Background: Primary prevention implantable cardioverter defibrillator (ICD) therapy is indicated in patients with a LVEF <35%, but most cardiac arrest survivors have a LVEF ≥35%. Increasing evidence suggests that the myocardial phenotype predicts ventricular arrhythmias.
Objective: To determine the cardiovascular magnetic resonance (CMR) characteristics of survivors of sustained ventricular tachycardia (VT) or fibrillation (VF) who underwent secondary prevention ICD or cardiac resynchronisation therapy with defibrillation (CRT-D).
Methods: In this observational study, ECG, coronary angiography, echocardiography and CMR were used for phenotypic characterization prior to ICD or CRT-D therapy. Patients with congenital heart disease, channelopathies, hypertrophic cardiomyopathy, arrhythmogenic right ventricular cardiomyopathy and chemotherapy-induced cardiomyopathy were excluded.
Results: Patients hospitalised for VF (55.4%) or VT with hemodynamic compromise underwent ICD (71.3%) or CRT-D (28.7%) implantation. Most (56.4%) had no previous history of cardiac disease. At the index hospitalisation, an ischaemic cause was identified in 69.3%, a
non-ischaemic cause in 24.8% and no cause emerged in 5.9%. The LVEF was ≤35% in 55.4% and >35% in 44.6%. Myocardial fibrosis was present in 85.1% (LVEF ≤35%: 91.1%; LVEF >35%: 77.8%; p=0.0619). Myocardial fibrosis was present in 98.6% of patients with ischaemic causes and in 68% with non-ischaemic causes.
Conclusions: Based on LVEF, a large proportion of survivors of sustained VT or VF would not have previously met primary prevention criteria for ICD therapy. In this ‘ICD treatment gap’, myocardial fibrosis was more prevalent than a LVEF≤35%. Prospective studies should on myocardial fibrosis rather than LVEF as an indication for primary prevention ICD therapy.