M Zietkiewicz

Calcification characteristics of porcine stentless valves in juvenile sheep

OBJECTIVE To compare calcification characteristics of two porcine stentless valves (Toronto SPV and Freestyle) with different designs, fixation and antimineralization techniques using a juvenile sheep model of valve implantation inside the circulation. METHODS The stentless valves (n = 2 x 6) were implanted in juvenile sheep in the pulmonary artery as an interposition, while the circulation was maintained with a right ventricular assist device. The model was validated by the implantation of, clinically well-known, porcine (Hancock II) and pericardial (Pericarbon) valves. Half of the valves were explanted after 3 months, the rest after 6 months. Valves were examined macroscopically, by X-ray, light microscopy (HE, Masson, Von Giesson, Von Kossa, PTAH stains), and transmission electron microscopy. Quantitative determination of the calcium content of the cusps was performed with atomic absorption spectrometry. RESULTS After 3 months, the Freestyle had an extensively calcified aortic wall, most prominent at the outflow side of the porcine valve. After 6 months, calcification increased transmurally, but the valve cusps were free of calcification, and the inflow side was only slightly calcified. The Toronto SPV valve also started to calcify at the inflow side of the valve after 3 months with increased calcification after 6 months. The base of the Toronto SPV valve cusps showed slight calcification after 6 months of implantation. CONCLUSIONS The pattern of calcification of the porcine aortic wall differs between the two studied stentless valves, with calcification located predominantly at the outflow side in the Freestyle valve, but also at the inflow side in the Toronto SPV valve. The cusps of the Freestyle valve were less prone to calcification than those from the Toronto SPV valve.

Micropumps to support the heart during CABG

OBJECTIVE To show the effect of myocardial support by micropumps during beating heart CABG for triple vessel disease. METHODS In 12 sheep, three coronary arteries (LAD, intermediate branch and circumflex) were consecutively occluded for 10 min. The animals were divided in two groups: group 1 without support (n=6) and group 2 with biventricular support of intravascular micropumps. The pumps (diameter 6.4 mm) were placed through peripheral access (femoral artery and jugular vein) and advanced under fluoroscopic guidance. The hemodynamic evolution was analyzed during the procedure and 2 h of reperfusion. Myocardial flow was assessed by colored microspheres. Differences between groups were analyzed by ANOVA for repeated measurements and post-hoc testing in case of significance. RESULTS All of the pump-supported animals survived the procedure, 1 of the control animals died of resistant ventricular fibrillation. At the end of the reperfusion period, the hemodynamic performance and myocardial contractility was significantly better in the pump-supported group (cardiac output: 2.4+/-0.9 vs. 3.3+/-0.9 l/min, P=0.0192; mean arterial blood pressure: 51+/-23 vs. 73+/-9 mmHg, P=0. 036; first derivative of the left ventricular pressure: 561+/-271 vs. 947+/-316 mmHg/s, P=0.0074). After the procedure, subendocardial blood flow was significantly better in all areas of the left ventricle in group 2 (0.935+/-0.427 ml/min per g vs. 0.409+/-0.183 ml/min per g in group 1; P=0.0366). CONCLUSION The supported heart is more resistant to repetitive local ischemia. Support by microaxial pumps can make beating heart surgery safer and applicable for more complex cases.

Coronary artery bypass graft with biventricular microaxial pumps.

Beating heart surgery is limited to patients with singleor double-vessel disease. Manipulation of the heart to reach the lateral wall leads to haemodynamic instability. The use of mechanical support systems to extend the indications for beating heart surgery has been investigated extensively.1–4 The use of the Medtronic Hemopump® Cardiac Assist System (Medtronic Inc., Minneapolis, MN, USA) (Hemopump) as a support device is especially interesting as invasiveness can be minimized.1,2,4 There are beneficial effects in myocardial unloading, increase of myocardial blood flow and overall haemodynamics.2,5,6 However, the use of the Hemopump as a left ventricular assist device is not sufficient to reach the lateral wall of the heart. During manipulation, kinking of the right ventricle leads to rapid haemodynamic instability. In addition, the left-sided assist does not result in a stable surgical field and the use of the Hemopump is extremely expensive.2 The objectives of this work were: (1) to improve current microaxial pumps, (2) to provide an application for the right-side of the heart and (3) to do all this at the lowest possible cost. Microaxial blood pumps