Heart Valve Replacement

A. Types

Porcine - average lifespan ~8-10 years
Metal - may have unlimited lifespan
1. Caged-ball (Starr-Edwards)
2. Single-tilting disk (Bjork-Shiley, Medtronic, Omnicarbon)
3. Bileaflet-tilting disk (St. Jude Medical, Carbomedics, Edwards-Duromedics)
Valve reconstruction can be performed in some cases
Majority of valve replacements require open surgery
Percutaneous placement of a pulmonary valve has been achieved [9]

B. Indications and Efficacy [1]

Valve Disease
1. Stenotic lesions tend to be more poorly tolerated than regurgitant lesions
2. Valve replacement usually undertaken for symptomatic valve disease
Timing of Valve Replacement
1. Usually based on symptoms that limit patient's lifestyle
2. Angina, dyspnea, syncope, congestive heart failure
3. Ventricular dilation (even without symptoms) may be an indication
4. Endocarditis, especially fungal or with abscess formation
5. Advanced ventricular arrhythmias
Efficacy
1. Porcine valves last an average of 8-10 years
2. Metal valves usually last 20-30 years

C. Risks Associated with Valve Replacement

Endocarditis
Stroke (usually with metal valves) [8]
Valve Dehiscence
1. Valve is sewed in surgically
2. Valve can dehisce, or come apart, usually at suture sites
3. Incidence of dehiscence is decreasing
4. When it occurs acutely, acute pulmonary edema ensues (congestive heart failure)
5. Acute pulmonary edema due to valve dehiscence is an emergency requiring re-operation
Atrial Fibrillation [6]
1. About half of patients undergoing valve replacement develop atrial fibrillation
2. May be related to valvular disease type
3. Pericardial trauma during surgery may predispose to arrhythmias
4. Emergent electrical cardioversion may be required
Surgical / Peri-Operative Mortality
1. 2-15% depending on patient and number of valve replacements
2. Comorbidities play major role in surgical risk
3. Valve replacement + bypass grafting carries higher mortality risk

D. Evaluation of Valve Function [1]

History of increasing cardiopulmonary symptoms is concerning for valve dysfunction
Physical Examination - metal valve sounds are loud (changes in sound are concerning) [5]
Transesophageal echocardiography may be preferred for evaluation of synthetic valve [2]
MRI can be performed in most patients but is usually not helpful for metal valve function

E. Anti-Coagulation Therapy [5,7]

Required for metal valves and initially (usually 3-6 months) for porcine valves
1. Patients should be stratified by low or high risk based on comorbidities
2. Many patients have atrial fibrillation
Combination of oral anticoagulants with antiplatelet agents reduce thromboembolism and overall mortality in patients with mechanical heart valves [10]
Embolic Stroke or Systemic Embolism
1. Overall risk ~1-2% / year on warfarin (INR ~2.5-3.5)
2. Risk is greatet in first year after heart valve
3. Increased risk when variability in anticoagulation levels is highest [8]
4. 15-75% of patients are adequately anticoagulated, depending on definition [8]
Risk of ischemic stroke was <1% / year on warfarin INR 2.5-4 in Dutch Study [3]
1. INR <4 asssociated with very low hemorrhagic stroke risk (<0.5% / year)
2. Recommendation in that study was for target INR of 3.0-4.0
Aspirin (100mg/day) + Warfarin [7,10]
1. Anti-platelet therapy alone provides ~50% reduction in thromboembolic risk
2. Lowers risk of embolic stroke to ~0.5% per year when combined with warfarin
3. Increases risk of bleeding 1.5 fold
4. Bleeding was mostly low grade GI bleeding, easily controlled
5. Benefits of ASA added to warfarin clearly outweighed risks
Dipyridamole also improves outcomes and mortality when added to warfarin [10]

References