Common cause of a junctional rhythm?

• A. Digitoxin Toxicity
• B. Hyperkalemia
• C. Atrial Fibrillation
• D. Ventricular Hypertrophy

Answer: (A)

A junctional rhythm occurs when the SA node is suppressed or fails, so the AV node takes over as the heart’s pacemaker. This often presents with a slower rate and P waves that are absent, inverted, or hidden because atrial activation may occur after the QRS due to retrograde conduction. Digitoxin (digitalis) toxicity is a classic cause because it increases vagal tone and suppresses the SA node while allowing the AV node to pace, producing a junctional rhythm.

Hyperkalemia tends to slow conduction and can cause bradycardia or a sine-wave pattern rather than a typical junctional rhythm. Atrial fibrillation produces an irregularly irregular rhythm with no discrete P waves, not a junctional rhythm. Ventricular hypertrophy is a structural change and doesn’t by itself commonly cause a junctional rhythm.