This study aimed to investigate the effect of both history of intermittent atrial tachyarrhythmias ( IAT ) and in-trial IAT on the risk of heart failure ( HF ) or death comparing cardiac resynchronization therapy with defibrillator ( CRT-D ) to implantable cardioverter-defibrillator ( ICD ) treatment in mildly symptomatic HF patients with left bundle branch block ( LBBB ) .