Blood flow patterns in an anatomically realistic coronary vessel: influence of three different reconstruction methods.

Many clinical studies suggest that local blood flow patterns are involved in the location and development of atherosclerosis. In coronary diseases, this assumption should be corroborated by quantitative information on local hemodynamic parameters such as pressure, velocity or wall shear stress. Nowadays, computational fluid dynamics (CFD) algorithms coupled to realistic 3-D reconstructions of such vessels make these data accessible. Nevertheless, they should be carefully analysed to avoid misinterpretations when the physiological parameters are not all considered. As an example, we propose here to compare the flow patterns calculated in a coronary vessel reconstructed by three different methods. In the three cases, the vessel trajectory respected the physiology. In the simplest reconstruction, the coronary was modelled by a tube of constant diameter while in the most complex one, the cross-sections corresponded to the reality. We showed that local pressures, wall shear rates and velocity profiles were severely affected by the geometrical modifications. In the constant cross-section vessel, the flow resembled to that of Poiseuille in a straight tube. On the contrary, velocity and shear rate exhibited sudden local variations in the more realistic vessels. As an example, velocity could be multiplied by 5 as compared to Poiseuille's flow and area of very low wall shear rates appeared. The results obtained with the most complex model clearly outlined that, in addition to a proper description of the vessel trajectory, the section area changes should be carefully taken into account, confirming assumptions already highlighted before the rise of commercially available and efficient CFD softwares.

[Right ventricular assistance by intrapulmonary counterpulsation]. / Assistance ventriculaire droite par contrepulsion intrapulmonaire.

Right ventricular failure is relatively frequent and constitutes one of the causes of post-operative heart failure. Few drugs are available to treat right ventricular failure. We present a simple and effective means of mechanical support available in all cardiovascular units: counterpulsation in the pulmonary artery. Our experience and a review of the literature have enabled us to determine the indications for this method to support a failing heart.

[Low molecular weight heparin in extracorporeal circulation. 1st clinical applications]. / Etude d'une héparine de bas poids moléculaire au cours des circulations extracorporelles. Premières applications cliniques.

The haemorrhagic complications inherent to the use of heparin during cardiac surgery led us, after a pilot experimental study, to try out a low molecular weight heparin (LMWH), PK 10169, which has weaker haemorrhagic effects in vitro. Our initial experience was confined to 23 patients with differing pathologies, undergoing cardiopulmonary bypass lasting 30 to 165 minutes. The modes of injection of YK 10169 varied according to the results, especially with respect to the limitation of peaks of anti-Xa activity; 8 patients were given one bolus intravenous injection, 9 were given a bolus injection and a continuous infusion, and 6 were only given the continuous infusion. Biological monitoring of anticoagulation was based on anti-Xa activity. Analysis of the biological results showed that the principal feature was the partial correction, and occasionally the non-correction of anti-Xa activity by protamine sulphate, with no correlation between this anti-Xa activity and postoperative bleeding. The authors report cases of severe postoperative bleeding despite the supposed theoretical and experimental weakly haemorrhagic properties of LMWH, and also discuss the inefficacy of protamine sulphate. The indications for LMWH for cardiopulmonary bypass which were retained, were the rare cases of heparin-induced thrombocytopaenia. In conclusion, it is possible to use LMWH during cardiac surgery but we do not advise using it routinely as its theoretical advantages are not confirmed in practice.