PEROPERATIVE HEMODYNAMIC-STUDY OF LEFT INTERNAL MAMMARY ARTERY GRAFTS

The present study was undertaken to analyse hemodynamic features of an arterial graft and to determine parameters which influence primarily flow and velocity. A total of 284 consecutive patients having isolated coronary bypass surgery underwent peroperative hemodynamic assessment by pulsed Doppler ultrasonics of a left internal mammary artery bypass graft implanted onto the left anterior descending artery. Internal mammary artery free flow was 109.2 +/- 3.7 ml/min and flow in the internal mammary artery measured after completion of the distal anastomosis was 70.9 +/- 2.7 ml/min. All values quoted are mean +/-standard error of the mean. Mean velocity was 21.2 +/- 0.6 cm/sec, internal diameter was 2.65 +/- 0.04 mm and pulsatility index was 2.24 +/- 0.12. Resistance was expressed as mmHg/(ml.min(-1)) and averaged 1.65 +/- 0.13 for total resistance, 0.87 +/- 0.05 for graft resistance, and 0.73 +/- 0.13 for coronary resistance. From a set of 35 variables, stepwise multiple regression analysis selected two parameters influencing independently flow in internal mammary artery (R(2) = 0.8762): flow velocity (p < 10(-4)) and internal diameter (p < 10(-4)). Variables influencing velocity (R(2) = 0.3071) were: pulsatility index, which is a dimensionless expression of peripheral resistance (p < 10(-4)), and free internal mammary artery flow (p = 0.0007). Furthermore, a significant correlation between internal diameter and total resistance was observed (R = -0.5363, p < 10(-4), Y = 1.676X(-1.545)), and the exponentially fitted regression line was characterized by a marked increase of resistance at diameters less than 2 mm. Flow in grafted internal mammary arteries was predominantly influenced by the internal diameter of the graft and by velocity, which was related to peripheral resistance. Total resistance, as measured in the graft, increased in an exponential way with the reduction of graft internal diameter.