The Journal of Thoracic and Cardiovascular Surgery, Vol 97, 870-877, Copyright © 1989 by The American Association for Thoracic Surgery and The Western Thoracic Surgical Association
Physical and mechanical effects of cardioplegic injection on flow distribution and myocardial damage in hearts with normal coronary arteries
JE Molina, CA Galliani, S Einzig, R Bianco, T Rasmussen and R Clack
Department of Surgery, University of Minnesota, Minneapolis.
The physical and mechanical effects of injecting crystalloid cardioplegic
solution under various pressures and flows was studied (in canine hearts)
to establish a safe method for administering it in the presence of normal
coronary arteries. A constant pressure system (300 mm Hg = 15 psi) was
maintained in the solution reservoir, and flows and pressures were varied
with the use of cannulas of different inner diameters: 0.8, 1.35, 1.6, 2.3,
2.58, and 2.80 mm. Cardioplegia distribution was measured by 15 microns
radioactive microspheres. Peak flow rate, total flow, and mean flow rate
per infusion were measured by an inline electromagnetic flowmeter probe.
Direct aortic root pressure, time to standstill, and myocardial
temperatures were recorded by continuous monitoring. Cardiac isoenzymes
were measured in the coronary sinus, peripheral blood, and directly in the
myocardial tissue. Histologic changes in the left ventricle were examined
by light microscopy. The results showed that the higher the flow and
pressure, the shorter the prearrest period, the better the flow
distribution, and the faster the myocardial temperature drop. Mean aortic
root pressures higher than 110 mm Hg and peak flow rates greater than 1500
ml/min caused a higher incidence of mechanical-physical trauma to the
vascular endothelium and the endocardium, but cellular protection was good.
Low pressure (less than 30 mm Hg) and peak flows (less than 125 ml/min)
showed a higher incidence of cellular (myocardial) ischemia, focal
necrosis, and uneven flow distribution. An aortic root pressure of 61 +/- 5
mm Hg, a mean peak flow rate of 622 +/- 52 ml/min, and a total flow of 600
ml for the first injection seem to offer the best cellular protection with
minimal physical injury to the endothelium and endocardium for a mean
canine heart weight of 236 gm.
