Protection of the myocardium during global ischemia: Is crystalloid cardioplegia effective in the immature myocardium?

Abstract

In pediatric cardiac operations, a high proportion of hospital deaths are believed to result from inadequate myocardial protection during the period of global ischemia. To investigate whether this may be due to an inherently lower resistance to myocardial ischemia or to the failure of conventional cardioplegia to afford adequate protection in the immature heart, we have conducted a series of studies with isolated hearts from neonatal (3 to 5 days old, body weight 6.3 to 13.4 gm) and adult (84 to 112 days old, 260 to 340 gm) rats. The efficacy of cardioplegia was assessed in neonatal hearts (n = 6 per group) subjected to various durations of normothermic ischemia, with and without a 2-minute preischemic infusion of the St. Thomas' Hospital cardioplegic solution. At all times studied, the use of cardioplegia resulted in a greater postischemic recovery of left ventricular developed pressure and first derivative of left ventricular pressure. After periods of ischemia lasting 30, 60, 90, 120, and 150 minutes in the absence of cardioplegia, left ventricular developed pressure recovered to 80% +/- 10%, 66% +/- 11%, 53% +/- 7%, 33% +/- 6%, and 21% +/- 4% of preischemic values, respectively; in the presence of cardioplegia, the values were 89% +/- 6%, 83% +/- 8%, 74% +/- 6% (p less than 0.05), 58% +/- 5% (p less than 0.05), and 41% +/- 7% (p less than 0.05), respectively. The corresponding values for first derivative of left ventricular pressure were 78% +/- 9%, 67% +/- 12%, 54% +/- 7%, 30% +/- 5%, and 19% +/- 3% in the absence of cardioplegia and 92% +/- 7%, 88% +/- 8%, 75% +/- 8%, 56% +/- 5% (p less than 0.05) and 39% +/- 6% (p less than 0.05) in the presence of cardioplegia. In the noncardioplegia groups, 90% of hearts exhibited ischemic contracture (mean time to onset = 24.7 +/- 1.1 minutes), whereas in the cardioplegia groups, only 63% exhibited contracture, and of a significantly delayed onset (37.0 +/- 1.5 min, p less than 0.05). Adult hearts (n = 5) subjected to 30 minutes of normothermic ischemic arrest, in the absence of cardioplegia, recovered 36% +/- 7% of the preischemic left ventricular developed pressure and 37% +/- 9% of the preischemic first derivative of left ventricular pressure on reperfusion; 100% of these hearts exhibited some degree of contracture (mean time to onset = 15.4 +/- 1.1 minutes) by the end of the ischemic period.(ABSTRACT TRUNCATED AT 400 WORDS)