Aortic Stenosis Murmur: Characteristic Features and Clinical Approach
The aortic stenosis murmur is a harsh, crescendo-decrescendo systolic ejection murmur best heard at the right upper sternal border (second right intercostal space) that radiates to the carotid arteries, but critically, murmur intensity does not correlate with stenosis severity—severe AS can present with a faint or even absent murmur, particularly in elderly patients or those with low cardiac output. 1, 2
Key Acoustic Characteristics
The classic AS murmur has several distinguishing features:
- Timing and quality: Mid-to-late peaking crescendo-decrescendo pattern with a harsh, "humming" quality 1, 3
- Location: Maximal at the right upper sternal border (aortic area) 1
- Radiation: Transmits to the carotid arteries; absence of carotid radiation makes severe AS unlikely (negative likelihood ratio 0.05-0.10) 4
- Peak timing: A late-peaking murmur significantly increases the probability of severe stenosis (positive likelihood ratio 8.0-101) 4
Critical Associated Physical Findings
Beyond the murmur itself, several examination findings help establish severity:
High-Specificity Signs for Severe AS
- Absent or markedly diminished A2 (second aortic sound): This is the single most specific bedside finding for severe AS (positive likelihood ratio 3.1-50), resulting from valve immobility due to calcification 1, 2, 4
- Single S2: When A2 disappears completely, only the pulmonic component remains audible 2, 5
- Palpable thrill: Indicates turbulent flow across a severely narrowed valve 1
- Slow-rising, diminished carotid pulse (parvus et tardus): Positive likelihood ratio 2.8-130 for severe AS 4
Important Caveat About Carotid Pulse
Elderly patients with arterial stiffening may lack the classic delayed carotid upstroke despite critical stenosis, so absence of this finding does not exclude severe disease. 2, 6
The Silent Murmur Phenomenon
A critical pitfall: severe AS can present with a grade 2/6 or softer murmur—or no audible murmur at all—especially in three scenarios: 2, 6
- Low cardiac output states: When left ventricular function is depressed, transvalvular flow velocity falls, producing a soft or inaudible murmur despite critical valve narrowing 2
- Elderly patients: Age-related changes mask both the murmur and classic pulse findings 2, 6
- Heart failure presentation: Severe AS may manifest primarily as unexplained heart failure with minimal murmur 2
Therefore, any elderly patient with exertional dyspnea, syncope, angina, or unexplained heart failure requires immediate echocardiography regardless of murmur intensity. 2, 6
Diagnostic Approach Algorithm
Step 1: Clinical Assessment
- Evaluate for the classic symptom triad: exertional dyspnea, syncope, or angina 1, 5
- Systematically assess exercise tolerance and daily activities (patients often under-report symptoms) 2, 6
- Examine for absent/diminished A2, carotid pulse character, and murmur radiation pattern 2, 4
Step 2: Immediate Echocardiography Indications
Order transthoracic echocardiography urgently for: 2, 6
- Any systolic murmur (any grade) PLUS exertional symptoms, syncope, angina, or heart failure signs
- Any elderly patient with a systolic murmur and ECG or chest radiograph abnormalities
- Absent or markedly diminished A2 on examination
Step 3: Echocardiographic Severity Grading
- Aortic valve area (AVA) ≤1.0 cm²
- Peak velocity ≥4.0 m/s
- Mean gradient ≥40 mmHg
Additional severity categories: 1
- Moderate AS: Mean gradient 30-49 mmHg, AVA 1.0-1.5 cm²
- Mild AS: Mean gradient <30 mmHg, AVA >1.5 cm²
Step 4: Low-Flow, Low-Gradient Assessment
When mean gradient is <40 mmHg but AVA ≤1.0 cm², distinguish true severe AS from pseudo-severe stenosis: 2, 6
- Calculate stroke volume index (SVi): Low flow defined as SVi <35 mL/m² 1
- Perform low-dose dobutamine stress echocardiography: 2, 6
- True severe AS: AVA remains ≤1.0 cm² despite increased flow
- Pseudo-severe AS: AVA increases >0.2 cm² with augmented flow
Step 5: Assess Left Ventricular Function and Calcification
- Document LV ejection fraction (LVEF) and presence of LV hypertrophy 1
- Grade valve calcification severity (mild, moderate, severe)—extensive calcification predicts worse outcomes 1, 7
Treatment Indications
Symptomatic Severe AS
Valve replacement is mandatory (Class I indication) for any patient with severe AS and symptoms (angina, dyspnea, syncope). 1, 5
Asymptomatic Severe AS
Proceed with valve replacement when: 6
- LVEF <50% (Class I)
- Peak velocity ≥5.0 m/s (very severe stenosis)
- Rapid hemodynamic progression on serial echocardiography
- Abnormal exercise testing (symptoms or abnormal blood pressure response)
Procedural Selection
- Calculate STS-PROM surgical risk score 5, 6
- Convene multidisciplinary Heart Team (cardiac surgery, interventional cardiology, imaging, anesthesiology, geriatrics) 5, 6
- Choose surgical AVR (SAVR) for low-moderate risk; transcatheter AVR (TAVR) for high/prohibitive risk 5, 8
Surveillance for Conservative Management
For asymptomatic patients not undergoing immediate intervention: 6, 8
- Annual transthoracic echocardiography for severe AS
- Every 1-2 years for moderate AS
- Every 3-5 years for mild AS
- Consider exercise testing to unmask latent symptoms (but avoid in already symptomatic patients)
Common Pitfalls to Avoid
- Never dismiss severe AS based on a soft murmur alone, especially in elderly or heart failure patients 2, 6
- Do not rely solely on carotid pulse character in elderly patients with arterial stiffening 2, 6
- If physical examination strongly suggests severe AS but echocardiography shows only mild disease, suspect underestimation and repeat imaging 2, 6
- Recognize that murmur intensity does not correlate with stenosis severity when cardiac output is compromised 2
Medical Therapy Limitations
No medical therapy halts AS progression—statins do not prevent disease advancement and should not be prescribed for this purpose. 5, 6, 9
Prognostic Context
Without valve replacement, one-year survival for symptomatic severe AS is approximately 67% versus 94% with replacement, underscoring the urgency of timely intervention. 5, 6