Risk/Benefit Comparison of Mechanical and Biologic Valve Replacements
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Risk/Benefit Comparison of Mechanical and Biologic Valve Replacements

Team Representative:
Joseph Woo, MD
Professor and Chair of  Cardiothoracic Surgery, Stanford Medicine
E-mail: joswoo@stanford.edu
Phone: (650) 725-3828

Media Contact:
Kris Newby
E-mail: krisn@stanford.edu
Phone: 650-867-8862

Summary of findings in layman's terms: 

Deciding between a mechanical and biologic prosthesis to replace a diseased heart valve is a complicated discussion that takes place on a daily basis between the patient and surgeon. While mechanical valves may last a lifetime, they come with an increased risk of blood clots necessitating the use of the blood thinner warfarin. On the other hand, biologic valves, which are made from pig or cow tissue, do not increase the risk of either bleeding or clotting but will wear out sooner. When the valve wears out, a potentially dangerous second surgery is often necessary. As a result, the discussion between the patient and surgeon has to take into account both lifestyle and expected life-span. Experts offer little guidance on the safe age at which to offer biologic valves to patients, and most of the available evidence is outdated.

In this study, researchers found that mechanical heart valves may be safer in younger patients, because patients lived longer despite the need for blood thinners. They also found that among patients 50-70 years old, the best choice can hinge on which valve is being replaced—a finding that has been under appreciated in the past. This study shows that a mechanical valve is actually beneficial for mitral valve replacement until the age of 70. For patients undergoing aortic valve replacement, the benefit of implanting mechanical valves ceased after the age of 55.

Given the potentially life-altering implications of the choice between mechanical and biologic heart valve prostheses, patients and their surgeons need the appropriate information to make these decisions on an individualized basis. This study was the first of its kind to provide large-scale real-world accounting of the tradeoff between these two approaches. 

Specific biological innovation of study:

Heart valve replacement is a common operation, but national practice guidelines do not distinguish between the aortic-valve and the mitral-valve. Mechanical valves are recommended in persons younger than 50 years of age, biologic valves in persons older than 70 years of age, and either type is considered reasonable for persons 50 to 70 years of age. However, these guidelines are based, in part, on data from underpowered, randomized trials of now-obsolete valves that were implanted more than 30 years ago. 

To compare the long-term risks and benefits of mechanical versus biological heart valves, researchers examined rates of mortality, stroke, bleeding and reoperation in patients who underwent heart-valve surgery at 142 hospitals in California between 1996 and 2013. Patient records were obtained from the California Office of Statewide Health Planning and Development databases. Researchers then examined the records of 9,942 patients who underwent aortic-valve replacement and 15,503 patients who underwent mitral-valve replacement during the study period. Their investigation contains the largest number of patients ever studied to examine this issue. From a clinical science perspective, the authors demonstrate how “big data” can be appropriately used—with the aid of advanced statistical methods—to answer important clinical questions when a randomized study is infeasible.

Patients receiving mechanical valves had better survival up until age 70 if the mitral-valve was replaced; patients receiving mechanical valves had better survival up until age 55 if the aortic-valve was replaced. These thresholds provide strong evidence that guidelines should be changed and that the trend towards replacing most valves with biologic prostheses should be tempered. Beyond the differences in mortality, patients receiving mechanical valves had a lower risk for repeat operations but had an increased risk of bleeding. 

Potential impact on patient care and/or how the findings contributed to an improved understanding:

In patients undergoing aortic-valve or mitral-valve replacement, either a mechanical or a biologic prosthesis can be used. Age has traditionally been a major factor in deciding between the two choices. More recently, biologic prostheses have been increasingly favored in younger patients given the desire to avoid blood thinners despite the existence of limited evidence to support this practice. This study is the first to provide solid evidence that surgeons and patients may have been moving too quickly away from mechanical valves. In many cases, this new information contradicts the recommendations in the national guidelines, which may have to be updated based on these findings.

Significant valve disease affects approximately 2.5% of Americans. The disease can be present at birth or result from infections, heart attacks, general wear-and-tear, or other heart conditions. When a valve becomes so diseased that it impedes the delivery of blood to the body, open-heart surgery to replace the valve with a new one generally is recommended. According to the Society of Thoracic Surgeons, one of the national societies of cardiac and thoracic surgeons more than 100,000 people in the United States undergo valve surgery each year. Given the broad impact, this study’s findings have the potential to substantially reduce mortality and second surgeries for this large patient population by helping patients and surgeons make appropriate decisions with respect to the type of valve to implant. 

Journal citation: 

Mechanical or Biologic Protheses for Aorta-Valve and Mitral-Valve Replacement Andrew B. Goldstone, M.D., Ph.D., Peter Chiu, M.D., Michael Baiocchi, Ph.D., Bharathi Lingala, Ph.D., William L. Patrick, M.D., Michael P. Fischbein, M.D., Ph.D., and Y. Joseph Woo, M.D.

N Engl J Med 2017; 377:1847-1857, November 9, 2017, DOI:10.1056/NEJMoa1613792