ESC Congress 2017 In Review – Focus on Arrhythmias - 14

Selected Content

Implantable Cardioverter
Defibrillators: Four Decades of
Evidence
Written by Brian Hoyle

The first automatic implantable cardioverter defibrillator (ICD), implanted first in the early 1980s, has evolved
and has become an indispensable life-saving facet of
cardiac care for patients with ischaemic and nonischaemic cardiomyopathy (NICM) and other conditions.
However, the DANISH study [Køber L et al. N Engl
J Med. 2016] questioned whether ICDs are life-saving
in NICM. As explained by Luigi Di Biase MD, PhD, Albert
Einstein College of Medicine at Montefiore Hospital, New
York, New York, USA. DANISH, a randomised controlled
trial, assigned 1116 patients with NICM, symptomatic systolic heart failure with an left ventricular ejection fraction
(LVEF) ≤35% to receive an ICD (n = 556) or usual clinical
care (n = 560). After about 68 months of follow-up, mortality from any cause was similar in the ICD and control
groups (21.6% vs 23.4%).
Dr Di Biase put the DANISH results into the context
of decades of data and the number of patients needed
to treat. Evidence for benefit from ICD therapy in ICM
patients come from the MADIT I trial of 196 patients,
MUSTT involving 351 patients with coronary artery disease (CAD), the MADIT II trial of 1,232 patients, and the
SCD-HeFT trial of 1,676 patients.
Before DANISH, evidence for the benefit of ICD
therapy in NICM was not definitive and had come from
CAT involving 104 patients, AMIOVIRT which included
103 patients, the DEFINITE trial involving 458 patients,
SCD-HeFT, the COMPANION trial, and two meta analyses
[Desai AS. JAMA. 2004; Theuns D. Europace. 2010].
The total weight of evidence still favours a survival
benefit for ICDs in the primary prevention of death in
patients with NICM, according to Dr Di Biase. The recent
DANISH trial results will likely not change the current
guidelines [Romero J, Di Biase L. Europace. In press].
Another contemporary issue concerning ICDs is the
identification of primary prevention patients who will
most benefit from the device. The present class I indication of primary prevention ICD therapy (LVEF ≤35%)
is limited in predicting the likelihood of sudden cardiac
death (SCD). Furthermore, the majority of SCDs occur
in patients with LVEF exceeding 35%. The risk of SCD is
highest in the first month following myocardial infarction
(MI). This risk is reduced in patients with an ICD. Ischaemic
patients with ventricular tachycardia are markedly more
likely to experience cardiovascular death or SCD versus
those with ischaemia alone or ventricular tachycardia
alone [Harkness JR et al. Am J Cardiol. 2011].
Individual risk markers cannot identify patients
effectively who might benefit more from an ICD. The
best solution, according to Alon Barsheshet, MD, Rabin

October 2017

Medical Center and Tel-Aviv University, Tel-Aviv, Israel, is
use of risk stratification algorithms.
Various markers to identify high risk of SCD are still
under evaluation including: biomarkers; LVEF; electrocardiogram data on depolarisation, repolarisation,
autonomic measurement, and nonsustained ventricular
tachycardia; electrophysiologic testing; myocardial scar
burden; and genetic testing.
The wearable cardioverter defibrillator, may help protect patients in the vulnerable period soon after MI before
an ICD is indicated [Epstein AE et al. J Am Coll Cardiol.
2013; Kutyifa V et al. Circulation. 2015]; it can be used to
identify patients who could benefit from implantation of a
permanent ICD [Kutyifa V et al. Circulation. 2015].
Scoring-related evaluation must consider time from MI.
The scoring needs to consider that many of these patients
are older and have other comorbidities contributing to
death by other mechanisms. The competing risks of nonarrhythmia comorbidities can affect the benefit of ICD. One
developed risk stratification score features 5 risk factors:
NYHA functional status > II, atrial fibrillation, QRS complex > 120 ms, age > 70 years, and blood urea nitrogen level
> 26 mg/dL. The scoring system allows patients at higher
risk to be identified up to 8 years after ICD implantation
[Barsheshet A et al. J Am Coll Cardiol. 2012]. The number
needed to treat to save one life is 6 in patients with lowand intermediate-risk of death as classified by this score.
In NICM, the presence in an electrocardiogram of
additional spikes in the QRS complex fragmented QRS
and of beat-to-beat variation in T-wave amplitude can
identify patients at high risk [Goldberger JJ et al. J Am
Coll Cardiol. 2014; Halliday BP et al. Circulation. May
2017]. Another potentially useful target is myocardial fibrosis, a strong predictor of death [Gulati A et al.
JAMA. 2013; Halliday BP et al. Circulation. July 2017].
Mutations in specific genes appear to heighten the
risk of SCD however, more data are required before DNA
variants can be used by clinicians as reliable risk indicators for SCD. This genetic susceptibility is likely influenced by a variety of factors (Figure 1) [Halliday BP et al.
Circulation. July 2017].
Figure 1. Influences on Genetic Susceptibility to Cardiomyopathy and
Sudden Cardiac Death

Alcohol

Chemotherapy
Anthracyclines &
Monoclonal Abs

Inflammatory

Pregnancy

Genetic susceptibility

Endocrine

Thyrold & Phaeo

Infection

Myocarditis & HIV

Idiopathic

Source: Halliday BP et al. Circulation. 2017;136:215-231.

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Table of Contents for the Digital Edition of ESC Congress 2017 In Review – Focus on Arrhythmias