VASCULAR AND CONTRACTILE FUNCTION AND TISSUE METABOLITES AFTER PROLONGED HYPOTHERMIC ISCHEMIA AND REPERFUSION - COMPARISON OF SINGLE-DOSE VERSUS MULTI-DOSE INFUSIONS WITH 2 CARDIOPLEGIC SOLUTIONS IN BLOOD-PERFUSED NEONATAL PIG HEARTS

The effects of single- and multi-dose cardioplegia on post-ischaemic v ascular function and contractile activity were compared in 69 blood-pe rfused neonatal pig hearts, as were the protective properties of two d ifferent cardioplegic solutions. Hearts (n=6 or 9 per group) from neon atal (3-5 days old) pigs were excised, arrested with a 2 min infusion (at 15 degrees C) of St Thomas' Hospital cardioplegic solution number 1 (STH1) or number 2 (STH2), and then maintained in a state of hypothe rmic (15 degrees C) ischaemia for 6 or 8 h. Hearts in the multi-dose g roups received cardioplegia every hour (2 min at 15 degrees C). At the end of ischaemia all hearts were reperfused (60 +/- 2 mmHg perfusion pressure) for 40 min with blood from a support pig. Systolic and diast olic functions were assessed with an intraventricular balloon, and end othelial and smooth muscle functions by measuring the response to infu sions of defined concentrations of acetylcholine (8, 16 and 32 mu g/mi n) and glyceryl trinitrate (40, 80 and 160 mu g/min). Hearts (n=9) not subjected to ischaemia were perfused for the same duration to act as aerobic controls. At the end of the perfusion period, hearts were froz en and taken for metabolite analysis. After 8 h ischaemia, the recover y of left ventricular developed pressure was greatest: in the multi-do se STH1 and single-dose STH2 groups (113 +/- 6 and 117 +/- 6 mmHg, res pectively, nu 128 +/- 9 mmHg in aerobic controls, at an end-diastolic pressure of between 3 and 9 mmHg; P=N.S.) and the poorest in the singl e-dose STH1 group (92 +/- 5 mmHg; P<0.05 nu controls). The recovery of diastolic function was greatest in the multi-dose STH2 group and agai n poorest in the single-dose STH1 group (left ventricular end-diastoli c pressure 1 +/- 2 and 30 +/- 10 mmHg, at a ventricular volume of 3,0 ml, nu - 1 +/- 1 mmHg in aerobic controls). Vascular responses to acet ylcholine and glyceryl trinitrate and the myocardial high-energy phosp hates content were better preserved in multi-dose groups and with STH2 . Inter-group differences were less when the duration of ischaemia was reduced to 6 h. In conclusion, the neonatal pig heart was best presen ted with multi-dose cardioplegia and STH2 was more efficacious than ST H1. However, not all indices were optimally protected by multi-dose ST H2. Thus, the best protection of systolic function was obtained with m ultidose STH1 and this was followed by single-dose STH2. Diastolic fun ction was best preserved with multi-dose STH1 as were vascular functio n and high-energy phosphates. (C) 1995 Academic Press Limited