Introduction to Valvular Heart Disease

1. Definition and Epidemiology

1.1 What is Valvular Heart Disease?

Valvular heart disease (VHD) refers to any structural or functional abnormality of one or more of the four cardiac valves—aortic, mitral, tricuspid, and pulmonary—that disrupts the normal unidirectional flow of blood through the heart. The abnormality may be:

Stenosis → narrowing of the valve orifice, obstructing blood flow.
Regurgitation (insufficiency/incompetence) → incomplete valve closure, allowing backward flow of blood.
Mixed lesions → both stenosis and regurgitation affecting the same valve.

Valvular dysfunction can cause pressure overload, volume overload, or both, leading to chamber remodeling, heart failure, arrhythmias, thromboembolism, and sudden death.

1.2 Epidemiological Trends

The epidemiology of VHD varies globally:

In low- and middle-income countries (LMICs), rheumatic heart disease (RHD) remains the leading cause, especially affecting young individuals.
In high-income countries, degenerative calcific valve disease dominates, particularly in the elderly.
Congenital valve anomalies (e.g., bicuspid aortic valve) are recognized as important contributors across populations.

Prevalence data:

The Framingham Heart Study estimated that ~2.5% of the U.S. population has moderate to severe VHD, with prevalence rising steeply after age 65.
In Europe, >10% of people aged >75 years are affected.
Globally, the Global Burden of Disease (GBD) Study estimated ~40 million cases of rheumatic valvular disease in 2019, with millions more suffering from degenerative forms.

1.3 Risk Factors

Age: The strongest determinant for calcific aortic stenosis and degenerative mitral regurgitation.
Rheumatic fever: Still endemic in sub-Saharan Africa, South Asia, and parts of Oceania.
Congenital abnormalities: Bicuspid aortic valve, Ebstein anomaly.
Infective endocarditis: Can damage any valve.
Metabolic contributors: Hypertension, hyperlipidemia, chronic kidney disease.

2. Types of Valves Affected

The human heart has four valves that ensure unidirectional, efficient blood flow. Understanding each valve’s anatomy and function helps in appreciating how disease alters physiology.

2.1 Aortic Valve

Located between the left ventricle and aorta.
Opens during systole to eject blood into systemic circulation.
Common pathologies:
- Aortic stenosis (AS): Often due to calcification or congenital bicuspid valve.
- Aortic regurgitation (AR): Due to root dilatation, endocarditis, or rheumatic disease.

2.2 Mitral Valve

Lies between the left atrium and left ventricle.
Opens during diastole to allow ventricular filling.
Common pathologies:
- Mitral stenosis (MS): Classic consequence of rheumatic fever.
- Mitral regurgitation (MR): May be degenerative, ischemic (secondary to MI), or rheumatic.

2.3 Tricuspid Valve

Separates the right atrium and right ventricle.
Opens during diastole to allow venous return into RV.
Common pathologies:
- Tricuspid regurgitation (TR): Usually functional, secondary to right ventricular dilatation from pulmonary hypertension.
- Tricuspid stenosis (TS): Rare, usually rheumatic.

2.4 Pulmonary Valve

Located between the right ventricle and pulmonary artery.
Opens during systole to permit blood flow into the lungs.
Common pathologies:
- Pulmonary stenosis (PS): Mostly congenital.
- Pulmonary regurgitation (PR): Often secondary to pulmonary hypertension or after surgical repair of congenital heart disease.

2.5 Hemodynamic Impact by Valve

Stenosis → pressure overload (e.g., LVH in AS, LAH in MS).
Regurgitation → volume overload (e.g., LV dilatation in AR, LA enlargement in MR).
Chronic overload leads to heart failure, arrhythmias, and increased mortality.

3. Global Burden and Mortality Impact

3.1 Worldwide Prevalence

Rheumatic VHD: ~40 million affected, with 305,000 deaths annually. Highest prevalence in Africa, South Asia, and Oceania.
Degenerative VHD: Leading cause in high-income countries, primarily aortic stenosis in elderly populations.
Congenital valve disease: Accounts for 10–20% of congenital heart defects.

3.2 Mortality Impact

Severe untreated VHD carries a poor prognosis:
- Symptomatic severe aortic stenosis: Average survival 2–3 years without valve replacement.
- Symptomatic mitral regurgitation: Associated with progressive LV dysfunction and increased mortality.
- Rheumatic mitral stenosis: Major cause of death in young adults in endemic regions.

3.3 Disability and Quality of Life

Leads to reduced exercise tolerance, recurrent hospitalizations, atrial fibrillation, stroke, and heart failure.
Contributes significantly to years lived with disability (YLDs) in global health metrics.

3.4 Economic Burden

Cost of surgical valve replacement or repair and lifelong anticoagulation (for mechanical valves) creates huge financial strain.
In LMICs, limited access to surgery leads to preventable deaths in young populations.
In HICs, aging populations increase demand for transcatheter therapies (TAVI, MitraClip), with escalating healthcare costs.

4. Clinical Importance

4.1 Symptom Recognition

VHD often remains silent for years before becoming symptomatic. When symptoms arise, they usually signify advanced disease.

Aortic stenosis → angina, syncope, dyspnea.
Mitral stenosis → exertional dyspnea, orthopnea, atrial fibrillation.
Mitral regurgitation → palpitations, fatigue, heart failure.
Tricuspid disease → peripheral edema, ascites.

4.2 Diagnostic Role of Modern Imaging

Echocardiography: Gold standard for assessing valve anatomy, gradients, and regurgitant severity.
Cardiac MRI & CT: Provide additional anatomical and functional information.
Catheterization: Used when non-invasive findings are inconclusive.

4.3 Complications of Untreated VHD

Progressive heart failure.
Arrhythmias (AF, ventricular arrhythmias).
Thromboembolism → stroke, systemic emboli.
Pulmonary hypertension.
Sudden cardiac death (notably in AS).

4.4 Therapeutic Implications

Medical therapy: Symptomatic relief (diuretics, anticoagulation, rate/rhythm control in AF).
Surgical therapy: Valve repair or replacement is curative in severe disease.
Transcatheter therapies: TAVI, MitraClip, tricuspid devices are rapidly expanding.

4.5 Public Health Relevance

VHD exemplifies the double burden of disease:
- Rheumatic VHD → affecting young populations in LMICs.
- Degenerative VHD → affecting elderly in HICs.
Highlights need for:
- Improved rheumatic fever prevention.
- Increased access to surgical and transcatheter interventions.
- Development of cost-effective screening and treatment strategies.