BLOOD CARDIOPLEGIA IN THE SENESCENT HEART

As an increasingly aged population undergoes cardiac surgery, myocardial protective strategies must address the fundamental differences between adult and senescent myocardium. In a test of the hypothesis that senescent myocardium is less tolerant of cardioplegic arrest, adult (0.5 to 1.0 years) and senescent (6 to 9 years) sheep underwent 55 minutes of hypothermic blood cardioplegic arrest, A 5-minute dose of terminal warm blood cardioplegic solution was administered followed by 30 minutes of vented reperfusion. Left ventricular volume was monitored by means of sonomicrometric crystals in three orthogonal planes, Myocardial function was assessed with the preload recruitable stroke work relationship. Diastolic function was assessed with two techniques: the ''stiffness'' coefficient (beta), derived from the exponential end-diastolic pressure-volume relationship, and the time constant of isovolumic left ventricular pressure decay (tan). Data were acquired before arrest and after the reperfusion period. Contractility in the adult hearts was well preserved (preload recruitable stroke work: 63.7 +/- 6.1 versus 56.8 +/- 4.1 mJ/beat per milliliter per 100 gm, prearrest versus postarrest, p = not significant). In contrast, senescent heart contractility was poorly preserved (56.8 +/- 4.1 versus 35.4 +/- 4.2 mJ/beat per milliliter per 100 gm, p < 0.025). Early diastolic relaxation (tau) was prolonged in the adult hearts (42.5 +/- 3.3 versus 48.8 +/- 3.5 msec prearrest versus postarrest, p < 0.05), whereas the senescent hearts were essentially unchanged (49.3 +/- 3.1 versus 52.3 +/- 4.5 msec, p = 0.35), Myocardial stiffness (beta) was unchanged in both groups. When compared with adult hearts, contractility in senescent hearts is poorly preserved after cold blood cardioplegic arrest. Active diastolic relaxation, however, is more prolonged in adult hearts. Passive diastolic properties are unchanged in both groups. Because there are specific age-related differences in tolerance to cardioplegic arrest, extrapolation of myocardial protective strategies from studies in adult hearts to elderly patients may not be appropriate.