Ventricular Characteristics
A large meta-analysis found that having a low left ventricular ejection
fraction (LVEF) (-10.5, 95% CI -18.23 to -2.78, P = 0.008), receiving
ventricular pacing (OR 6.44 95% CI 2.57 to 16.16, P < 0.0001)
and having a history of complete heart block (CHB) (OR 2.19, 95% CI
1.20 to 3.99, P = 0.01) predict appropriate therapy. Regarding ejection
fraction, mean LVEF was generally shown to be lower in those who
experienced appropriate therapy when compared to those who did not
receive appropriate therapy, and furthermore, no patients within the
group with a higher ejection fraction required transplant or died. These
findings emphasise the highly arrhythmogenic nature of those with CS and
a reduced LVEF, supporting the recommendations in the 2014 HRS
Consensus, 2017 AHA/ACC/HRS and 2022 ESC Guidelines of implanting an ICD
in order to prevent sudden cardiac death (SCD).(21–23)
A recent 2022 study found that
2nd/3rd degree atrioventricular
block (AVB) and prior ventricular arrhythmias were indicative of
patients receiving appropriate therapy(10). Interestingly, in contrast
with the aforementioned meta-analysis, there was no significant
difference in LVEF between those who received appropriate therapy and
those who did not. As discussed by the authors, this may be as a
contribution from the greater prevalence of high degree AVB in their
population, and it’s previously shown association with VA, even in
patients with a preserved LVEF(24). Prior to this study, AVB had been
shown to be predictive of appropriate ICD therapy, a finding which
likely corresponds to the greater severity and extent of disease in
order for AVB to manifest which, as such, will predispose individuals to
increased risk of arrhythmias(8).
This increased risk of arrythmia, and as such appropriate therapy, in
those with CS was further explored in a different meta-analysis from
Franke et al. In those studies which analysed individuals who received
multiple shocks, nearly 1 in 5 patients received ≥5 therapies. They
found that combined overall rates of appropriate ICD therapy or SCD were
29.0%, and that across the entire cohort, 39.0% of patients received
an ICD. As expected, the results showed higher rates of appropriate
therapy in those who met secondary prevention indications when compared
with primary prevention (22.7% vs 58.4%)(9).