How does coronary artery disease primarily affect the heart's conduction system?
By increasing the threshold for myocardial depolarization
By increasing the heart rate through sympathetic stimulation
By enhancing electrical conductivity in the myocardium
By causing ischemia to the sinoatrial and atrioventricular nodes
The Correct Answer is D
A. By increasing the threshold for myocardial depolarization:
While ischemia can affect depolarization, the primary effect of CAD is not a generalized change in the threshold of myocardial cells; instead, conduction problems occur due to localized ischemia.
B. By increasing the heart rate through sympathetic stimulation:
CAD does not inherently increase heart rate. Tachycardia may occur as a compensatory response, but it is not the primary mechanism by which CAD affects the conduction system.
C. By enhancing electrical conductivity in the myocardium:
CAD does not improve conduction. In fact, ischemia impairs conduction by damaging cardiac cells, which can lead to arrhythmias.
D. By causing ischemia to the sinoatrial and atrioventricular nodes:
CAD reduces blood flow through coronary arteries, which can lead to ischemia in the SA and AV nodes, causing bradyarrhythmias, heart blocks, or conduction delays. This is a direct consequence of insufficient oxygen supply to the conduction tissue.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is C
Explanation
A. S3:
S3 occurs during rapid ventricular filling in early diastole and may indicate volume overload or heart failure. It is not related to valve closure.
B. S1:
S1 corresponds to the closure of the atrioventricular (mitral and tricuspid) valves at the beginning of systole.
C. S2:
S2 occurs at the closure of the semilunar valves (aortic and pulmonic) at the end of systole, marking the onset of ventricular diastole. It is best heard at the base of the heart and is the normal “dub” sound.
D. S4:
S4 occurs during atrial contraction at the end of diastole and is associated with a stiff or hypertrophic ventricle. It is not a normal sound and does not correspond to semilunar valve closure.
Correct Answer is A
Explanation
A. To increase blood volume and systemic vascular resistance:
The RAAS system increases blood pressure by two main mechanisms: angiotensin II causes vasoconstriction, raising systemic vascular resistance, and aldosterone promotes sodium and water retention, increasing blood volume. Together, these actions restore perfusion pressure in hypotensive states.
B. To decrease heart rate and reduce cardiac output:
RAAS does not directly affect heart rate; it works primarily on vascular tone and fluid retention, not cardiac chronotropy.
C. To regulate oxygen levels in the blood:
Oxygen sensing is mainly controlled by chemoreceptors, not RAAS.
D. To control nerve impulses to the heart:
RAAS does not directly regulate cardiac conduction or nerve impulses; it acts on vascular smooth muscle and renal sodium retention.
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