Atypical systolic clicks produced by prolapsing mitral valve masses

Mid- or late-systolic clicks were originally thought to be extracardiac in origin.¹ It was not until the 1960s that these clicks were demonstrated by angiography to be associated with late systolic prolapse of the mitral valve and mitral regurgitation.² This was subsequently confirmed by intracardiac phonocardiographic recording of clicks and late systolic murmurs in the left (but not the right) atrium.³ Since that time, occasional cases of mid- and late-systolic sounds have been described in the absence of mitral valve prolapse. These include a left ventricular tumor prolapsing into the left atrium,⁴ a right ventricular tumor prolapsing across the pulmonic valve,⁵ right atrial myxomas "plopping" in and out of the right ventricle,⁶ severe aortic regurgitation⁷ and prolapse of the tricuspid valve.⁸ The present report reviews a previous case we described of a midsystolic click produced by a prolapsing prosthetic mitral valve vegetation⁹ and describes 2 additional cases of atypical midsystolic clicks associated with prolapsing mitral valve masses. We propose that the mechanism of sound production was the same in all 3 cases and was associated with abrupt movement of a mitral leaflet toward the left ventricle during "disengagement" of the mass from the mitral valve apparatus, and prolapse into the left atrium.