EFFECTS OF CARDIOPLEGIC ARREST ON LEFT-VENTRICULAR SYSTOLIC AND DIASTOLIC FUNCTION OF THE INTACT NEONATAL HEART

The effects of cardiopulmonary bypass and cardioplegic arrest on left ventricular systolic and diastolic function were studied in 20 intact neonatal lambs instrumented with ultrasonic dimension transducers and micromanometers for collection of left ventricular pressure-dimension data. Group I lambs underwent 2 hours of hypothermic cardiopulmonary b ypass (25 degrees C) alone; group II lambs underwent 2 hours of hypoth ermic cardiopulmonary bypass (25 degrees C) with 1 hour of multidose, cold, crystalloid cardioplegic arrest (St. Thomas' Hospital No. 2 solu tion). The control neonatal lamb left ventricle was found to be relati vely stiff, with the limit of diastolic filling reached at physiologic left ventricular filling pressures, resulting in apparent descending limbs of left ventricular function. After cardiopulmonary bypass, iden tical results were obtained in groups I and II. A significant loss of left ventricular compliance limited left ventricular performance via t wo mechanisms. First, left ventricular preload was significantly decre ased, with a concomitant diminution in left ventricular stroke work; a fterload (pressure work) was maintained at the expense of volume work (flow), which declined significantly. Second, preload behaved as thoug h fixed, resulting in a loss of impedance matching (afterload mismatch ). Although contractility as assessed by the end-systolic pressure-dim ension relationship was significantly increased (because of increased levels of circulating catecholamines), global systolic performance as quantified by the stroke work/end-diastolic length relationship remain ed unchanged, reflecting the afterload sensitivity of the latter param eter in the face of fixed preload. We conclude that cardiopulmonary by pass in the intact neonate results in a loss of compliance and impedan ce matching rather than a loss of contractility; however, the addition of 1 hour of cold, crystalloid cardioplegic arrest results in no dysf unction beyond that attributable to cardiopulmonary bypass alone.