BLOOD CARDIOPLEGIA IN THE SENESCENT HEART

As an increasingly aged population undergoes cardiac surgery, myocardi al protective strategies must address the fundamental differences betw een adult and senescent myocardium. In a test of the hypothesis that s enescent myocardium is less tolerant of cardioplegic arrest, adult (0. 5 to 1.0 years) and senescent (6 to 9 years) sheep underwent 55 minute s of hypothermic blood cardioplegic arrest, A 5-minute dose of termina l warm blood cardioplegic solution was administered followed by 30 min utes of vented reperfusion. Left ventricular volume was monitored by m eans of sonomicrometric crystals in three orthogonal planes, Myocardia l function was assessed with the preload recruitable stroke work relat ionship. Diastolic function was assessed with two techniques: the ''st iffness'' coefficient (beta), derived from the exponential end-diastol ic pressure-volume relationship, and the time constant of isovolumic l eft ventricular pressure decay (tan). Data were acquired before arrest and after the reperfusion period. Contractility in the adult hearts w as well preserved (preload recruitable stroke work: 63.7 +/- 6.1 versu s 56.8 +/- 4.1 mJ/beat per milliliter per 100 gm, prearrest versus pos tarrest, p = not significant). In contrast, senescent heart contractil ity 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) w as prolonged in the adult hearts (42.5 +/- 3.3 versus 48.8 +/- 3.5 mse c 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. Whe n compared with adult hearts, contractility in senescent hearts is poo rly preserved after cold blood cardioplegic arrest. Active diastolic r elaxation, however, is more prolonged in adult hearts. Passive diastol ic properties are unchanged in both groups. Because there are specific age-related differences in tolerance to cardioplegic arrest, extrapol ation of myocardial protective strategies from studies in adult hearts to elderly patients may not be appropriate.