What are the characteristics of the aortic stenosis murmur and how should it be evaluated?

Aortic Stenosis Murmur: Characteristics and Evaluation

The aortic stenosis murmur is a crescendo-decrescendo systolic ejection murmur heard best at the second right intercostal space, radiating to the carotid arteries, with maximal intensity in mid-to-late systole. 1

Key Auscultatory Characteristics

Murmur Quality and Timing

• Crescendo-decrescendo (diamond-shaped) contour that begins shortly after S1, peaks in mid-to-late systole, and ends before S2 2
• The timing mirrors left ventricular pressure rise and accelerating-then-decelerating flow across the narrowed valve 2
• Late-peaking murmur indicates more severe stenosis, while earlier peaking suggests less severe disease 3
• Harsh, rasping quality at the base that may become softer toward the apex 3

Location and Radiation

• Maximal intensity at the second right intercostal space (aortic area) 1
• Radiates to the carotid arteries in 50-75% of cases 1, 3
• A palpable thrill may be present at the same location 1

Critical Physical Examination Findings

Signs of Severe Aortic Stenosis

A soft or absent aortic component (A2) of the second heart sound is highly specific for severe aortic stenosis and mandates immediate echocardiography. 2, 4 This occurs because valve calcification and immobility prevent normal forceful leaflet closure 4

Additional high-yield findings include:

• Paradoxical (reversed) splitting of S2 where the sound is single during inspiration and split during expiration 1
• Pulsus parvus et tardus: delayed, diminished carotid upstroke with positive likelihood ratios of 2.8-130 for severe stenosis 2, 4
• Ejection click heard throughout the respiratory cycle suggests bicuspid aortic valve 1
• Fourth heart sound (S4) when stenosis is severe 1

Dynamic Auscultation Maneuvers

• Valsalva maneuver and standing decrease murmur intensity 1
• Squatting markedly increases murmur intensity by augmenting preload and afterload 2
• Post-ventricular premature beat: pulse pressure increases 1

Critical Pitfall: The Silent Murmur

Do not exclude severe aortic stenosis based on a faint or absent murmur, especially in elderly patients or those with heart failure. 4, 5

• Low cardiac output states reduce transvalvular flow velocity, producing a soft or inaudible murmur despite critical valve narrowing 4
• Murmur intensity correlates with peak momentum transfer and body size, so loud murmurs predict severe disease less reliably in larger patients 6
• Age-related arterial stiffening in elderly patients can mask the classic pulsus parvus et tardus 4, 5
• Any elderly patient with exertional dyspnea, syncope, or angina requires immediate echocardiography regardless of murmur intensity 4, 5

Differential Diagnosis

Key distinguishing features from other left ventricular outflow obstructions 1:

Feature	Valvular AS	Hypertrophic Cardiomyopathy
Valsalva effect	Decreases murmur	Increases murmur
Carotid pulse	Parvus et tardus	Brisk, jerky, systolic rebound
Maximal murmur location	2nd right intercostal space	4th left intercostal space
Ejection click	Present (unless calcified)	Uncommon or absent

Immediate Echocardiography Indications

Order transthoracic echocardiography immediately for: 1

• Any systolic murmur ≥ grade 3/6
• Murmurs with soft/absent A2 or paradoxical S2 splitting
• Any elderly patient with a systolic murmur (any grade) plus exertional symptoms, syncope, angina, or heart failure signs 4, 5
• Abnormal ECG (ventricular hypertrophy) or chest X-ray in the setting of any cardiac murmur 1
• Murmurs radiating to the neck or back 1

Echocardiographic Severity Criteria

Severe aortic stenosis is defined by: 1

• Aortic valve area (AVA) < 1.0 cm² or indexed AVA < 0.6 cm²/m²
• Peak velocity ≥ 4.0 m/s
• Mean gradient ≥ 50 mmHg (at normal transvalvular flow)

Low-Flow, Low-Gradient Assessment

When mean gradient < 40 mmHg with AVA ≤ 1.0 cm², perform low-dose dobutamine stress echocardiography to distinguish: 4, 5

• True severe stenosis: valve area remains < 1.0 cm² with increased flow
• Pseudo-severe stenosis: valve area increases > 0.2 cm² with augmented flow

Ancillary Testing

Electrocardiography

• Left ventricular hypertrophy with or without strain pattern suggests significant stenosis 1
• Absence of LVH is reassuring but does not exclude severe AS 1

Chest Radiography

• Valve calcification common after age 40 1
• Dilated ascending aorta common after age 40 1
• Post-stenotic dilation may be visible 1

Distinguishing Aortic Sclerosis from Stenosis

Aortic sclerosis is defined by focal leaflet thickening and increased echogenicity without restriction of motion and peak velocity < 2.0 m/s 1. This finding should prompt aggressive coronary disease prevention but does not require valve intervention 1