A 5-year-old patient overdoses on a beta-blocker. What cardiac effect is most likely?

A 5-year-old patient overdoses on a beta-blocker. What cardiac effect is most likely?

• A. Tachycardia
• B. Bradycardia
• C. Hypertension
• D. Mydriasis

Answer: (B)

Beta-blockers block the receptors in the heart that normally speed up and strengthen its activity. When these receptors are blocked, the heart loses that stimulatory drive, so the pacemaker in the SA node fires more slowly and the conduction through the AV node slows. In overdose, this effect becomes pronounced, leading to a marked decrease in heart rate—that is, bradycardia. Tachycardia would imply increased sympathetic activity or a different mechanism, hypertension would result from increased vascular resistance or vasoconstriction, and mydriasis is a pupil dilation effect not related to the heart’s rhythm. So bradycardia is the most likely cardiac effect in beta-blocker overdose.

Beta-blockers block the receptors in the heart that normally speed up and strengthen its activity. When these receptors are blocked, the heart loses that stimulatory drive, so the pacemaker in the SA node fires more slowly and the conduction through the AV node slows. In overdose, this effect becomes pronounced, leading to a marked decrease in heart rate—that is, bradycardia.

Tachycardia would imply increased sympathetic activity or a different mechanism, hypertension would result from increased vascular resistance or vasoconstriction, and mydriasis is a pupil dilation effect not related to the heart’s rhythm. So bradycardia is the most likely cardiac effect in beta-blocker overdose.