Relationships of Left Ventricular Systolic Time Intervals with Hemodynamic Variables in Intact and Failing Hearts

Deviation of systolic time intervals (STI) from the regression lines obtained from 122 normal subjects was studied in 22 healthy adults (Group 1), 18 N.Y. functional class I cardiac patients (Group II) with ischemic (IHD) or primary myocardial disease (PMD), and 15 similar patients (pts) but N.Y. functional class II with prior heart failure (Group III). STIc (corrected for heart rate) were normal in Groups I and II. Supine exercise caused shortening of pre-ejection period PEPc and prolongation of left ventricular ejection time ETc in both groups. Group III pts had a significantly longer PEPc and shorter ETc at rest. Supine exercise caused further prolongation of PEPc and a slight prolongation of ETc in this group. In 8 mongrel dogs, the effect of controlled changes of hemodynamic variables on STI was studied with intact hearts and repeated after myocardial impairment has been induced by pentobarbital. Doubling of venous return while the heart was intact produced changes in STI similar to the effects of supine exercise in Groups I and II human subjects. With myocardial impairment, comparable increase in venous return had an effect on STI similar to the effect of supine exercise Group III patients. Controlled increase in each of heart rate or blood pressure, with other hemodynamic variables kept constant, produced changes in STI different from the effect of supine exercise on human subjects. The study suggests that the value of supine exercise induced changes in STI in reflecting left ventricular performance is attributable primarily to increased volume load. In this resepct supine exercise is probably superior to other forms of exercise in disclosing impaired left ventricular performance.