Adrenaline exerts all of the following cardiac effects except__________________?
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Answer: B. Decreases myocardial irritability
Explanation
Adrenaline enhances myocardial contractility and automaticity across cardiac muscle fibers. This increased electrical irritability raises the likelihood of generating ectopic beats. Decreasing myocardial irritability contradicts the known arrhythmogenic effects of adrenaline. Beta-one adrenergic receptors mediate the stimulatory effects of adrenaline on the heart. Sympathetic stimulation increases both heart rate and the speed of impulse conduction. Oxygen demand rises significantly due to increased mechanical and electrical work.
High circulating adrenaline during stress can trigger dangerous cardiac arrhythmias. Therapeutic doses must be monitored carefully to avoid inducing myocardial ischemia. Cardiac resuscitation protocols utilize adrenaline to restart arrested hearts. Increasing heart rate is a primary and well-documented cardiac effect of adrenaline. Increasing force of contraction enhances stroke volume during sympathetic activation. Increasing oxygen uptake matches the heightened metabolic demands of the working heart.
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