Cardiology Clinical Case / MCQS / Uworld for Usmle step 2 / case 4 with answer and explanation and references and Educational objective
A
46-year-old man comes to the physician with exertional dyspnea and dry cough.
He also has occasional episodes of suffocating nighttime cough that is only
relieved by sitting up. Past medical history is significant for myocardial
infarction 6 months ago and hypercholesterolemia. Current medications include
metoprolol, aspirin, and rosuvastatin. The patient does not use tobacco or
illicit drugs but drinks alcohol on social occasions. His father died of a
stroke and his mother has type 2 diabetes mellitus. His blood pressure is 150/1
00 mm Hg and pulse is 60/min. Chest examination shows bibasilar crackles. The
cardiac apex is palpated in the left sixth intercostal space. Bilateral pitting leg edema is present. Which
of the following is most likely to be associated with this patient's condition?
|
A. Constriction of the efferent renal
arterioles B. Decreased intraglomerular pressure C. Decreased renal venous pressure D. Decreased plasma colloid pressure E. High sodium delivery to the distal
tubule F.
Increased renal blood flow |
Answer : A
Explanation
:
This
patient's presentation (exertional dyspnea, paroxysmal nocturnal dyspnea, pulmonary
and peripheral edema) and history of myocardial infarction suggest decompensated
systolic congestive heart failure (CHF). Decreased cardiac output in such
patients leads to neurohumoral adaptations, including increased sympathetic nervous
system tone, activation of the renin-angiotensin-aldosterone system (RAAS), and
increased secretion of antidiuretic hormone. These compensatory mechanisms
attempt to maintain cardiac output and systemic pressure by increasing myocardial
contractility, peripheral vasoconstriction, and expansion of extracellular
fluid volume.
Decreased
renal perfusion seen in CHF and subsequent RAAS activation lead to increased
angiotensin II levels. Angiotensin II causes numerous effects including:
• Vasoconstriction of both the afferent and
efferent glomerular arterioles, leading to an increase in renal vascular
resistance and a net decrease in renal blood flow (Choice F).
• Preferential vasoconstrict ion of
efferent renal arterioles, which increases intraglomerular pressure (Choice B)
in an attempt to maintain adequate glomerular filtration rate (GFR).
• Direct stimulation of sodium resorption in the
proximal tubules and increased secretion of aldosterone from the adrenal
glands, which in turn promotes further sodium resorption in the cortical
collecting tubule. These actions lead to decreased sodium delivery to the
distal tubule (Choice E) and an increase in extracellular fluid volume.
(Choice
C) Patients with systolic CHF and reduced cardiac output have an increase in renal
vascular resistance and overall venous pressures due to activation of the sympathetic
nervous system and RAAS.
(Choice
D) Decreased plasma colloid pressure is the mechanism responsible for peripheral
and/or generalized edema in patients with severe proteinuria and hypoalbuminemia.
Educational
objective:
In
patients with congestive heart failure, activation of the
renin-angiotensin-aldosterone system (RAAS) and production of angiotensin II
causes preferential vasoconstriction of efferent renal arterioles, which
increases intraglomerular pressure in order to maintain adequate glomerular
filtration rate (GFR).
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Cases / MCQS / Uworld for Usmle step 2 / with answer and
explanation and references and Educational objective
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