Tricuspid component of first heart sound.

Right and left atrial pressures with a simultaneous external phonocardiogram and standard lead II electrocardiogram were recorded during routine cardiac catheterization in i5 patients. With one exception, the onset of the second (T1) major component of the first sound coincided with the peak of the right atrial c wavejust as the major left-sided component (M1), previously studied in this laboratory, coincides with the peak of the left atrial c wave. Right and left atrial c waves were synchronous in the exception and in that instance separate major components were not identified. These observations provide further evidence that T1 arises at the tricuspid valve. Analogous to the mode ofproduction ofM1, it is believed that after tricuspid valve closure the apposed leaflets are billowed into the right atrial cavity resulting in right atrial c waves, at the peak of which tension on the chordae tendineae and leaflets themselves produces T1. Some factors affecting the timing and intensity ofM1 and T1 are mentioned.