The Journal of Thoracic and Cardiovascular Surgery, Vol 93, 728-740, Copyright © 1987 by The American Association for Thoracic Surgery and The Western Thoracic Surgical Association
Correlation between the linearized Frank-Starling relationship and myocardial energetics in the ejecting heart. Afterload independence and sensitivity to inotropic state
IB Krukenkamp, NA Silverman, A Pridjian and S Levitsky
Previous studies suggest that the relationship between end-diastolic volume
and stroke work calculated as the area of the pressure-volume work loop is
linear, afterload independent, and sensitive to the inotropic state. The
correlation of myocardial oxygen consumption with this stroke work could
provide an integrated measure of cardiac performance and metabolism to
assess perturbations induced by ischemia or pathologic loading conditions.
Fourteen canine hearts instrumented for computerized acquisition of
instantaneous pressure-volume data and quantitation of myocardial oxygen
consumption were studied during progressive volume infusion on right heart
bypass (1.5 to 3.5 L/min in 250 ml/min increments). Data acquisition both
in the control state and during continuous infusion of calcium chloride
(0.03 mEq/kg/min, n = 7) to increase contractility or phenylephrine (2
micrograms/kg/min, n = 7) to alter afterload facilitated the construction
of stroke work versus end-diastolic volume and myocardial oxygen
consumption versus stroke work relationships by least-squares regression
analysis. The cardiac mechanics assessment for this group of dogs confirmed
a highly linear (mean r = 0.984) work versus preload relationship that was
unaffected by changes in afterload but sensitive to increased contractility
(71% increase in slope). The myocardial energetics correlation was also
linear (mean r = 0.939) and demonstrated an increased oxygen utilization
characteristic of the higher inotropic state produced by calcium chloride
infusion (0.047 +/- 0.003 versus 0.070 +/- 0.008 ml oxygen/beat/100 gm left
ventricular weight, p = 0.008). Although phenylephrine administration
produced variable perturbations of myocardial oxygen consumption, the
energetics relationship for this subgroup was not statistically altered by
changes in afterload. The features of this cardiac energetics assessment
suggest its value as a biological marker to evaluate the postischemic,
hypertrophied, or failing heart.
