Intraindividual comparison of human radial and internal thoracic arteries in vitro and the effect of preoperative calcium blocker therapy

Despite post-operative calcium entry blocker (Ca2+eB) therapy the patency rate of radial artery (RA) conduits is expected to be lower than that of internal thoracic artery (ITA) grafts. The evidence suggests that this is due to a higher incidence of vasospasm of RA conduits. This study compared intraindividually the pharmacological reactivity of the RA with that of the ITA and investigated the effect of preoperative Ca2eB therapy.

RA and ITA segments were taken from 76 patients undergoing elective myocardial revascularization. Changes in tension were monitored isometrically on ring preparations from both arteries suspended in 10ml organ baths filled with modified Krebs-Henseleit solution.

Maximal receptor-mediated contractile responses to noradrenaline and endothelin-1 and endothelium-dependent acetylcholine-induced relaxant responses revealed no differences between both arteries in the same patient. By contrast, depolarisation-induced contractions to potassium chloride (KCl) appeared considerably higher in RA than in ITA. Further analysis revealed that this difference was dependent on preoperative Ca2+eB therapy. Maximal responses to KCl were significantly attenuated in the ITA (1.6±0.2g, n=14 vs. 3.2±0.4g, n=19, p<0.05) but unchanged in RA when arteries were obtained from patients with preoperative Ca2+eB therapy as compared to arteries taken without preoperative Ca2eB therapy.

The present results suggested that functional responses to pharmacological stimuli of both RA and ITA are similar. Preoperative Ca2+eB therapy, however, attenuated significantly responses to KCl of the ITA but left those of the RA unchanged. This observation questions the effectiveness of post-operative Ca2+eB treatment to avoid spasm in RA conduits.