European Journal of Cardio-Thoracic Surgery, Vol 12, 436-442, Copyright © 1997 by European Association for Cardio-thoracic Surgery
What in-vitro method should surgeons use to evaluate the clinical behavior of arterial bypass conduits
WD Montgomery, G Vitolla, A Ali, S Pagni, JL Ballen, WP Santamore, AM Calafiore and PA Spence
University of Louisville, Division of Cardiovascular and Thoracic Surgery, Kentucky, USA.
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 [ED50] 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.
