**Core Concept**
Atrial flutter is a type of supraventricular tachycardia characterized by rapid and regular atrial contractions at a rate of 300 beats per minute, resulting in a characteristic "sawtooth" pattern on the ECG. The 2:1 AV conduction refers to the blockage of two atrial impulses for every ventricular impulse, which leads to a slower ventricular rate, typically around 150 beats per minute.

**Why the Correct Answer is Right**
The ECG shows a regular rhythm with a rate of approximately 150 beats per minute. The presence of a "sawtooth" pattern in the atrial complexes, with a distinct "f" wave, is characteristic of atrial flutter. The 2:1 AV conduction is evident from the fact that every other P wave is associated with a QRS complex, indicating that two atrial impulses are being blocked for every ventricular impulse. This type of AV conduction is a common feature of atrial flutter.

**Why Each Wrong Option is Incorrect**
**Option A:** Ectopic atrial tachycardia typically presents with an irregular rhythm and an increased PR interval, which is not consistent with the regular rhythm seen in this ECG.

**Option C:** Sinus tachycardia is characterized by a regular rhythm with a normal PR interval, which is not consistent with the 2:1 AV conduction seen in this ECG.

**Option D:** Supraventricular tachycardia is a broad term that encompasses several types of tachycardias, but it does not specifically refer to the "sawtooth" pattern and 2:1 AV conduction seen in atrial flutter.

**Clinical Pearl / High-Yield Fact**
Atrial flutter is often associated with structural heart disease, such as cardiomegaly and pulmonary hypertension, as seen in this patient. It is essential to recognize the characteristic ECG pattern and AV conduction to diagnose atrial flutter accurately.

**✓ Correct Answer: B. atrial flutter with 2 :1 AV conduction**