The mechanism of the generation of the third and fourth heart sounds. Circulation

past have prevenited a preeise correlation of initracardiae pressure events and sounid 1)ro(IuetioIl in relation to the third anid fourth hleart souniids. The thlird hieart sounid (S8) and its exaggerated counter)art, the ventricular or)rotodiastolic gallop, occur during rap)id early diastolic venitricular fillingr. Earlier ini-vestigators have suggested that pressure waves produced by rapid ventricular filling reflect off the ventric-ular wall possibly retens-inge arid reclosingr the atriovelltricular (AV) v<atve.s g,,eneratingr the thlird lbeatt sounid.-3 If this takes place, ventricular pressure slhould exceed atrial pressure during the oceiurrence of this sound. likewise, witlh shiultanieouis technlies, the third sounid should be reeorded withini both the ventricle amid atriumii with the suddeni tensing or reclosure of the valves (fig. 111). Recenit correlations fromii externial)110-nocardiography aInd eardiac. c<atheterization sun("ests that atrial pressure exceeds ventritnc ular pressure durinig the occurrence of both the tlhird and fourth lheart sound(is amid sl-gests that these sounids occur duringy (ntiin-nted ventricular fillinig. Sinee atrial pressutre ext-eeeded ventricular pressure, it seems valid that the AV valves ar e open.4 A previous study hlas suggested that a wave of rapid venitricular filling was inidispenlsable for- this sounid.3l This evideniee strongly supp)orts the eoneept that the third lheart soilld or- yen-tricuilr filling souInd is related to rapid early liastolic fillincg with the prodluctioni of venl-t rieular miuscular vibrations (fig. lA). rrhe fourth lheart sounid ( 84) or its path-ologie counterpart, the presvstolic gallop, lias From the Departnents of Medicinie aind Surgery