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 longaxis diastolic expansion activity which is present in both hyper- and hypodynamic left ventricular filling.