Relationship of the fourth heart sound to atrial systolic
transmitral flow deceleration.
McGuire, Abigail Manson, Michael T. Hagley, Andrew F. Hall, and
S[acute]andor J. Kov[acute]acs.
Cardiovascular Biophysics Laboratory, Barnes-Jewish Hospital,
Washington University Medical Center, St. Louis, MO. 63110
APStracts 3:0406H, 1996.
The fourth heart sound is thought to be due to cardiohemic vibrations
powered by deceleration of transmitral blood flow, which occur when
atrial systole leads to a disproportionately high rise in ventricular
end-diastolic pressure (relative to diastasis), associated with an
enhanced atrial systolic blood filling volume or a stiff ventricular
wall. To characterize S4 production, we modelled the cardiohemic
system as a forced, damped, nonlinear harmonic oscillator. The
forcing term used a closed-form expression for the Doppler A-wave
contour. We simultaneously recorded transthoracic phonocardiograms
and Doppler A-waves in subjects with and without audible S4's and
compared the model's predictions for S4 amplitude, frequency and
power spectrum to those of the recorded S4's. Excellent agreement was
observed between the model predicted amplitude, duration, timing, and
power spectrum to those of the phonocardiographic S4. We conclude
that, with a normal mitral valve, there should always be an
oscillation of the cardiohemic system during A-wave deceleration.
However, oscillations may not have high enough amplitude, frequency,
or coupling to the chest wall to be clinically audible as an S4.
Received 30 June 1995; accepted in final form 2 August 1996.
APS Manuscript Number H602-5.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 7 October 1996