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Slight revisions have been made in what is considered to be normal QRS duration.
In children < 4yo, a normal QRS duration is < 90ms.
In children 4-16yo, a normal QRS duration is < 100ms.
Above the age of 16, a normal QRS duration is < 110m.
Consider these numbers when evaluating patients for aberrant conduction (e.g. toxicologic reasons as well) and when defining conduction blocks.
Reference:
Surawicz B, Childers R, Deal BJ, et al. AHA/ACCF/HRS Recommendations for the standardized interpretation of the electrocardiogram, Part III: Intraventricular conduction disturbances. A scientific statement from the American Heart Association Electrocardiography and Arrhythmias Committee, Council on Clinical Cardiology; the American College of Cardiology Foundation; and the Heart Rhythm Society. J Am Coll Cardiol 2009;53(11):976-981.