Delayed Prolongation of the QRS Interval in Patients with Left Ventricular Dysfunction

Aims: Patients with left ventricular dysfunction (LVD) and prolonged QRS on surface electrocardiogram are at increased risk for heart failure and mortality and may benefit from resynchronization therapy. However, patients with narrow QRS on presentation may still prolong their QRS during the disease course. The occurrence of delayed QRS prolongation, its predictors and associated risk of death are currently unknown and the subject of this investigation.

Methods & Results: Patients with LVD (moderate-severe or severe LVD on TTE), QRS130ms. Impact on mortality was assessed using Cox regression with QRS>130ms as a time dependent covariate. Following 178 patients for 30(10; 59) median (IQR) months, 28(16%) prolonged their QRS to >130ms (140±9ms); LBBB pattern was diagnosed among 15 (53%). Patients with QRS prolongation were older (71.9±11.8 vs 64.4±15.1 years p=0.014), had larger left ventricle and left atrial diameters (6.3±0.9 vs 5.7±0.9 p=0.010; 4.9±0.6 vs 4.5±0.7 p=0.006 cm, respectively) and wider baseline QRS (104.8±12.6 vs 91.4±14.5 ms p<0.001) which had a linear association with late QRS prolongation (p for trend<0.0001). In a multivariable model age and initial baseline QRS width were significantly associated with late QRS prolongation. QRS prolongation at follow-up was not found to confer a significant risk of death (HR=1.54, 95%CI 0.8-2.95, p=0.196).

Conclusion: The QRS has a dynamic nature and may prolong over time in a significant proportion of patients with LVD, justifying routine monitoring. Physicians may choose to plan ahead for resynchronization therapy in patients at risk for QRS prolongation.