Background/Introduction: Electrical storm (ES) is a condition defined as three or more episodes of ventricular fibrillation (VF) or ventricular tachycardia (VT) within 24 hours, and usually coexist with advanced heart failure in patients with structural heart disease. It has also been suggested that, in patients with HF secondary to structural heart disease and ICD, the occurrence of ES could represent a clinical manifestation of HF worsening rather than an independent event. The aim of the present study is to determine whether CRT can be associated with a reduction in the incidence of ES, and whether this association could vary according to the clinical and echocardiographic response to resynchronization.
Methods: The OBSERVO-ICD (NCT02735811) is a multicenter, retrospective registry, enrolling all consecutive patients undergoing ICD or CRT-D implantation from 2010 to 2012 in five Italian high-volume arrhythmia centers. A propensity score matching was used to compare two equally sized cohorts of ICD and CRT-D patients with similar characteristics according to 25 variables. The primary endpoint was the time free from ES in patients with ICD or CRT-D. Secondary endpoints were: a) time free from unclustered VT/VF episodes; b) time free from ES in CRT-D patients according to the clinical or echocardiographic response after six months. Clinical response to CRT was defined as an improvement of at least one NYHA functional class at 6-month follow-up. The echocardiographic response was defined as an increase in left-ventricular end-systolic volume ≥10% at 6-month.
Results: After propensity score matching for the likelihood of having a CRT-D implanted, 364 ICD and 364 CRT-D patients with similar baseline characteristics on 25 variables were selected. CRT-D was associated with a 45% relative risk reduction in ES when compared to ICD (5.6% vs. 12.3%; log rank p=0.014) with an annualized ES rate of 1.7% and 3.7%, respectively (Figure 1). The first ES in the CRT-D and ICD groups occurred respectively 14 and 6 days after implantation. Lower estimate rates of ES were seen for both clinical (0.9% vs. 11.7%; log-rank p=0.011) and echographic responders (1.0% vs. 15.8%; log-rank p<0.001). No ES was detected in any of the 133 full-responders to CRT-D. Clinical and echographic positive responses, but not CRT-implant per se, were also associated with lower estimate rates of unclustered VTs/VFs (12.4% vs. 28.2%; log-rank p=0.003 for the clinical response and 14.6% vs. 30.9%; log-rank p<0.001 for the echographic response).
Conclusion: Patients with CRT had a lower incidence of ES when compared to propensity-matched ICD patients. TThe long-term benefit of CRT seems to be due to the improved hemodynamics, as CRT-responders experienced very low rates of ES. The present data strengthen the evidence that, in patients with HF and an ICD, ES should be considered as a warning sign of impending pump failure rather than an incidental bystander.