QRS fragmentation is associated with increased risk of ventricular arrhythmias in high‐risk patients; Data from the SMASH 1 Study

INTRODUCTION: QRS fragmentation (fQRS), defined as the presence of additional spikes within the QRS complex, has been associated with myocardial conduction abnormalities and arrhythmogenicity. OBJECTIVE: We aimed to assess whether fQRS is associated with incident ventricular arrhythmias (VA) in high‐risk patients treated with implantable cardioverter‐defibrillator (ICD) for primary and secondary prevention. METHODS: In a prospective observational multicenter study, we included 495 patients treated with ICD. fQRS was analyzed according to previously validated criteria, by two physicians blinded for outcome data. Incident VA were obtained from ICD recordings. RESULTS: ECG recordings interpretable for fQRS were available in 459 patients (93%), aged 66 ± 12 years with left ventricular ejection fraction 40% ± 13%. fQRS was present in 52 patients (11%) with comparable baseline characteristics to patients without fQRS, except higher age, higher prevalence of coronary artery disease (CAD), lower prevalence of cardiomyopathy, and more frequently a secondary prevention ICD indication. Among patients with native QRS, those with fQRS had similar QRS duration and axis to those without fQRS. During 3.1 ± 0.7 years follow‐up, 126 patients (28%) had ≥1 VA . fQRS was associated with increased risk of VA (HR 3.41 [95% CI 2.27–5.13], p < .001), which persisted after adjusting for age, gender, sex, BMI, CAD, heart failure, renal function, ICD indication, QRS duration, QRS axis, Q waves, and bundle branch block. fQRS was more strongly associated with VA in patients with a primary (HR 6.05 [95% CI 3.16–11.60]) versus secondary (HR 2.39 [95% CI 1.41–4.04]) ICD indication (p‐for‐interaction = .047). CONCLUSIONS: fQRS is associated with threefold increased risk of VA in high‐risk patients, independent of established risk factors.