Sinus or no Sinus, that is the question

12 years old girl. ECG taken throughout sports participation screening. Is it Sinusrhythm?

The natural pacemaker of the heart is the Sinusnode (SN). It is located at the junction of the superior vena cava and the right atrium, and automatically depolarizes at a rate of 60 to 80 beats per minute. The impulse then travels from the SN to the AV node and depolarizes the atria. Looking at an ECG tracing, the P wave represents atrial depolarization. The P wave axis during Sinusrhythm usually is +60°. Therefore, P waves should be positive in lead II. Also, P waves should be present in front of every QRS complex, with constant PR (or PQ) interval. So the answer is YES, the girl is in Sinusrhythm.

Resting ECG tracing of a 12-year old girl.

In the figure below, a 12-lead ECG tracing of another 12-year old girl is displayed. Is this Sinusrhythm?

Resting ECG tracing of a 12-year old girl. Speed 50 mm/s.