On an ECG, atrial fibrillation is characterized by absence of P-waves and irregular narrow QRS complexes.

在ECG上，心房颤动的特征是没有P波和不规则的窄QRS波群。

Absence of P waves and presence of irregular narrow QRS complexes are the hallmark of atrial fibrillation.

无P波和不规则窄QRS波是心房颤动的特征。