The mitral valve separates the left upper chamber of the heart (atrium) from the left lower chamber (ventricle). In mitral regurgitation this valve does not close properly, which causes some blood to backwash into the heart from the left ventricle instead of being pumped out to the rest of the body. The left atrium typically enlarges due to this pressure, and as a result of this compensation the patient may not experience symptoms initially. As the disease progresses, symptoms may include fatigue, exhaustion, light-headedness, shortness of breath and heart palpitations.
Mitral regurgitation of moderate degree or more is frequent, particularly in the aging population. It is estimated that 2 to 2.7 million Americans are afflicted by this condition and that this number will rise to 3.8 to 4.8 million Americans by 2030.
The Mayo Clinic researchers used Doppler echocardiography - ultrasound images of the heart and its blood flow patterns - to determine which physical characteristics predicted patient outcomes. Age and diabetic status were strongly associated with poorer outcomes. However, the most important finding was that the effective regurgitant orifice area - the cross-sectional size of the jet stream of blood backwashing into the atrium - was the strongest determinant of outcome.
Patients with a regurgitant orifice larger than 40 mm2 who were treated only with medication were more than five times more likely to die than those with the same severity of regurgitation who underwent valve repair surgery.
Dr. Sarano says the quantitative data from this study, combined with advances in surgical techniques and improved surgical results, help define at what severity of regurgitation patients should strongly consider valve surgery.
"The mortality for valve surgery is very low, but it is not zero," Dr. Sarano explains. "Previously, with patients who were asymptomatic, we had no well-defined quantitative method to determine when the risk of continuing to rely on medication alone exceeded the risk of surgery. Now we have a threshold established through this large study, where continuing medical management carries a much higher risk and surgery can restore normal life expectancy."
Dr. Sarano says the study has important implications for patients and the physicians who treat them. "We examined dozens of variables in this study, and the one physical measurement that strongly predicted survival was regurgitant orifice," he explains. "Patients should be aware that severe mitral regurgitation increases their risk of dying even if they don't have symptoms, and that now we have a measurement technique to determine how severe is too severe and who benefits the most from early intervention."
Other authors of the paper include Jean-Francois Avierinos, M.D.; David Missika-Zeithoun, M.D.; Delphine Detain, M.D.; Maryann Capps; Vuyisile Nkomo, M.D.; Christopher Scott; Hartzell Schaff, M.D. and A. Jamil Tajik, M.D., all of Mayo Clinic.