What is the QRS (Quadrature Amplitude Modulation duration) duration?

From the Guidelines

QRS duration is a critical measure in assessing ventricular function and electrical conduction efficiency, with a normal duration ranging from 80-100 milliseconds, and prolongation (>120 ms) indicating potential cardiac conduction abnormalities. When evaluating QRS duration, it is essential to consider the clinical context, including the presence of heart failure, left ventricular ejection fraction (LVEF), and symptoms. According to the most recent guidelines, a QRS duration of 150 ms or greater is a significant indicator for cardiac resynchronization therapy (CRT) in patients with heart failure 1. The 2022 AHA/ACC/HFSA guideline for the management of heart failure recommends CRT for patients with LVEF ≤35%, sinus rhythm, left bundle-branch block (LBBB) with a QRS duration of 120 to 149 ms, and NYHA class II, III, or ambulatory IV symptoms on guideline-directed medical therapy (GDMT) 1. Key points to consider when evaluating QRS duration include:

• Prolonged QRS duration is associated with increased risk of arrhythmias, sudden cardiac death, and heart failure progression
• QRS duration helps guide treatment decisions, particularly regarding CRT in heart failure patients
• A QRS duration of less than 120 ms is not recommended for CRT 1
• The measurement is obtained from a standard 12-lead ECG, with lead V1 often providing the clearest view of the QRS complex. Overall, accurate assessment and interpretation of QRS duration are crucial in managing patients with heart disease, particularly those with heart failure 1.

From the Research

QRS Duration and Its Prognostic Significance

• QRS duration is a significant predictor of adverse outcomes in patients with acute coronary syndromes, with prolonged QRS duration (>120 milliseconds) associated with higher in-hospital and 1-year mortality 2.
• The presence of bundle branch block (BBB), particularly left BBB, is an independent predictor of 1-year mortality in patients with acute coronary syndromes 2.
• QRS duration and morphology can provide useful prognostic information regarding the risk of subsequent cardiac events or therapeutic outcomes, with prolonged QRS duration often associated with depressed ejection fraction or enlarged left ventricular volumes 3.

Association of QRS Duration with Outcomes

• Prolonged QRS duration is associated with adverse outcomes in patients with idiopathic pulmonary arterial hypertension (IPAH), including increased risk of mortality and worse World Health Organization functional class 4.
• In the post-myocardial infarction setting, increasing QRS duration is associated with a higher incidence of heart failure, sudden death, and cardiovascular death, although it may not be an independent predictor of adverse outcome after adjusting for baseline covariates 5.
• Factors associated with the development of prolonged QRS duration over 20 years in healthy young adults include white race, male sex, ECG-left ventricular mass index, and baseline QRS duration 6.

Clinical Implications

• QRS duration should be considered a predictor of death or sudden death in patients after myocardial infarction and in those suspected of coronary artery disease 3.
• QRS duration and morphology can predict benefit from cardiac resynchronization therapy in patients with heart failure, whether of ischemic or non-ischemic origin 3.
• Prolonged QRS duration may be a new predictor of adverse outcome in patients with IPAH, and its association with clinical severity and cardiopulmonary mortality should be considered in clinical practice 4.