What is the primary goal of a mechanical (mechanical heart valve) valve?

Primary Goal of Mechanical Heart Valves

The primary goal of a mechanical heart valve is to provide durable, long-term valve replacement that avoids structural valve deterioration and the need for reoperation, accepting the trade-off of lifelong anticoagulation to prevent thromboembolism and valve thrombosis. 1

Core Objectives

Durability and Structural Stability

• Mechanical valves are designed to eliminate structural valve failure, which is the primary limitation of bioprosthetic valves 1
• Ball-and-cage prostheses have demonstrated excellent mechanical stability at follow-up intervals exceeding 30 years 1
• Modern bileaflet valves (St. Jude, CarboMedics, ATS Medical, On-X) appear mechanically stable and are relatively hemodynamically efficient 1
• The structural stability translates to freedom from reoperation due to valve deterioration, unlike bioprosthetic valves where approximately 50% fail by 10 years in patients under 40 years of age 1

Prevention of Thromboembolism Through Anticoagulation

• All patients with mechanical valves require lifelong anticoagulation with a vitamin K antagonist (VKA) to prevent valve thrombosis and thromboembolic events 1
• The thrombogenicity of mechanical valves stems from the intravascular prosthetic material and abnormal flow conditions that create zones of low flow and high-shear stress, causing platelet activation 1
• Without anticoagulation, the incidence of valve thrombosis or embolism is 8.6 per 100 patient-years, which is reduced to 1.8 per 100 patient-years with VKA therapy 1
• VKA therapy is protective against valve thrombosis (OR: 0.11) and thromboembolic events (OR: 0.21) 1

Target Anticoagulation Strategy

INR Goals

• For the first 3 months after mechanical aortic valve replacement: INR target of 2.5-3.5 1
• Beyond 3 months: INR target of 2.0-3.0 1
• For mechanical mitral valves: INR target of 2.5-3.5 indefinitely 1, 2
• Low-dose aspirin (75-100 mg daily) should be added to warfarin for all mechanical valves 1

Critical Caveat

• Direct oral anticoagulants (DOACs) are contraindicated for mechanical valves 2
• The RE-ALIGN trial demonstrated increased thromboembolic and bleeding complications with dabigatran compared to warfarin in mechanical valve patients 1, 2

Trade-offs Accepted

Risks Inherent to Mechanical Valves

• Annual bleeding risk of 1-2% with appropriate anticoagulation 1
• Persistent thromboembolism risk despite warfarin therapy 1
• Prosthetic valve endocarditis risk 1
• Hemodynamic inefficiency in smaller valve sizes 1
• Potential need for reoperation due to valve thrombosis, tissue ingrowth, periprosthetic leak, or multiple bleeding episodes 1

Engineering Goal Not Yet Achieved

• Although the goal of mechanical valve engineering has been to produce a valve that does not require anticoagulation with warfarin, this has not been achieved 1
• Trials attempting to diminish or eliminate warfarin, or substitute platelet inhibitors, have demonstrated high rates of thromboembolism 1

Clinical Context

When Mechanical Valves Achieve Their Goal

• Younger patients (typically <60-65 years) who can tolerate lifelong anticoagulation benefit most from mechanical valves' durability 3
• Patients already requiring anticoagulation for other conditions (e.g., atrial fibrillation) gain the durability benefit without additional anticoagulation burden 3
• The goal is realized when patients avoid the 40-50% structural valve deterioration rate seen with bioprosthetic valves at 18 years 1