Valvular Heart Disease

Valvular heart disease encompasses disorders affecting the four cardiac valves: aortic, mitral, tricuspid, and pulmonary. These conditions result from structural abnormalities that impair normal valve function, leading to either stenosis (narrowed valve opening) or regurgitation (incomplete valve closure). The pathophysiology varies significantly based on the affected valve and type of dysfunction.

Stenotic lesions create pressure overload on the chamber proximal to the affected valve. In aortic stenosis, the left ventricle faces increased afterload, leading to compensatory concentric hypertrophy. This adaptation initially maintains cardiac output but eventually progresses to systolic dysfunction. The pressure gradient across the stenotic valve correlates with disease severity and clinical symptoms.

Regurgitant lesions cause volume overload as blood flows backward during the cardiac cycle. In mitral regurgitation, the left ventricle experiences both preload and afterload changes. The regurgitant volume returns to the ventricle during diastole (increased preload), while the effective forward stroke volume may be reduced (functional afterload reduction due to low-resistance pathway into the atrium).

Compensatory mechanisms include ventricular remodeling, neurohormonal activation, and altered loading conditions. Initially, these adaptations maintain hemodynamic stability. However, chronic volume or pressure overload eventually leads to myocardial dysfunction, arrhythmias, and heart failure.

Classification systems help guide management decisions. Valvular disease severity is typically graded as mild, moderate, or severe based on echocardiographic parameters including valve area, pressure gradients, and regurgitant volume. The American College of Cardiology/American Heart Association guidelines provide specific criteria for each valve lesion.

Understanding the underlying pathophysiology is crucial for recognizing clinical presentations, interpreting diagnostic studies, and determining optimal timing for interventions. The natural history of valvular disease varies considerably, with some lesions remaining stable for years while others progress rapidly to hemodynamic compromise.

Aortic stenosis (AS) represents narrowing of the aortic valve orifice, creating obstruction to left ventricular outflow. The normal aortic valve area measures 3-4 cm², with severe AS defined as valve area <1.0 cm² or mean gradient >40 mmHg.

Etiology varies by age group:

• Congenital bicuspid valve (most common cause in patients <70 years): Affects 1-2% of the population, typically presenting in the 5th-6th decades
• Degenerative calcific AS (most common cause in patients >70 years): Results from calcium deposition on normal tricuspid valves
• Rheumatic heart disease (now rare in developed countries): Causes commissural fusion and calcification

Pathophysiology: Progressive valve narrowing increases left ventricular systolic pressure, leading to concentric hypertrophy. Initially, this maintains normal wall stress (Laplace's law) and preserves ejection fraction. Eventually, hypertrophy becomes inadequate, wall stress increases, and systolic function deteriorates.

Clinical presentation follows the classic triad of symptoms in severe AS:

1. Exertional dyspnea (heart failure)
2. Angina pectoris (increased oxygen demand from hypertrophy)
3. Syncope (fixed stroke volume with exercise)

Physical examination reveals a harsh systolic ejection murmur, best heard at the right sternal border with radiation to the carotids. The murmur intensity correlates poorly with severity. Additional findings include slow-rising carotid upstroke (pulsus tardus), narrow pulse pressure, and paradoxical splitting of S2 in severe cases.

Diagnostic evaluation: Echocardiography remains the gold standard, measuring valve area, mean gradient, and left ventricular function. Cardiac catheterization is reserved for cases with discordant clinical and echocardiographic findings.

Management: Asymptomatic patients with severe AS require serial monitoring. Symptomatic severe AS mandates intervention (surgical or transcatheter aortic valve replacement) given the poor prognosis without treatment. Medical therapy plays a limited role, focusing on heart failure management when surgery is contraindicated.

Mitral regurgitation (MR) involves retrograde blood flow from the left ventricle to the left atrium during systole due to incomplete mitral valve closure. Understanding the underlying mechanism is crucial for determining appropriate treatment strategies.

Classification by mechanism:

• Primary (degenerative) MR: Structural valve abnormalities including mitral valve prolapse, rheumatic disease, infective endocarditis, or ruptured chordae tendineae
• Secondary (functional) MR: Normal valve leaflets with regurgitation due to left ventricular dysfunction, annular dilatation, or papillary muscle displacement

Pathophysiology: MR creates volume overload with both preload and afterload alterations. The regurgitant volume returns to the left ventricle during diastole (increased preload), while ejection into the low-pressure atrium reduces effective afterload. This initially maintains high ejection fraction despite reduced forward stroke volume. Chronic MR leads to left ventricular dilatation and eventual systolic dysfunction.

Clinical presentation varies with acuity:

• Acute MR (papillary muscle rupture, endocarditis): Sudden onset pulmonary edema, cardiogenic shock
• Chronic MR: Gradual onset exertional dyspnea, fatigue, atrial fibrillation

Physical examination: The classic finding is a holosystolic murmur at the apex radiating to the axilla. Murmur intensity may not correlate with severity. Additional findings include laterally displaced PMI (volume overload), S3 gallop, and signs of heart failure in advanced cases.

Diagnostic evaluation: Echocardiography assesses regurgitation severity using multiple parameters including regurgitant volume, effective regurgitant orifice area, and vena contracta width. Left ventricular dimensions and function guide timing of intervention.

Management strategies:

• Primary MR: Surgical repair (preferred over replacement when feasible) for symptomatic severe MR or asymptomatic severe MR with LV dysfunction (EF <60% or LV end-systolic diameter >40mm)
• Secondary MR: Optimize heart failure therapy; surgical intervention controversial and typically reserved for severe cases with persistent symptoms despite optimal medical therapy
• Medical therapy: ACE inhibitors may benefit patients with chronic MR by reducing regurgitant volume through afterload reduction

Rheumatic heart disease (RHD) results from an autoimmune response following group A streptococcal pharyngitis, leading to inflammatory damage of cardiac structures. While rare in developed countries, RHD remains a significant cause of valvular disease in developing nations, affecting approximately 15-20 million people worldwide.

Pathogenesis: Molecular mimicry between streptococcal M protein and cardiac myosin triggers cross-reactive antibodies that attack cardiac tissues. The inflammatory process involves all three cardiac layers but predominantly affects the endocardium, particularly valve leaflets. Aschoff bodies (pathognomonic inflammatory nodules containing multinucleated giant cells) characterize the acute phase.

Valve involvement patterns:

• Mitral valve (most commonly affected): Commissural fusion, chordal thickening and fusion, leaflet retraction leading to mixed stenosis and regurgitation
• Aortic valve: Commissural fusion and leaflet thickening, typically causing combined stenosis and regurgitation
• Tricuspid and pulmonary valves: Less frequently involved, usually in severe cases

Clinical phases:

1. Acute rheumatic fever: Follows streptococcal pharyngitis by 2-6 weeks, diagnosed using Jones criteria (major criteria include carditis, polyarthritis, chorea, erythema marginatum, subcutaneous nodules)
2. Chronic rheumatic heart disease: Progressive valve fibrosis and calcification developing over years to decades

Mitral stenosis characteristics: Rheumatic mitral stenosis typically presents with a low-pitched diastolic rumble at the apex, opening snap, and symptoms of left atrial enlargement (atrial fibrillation, embolic events). Severe stenosis (valve area <1.5 cm²) may cause pulmonary hypertension and right heart failure.

Diagnostic evaluation: Echocardiography reveals characteristic features including commissural fusion, diastolic doming of anterior mitral leaflet, and thickened, calcified valve apparatus. The mitral valve score (leaflet mobility, thickening, calcification, and subvalvular disease) helps determine suitability for balloon valvotomy.

Management: Primary prevention involves prompt treatment of streptococcal pharyngitis. Secondary prevention requires long-term antibiotic prophylaxis (penicillin) to prevent recurrent episodes. Valve intervention (surgical repair/replacement or percutaneous balloon valvotomy for mitral stenosis) is indicated based on symptoms and hemodynamic severity. Anticoagulation is essential for patients with atrial fibrillation or history of embolic events.

Prosthetic valve replacement has revolutionized the treatment of severe valvular disease. Understanding the different valve types, their characteristics, and potential complications is essential for optimal patient management and long-term care.

Valve types and characteristics:

Mechanical valves:

• Bileaflet valves (St. Jude, ATS): Most commonly used, excellent hemodynamics
• Tilting disc valves (Björk-Shiley): Single occluder, good hemodynamics
• Caged ball valves (Starr-Edwards): Rarely used today, excellent durability
• Advantages: Exceptional durability (>30 years), no structural deterioration
• Disadvantages: Lifelong anticoagulation required, risk of bleeding complications

Bioprosthetic valves:

• Porcine aortic valves: Treated with glutaraldehyde for tissue fixation
• Bovine pericardial valves: Currently preferred due to superior hemodynamics
• Advantages: No anticoagulation required (except first 3-6 months), lower bleeding risk
• Disadvantages: Limited durability (10-20 years), structural valve deterioration

Transcatheter valves (TAVR/TAVI): Minimally invasive option for high-risk patients, expanding to intermediate and low-risk populations.

Anticoagulation management:

• Mechanical valves: Target INR 2.5-3.5 (aortic) or 3.0-4.0 (mitral), lifelong warfarin
• Bioprosthetic valves: Warfarin for 3-6 months post-implantation, then aspirin alone
• High-risk patients: Consider additional aspirin with warfarin

Prosthetic valve complications:

Structural complications:

• Prosthetic valve endocarditis: Higher mortality than native valve endocarditis, often requires surgical intervention
• Paravalvular leak: More common with mechanical valves, may cause hemolysis
• Structural valve deterioration: Primarily affects bioprosthetic valves, presents as stenosis or regurgitation
• Thrombosis: More common with mechanical valves, may present as acute obstruction

Non-structural complications:

• Bleeding: Related to anticoagulation, particularly with mechanical valves
• Thromboembolism: Despite adequate anticoagulation, annual risk 1-2%
• Hemolytic anemia: Usually mild, more common with mechanical valves

Follow-up and monitoring: Annual echocardiography to assess valve function, anticoagulation monitoring for mechanical valves, and prompt evaluation of new symptoms suggesting valve dysfunction.

Accurate diagnosis of valvular disease requires systematic integration of clinical assessment, physical examination, and appropriate imaging studies. The diagnostic approach should be tailored to the suspected valve lesion and clinical presentation.

Clinical assessment: A detailed history focusing on symptom onset, exercise tolerance, and associated conditions provides crucial diagnostic clues. Key symptoms include dyspnea (suggests heart failure), chest pain (may indicate coronary disease or severe AS), syncope (concerning for severe AS), and palpitations (suggests arrhythmias).

Physical examination remains fundamental:

• Inspection: Assess for signs of heart failure, cyanosis, or syndromic features
• Palpation: Evaluate PMI location and character, assess for thrills
• Auscultation: Systematic evaluation of murmur timing, location, intensity, and radiation

Murmur characteristics by valve lesion:

Echocardiographic evaluation:

• Transthoracic echocardiography (TTE): First-line imaging modality, assesses valve morphology, function, and hemodynamics
• Transesophageal echocardiography (TEE): Superior visualization of mitral valve, assessment for endocarditis, guidance for interventions
• Stress echocardiography: Evaluates asymptomatic severe AS or low-gradient AS with reduced EF

Key echocardiographic parameters:

Aortic stenosis severity:

• Mild: Valve area >1.5 cm², mean gradient <25 mmHg
• Moderate: Valve area 1.0-1.5 cm², mean gradient 25-40 mmHg
• Severe: Valve area <1.0 cm², mean gradient >40 mmHg

Mitral regurgitation severity:

• Mild: Regurgitant volume <30 mL, ERO <0.2 cm²
• Moderate: Regurgitant volume 30-60 mL, ERO 0.2-0.4 cm²
• Severe: Regurgitant volume >60 mL, ERO >0.4 cm²

Additional imaging:

• Cardiac MRI: Accurate assessment of regurgitant volume, ventricular function in poor echo windows
• Cardiac catheterization: Reserved for discordant findings, assessment of coronary disease before surgery
• CT imaging: Increasingly used for transcatheter valve planning, assessment of valve morphology

Laboratory studies: BNP/NT-proBNP levels correlate with symptom severity and prognosis, particularly useful in asymptomatic patients with severe valve disease.

The management of valvular heart disease requires careful consideration of disease severity, symptom status, ventricular function, and patient-specific factors. Treatment strategies range from medical management and surveillance to surgical or percutaneous interventions.

Medical management principles:

• Asymptomatic patients: Regular surveillance with serial echocardiography, patient education about symptom recognition
• Symptomatic patients: Heart failure management, rate control for atrial fibrillation, anticoagulation when indicated
• Specific medical therapies: Limited role in valvular disease, primarily supportive care

Intervention timing guidelines:

Aortic stenosis:

• Class I indications: Symptomatic severe AS, asymptomatic severe AS with EF <50%, asymptomatic severe AS undergoing cardiac surgery
• Class IIa indications: Very severe AS (valve area <0.6 cm²), rapid progression, abnormal exercise test

Mitral regurgitation:

• Primary MR: Symptomatic severe MR, asymptomatic severe MR with EF 30-60% or LV end-systolic diameter ≥40 mm
• Secondary MR: Optimal medical therapy first, surgery for persistent severe symptoms

Surgical options:

Valve repair vs. replacement:

• Mitral repair: Preferred when feasible, lower operative mortality, preserves LV function, no anticoagulation
• Aortic repair: Limited to specific conditions (bicuspid valve, root aneurysm)
• Valve replacement: Required when repair not feasible

Prosthetic valve selection considerations:

• Age: Bioprosthetic valves preferred in patients >65-70 years
• Anticoagulation risk: Bioprosthetic valves for high bleeding risk
• Patient preference: After thorough counseling about risks/benefits
• Life expectancy: Mechanical valves for younger patients with longer life expectancy

Transcatheter interventions:

• TAVR: Established for high and intermediate-risk AS patients, expanding to low-risk
• MitraClip: Percutaneous mitral repair for high-risk surgical candidates
• Balloon valvotomy: Limited to selected mitral stenosis cases (young patients, favorable valve morphology)

Risk assessment: Surgical risk stratification using STS score, EuroSCORE, or frailty assessment helps determine optimal intervention strategy. High-risk patients may benefit from transcatheter approaches.

Post-intervention care:

• Anticoagulation management: Based on valve type and patient factors
• Surveillance: Regular echocardiographic follow-up to monitor valve function
• Endocarditis prophylaxis: Recommended for prosthetic valves, prior endocarditis
• Activity restrictions: Generally liberalized after successful intervention

Special considerations: Pregnancy, concurrent coronary disease, multiple valve involvement, and connective tissue disorders require specialized management approaches with multidisciplinary team involvement.