FUNCTIONAL CHARACTERISTICS OF THE LEFT VENTRICULAR INFLOW AND OUTFLOW TRACTS.

Abstract

Simultaneous pressures were recorded from the left ventricular inflow and outflow tracts in 14 dogs. In 10 the inflow tract entered systole 4 to 18 msec before the corresponding outflow tract. In 12 additional animals, differential pressure recordings from the two tracts confirmed precedence in the inflow tract. In four animals, strain gauge recordings from the epicardial surfaces of the inflow and outflow tracts exhibited asynchrony with precedence in the inflow tract. Hearts excised from freshly-sacrificed animals or hearts stopped in diastole by KCI infusion showed a single, openly-communicating ventricular chamber. In contrast, hearts arrested in systole by infusion of CaCl 2 revealed a separation of the left ventricle by the apposition of the anterior and posterior papillary muscles and the dependent mitral valve leaflet. The apparent conduction velocity of an impact pressure wave from inflow to outflow tract depended upon the portion of the cardiac cycle during which it was delivered. From a maximum of 14 M/sec in mid and late diastole, it decreased to 6.9 M/sec in early systole and 5.5 M/sec in early diastole. Complete attenuation of pressure wave transmission often occurred during maximum systole. These data support the concept that the left ventricle may become separated, during systole, into an inflow and outflow tract. It appears that the division is accomplished by a change in the systolic ventricular architecture, with apposition of the anterior and posterior papillary muscles and the downward movement of the mitral valve leaflets. It is probable that this phenomenon is functional in hearts working near the lower limits of their systolic reserve.