American Journal of Thoracic and Cardiovascular Surgery

The objective of the study was to estimate the contractility characteristics and electromechanical coupling of human internal thoracic artery (ITA) by mechanography and double sucrose gap technique to compare the effect of nitroglycerin with other pharmacological agents. The study of mechanical tension (mechanography) of the ITA segments has been performed in 14 patients undergone coronary artery bypass grafting (CABG). After provisional straining by 500 mg preload, the mechanical tension was registered in real time on two-coordinate plotter of mechanoelectrical converter. For simultaneous registration of membrane potential (MP) and mechanical tension (MT) during cultivation in pharmaceuticals, the method of double sucrose gap technique was used. The maximal MT of ITA segments was achieved under the exposure to potassium chloride. Paradoxical ITA contractility reaction was observed during the application of niflumic acid. Phenylephrine had no statistically significant effect on the ITA MT even at high concentrations. Epinephrine caused a pronounced contractile response of the ITA segments, which was similar to potassium chloride. Hyperpotassium-induced MT of the distal ITA segments was 3.5 times higher than this of the proximal ones. There were no statistically significant differences in the contractile response of the ITA segments studied on the same day as a surgery or the next day. A direct correlation between nitroglycerin vasodilating effect and its dose has been found. There was no restoration of the MT to the baseline values after the nitroglycerin-induced maximal relaxation followed by a wash with Krebs solution. There was an exponential relationship between the concentrations of nitroglycerin required to achieve the maximal relaxation and the initial MP. Conclusion: The maximum potassium-induced MT of the distal ITA segments was significantly higher than this of the proximal ones. There was no effect of phenyephrine on the ITA MT. Epinephrine and niflumic acid cause pronounced ITA contractile response. Nitroglycerin has a marked relaxing influence on ITA and a maximal effect at a low level of initial MP. Therefore, if MP increases, high doses of nitroglycerin are required to achieve maximum vasodilation.