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Funding Acknowledgements Type of funding sources: None. Background Data about VT ablation in patients with electrical storm (ES) is limited. This study sought to compare the prognostic outcome of patients undergoing VT ablation after electrical storm with and without a septal substrate on mortality, VT recurrence rates, rehospitalization rates and major adverse cardiac events (MACE). Methods In this large single-centre study patients presenting with ES and undergoing VT ablation were included from June 2018 to April 2021. Patients with septal substrate were compared to patients without septal substrate. The primary prognostic outcome was cardiovascular mortality, secondary endpoints were VT recurrence rates, rehospitalization rates and MACE all after a median follow-up of 22 months. Results A total of 108 patients underwent a first VT ablation due to electrical storm and were included (65 ± 13 years; 86% male; 45% ischemic cardiomyopathy). Cardiovascular risk factors were equally distributed among both groups (all p>0.05). Major complications occurred in 11% of all patients with increased postinterventional third degree AV blocks among patients with septal substrate (9% vs 0%; p=0.062). Noninducibility of the clinical VT was achieved in 98% of all patients without a septal substrate and in 91% of all patients with a septal substrate (p=0.136). Noninducibility of any VT was achieved in 88% without a septal substrate and in 66% with a septal substrate (p=0.011). However, in non-invasive programmed stimulation before hospital discharge VT inducibility did not differ among both groups (p>0.05). After 1 year and a median of 22 months follow-up, patients with septal substrate died significantly more often due to cardiovascular causes (25% vs. 7%; log-rank p=0.021). In univariate analysis cardiovascular mortality for ES patients with septal substrate was 3.9 fold higher (HR 3.979; CI 95% 1.124 – 14.092; p=0.032). Independent predictors of adverse outcome in multivariable regression analysis were presence of septal substrate (HR 4.836; p=0.026) and increased numbers of VTs inducible during VT ablation (HR 1.635; p=0.007). VT recurrence during follow-up was 59% and equally distributed among both groups (log rank p=0.911). Rehospitalization rates (log rank p=0.532) and rates of MACE (log rank p=0.463) were equal. Conclusions Presence of a septal substrate is associated with adverse long-term cardiovascular mortality in patients admitted for VT ablation after electrical storm. Despite decreased ablation success in these patients VT recurrence rates were not increased during follow-up.

Funding Acknowledgements Type of funding sources: None. Background Data about VT ablation in patients with electrical storm (ES) is limited. This study sought to compare the prognostic outcome of patients with ES to those with ventricular tachyarrhythmias but without ES undergoing VT ablation on mortality, VT recurrence rates, rehospitalization rates and major adverse cardiac events (MACE). Methods In this large single-centre study patients presenting with ES and undergoing VT ablation from June 2018 to April 2021 were compared to patients undergoing VT ablation due to ventricular tachyarrhythmias but without ES. The primary prognostic outcome was cardiovascular mortality, secondary endpoints were VT recurrence rates, rehospitalization rates and MACE all after a median follow-up of 22 months. Results A total of 311 patients underwent a first VT ablation due to ventricular tachyarrhythmias and were included (63 ± 14 years; 86% male). Of them 108 presented with ES. In the ES cohort dilated cardiomyopathy as underlying heart disease was significantly increased (p=0.008), whereas all other cardiomyopathies were equally distributed. Major complications were equal among both groups (p>0.05). Ablation of the clinical VT was achieved in 95% of all patients without ES and in 94% of all patients with ES (p>0.05). Noninducibility of any VT was achieved in 91% without ES and in 76% with ES (p=0.001). This was also reflected in higher VT induction rates in non-invasive programmed stimulation before hospital discharge among ES patients (40% vs. 19%; p=0.031). After a median of 22 months of follow-up, patients with ES revealed slightly increased cardiovascular mortality rates (17% vs. 9%; log-rank p=0.061; HR 1.902; CI 95% 0.961 – 3.765; p=0.061). Furthermore, ES patients suffered from increased VT recurrence rates (59% vs. 40%; log rank p=0.006), rehospitalization rates (73% vs. 49%; log rank p=0.001) and MACE (71% vs. 45%; log rank p=0.001). ES patients displayed a 1.7-fold increased risk for VT recurrence (HR 1.701; CI 95% 1.160 – 2.493; p=0.006), a 1.9-fold increase for rehospitalization (HR 1.885; CI 95% 1.366 – 2.600; p=0.001) and a 1.9-fold increase for occurrence of MACE (HR 1.935; CI 95% 1.398 – 2.679; p=0.001). Presence of ES was the only independent predictors of VT recurrence and occurrence of MACE, whereas ES and decreased LVEF were independent predictors of rehospitalization. Conclusions VT ablation in patients with ES is challenging and these patients reveal highest risk for recurrent VTs, rehospitalization and MACE. These patients need close follow-ups and optimal guideline-directed therapy.