The phonocardiographic characteristics of the porcine bioprosthesis in the aortic position were evaluated in 24 asymptomatic patients. A medium to high frequency early systolic sound (AO) was present in 16 of 24 patients; abrupt "halting" of the stiff cusps of the porcine bioprosthesis during early left ventricular ejection seems to be the likely mechanism for the genesis of this sound. An unusually high amplitude aortic closing sound (AC) was present in all patients. A high frequency crescendo-decrescendo systolic murmur in early to mid systole was present in 22 patients. Possible mechanisms for the systolic murmur include: 1) altered resonating properties of the cusps, 2) functional bioprosthetic stenosis, and 3) the presence of a flexible stent.
An early systolic opening sound preceding a short systolic murmur and a loud closing sound are common phonocardiographic findings of an uncomplicated porcine bioprosthesis in the aortic position. Therefore, absence of the aortic opening sound, alterations in the amplitude of the aortic closing sound, or an increase in the length of the systolic murmur may suggest bioprosthetic malfunction.