PHONOCARDIOGRAPHY 



713 



duration of this interval has been used clinically to 

 assess the severity of the stenosis of the atrioventricular 

 valve. It has been reasoned that as the stenosis be- 

 comes more severe the atrial pressure rises and this 

 causes an earlier appearance of the opening snap. 

 Whereas there is generally good agreement between 

 the severity of the mitral stenosis and the shortening 

 of the A2-OS interval (aortic closure to opening snap) 

 (79) there are a number of other factors which con- 

 tribute to the duration of this interval. These must be 

 accounted for before any widely applicable formula 

 can be suggested. Such parameters as the presence of 

 abnormalities of the semilunar valve, the pressure at 

 which that valve closes, the rate of decline of ven- 

 tricular pressure, and the presence of coexisting mitral 

 insufficiency must play a part. In our limited experi- 

 ence, the use of this interval in noting the degree of 

 mitral stenosis in absolute terms has been more 

 meaningful when comparison is limited to an indi- 

 vidual subject, as, for example, comparing values ob- 

 tained postoperatively with those noted preoperatively. 

 That there is good agreement between the level of 

 atrial pressure and the appearance time of the opening 

 snap in one subject can also be seen in records ob- 

 tained from patients with atrial fibrillation. Here, with 

 variations in the cycle length there are inverse vari- 

 ations in ventricular filling. A short diastole, which 

 will not allow for as complete emptying of the atrium 

 into the ventricle as a long diastole, leaves atrial 

 pressure higher at the end of the next ventricular 

 systole and consequently causes an earlier appearance 

 of the opening snap. In certain clinical situations, 

 wide splitting of the second sound as well as a proto- 

 diastolic gallop sound may resemble an opening snap, 

 and precise identification may be important. For 

 example, whereas an opening snap is often part of 

 the picture of severe mitral stenosis, a protodiastolic 

 gallop from the left ventricle would not be expected 

 to occur. This is based on the fact that a significant 

 grade of obstruction to ventricular inflow removes the 

 possibility for rapid inflow, a prerequisite for the early 

 gallop sound. Differentiation between these two 

 acoustic events has been alluded to above in the 

 relationship between the gallop sound and the out- 

 ward movement of the ventricle as seen in the low 

 frequency recordings of the chest wall (apex cardio- 

 gram). The gallop sound occurs at the end of the 

 outward movement and the opening snap at the be- 

 ginning. 



Differentiation of an opening snap from the second 

 component of the second sound, usually pulmonic, 

 can be carried out by resorting to fluctuations in 



duration of mechanical systole of the ventricle and 

 left atrial pressure with changes in flow. With increases 

 in flow, as with exercise, the apparent prolongation 

 of right v'entricular systole over that of the left is 

 associated with a wider degree of splitting of the 

 second sound. On the other hand, as noted above, 

 increase in flow cannot be handled well by the stenotic 

 mitral orifice, and as left atrial pressure rises the 

 opening snap occurs earlier. Since the two events 

 move in opposite directions with changes in flow 

 (either increase or decrease) precise identification 

 becomes possible. 



SYSTOLIC CLICKS, SYSTOLIC GALLOPS, AND EJECTION 



SOUNDS. There are a number of abnormal sounds that 

 occur during systole and these have received various 

 names. The current nomenclature is often confusing, 

 probably due in part to imprecise information re- 

 garding the detailed nature of these events. 



First, the term systolic gallop has been used to 

 refer to certain sounds occurring in systole which 

 render a triple rhythm. From the definition of a 

 gallop sound given above, which relates the acoustic 

 event to the rapid phases of ventricular filling, the 

 words "systolic gallop" would seem to be mutually 

 contradictory. Furthermore, since such a use of the 

 word gallop may have the tendency to confuse, it 

 would seem best until more information is gathered 

 to withhold this term from general use as Minhas & 

 Gasul (73) have suggested. 



Second, the term ejection sound has been used to 

 refer to the acoustic event which occurs during the 

 early rapid phase of ventricular ejection. It has been 

 suggested that the sound arises from either great 

 vessel (aorta or pulmonary artery) in situations in 

 which there is dilatation of the vessel and/or hyper- 

 tension in it. It has been said that it is due to a sudden 

 distention of the vessel imparted by the nature of the 

 force of ventricular ejection. For example, in mild 

 degrees of valvular pulmonic stenosis in which there 

 is some dilatation of the vessel immediately beyond 

 the valve (poststenotic dilatation) and in which ven- 

 tricular ejection is not impaired, an early systolic 

 ejection sound can be observed (54). With more 

 severe degrees of stenosis while there is still vessel 

 dilatation, the impairment of ventricular ejection (not 

 in total stroke volume but presumably in the rate of 

 ejection) may not produce an ejection sound (20, 23, 

 55, 108). The exact hemodynamic correlate of the 

 ejection sound and its genesis deserve further investi- 

 gation. There is some question as to whether the 

 event represents an exaggeration of the normally oc- 



