Origin of the third heart sound: comparison of ventricular wall dynamics in hyperdynamic and hypodynamic types.

To investigate the left ventricular wall dynamics conducive to the third heart sound (S3) in both hyper- and hypodynamic filling conditions, eight dogs were studied in which an S3 was produced by hypoxemia and in eight others by acute mitral regurgitation. Pulse transit sonomicrometry crystals were used to measure external left ventricular dimension dynamics in the two principal axes. A miniature accelerometer was used to detect the epicardial S3 vibration. The development of the S3 was invariably associated with an increased peak velocity of long-axis external dimensional expansion in early diastole. This enhanced long-axis filling activity was not dependent on increased global chamber or short-axis filling dynamics and sometimes occurred when global filling rate was unchanged. In addition, the short-axis filling rate was sometimes reduced as the S3 developed. It is concluded that the common denominator of S3 generation in this acute dog model is exaggerated long-axis diastolic expansion activity which is present in both hyper- and hypodynamic left ventricular filling.