WHAT IN-VITRO METHOD SHOULD SURGEONS USE TO EVALUATE THE CLINICAL BEHAVIOR OF ARTERIAL BYPASS CONDUITS

Surgeons have traditionally relied on ring preparations to predict how arterial bypass conduits will behave in the postoperative circulation . Objective: This study compared pharmacologic [norepinephrine (NE) ch allenge] and physiologic [arterial preload] responses of gastroepiploi c (GEA) and internal thoracic (ITA) arteries in a standard static ring preparation and a dynamic perfusion system. Methods: Six GEAs (1.0-1. 5 mm dia.) and six ITAs (1.5-2.0 mm dia.) 11 cm long were harvested fr om adult pigs and mounted on a computer controlled perfusion system. i nflow pressure was set at 80 mmHg and outflow resistance was adjusted to simulate high (80-90 ml/min) and low (15-20 ml/min) flow demands. N E response (10(-9)-10(-5) M) was measured under low flow conditions an d at high flow conditions when distal arterial pressure (load) was red uced. NE response (10(-9)-10(-5) M) was also evaluated in arterial rin gs (ITA N = 6, GEA N = 6) with tensions adjusted to simulate the lends occurring at low flow (50 mmHg) and high flow (60 mmHg) situations, R esults: In the static ring preparation, NE response [ED50] was similar for both GEA and ITA and was not affected by load. The dynamic prepar ation demonstrated that the GEAs were significantly more responsive to NE than the ITAs [ED50 high flow: ITA 6.1 +/- 0.3*, GEA 7.2 +/- 0.3* *, *P < 0.05 versus baseline, **P < 0.05 versus low flow values, ***P < 0.05 versus ITA]. Furthermore, in the dynamic preparation, NE respo nse nas profoundly affected by reduced load which occurs under high fl ow conditions [7.18 +/- 0.3 versus 6.1 +/- 0.3 under high flow and 5.8 +/- 0.1 versus no response under low flow conditions]. Conclusion: St atic ring preparations do not discern differences between ITA and GEA susceptibility to spasm and fail to detect the effect of load. The dyn amic preparation demonstrated significant differences between the GEA and ITA potential to spasm which is consistent with widespread clinica l experience. Furthermore a dynamic preparation is highly sensitive to reduced load which occurs under high how conditions, Although it is m ore demanding, the dynamic preparation provides superior information t o the surgeon in predicting the behavior of arterial bypass grafts. (C ) 1997 Elsevier Science B.V.