Left intraventricular pressure-impedance diagrams (DPZ) to assess cardiac function. Part II: determination of end-systolic loci.

UNLABELLED: By means of tetrapolar intraventricular impedancimetric measurements and by modifying the aortic impedance with a brief volume unit step afterload increase, with a balloon catheter, we obtained the geometric locus of the end-systolic pressure-admittance points (PES-YES) from the beat to beat pressure-impedance diagram (DPZ), usually three or four beats after inflation. Six experiments in five anesthetized mongrel dogs (average weight 21.6 kg, SD 2.5) were carried out under control conditions and after a slow infusion (4 micrograms/kg/min) of epinephrine to change the myocardial inotropic state. In control, the PES-YES points fell in all cases on a straight line (average correlation 0.968, SD 0.033). After epinephrine, linearity was still good in four experiments (average correlation 0.938, SD 0.059). All animals showed displacements of the regression lines after epinephrine with respect to control. However, the direction of the shifts was not always consistent: three dogs yielded an upward-leftward shift; one showed a crossing point between the two regression lines with an increase in slope after epinephrine; in the remaining two experiments (same dog in different days), the post-epinephrine regression lines of the pressure-admittance end-systolic points were displaced downwards and rightwards. Five out of the six experiments increased the slopes of the lines after infusion of epinephrine. IN
CONCLUSION: the method supplied the end-systolic point locus obtained from simple cardiac catheterization and this locus was altered by inotropic intervention.