From the Research
Left bundle branch block (LBBB) in a 1-week-old infant is diagnosed using specific ECG criteria, including a QRS duration greater than 80 milliseconds, a broad, notched or slurred R wave in leads I, aVL, V5, and V6, absence of Q waves in leads I, V5, and V6, and a prolonged R wave peak time in V5 and V6, as well as ST segment and T wave changes opposite to the major QRS deflection, as noted in the context of neonatal cardiac physiology 1. The diagnostic criteria for LBBB in infants differ from those in adults due to the unique cardiac physiology of neonates.
- A QRS duration greater than 80 milliseconds is considered prolonged for infants, as normal neonatal QRS duration is typically 50-70 ms.
- A broad, notched or slurred R wave in leads I, aVL, V5, and V6 is a key characteristic of LBBB in infants.
- Absence of Q waves in leads I, V5, and V6 is also a diagnostic criterion.
- Prolonged R wave peak time in V5 and V6, as well as ST segment and T wave changes opposite to the major QRS deflection, are additional criteria. These criteria must be interpreted in the context of the infant's age, as cardiac conduction parameters evolve rapidly during early development, and LBBB is extremely rare in neonates, usually indicating significant underlying cardiac pathology such as congenital heart disease, cardiomyopathy, or myocarditis, as suggested by studies on the relationship between QRS duration and left ventricular dyssynchrony in patients with LBBB 2. Immediate cardiology consultation is essential as LBBB in this age group often requires comprehensive cardiac evaluation including echocardiography, continuous monitoring, and possibly additional imaging or electrophysiology studies to determine the underlying cause and appropriate management, considering the potential implications for left ventricular lead placement during CRT implantation 3.