This ECG rhythm strip displays a rapid, regular rhythm with narrow QRS complexes, but crucially, it lacks discernible P waves. The absence of P waves eliminates sinus tachycardia. The consistent R-R intervals and narrow QRS complexes point to a supraventricular origin. Given the lack of P waves, the most likely source is the AV node, indicating junctional tachycardia. In this rhythm, the AV node paces the heart, leading to a rapid, regular rate without preceding atrial depolarization. Therefore, junctional tachycardia is the correct interpretation, distinguishing it from sinus tachycardia and other rhythms.