Preventing gastroepiploic artery spasm: papaverine vs calcium channel blockade

The gastroepiploic artery (GEA) is a highly vasoactive artery gaining wider acceptance as a conduit for coronary artery bypass surgery. A variety of agents are used to dilate the GEA prior to grafting; however, little is known about the duration of their effect in the immediate postoperative period. This study evaluated three calcium channel blockers and papaverine in preventing graft spasm.

Porcine GEA segments (10-12 cm in length) were connected to a computer-controlled perfusion system with a constant in-flow pressure and distal resistance to simulate bypass flow (80-100 ml/min). Norepinephrine (NE; 10(-9) to 10(-5) M) was given in incremental doses at baseline before the vasodilator, immediately after (0 hr), and again at 2 hr after the vasodilator. Changes in flow and ED50 were recorded. Group INT (N = 25) received papaverine (PAP), diltiazem, nifedipine (NFP), or verapamil (VPL) intraluminally, while group EXT (N = 25) received the same dilators externally.

All arteries showed dose-dependent vasoconstriction to NE prior to treatment. Immediately after receiving the vasodilator, arteries in both groups (INT and EXT) showed initial protection against NE-induced spasm with the exception of arteries receiving NFD externally. However, at 2 hr, for group INT, only VPL and NFD prevented NE-induced graft spasm (VPL: 40.4 +/- 6.8 ml/min vs 17.9 +/- 3.3 ml/min and NFD: 27.0 +/- 6.5 ml/min vs 13.1 +/- 0.9 ml/min, P < 0.02). In group EXT, after 2 hr, only VPL- and PAP-treated grafts showed resistance to NE-induced vasospasm (VPL: 35.6 +/- 7.3 ml/min vs 15.0 +/- 6.9 ml/min and PAP: 47.4 +/- 15.1 ml/min vs 8.0 +/- 2.0 ml/min, P < 0.001).

Papaverine, a lipophilic vasodilator, when given externally on the perivascular fat of the GEA, prevented graft spasm for up to 2 hr. In contrast, intraluminally applied papaverine did not show graft protection against NE-induced spasm. Nifedipine prevented NE-induced spasm only when given intraluminally. Verapamil proved to be the most potent and versatile vasodilator with effective graft protection of up to 2 hr whether applied externally or internally and was the preferred agent for protecting against GEA spasm.