What is the heart rate threshold for treating irregular narrow complex tachycardia?

• A. HR ≥ 100
• B. HR ≥ 120
• C. HR ≥ 150
• D. HR ≥ 180

Answer: (C)

When a patient has irregular narrow complex tachycardia, such as atrial fibrillation with rapid ventricular response, the goal is to control the ventricular rate to protect cardiac output and relieve symptoms. A heart rate around 150 beats per minute is a practical threshold at which rate-control therapy is typically started. At or above this level, the risk of hypoperfusion and tachycardia‑induced symptoms increases, so slowing the AV node conduction helps stabilize the patient. Below this rate, many stable patients tolerate the rhythm without aggressive intervention, so treatment can be more conservative or monitored.

First-line treatment for a stable patient is a rate-control medication, like a beta-blocker or a nondihydropyridine calcium channel blocker, provided there are no contraindications. If those drugs are unsuitable due to hypotension, heart failure, or other issues, alternatives such as digoxin or amiodarone may be considered. If the patient is unstable with signs of shock or severe perfusion problems, synchronized cardioversion is indicated regardless of the rate.

The 150 bpm threshold is a practical guideline used to decide when to initiate rate control, balancing the benefit of slowing the rate against the risks of medications.