Cardiac resynchronization therapy (CRT) reduces the risk of ventricular arrhythmias (VA) in heart failure (HF) patients with left bundle branch block (LBBB) while the effect is less clear among non-LBBB patients. This study aimed to investigate if absence of LBBB features whether by echocardiography or strict ECG criteria would identify patients at risk of developing VA in a cohort with LBBB according to conventional ECG criteria. Two hundred six CRT candidates were prospectively included from 2 centers. Prior to CRT presence of a typical LBBB contraction pattern was identified using longitudinal strain in the apical 4-chamber view. All preimplantation ECGs were categorized as LBBB or non-LBBB according to Strauss´ strict criteria. Primary end-point was defined as any appropriate antitachycardia pacing (ATP) or shock therapy within 2 years after CRT implantation. A total of 129 (63%) patients had a typical LBBB contraction pattern, while 134 (66%) met the strict ECG criteria. Over 2 years, 45 patients (22%) experienced VA. Absence of a typical LBBB contraction pattern was independently associated with an increased risk of VA (hazard ratio ([HR] 1.89; 95% CI 1.04 to 3.44; p: 0.036). Strict LBBB was not independently associated with the occurrence of VA. Fulfilling neither strict ECG nor echocardiographic criteria for LBBB was associated with a 3.3-fold increase in risk of VA ([HR] 3.34; 95% CI 1.75 to 6.94; (p < 0.001). The risk of VA was almost 2-fold higher if a typical LBBB contraction pattern was absent prior to CRT.