If the parasympathetic neurotransmitter releases acetylcholine, the nurse should anticipate observing what changes in the ECG pattern?
A) Heart rate 150 beats/minute, labeled as supraventricular tachycardia
B) Disorganized ventricular fibrillation
C) Complete cardiac standstill
D) Slowing of heart rate to below 60 beats/minute
Ans: D
Feedback:
Acetylcholine, the parasympathetic neurotransmitter released during vagal stimulation of the heart, slows down the heart rate by decreasing the slope of phase 4. The catecholamines, the sympathetic nervous system neurotransmitters epinephrine and norepinephrine, increase the heart rate by increasing the slope or rate of phase 4 depolarization. Fibrillation is the result of disorganized current flow within the ventricle (ventricular fibrillation). Fibrillation interrupts the normal contraction of the atria or ventricles. In ventricular fibrillation, the ventricles quiver but do not contract. Thus, there is no cardiac output, and there are no palpable or audible pulses (i.e., cardiac standstill).
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