Metabolic characteristics of immature myocardium

Abstract

Myocardial protection has been recognized to have contributed enormously to the improvement of operative results in cardiac surgery, which has been attributed to basic and clinical research aimed at better protective methods in many medical institutions since 1970s. Especially, postoperative outcomes of adult cardiac surgery have recently improved and become stable. In March 2007, the Japanese Meeting of Research for Myocardial Protection, a nationwide annual meeting aimed at improving surgical myocardial protection, was dissolved so a better organization might be formed in an attempt at collaboration among various research fi elds. There was a need for such collaboration because heart research regarding myocardial protection has become methodologically specialized and recently involved in a fi eld of regeneration medicine that may be technically diffi cult for clinicians such as cardiovascular surgeons. Historically, around the world, surgical myocardial protection in adults has been extensively studied, whereas in the fi eld of congenital cardiac surgery (with a higher postoperative mortality compared to adult cardiac surgery) there is no established method for surgical myocardial protection, refl ected in lower research activity in terms of immature myocardium. A discrepancy in myocardial protection during open heart surgery between adults and children has been considered to depend on the differences in myocardial characteristics in various aspects. This background difference between the mature and immature myocardium may raise a question: “Would it be possible to use a cardioplegic solution for mature hearts in congenital heart surgery?” Especially, the infl uence of long-term preexisting cyanosis after birth on the protective effect of a cardioplegic solution should be investigated in detail to establish a method of myocardial protection for congenital heart surgery. Is there any difference in the physiological and biochemical aspects between the mature and immature myocardium? Doenst and Taegtmeyer widely reviewed studies dealing with immature myocardium and reported in detail the difference between the mature and immature myocardium in terms of the effects of energy substrate utilization on ischemic preconditioning. In 1983, Rolph and Jones, in their study using guinea pigs, reported that energy-producing metabolism in the immature myocardium is more dependent on glycolysis than that in the mature myocardium. In 1991, Lopaschuk et al. concluded that in human myocardium glycolysis is the predominant source of ATP production immediately after birth. Grosso et al. reported in 1992 that less 5′nucleotidase activity in the immature myocardium is associated with more preservation of high-energy phosphate. Bolling et al. demonstrated in 1992 that it resulted in enhanced myocardial protection, and Pridjian et al. reported in 1994 that the cardioprotective effect of inhibiting 5′-nucleotidase activity may have developmental changes. Myocardium produces ATP and uses it as an energy source. Energy substrates for ATP production include fatty acid, glucose, and lactate. Fatty acid is a main energy substrate in the mature myocardium, whereas glucose is the main one in immature myocardium. This difference is known to be caused by differences in the Received: 17 July 2009 © The Japanese Association for Thoracic Surgery 2010