narrowcomplex

Narrowcomplex is a term used in electrocardiography to describe QRS complexes that are narrow, indicating that ventricular activation occurs via the normal His-Purkinje conduction system. In standard measurements, a QRS duration of less than about 120 milliseconds is considered narrow. The term is commonly applied when assessing rhythm disorders on the surface ECG and helps distinguish supraventricular processes from those involving the ventricles.

Narrowcomplex rhythms are typically of supraventricular origin. Common examples include sinus tachycardia, atrial tachycardia, atrial flutter with rapid conduction, and tachycardias such as AV nodal reentrant tachycardia or orthodromic AV reentrant tachycardia. When a tachycardia presents with a narrow QRS, clinicians first consider whether the rhythm originates above the ventricles and whether there is intact conduction through the His-Purkinje system.

Diagnosis relies on careful ECG analysis. Key features include QRS duration, the relationship between P waves and QRS complexes, rhythm regularity, and the response to maneuvers or medications. Clinicians also differentiate narrowcomplex tachycardias from wide complex tachycardias, where QRS duration is prolonged (often due to ventricular origin or aberrant conduction), because the latter can imply different therapies and prognosis.

Management is rhythm-specific and ranges from noninvasive strategies, such as vagal maneuvers, to pharmacologic interventions like rate or rhythm control agents. In unstable patients, urgent stabilization is required. Overall prognosis depends on the underlying rhythm or condition; many narrowcomplex tachycardias are treatable and have favorable outcomes with appropriate management.