Aortic Stenosis

Detailed Overview

Aortic stenosis is the most common valvular heart disease in developed countries. The pathogenesis mimics atherosclerosis, involving endothelial dysfunction, lipid deposition, and active osteoblastic calcification of the valve leaflets. A bicuspid aortic valve (congenital) severely accelerates this process, causing stenosis in patients aged 40-60, whereas degenerative tricuspid AS typically presents after age 70. Once patients become symptomatic, the mortality rate is extremely high (50% at 2 years) without mechanical or surgical intervention. Medical therapy is ineffective at halting disease progression.

Epidemiology & Demographics

Affects approximately 2-7% of adults older than 65 years. Bicuspid aortic valve is the most common congenital heart defect (1-2% of the population) and is the primary cause of AS in patients under 65.

Etiological Mechanism

1) Senile degenerative calcification of a normal tricuspid valve. 2) Congenital bicuspid aortic valve (BAV). 3) Rheumatic heart disease (typically accompanied by mitral valve involvement; common in developing nations).

Primary Causes

Active osteogenic processes in the valve interstitial cells, triggered by shear stress, hyperlipidemia, and inflammation, lead to calcium deposition restricting leaflet mobility.

• Age: Advancing age (>65) drives the wear-and-tear and calcification of the valve.
• Bicuspid Aortic Valve: Abnormal valve architecture subjects leaflets to high mechanical stress, causing stenosis 10-20 years earlier than normal.
• Cardiovascular Risk Factors: Hypertension, dyslipidemia, diabetes, and smoking accelerate valve calcification identically to vascular atherosclerosis.

The fixed narrowing of the aortic orifice creates a pressure gradient between the LV and the aorta. To maintain stroke volume against this high afterload, the LV undergoes concentric hypertrophy (thickening of the wall). This hypertrophy reduces LV compliance, increasing left ventricular end-diastolic pressure (LVEDP). The thickened myocardium also outgrows its capillary supply, leading to subendocardial ischemia even without coronary artery disease (causing angina). Eventually, compensatory mechanisms fail, LV dilation occurs, and stroke volume drops, resulting in heart failure and exertional syncope.

Characteristic Clinical Presentation

• Exertional Angina: Chest pain during exercise due to myocardial oxygen demand outstripping supply in the hypertrophied ventricle.
• Exertional Syncope: Fainting during exercise because the fixed cardiac output cannot match the vasodilation of exercising muscles.
• Heart Failure: Dyspnea on exertion, orthopnea, and lower extremity edema.

Physical Examination Signs

• Murmur: Harsh, crescendo-decrescendo systolic ejection murmur heard best at the right 2nd intercostal space, radiating to the carotids.
• Pulsus Parvus et Tardus: Weak and delayed carotid upstrokes.
• S4 Gallop: Heard at the apex due to atrial contraction into a stiff, hypertrophied left ventricle.

• Sudden Cardiac Death: Risk increases to 1-2% per year once severe AS becomes symptomatic.
• Heyde Syndrome: Bleeding from gastrointestinal angiodysplasia due to destruction of von Willebrand factor multimers as blood squeezes through the tight valve.

Diagnostic Criteria & Guidelines

Diagnosis is definitively established by Transthoracic Echocardiography (TTE). Severe AS is defined by an Aortic Valve Area (AVA) < 1.0 cm², a mean transvalvular gradient ≥ 40 mmHg, or a peak aortic jet velocity ≥ 4.0 m/s.

Differential Diagnosis

• Hypertrophic Obstructive Cardiomyopathy (HOCM) - murmur increases with Valsalva.
• Aortic Sclerosis - thickened valve but no significant hemodynamic gradient.
• Coronary Artery Disease - can cause identical angina symptoms.

Laboratory Tests & Biomarkers

• BNP / NT-proBNP: Elevated in patients with decompensated heart failure due to severe AS.
• Troponin: May be chronically, mildly elevated due to microvascular subendocardial ischemia.

Imaging Modalities & Findings

• Transthoracic Echocardiogram (TTE):
• ECG:
• Cardiac Catheterization:

• Mild AS
  Aortic Valve Area (AVA) > 1.5 cm², mean gradient < 20 mmHg. Asymptomatic.
• Moderate AS
  AVA 1.0 - 1.5 cm², mean gradient 20-39 mmHg. Usually asymptomatic.
• Severe AS
  AVA < 1.0 cm², mean gradient ≥ 40 mmHg, peak velocity ≥ 4.0 m/s. Onset of classic symptoms (SAD: Syncope, Angina, Dyspnea).

Second-Line & Adjunctive Therapy

For patients awaiting surgery, avoid aggressive vasodilation. Use caution with ACE inhibitors and nitrates, as severe AS relies on adequate preload and afterload to maintain cardiac output. Beta-blockers must be titrated very carefully. Diuretics (e.g., Furosemide 20-40 mg IV/PO) are used cautiously for volume overload.

Surgical & Procedural Management

Mechanical valve replacement (requires lifelong warfarin, INR 2.0-3.0) is preferred in younger patients (< 50-65 years) due to durability. Bioprosthetic tissue valves (SAVR or TAVR) are preferred in older patients (> 65 years) to avoid anticoagulation. Balloon Aortic Valvuloplasty (BAV) is a temporary bridge to definitive surgery in hemodynamically unstable patients.

Recommended Lifestyle Changes

• Asymptomatic severe AS patients must strictly avoid heavy physical exertion and competitive sports.
• Maintain meticulous dental hygiene to prevent infective endocarditis.

Patient Counseling & Advice

Educate the patient that the onset of ANY new symptom (chest pain, lightheadedness, shortness of breath) is a medical emergency requiring immediate evaluation, as survival drops sharply without valve replacement.

Follow-Up & Monitoring Schedule

Asymptomatic severe AS: TTE and clinical evaluation every 6-12 months. Moderate AS: TTE every 1-2 years. Mild AS: TTE every 3-5 years.

Preventive Strategies

Statins do NOT halt the progression of aortic valve calcification, despite shared risk factors with atherosclerosis. Strict blood pressure control is essential to prevent additional afterload burden on the LV.

Asymptomatic patients have an excellent prognosis. However, once symptoms appear, median survival is 5 years with angina, 3 years with syncope, and 2 years with heart failure. Following successful valve replacement, survival matches the age-matched normal population.