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).