) and device-delivered shocks. Hospital records were reviewed
to assess for patient mortality up to 10 years following device implant.