Numerical modeling of simulated blood flow in idealized composite arterial coronary grafts: steady state simulations.

This paper presents a comparative study of simulated blood flow in different configurations of simplified composite arterial coronary grafts (CACGs). Even though the composite arterial grafting is increasingly used in cardiac surgery, it is still questionable whether or not the blood flow in such grafts can adequately meet the demands of the native myocardial circulation. A computational fluid dynamics (CFD) model was developed to conduct computer-based studies of simulated blood flow in four different geometric configurations of CACGs, corresponding to routinely used networks in cardiac surgery coronary grafts (T, Y, Pi and sequential). The flow was assumed three-dimensional, laminar and steady and the fluid as Newtonian, while the vessel walls were considered as inelastic and impermeable. It was concluded that local haemodynamics, practically described by velocity, pressure drop, wall shear stress (WSS) and flow rates, may be strongly influenced by the local geometry, especially at the anastomotic sites. The computations were made at mean flow rates of 37.5, 75 and 150ml/min. The side-branch outflow rates, computed for each bypass graft, showed noticeable differences. The results, which were found both qualitatively and quantitatively consistent with other studies, indicate that the Pi-graft exhibits significantly less uniform distribution of outflow rates than the other geometric configurations. Moreover, prominent variations in WSS and velocity distribution among the assessed CACGs were predicted, showing remarkable flow interactions among the arterial branches. The lowest shear stress regions were found on the lateral walls of bifurcations, which are predominantly susceptible to the occurrence of coronary artery disease (CAD). In contrast, the highest WSS were observed at the turn of the arterial branches.

Mitral valve replacement in a Jehovah's Witness with dextrocardia and situs solitus.

BACKGROUND AND AIMS OF THE STUDY: Dextrocardia with situs solitus and mitral valve insufficiency requiring surgical treatment is a rare presentation. Jehovah's Witnesses (JW), a specific religious group, deny any blood transfusion and for this reason the cardiac surgeon has to plan his operation well in advance, particularly in the case of adhesions from previous thoracic procedures. MATERIALS AND METHODS: A 50-year-old white female Jehovah's Witness with dextrocardia and situs solitus was referred for surgical treatment of massive mitral valve insufficiency of rheumatic etiology. Due to multiple adhesions from previous bilateral thoracotomies and the inverted position of the heart, cardiopulmonary bypass (CPB) was initiated with an aortic and a left common femoral vein cannulae. CPB was completed with an additional SVC cannula. The surgeon, having excellent exposure from the opposite side of the table, was able to perform a mitral valve replacement (MVR) with a 31 mm St. Jude Medical valve prosthesis, through a giant left atrium under moderate hypothermia and crystalloid cardioplegia. The operation was bloodless, with only two units of autotransfused blood being used with a postoperative hematocrit of 34%. RESULTS: The patient had an uneventful recovery and has been in NYHA class I for 24 months now. CONCLUSIONS: The case is presented for the safety of the approach, the excellent exposure from the left side in a dextrocardia case and the avoidance of blood transfusion in a Jehovah's patient.