🧠 QT Prolongation on USMLE Step 1: Mechanism, Risky Drugs, and Torsades de Pointes

The QT interval is more than a squiggle on an EKG — it represents the time between ventricular depolarization and repolarization. On USMLE Step 1, you’ll often be asked to:

• Identify drugs that prolong the QT interval

• Know when it becomes dangerous (hint: Torsades de Pointes)

• Understand the molecular ion channel mechanisms involved

Let’s break it all down visually and step-by-step.

💊 Drugs That Prolong the QT Interval (Step 1 Must-Know List)

Category	Examples
Antiarrhythmics (Class IA, III)	Quinidine, Procainamide, Sotalol, Amiodarone
Antibiotics	Macrolides (Erythromycin), Fluoroquinolones
Antipsychotics	Haloperidol, Ziprasidone
Antidepressants	TCAs, SSRIs (Citalopram)
Antiemetics	Ondansetron
Others	Methadone, Arsenic, HIV drugs

🧠 Mnemonic:
“ABCDE”

• Antiarrhythmics

• Bacteria killers (antibiotics)

• CNS drugs (antipsychotics, antidepressants)

• Depression drugs

• Emetics (anti-nausea)

🧬 Congenital Long QT Syndromes

1. Romano-Ward Syndrome

• AD inheritance

• Only cardiac symptoms (normal hearing)

2. Jervell and Lange-Nielsen Syndrome

• AR inheritance

• QT prolongation + sensorineural deafness

🩺 Clinical Scenario: Step 1 Style

A patient develops syncope after starting erythromycin and methadone. EKG shows QTc 530 ms. Which electrolyte imbalance is most likely?

✅ Answer: Hypokalemia or hypomagnesemia
(Low K⁺ or Mg²⁺ increases risk of torsades!)

🎯 Call-To-Action

Ready to dominate cardiac pharmacology + EKG interpretation?

🧠 Try the KOTC Adaptive Qbank + Multiplayer Mode:
🔗 https://kingofthecurve.org/trial-sessions

📲 Or upgrade to lifetime access and get visual reviews for all arrhythmias:
🔗 https://kingofthecurve.org/free-lifetime

---

---

Frequently Asked Questions (FAQs)

• How many hours should I study for the MCAT each day?

  Aim for 4-6 focused hours, ensuring you incorporate breaks to avoid burnout.

• What is the best way to handle test anxiety?

  Practice mindfulness techniques, take practice exams under realistic conditions, and maintain a balanced lifestyle.

• How can I stay motivated during the long application process?

  Set short-term goals, seek support from mentors, and reward yourself for small achievements.

• What role does exercise play in MCAT preparation?

  Regular exercise improves focus, reduces stress, and enhances overall mental clarity.

• How does King of the Curve help with MCAT preparation?

  KOTC offers personalized learning tools, gamification features, and adaptive question banks to help students stay on track without burnout.