Aortic stenosis narrows the outflow from the left ventricle, so the ventricle must generate far higher pressure than the aorta receives. That pressure gradient explains everything: the crescendo–decrescendo murmur, the slow-rising pulse, the thickened ventricle, and the symptoms that signal a poor prognosis. Step 1 tests the causes, the pressure tracing, the physical exam, and why symptoms demand valve replacement.
Evidence-based · For exam prep, not medical advice
update Updated October 2026
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Written for USMLE Step 1 · Free to read
bolt The 60-second version
Aortic stenosis narrows the outflow from the left ventricle, so the ventricle must generate far higher pressure than the aorta receives. That pressure gradient explains everything: the crescendo–decrescendo murmur, the slow-rising pulse, the thickened ventricle, and the symptoms that signal a poor prognosis.
check_circleSystolic pressure gradient between LV and aorta → concentric LV hypertrophy → stiff ventricle, S4, and diastolic dysfunction.
check_circleMurmur: crescendo–decrescendo systolic ejection murmur at the right 2nd ICS radiating to the carotids; soft or absent A2 and paradoxical splitting when severe.
check_circlePulsus parvus et tardus — weak, delayed carotid upstroke.
check_circleSymptoms — angina, syncope (exertional), heart failure — predict death within years without valve replacement.
check_circleTreatment: valve replacement (surgical or transcatheter, TAVR) once symptomatic or LV function falls; avoid aggressive vasodilators and volume depletion.
target What you'll be able to do · aligned to USMLE Step 1 · Cardiovascular
PATHIdentify the causes of aortic stenosis by age and associated conditions.
PHYSInterpret the LV–aortic pressure gradient and explain the resulting concentric hypertrophy.
CARDIORecognize the physical exam findings and symptom triad of severe aortic stenosis.
CARDIODescribe the indications for and options in aortic valve replacement.
How aortic stenosis is tested on Step 1
Classic vignettes describe an older patient with exertional syncope or chest pain and a murmur radiating to the carotids, or a younger patient with a bicuspid valve, and ask about the pressure tracing, LV remodeling, or prognosis.
workspace_premium Symptoms change everything
Asymptomatic aortic stenosis can be watched. Once angina, syncope, or heart failure appear, survival without valve replacement falls to roughly 5, 3, and 2 years respectively.
Causes
Calcific degeneration shares risk factors with atherosclerosis: age, hypertension, hyperlipidemia, smoking, and chronic kidney disease.
Cause
Typical age
Features
Age-related calcific degeneration
> 70 years
Dystrophic calcification of a tricuspid valve; most common in developed countries
Bicuspid aortic valve
50s–60s
Most common congenital heart defect (1–2%); associated with Turner syndrome and aortic coarctation, aortic dilation
Rheumatic heart disease
Variable
Commissural fusion; almost always with mitral disease
A bicuspid valve calcifies earlier because of abnormal mechanical stress on two leaflets.
The pressure gradient
In a normal heart, LV and aortic systolic pressures are nearly equal. In aortic stenosis, the LV peak far exceeds the aortic peak, and the aortic rise is slow.
Pressure gradient. The gap between LV and aortic pressure is the transvalvular gradient; severe stenosis is a mean gradient ≥ 40 mm Hg or valve area < 1.0 cm².Pathophysiology. Exertional syncope occurs because cardiac output cannot rise across the fixed obstruction while muscle vessels dilate.
Physical exam
Exam findings track severity.
Finding
Explanation
Crescendo–decrescendo systolic murmur, right 2nd ICS → carotids
Turbulent ejection; later peak = more severe
Pulsus parvus et tardus
Small, late carotid upstroke from slow ejection
Soft or absent A2
Calcified, immobile leaflets
Paradoxical splitting of S2
Prolonged LV ejection delays A2
S4
Atrial kick into a hypertrophied, stiff ventricle
Sustained apical impulse
LV hypertrophy
Heyde syndrome: aortic stenosis with GI bleeding from angiodysplasia and acquired von Willebrand factor deficiency (shear stress cleaves vWF multimers).
Management
No drug relieves the obstruction; definitive treatment is valve replacement.
Valve replacement. Balloon valvuloplasty alone is a temporary bridge in adults because restenosis is rapid.
functions Worked example — syncope on the stairs
A 78-year-old man faints while climbing stairs. He has a harsh systolic murmur at the right upper sternal border radiating to both carotids, a weak delayed carotid pulse, and a single S2. Why did he faint, and what is the next step?
The murmur, delayed pulse, and soft A2 indicate severe calcific aortic stenosis.
With exercise, muscle arterioles dilate and blood pressure depends on increasing cardiac output.
The fixed valve prevents output from rising, so cerebral perfusion falls.
Symptomatic severe aortic stenosis carries high short-term mortality.
Answer. Exertional syncope from a fixed outflow obstruction. Confirm with echocardiography and refer for aortic valve replacement (TAVR or surgery).
1. A patient with Turner syndrome is most at risk for which valve lesion?
Explanation. Turner syndrome is associated with bicuspid aortic valve and coarctation of the aorta.
2. Severe aortic stenosis causes which change in S2?
Explanation. Prolonged LV ejection delays A2, and calcified leaflets may make A2 inaudible.
3. An elderly patient with aortic stenosis has recurrent GI bleeding from angiodysplasia. What hematologic abnormality contributes?
Explanation. Shear stress across the valve cleaves large vWF multimers (Heyde syndrome).
Frequently asked questions
What is the most common cause of aortic stenosis?expand_more
Age-related calcific degeneration of a normal three-leaflet valve in people over 70. A bicuspid valve is the most common cause in younger adults.
What are the symptoms of severe aortic stenosis?expand_more
Angina, exertional syncope, and heart failure. Their appearance marks a sharp drop in survival without valve replacement.
What does the aortic stenosis murmur sound like?expand_more
A harsh crescendo–decrescendo systolic ejection murmur at the right second intercostal space radiating to the carotids. A later peak and soft A2 indicate more severe disease.
What is pulsus parvus et tardus?expand_more
A weak (parvus) and delayed (tardus) carotid upstroke caused by slow ejection through a narrowed aortic valve.
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