Lethal degeneration of a silicone rubber ball of a Starr-Edwards mitral prosthesis implanted for 78 months occurred. Variance of mitral silicone rubber poppets requires longer periods of implantation than required for degeneration of aortic poppets. Syncope or near syncope and congestive cardiac-failure appearing more than four years after mitral replacement with a silicone rubber poppet suggests ball variance. Alterations in intensity of the opening sound of the mitral prosthesis in the absence of arrhythmias further suggests this diagnosis.
Roberts WC, Levinson GE, Morrow AG. Lethal Ball Variance in the Starr-Edwards Prosthetic Mitral Valve. Arch Intern Med. 1970;126(3):517-521. doi:10.1001/archinte.1970.00310090147021