Answer: Artifact simulating either atrial flutter or ventricular tachycardia during a regular sinus rhythm.

Discussion

Narrow QRS complexes occur regularly. This tracing suggests either atrial flutter or ventricular tachycardia.

It is not atrial flutter, however. If it were, the QRS complexes occurring regularly would mean there is a fixed AV (atrioventricular) conduction ratio. If so, the QRS complexes and the flutter waves would maintain a fixed relationship. That is not happening here. It is also not ventricular tachycardia because the narrow QRS complexes march through. This tracing is an example of muscle tremors simulating either atrial flutter or ventricular tachycardia.