Prosthetic valves are divided into two basic groups: mechanical and bioprosthetic. Mechanical valves are more durable with lower failure rates but have a higher risk for thromboembolic complications. Life-long anticoagulation is necessary to reduce the thrombotic risk. Bioprosthetic valves, from porcine, bovine, or human sources, are less thrombogenic but are more likely to fail and require repeat surgery.
Systemic thromboembolism is a common complication of mechanical heart valves. Without anticoagulation, the risk of valve thrombosis or thromboembolism is about 8%, and falls to 1% to 2% per year with anticoagulation.20,21 Embolic risk is highest during the first 3 postoperative months, and emboli are more common from mitral rather than from aortic valves. Antiplatelet therapy is recommended for all patients with prosthetic valves. In all patients with mechanical valves, lifelong anticoagulation is recommended.10 The rate of bleeding complications is dependent on the type and intensity of anticoagulation. Major bleeding complications from warfarin occur in approximately 1.4% of prosthetic valve patients per year.22
Prosthetic valves may malfunction in a number of ways, including thrombosis, dehiscence of sutures, gradual degeneration, or even sudden fracture. Symptoms are often slowly progressive, but in acute failures, severe symptoms and death may occur before corrective surgery can be accomplished.
Prosthetic valve endocarditis occurs in up to 6% of patients within 5 years of surgery.23 Early cases (within the first year) are more commonly caused by Staphylococcus epidermidis and S. aureus.24 Late cases of endocarditis are caused by similar organisms as those affecting native valves.24 The most frequent organism is Streptococcus viridans, but Serratia and Pseudomonas are also implicated. Regardless of source, prosthetic valve endocarditis carries a high mortality rate.25
Although valve replacement relieves valvular obstruction and regurgitation, cardiac remodeling persists, and many patients have persistent cardiac symptoms after valve replacement. Long-standing volume or pressure overload leads to ventricular dysfunction, and many patients continue to have dyspnea and symptoms of heart failure. Patients are also likely to have concomitant coronary artery disease, systemic hypertension, or atrial fibrillation.
Symptoms of prosthetic valve dysfunction depend on the type and location of the valve. Patients with prosthetic valves experience some symptoms specific to the presence of the artificial valve. Thromboembolism may cause systemic symptoms such as transient neurologic symptoms, amaurosis fugax, or self-limited ischemic episodes in the extremities or organs. Major embolic events include stroke, mesenteric infarction, or sudden death. Prophylaxis against thrombotic complications of prosthetic valves with systemic anticoagulation may cause major bleeding, with hemorrhagic stroke being the most common lethal bleeding complication.
Acute onset of respiratory distress, pulmonary edema, and cardiogenic shock may be associated with mechanical valve failure, tearing of a bioprosthesis, or a large clot obstructing the valve or preventing closure. Failures often result in sudden death before corrective surgery can be done. A paravalvular leak also presents with congestive heart failure. The severity of symptoms is dependent on leak size and how rapidly the leak develops. Slowly progressive development of heart failure may occur with gradual accumulation of a prosthetic valve thrombus.
Patients with bioprostheses usually have a normal S1 and S2, with no abnormal opening sounds. Mechanical valves normally have a loud, clicking, metallic sound associated with valve closure. Systolic murmurs of prosthetic aortic valves are common, but loud diastolic murmurs should be considered pathologic. A "quiet" mechanical valve is concerning. A loud holosystolic murmur indicates prosthetic mitral valve dysfunction. Aortic bioprostheses usually cause a short mid-systolic murmur, and mitral bioprostheses may cause a short diastolic rumble.
DIAGNOSIS OF PROSTHETIC VALVE DYSFUNCTION OR COMPLICATIONS
Think of potential prosthetic valve dysfunction in any patient with a valve replacement and new or progressive dyspnea, congestive heart failure, decreased exercise tolerance, or chest pain. Suspect thromboembolism, septic embolism, or intracranial hemorrhage in any patient with a prosthetic valve and new focal neurologic deficit. Finally, consider endocarditis in prosthetic valve patients with persistent fever or fever without a clear source.
Echocardiography is the diagnostic test of choice. Chest radiography lacks sensitivity and specificity but may show a change in valve position or signs of heart failure. Obtain a head CT in patients with focal neurologic deficits to evaluate for hemorrhage or embolic stroke. Patients on warfarin may require a complete blood count and coagulation studies. Obtain blood cultures for suspected endocarditis.
TREATMENT AND DISPOSITION
Emergency treatment for acute prosthetic valve dysfunction requires cardiology and cardiothoracic surgery consultation. Emergent surgery and thrombolytic therapy are potential therapies for acute valve thrombosis. Lesser degrees of obstruction should be treated by optimizing anticoagulation. Obtain consultation before discharging a patient with suspected prosthetic valve dysfunction.
REVERSAL OF ANTICOAGULATION WITH PROSTHETIC VALVES
Management of patients with prosthetic valves in the ED requires knowledge of the recommendations on anticoagulation and reversal of excessive anticoagulation. Mechanical mitral valves require an INR of 2.5 to 3.5, whereas bileaflet mechanical valves in the aortic position require an INR of 2.0 to 3.0.3,10 Aspirin is recommended for all patients with prosthetic valves—mechanical or bioprosthetic.10
For the emergency physician, the greatest dilemma regarding anticoagulation is not who should be on anticoagulation, but how to treat supratherapeutic anticoagulation with or without bleeding. An INR >5 poses a significant risk of excess bleeding, but rapid changes in anticoagulation pose an equally ominous risk of valve thrombosis and thromboembolism. Patients with an INR of 5 to 10 without bleeding may be treated by withholding warfarin or administering 1.0 to 2.5 milligrams of oral vitamin K. Patients with severe bleeding complications are best treated with fresh frozen plasma or prothrombin complex concentrate.3 Avoid parenteral, high-dose vitamin K due to risk of overcorrection.9