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) challenge] and physiologic [arterial preload] responses of gastroepiploic (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 from adult pigs and mounted on a computer controlled perfusion system. Inflow 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. NE response (10 -9 -10 -5 M) was measured under low flow conditions and at high flow conditions when distal arterial pressure (load) was reduced. NE response (10 -9 -10 -5 M) was also evaluated in arterial rings (ITA N = 6, GEA N = 6) with tensions adjusted to simulate the loads occurring at low flow (80 mmHg) and high flow (60 mmHg) situations. Results: In the static ring preparation, NE response [ED 50 ] was similar for both GEA and ITA and was not affected by load. The dynamic preparation 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 response was profoundly affected by reduced load which occurs under high flow 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: Static ring preparations do not discern differences between ITA and GEA susceptibility to spasm and fail to detect the effect of load. The dynamic preparation demonstrated significant differences between the GEA and ITA potential to spasm which is consistent with widespread clinical experience. Furthermore a dynamic preparation is highly sensitive to reduced load which occurs under high flow conditions. Although it is more demanding, the dynamic preparation provides superior information to the surgeon in predicting the behavior of arterial bypass grafts.