AimsVentricular arrhythmias (VA) occur frequently after permanent left ventricular assist device (LVAD) implantation in end stage heart failure. Left ventricular assist device patients require rhythm control in contrast to patients with biventricular support. However, the rationale for implantable cardioverter-defibrillator (ICD) utilization in LVAD patients remains unclear. This study investigated the safety and efficacy of primary prevention ICD therapy and the rate of appropriate ICD interventions in LVAD patients. Methods and resultsWe prospectively collected data from patients receiving LVADs. Patients without previous ICD received an ICD after LVAD implantation for primary prevention. Sixty-one patients with LVAD and ICD were followed prospectively for 365 + 321 days. Nine patients died from thromboembolism or haemorrhage. Overall, the rate of appropriate ICD interventions was 34%, mostly for treatment of monomorphic VT in 52%, polymorphic VT in 13%, and VF in 35%. Seventy-one percent of VA were terminated by overdrive pacing, 29% by shock. Patients with a history of VA before LVAD implantation had a significantly higher 1-year rate for ICD therapy compared with LVAD patients with a primary prevention ICD indication LVAD patients (50 vs. 24%). Similarly, patients with non-ischaemic cardiomyopathy had a significantly higher risk for ICD therapy than patients with ischaemic heart disease (50 vs. 22%). ConclusionImplantable cardioverter-defibrillator therapy is safe and effective in LVAD patients. Ventricular arrhythmias leading to ICD intervention occur frequently in 34% of LVAD patients after 1 year, with large variations depending on the underlying cardiac disease and previous arrhythmia history. Primary prevention ICD indication after LVAD implantation yields high rates of ICD intervention. A history of previous VA strongly predicts future use of ICD treatment after LVAD implantation.--