Which of the following is NOT an example of irregular narrow complex tachycardia?

Sinus tachycardia is characterized by a regular rhythm that typically results from increased heart rate due to physiological or pathological conditions, such as exercise, fever, or anxiety. In sinus tachycardia, the QRS complexes are narrow and occur in a consistent pattern, indicating a stable and regular conduction through the atria and ventricles.

In contrast, irregular narrow complex tachycardia refers to arrhythmias where the heart rate is rapid and lacks the regularity seen in sinus tachycardia. Atrial fibrillation is an exemplar of this irregularity, as it results in a chaotic atrial rhythm leading to varying ventricular responses. Similarly, variable conduction in atrial flutter can create an irregular pattern, especially when there are varying degrees of block in the AV node.

Therefore, sinus tachycardia does not fit the definition of irregular narrow complex tachycardia, making it the correct choice as the example that does not belong in this context.