Paced QRS morphology predicts incident left ventricular systolic dysfunction and atrial fibrillation

Background: The prognostic significance of paced QRS complex morphology on surface ECG remains unclear. This study aimed to assess long-term outcomes associated with variations in the paced QRS complex. Methods: Adult patients who underwent dual-chamber pacemaker implantation with 20% or more ventricular pacing and a 12-lead ECG showing a paced complex were included. The paced QRS was analyzed in leads I and aVL. Long-term clinical and echocardiographic outcomes were compared at 5 years. Results: The study included 844 patients (43.1% female; age 75.0 ± 12.1). Patients with a longer paced QRS (pQRS) duration in lead I had a lower rate of atrial fibrillation (HR 0.80; p = 0.03) and higher rate of systolic dysfunction (HR 1.17; p < 0.001). Total pacing complex (TPC) duration was linked to higher rates of ICD implantation (HR 1.18; p = 0.04) and systolic dysfunction (HR 1.22, p < 0.001). Longer paced intrinsicoid deflection (pID) was associated with less atrial fibrillation (HR 0.75; p = 0.01), more systolic dysfunction (HR 1.17; p < 0.001), ICD implantation (HR 1.23; p = 0.04), and CRT upgrade (HR 1.23; p = 0.03). Exceeding thresholds for TPC, pQRS, and pID of 170, 146, and 112 ms in lead I, respectively, was associated with a substantial increase in systolic dysfunction over 5 years (p < 0.001). Conclusions: Longer durations of all tested parameters in lead I were associated with increased rates of left ventricular systolic dysfunction. ICD implantation and CRT upgrade were also linked to increased TPC and pID durations. Paradoxically, patients with longer pID and pQRS had less incident atrial fibrillation.