Editing Anatomy and Physiology – RN Practice Questions (section)

==Question 13==
A patient with a history of heart failure develops new-onset atrial fibrillation with a ventricular rate of 168 beats per minute and reports chest pressure. Which physiologic explanation should guide the nurse's understanding of the chest pain?
# The rapid rate increases coronary artery filling and causes vessel distention.
# The rapid rate shortens diastole, reducing coronary artery perfusion and cardiac filling time.
# The loss of the P wave increases stroke volume and myocardial workload.
# The rapid rate increases parasympathetic tone and produces coronary vasospasm.

'''Answer:''' 2 (B). The rapid rate shortens diastole, reducing coronary artery perfusion and cardiac filling time.

''Rationale:'' The coronary arteries fill during diastole, when the myocardium is relaxed and the aortic valve has closed. As heart rate rises, diastole shortens far more than systole does, so coronary blood flow falls at the very moment myocardial oxygen demand is highest. Shortened diastole also reduces ventricular filling and therefore stroke volume. In atrial fibrillation the loss of organized atrial contraction removes the atrial kick, further reducing filling, which makes option 3 incorrect because stroke volume decreases rather than increases. Option 1 reverses the relationship. Option 4 is incorrect because tachydysrhythmias reflect reduced parasympathetic and increased sympathetic influence.