A 54-year-old man comes to the emergency department because of episodic palpitations for the past 12 hours. He has no chest pain. He has coronary artery disease and type 2 diabetes mellitus. His current medications include aspirin, insulin, and atorvastatin. His pulse is 155/min and blood pressure is 116/77 mm Hg. Physical examination shows no abnormalities. An ECG shows monomorphic ventricular tachycardia. An amiodarone bolus and infusion is given, and the ventricular tachycardia converts to normal sinus rhythm. He is discharged home with oral amiodarone. Which of the following is the most likely adverse effect associated with long-term use of this medication?

Chronic interstitial pneumonitis

Progressive multifocal leukoencephalopathy

A 64-year-old man presents to his physician for a scheduled follow-up visit. He has chronic left-sided heart failure with systolic dysfunction. His current regular medications include captopril and digoxin, which were started after his last episode of symptomatic heart failure approximately 3 months ago. His last episode of heart failure was accompanied by atrial fibrillation, which followed an alcohol binge over a weekend. Since then he stopped drinking. He reports that he has no current symptoms at rest and is able to perform regular physical exercise without limitation. On physical examination, mild bipedal edema is noted. The physician suggested to him that he should discontinue digoxin and continue captopril and scheduled him for the next follow-up visit. Which of the following statements best justifies the suggestion made by the physician?

Digoxin is useful to treat atrial fibrillation, but does not benefit patients with systolic dysfunction who are in sinus rhythm.

Long-term digoxin therapy produces significant survival benefits in patients with heart failure, but at the cost of increased heart failure-related admissions.

Both captopril and digoxin are likely to improve the long-term survival of the patient with heart failure, but digoxin has more severe side effects.

Captopril is likely to improve the long-term survival of the patient with heart failure, unlike digoxin.

Digoxin does not benefit patients with left-sided heart failure in the absence of atrial fibrillation.

Secondary arrhythmias (electrolyte, drug-induced) for USMLE Step 1: High-Yield Internal Medicine Lessons

Electrolyte Arrhythmias - The Ion Imbalance

Core Principle: Imbalances in key ions ($K^+$, $Ca^{2+}$, $Mg^{2+}$) alter myocardial action potentials, leading to arrhythmias.

Electrolyte Imbalances and EKG Changes

Electrolyte	ECG Findings	Clinical Notes / Associations
Potassium ($K^+$)	Hyperkalemia (>5.5): Peaked T waves → Wide QRS → Sine wave. Hypokalemia (<3.5): U waves, Flat T waves, ST depression.	Hyper: Renal failure, ACE-I/ARBs, DKA. Hypo: Diuretics, diarrhea, vomiting.
Calcium ($Ca^{2+}$)	Hypercalcemia (>10.5): Short QT interval. Hypocalcemia (<8.5): Long QT interval.	Hyper: Malignancy, hyperparathyroidism. Hypo: Hypoparathyroidism, CKD.
Magnesium ($Mg^{2+}$)	Hypermagnesemia (>2.5): ↑PR, Wide QRS (rare). Hypomagnesemia (<1.5): Torsades de Pointes (TdP).	Hyper: Iatrogenic, renal failure. Hypo: Alcoholism, diuretics, PPIs.

Drug-Induced Arrhythmias - Pharma's Funky Rhythms

Many drugs can prolong the QT interval, increasing the risk for Torsades de Pointes (TdP), a polymorphic ventricular tachycardia. A corrected QT ($QT_c$) interval > 500 ms is a major risk factor.

📌 Mnemonic for QT-prolonging drugs: 'ABCDE'

Antiarrhythmics (Class IA, III)
- Quinidine, Procainamide, Amiodarone, Sotalol
Antibiotics (Macrolides, Fluoroquinolones)
- Erythromycin, Azithromycin, Ciprofloxacin
Anticychotics (Typical & Atypical)
- Haloperidol, Olanzapine, Risperidone
Antidepressants (TCAs, SSRIs)
- Amitriptyline, Citalopram
Antiemetics
- Ondansetron, Promethazine

ECG: Torsades de Pointes with polymorphic VT

⭐ Exam Favourite: Amiodarone causes significant QT prolongation but has a surprisingly low incidence of Torsades de Pointes compared to other Class III antiarrhythmics.

Clinical Approach - Taming the Rogue Wave

Initial management focuses on stabilization and identifying the underlying reversible cause. The goal is to treat the trigger, not just the rhythm.

⭐ For Torsades de Pointes (TdP), the first-line treatment is IV Magnesium Sulfate, which works by stabilizing the cardiac membrane, even in patients with normal serum magnesium levels.

High‑Yield Points - ⚡ Biggest Takeaways

Hyperkalemia causes peaked T waves, a widened QRS, and ultimately a sine wave pattern.

Hypokalemia presents with U waves and flattened T-waves, increasing risk for Torsades de Pointes (TdP).

Hypomagnesemia is a key cause of refractory TdP, often co-occurring with hypokalemia.

QT prolongation from drugs (Class IA/III antiarrhythmics, macrolides, antipsychotics) is a major TdP risk.

Digoxin toxicity classically causes "scooped" ST segments and atrial tachycardia with AV block.

Remember QT interval effects: hypocalcemia prolongs, while hypercalcemia shortens.

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