A client with rapid rate atrial fibrillation asks a nurse why the physician is going to perform carotid massage. The nurse responds that this procedure may stimulate the:
A. Vagus nerve to slow the heart rate.
B. Vagus nerve to increase the heart rate; overdriving the rhythm.
C. Diaphragmatic nerve to slow the heart rate.
D. Diaphragmatic nerve to overdrive the rhythm.
Correct Answer: A. Vagus nerve to slow the heart rate.
Carotid sinus massage is one of the maneuvers used for vagal stimulation to decrease a rapid heart rate and possibly terminate a tachydysrhythmias. The others include inducing the gag reflex and asking the client to strain or bear down. Medication therapy often is needed as an adjunct to keep the rate down or maintain the normal rhythm. Vagal maneuvers are techniques used to increase vagal parasympathetic tone in an attempt to diagnose and treat various arrhythmias. They are often utilized first in an effort to abort episodes of stable supraventricular tachycardia (SVT) or differentiate SVT from ventricular tachycardias (VT).
Option B: Vagal maneuvers, including Carotid Sinus Massage and Valsalva Maneuver, transiently increase the arterial pressure in the carotid sinuses and aortic arch. This action triggers the baroreceptor reflex, which results in increased parasympathetic output to the heart via the vagus nerve (cranial nerve X).
Option C: The location of the carotid sinus is at the bifurcation of the internal and external carotid artery from the common carotid artery. The sinus contains baroreceptors that sense changes in blood pressure. Afferent signals are then transmitted via the glossopharyngeal nerve (cranial nerve IX) to the nucleus tractus solitarius (NTS) within the medulla.
Option D: Within the heart, the right vagus nerve serves to stimulate the sinoatrial (SA) node, the pacemaker of the healthy heart, in the right atrium; this causes slowed electrical activity within the SA node. The left vagus nerve mostly innervates atrioventricular (AV) node, which slows conduction between the atria and the ventricles. The end product of vagal stimulation is a decrease in the speed and frequency of electrical impulses in the heart, which could ultimately slow or terminate a tachydysrhythmia.
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