Perfusate calcium: effect on cardiac stability and response to ischemia and reperfusion

The aim of this study was to characterize the relationship of perfusate calcium concentration, contractile state and stability of the isolated crystalloid perfused working rat heart preparation, to ischemic duration and functional recovery, at a physiological perfusate calcium concentration.

In the first protocol, hearts (n = 6 per group) were aerobically perfused for up to 300 mins with Krebs Henseleit solution containing calcium concentrations (total) of 1.0, 1.2, 1.4, 1.6, 1.8 and 2.5 mmol/L (equivalent to ionized concentrations of 0.76, 0.94, 1.15, 1.21, 1.58 and 2.25 mmol/L, respectively). After 120 mins, aortic flow decreased by less than 20% in all preparations except those perfused with 1.0 mmol/L, which fell by over 60%. For subsequent studies, a calcium concentration of 1.4 mmol/L (ionized calcium 1.15 mmol/L, a value equivalent to plasma ionized calcium) was identified as ideal and shown to be associated with stable function and adequate inotropic reserve. The second protocol was as follows: In additional studies (n = 6 per group), the relationship between normothermic global ischemic duration (with or without cardioplegic arrest) and post ischemic functional recovery was characterized. Increasing the ischemic duration (10, 15, 20, 25, 30, 35 or 40 mins) progressively impaired recovery of aortic flow to 86.7 +/- 3.2%, 71.7 +/- 4.9%, 27.7 +/- 5.0%, 14.5 +/- 12.3%, 0%, 0% and 0%, respectively, in the noncardioplegia group, and to 84.7 +/- 1.7%, 85.0 +/- 2.9%, 78.0 +/- 2.4%, 56.0 +/- 7.8%, 32.2 +/- 6.0%, 6.5 +/- 3.7% and 0%, respectively, in the cardioplegia group. These results were similar to those of previous studies in which 2.5 mmol/L calcium was used in the perfusate.

Perfusion of isolated hearts with perfusate calcium concentrations up to 2.5 mmol/L (total) had no apparent detrimental effect on the stability of the preparation; however, a calcium concentration of 1.0 mmol/L resulted in a rapidly deteriorating preparation. In addition, under the conditions prevailing in the present study, a perfusate calcium content within the physiological range (1.4 mmol/L) appeared not to alter the vulnerability of the rat heart to injury during ischemia and reperfusion.