Which of the following is NOT classified as a common arrhythmia?

Normal sinus rhythm is considered the standard or baseline heart rhythm from which arrhythmias are identified. It represents a healthy and coordinated electrical activity of the heart, characterized by a consistent heart rate that typically ranges from 60 to 100 beats per minute, with regular intervals between beats. Since it indicates normal cardiac function, it does not fall under the category of arrhythmias, which are defined as abnormal heart rhythms.

In contrast, atrial fibrillation, AV block, and ventricular tachycardia are all classified as common arrhythmias. Atrial fibrillation involves irregular and often rapid heart rate due to chaotic electrical signals in the atria. AV block refers to a disruption in the electrical signals between the atria and ventricles, which can lead to slower heart rates or missed beats. Ventricular tachycardia is characterized by a fast heart rhythm originating from the ventricles, which can be serious and life-threatening. These conditions represent disturbances in the heart's normal rhythm, highlighting why Normal Sinus Rhythm is not classified among them.