THE EFFECTS OF CARDIOPLEGIC ARREST AND REPERFUSION ON THE MICROVASCULATURE OF THE HEART

Objectives: Despite laboratory evidence of leucocyte involvement in re perfusion injury, cardiac surgical clinical trials do not support the therapeutic effectiveness of leucocyte filtration. Furthermore, the di rect effects of crystalloid cardioplegia and reperfusion on the capill aries of the heart have yet to be elucidated. We tested the effects of cardioplegic arrest and reperfusion both with and without leucocyte d epletion, in a model of cardiopulmonary bypass that mimics clinical ca rdiac surgical conditions. Methods: Four groups of Landrace pigs were studied. Group A (n = 6) underwent 30 min of hypothermic (28 degrees C ) cardiopulmonary bypass. Groups B (n = 6), C (n = 6) and D (n = 6) al so had 90 min of cardioplegic arrest. Group C was then reperfused with whole blood, while Group D was reperfused with leucocyte-depleted blo od. Microvascular methylmethacrylate corrosion casts were made at the end of the experimental period. Myocardial vascular anatomy was define d by electron microscopy and capillary abundance derived from this and from the weight of casts from representative areas. Leucocyte deposit ion was assessed using radioisotope-labelled leucocytes. Ischaemic dam age to tissues was graded according to light and electron microscopic findings. Results: In Group A the mean (+/-S.D.) vascular cast weight/ volume of myocardium (density) was 125 +/- 9 mg/mm(3). After cardiople gic arrest (Group B), it fell to 74 +/- 7 mg/mm(3) (P < 0.0001) due to absence of capillaries, although arterioles, venules and non-nutritiv e bypass vessels remained patent. Following reperfusion with whole blo od (Group C), capillary numbers partially recovered but luminal diamet ers were reduced with a cast density of 94 +/- 5 mg/mm(3) (P < 0.0001 versus Group A and B). Leucocyte-depleted (87-92%) reperfusion in Grou p D did not affect cast density (90 +/- 3 mg/mm(3); P = 0.17). Coronar y vascular resistances in Groups C and D rose slightly, but not signif icantly, during reperfusion. Conclusions: Following cardioplegic arres t, microvascular changes are marked. These changes are partially rever sed by 30 min reperfusion. Leucocyte depletion does not ameliorate the se effects in this model. (C) 1997 Elsevier Science B.V.