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Question 458
Pharmacology → General
Classification
Question
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Propranolol is prescribed to limit the ventricular rate in a patient with a supraventricular tachyarrhythmia. Which additional effect follows most directly from its cardiac beta-1 antagonism?
Question Stem
Select the single best answer.
Options
A
Positive chronotropy with increased myocardial oxygen consumption
B
Negative chronotropy with reduced myocardial oxygen consumption
C
Bronchodilatation with increased myocardial oxygen consumption
D
Positive inotropy with reduced myocardial oxygen consumption
E
Selective peripheral alpha-1 vasodilatation
Explanation
Propranolol as a non-selective beta-adrenoceptor antagonist. Cardiac beta-1 antagonism produces negative chronotropy and reduces myocardial oxygen consumption, accounting for its usefulness in conditions including angina and rate limitation in supraventricular tachyarrhythmias.
Option Validity
A) Beta-1 antagonism reduces rather than increases heart rate and myocardial oxygen demand.
C) Propranolol is non-selective and bronchial beta-receptor blockade may cause bronchoconstriction rather than bronchodilatation.
D) Beta-1 blockade does not produce positive inotropy; it suppresses cardiac sympathetic effects.
E) Propranolol acts at beta-adrenoceptors and is not a selective alpha-1 antagonist.
Further Reading
Saxena R. Textbook for MRCOG-1. Chapter 12: Pharmacology. Beta Blockers, p.345.