G. Van Nooten

Phosphorylcholine coating of extracorporeal circuits provides natural protection against blood activation by the material surface

OBJECTIVE The aim of this study is to evaluate the use of a new coating, mimicking the outer cell membrane, in paediatric cardiac surgery. METHODS Two groups of ten patients with a body weight below 8 kg, undergoing elective cardiac operations for different congenital anomalies, were prospectively enrolled in this study. In one group the whole extracorporeal circuit, including the cannulas, was coated with phosphorylcholine (PC). In the second group the same circuit was used without coating. Platelet activation (thromboxane B2 (TXB2), beta-thromboglobulin (betaTG)), activation of the coagulation system (F1+2), leukocyte activation (CD11b/CD18) and terminal complement activation (TCC) were analyzed pre-cardiopulmonary bypass (CPB), at 15, 60 min of CPB, at the end of CPB, 20 min post CPB and at postoperative day 1 and 6. RESULTS No statistical differences were found for F1+2 and CD11b/CD18. After onset of CPB mean levels of TCC remained stable in the PC group whereas an increase was observed in the control group. During CPB betaTG values in both groups increased to a maximum at the end of CPB. Within groups the increase in betaTG levels during CPB was statistically significant (P<0.05) from baseline in the control group starting from 60 min of CPB whereas no statistical difference was observed in the PC group. After the start of CPB TXB2 mean levels increased to 405+/-249 pg/ml in the PC group vs. 535+/-224 pg/ml in the control group. After this initial increase there was a small decline in the PC group with further increase. This was in contrast to the control group were TXB2 levels further increased up to a mean of 718+/-333 pg/ml at the end of CPB (P=0.016). CONCLUSIONS Phosphorylcholine coating had a favourable effect on blood platelets, which is most obvious after studying the changes during cardiopulmonary bypass. A steady increase of TXB2 and betaTG was observed in the control group, whereas plateau formation was observed in the phosphorylcholine group. Clinically, this effect may contribute to reduced blood loss and less thromboembolic complications. Complement activation is lower in the coated group.

Short-term and long-term neuropsychological consequences of cardiac surgery with extracorporeal circulation

OBJECTIVE Cognitive dysfunction after extracorporeal circulation is a major continuing problem in modern cardiac surgery. We designed this prospective study to update the incidence of postoperative neuropsychological changes after routine cardiopulmonary bypass (CPB) and to identify perioperative variables associated with these complications. METHODS We assessed the patients with a comprehensive neuropsychological test battery 1 day before, 7 days after (n = 109) and 6 months after (n = 91) cardiopulmonary bypass. We used patients undergoing major vascular or thoracic surgery as a surgical control group (n = 20). RESULTS Repeated measures multivariate analysis of variance (using surgical group as a between-subjects factor) on the group data revealed significant changes early after surgery compared with the preoperative performance (P = 0.001). The early changes are characterized by a significant decrease of visual attention and verbal memory performance (univariate F-tests, always P < 0.05). Cardiac patients showing cognitive impairment after cardiac surgery had lower preoperative ejection fractions (P = 0.014) and a more complicated medical history (P = 0.046). At 6-month follow-up, the patients performed significantly better than before surgery (P < 0.001). CPB patients showing persistent cognitive impairment at follow-up were significantly older at the time of surgery (P = 0.005). Individual comparisons revealed that 45% of the patients undergoing CPB showed evidence of cognitive impairment soon after surgery. In 12% of the patients, the cognitive sequelae persisted at follow-up. Both group data and individual incidence rates revealed neither significant pre-post differences between the surgical groups nor a time-by-group interaction effect. Variables directly associated with CPB were not significantly associated with the occurrence of cognitive impairment after surgery. CONCLUSIONS We conclude that an important proportion of the cognitive impairment after cardiac surgery is likely to be due to nonspecific effects of surgery.

Phosphorylcholine coating offers natural platelet preservation during cardiopulmonary bypass

Return of blood activated by tissue factor is the main culprit for triggering the coagulation cascade. When this activated blood is diverted from the cardiopulmonary bypass (CPB) circuit, it becomes possible to evaluate the effect of surface treatment on platelet and complement activation. Twenty adult patients undergoing elective coronary artery bypass grafting (CABG) were randomly assigned either to a control group ( n = 10) or to a group in which the CPB circuit was completely coated with phosphorylcholine ( n = 10). Plasma concentrations of platelet factor 4 (PF4), β-thromboglobulin (βTG), C3, C3d, C4, TCC, thrombin generation, haptoglobin and free haemoglobin, as well as blood loss, were measured. No significant differences between the two groups were found for haemolysis and thrombin generation. The mean total release of PF4 and βTG during CPB was 9338± 17303 IU/ml/CPB and 3790± 4104 IU/ml/CPB in the coated group versus 22192± 13931 IU/ml/CPB ( p = 0.011) and 8040± 3986 IU/ml/CPB ( p = 0.005) in the control group. Blood loss was 30% less in the coated group compared to the control group. Phosphorylcholine coating appears to have a favourable effect on blood platelets, which is most obvious after studying the changes during CPB. Clinically, this effect resulted in a 30% reduction in blood loss.

Valve replacement with the ATS open pivot bileaflet prosthesis

OBJECTIVE We sought to evaluate the ATS open pivot bileaflet valve with respect to haemodynamics and thromboembolism. METHODS We prospectively studied 200 consecutive patients aged 13-80 years. One hundred and nineteen aortic, 103 mitral and 11 tricuspid valves were replaced in 172 single, 23 double and 5 triple valve procedures. Thirty-eight were re-operations and 51 underwent coronary bypass. Transvalvular gradients were determined by transoesophageal and transthoracic echocardiography. Patients were followed for 12 months to 3 years. RESULTS There were four hospital (2%) and three late deaths, each non-valve related. Two patients were reoperated for partial valve dehiscence. One aortic reoperation patient suffered a potential transient thromboembolic event. One tricuspid prosthesis thrombosed after anticoagulation was discontinued but thrombolysis resolved this problem. There were no other thromboembolic events. Valve gradients were equivalent or better than those for other bileaflet valves. CONCLUSIONS The ATS valve has excellent haemodynamic characteristics and a very low thromboembolic rate, probably related to the convex self-washing hinge mechanism. Consequently, we have reduced anticoagulant levels to INR (international normalised ratio) 1.5 to 2.0 for aortic valve patients in sinus rhythm. Early experience suggests that the ATS valve functions well in the tricuspid position.

Operative outcome of minimal access aortic valve replacement versus standard procedure.

Abstract Background: to determine the advantages and/or risks of minimal access aortic valve replacement compared to standard sternotomy procedure. Methods: from January 1997 to December 2001, 271 consecutive adult patients underwent isolated aortic valve replacement of which 174 underwent a minimal access procedure (Group 1) and 97 a standard procedure (Group 2).The preoperative variables of both groups were comparable. Retrospective analysis of postoperative outcome was performed. Results: follow-up was complete and ranged from 6 months to 4 years. Overall in-hospital mortality was 3.3% (respectively 2.8 and 4.1%). No statistical difference was noted regarding operative time variables, mortality rate and hospital stay. There was a significant higher incidence of revision (p = 0.018) and late pericardial effusion (p = 0.022) in the minimal access group. Also trends were in favour of the standard group for incidence of postoperative pneumothorax and pericarditis constrictiva. Conclusions: minimal access aortic valve replacement is a safe and reliable technique, but carries the risk of incision-related morbidity. Proper patient selection and perioperative management is mandatory.

HYDRODYNAMICAL COMPARISON OF AORTIC ARCH CANNULAE

The high velocity of blood flow exiting aortic arch cannulae may erode atherosclerotic material from the aortic intima causing non-cardiac complications such as stroke, multiple organ failure and death. Five 24 Fr cannulae from the Sarns product line (straight open tip, angled open tip with and without round side holes, straight and angled closed tip with four rectangular, lateral side holes), and a flexible cannula used at the University Hospital of Gent (straight open tip) are compared in an in vitro steady flow setup, to study the spatial velocity distribution inside the jet. The setup consists of an ultrasound Doppler velocimeter, mounted opposite to the cannula tip in an outflow reservoir. An elevated supply tank supplies steady flow of 1.3 L/min of water. Exit forces at various distances from the tip are calculated by integrating the assessed velocity profiles. The pressure drop across the cannula tip is measured using fluid filled pressure transducers. The four sidehole design provides the lowest exit velocity (0.85 versus 1.08 m/s) and force per jet (0.03 vs 0.15–0.20 N). The round sideholes are useless as less than 1% of the flow is directed through them. Furthermore, the use of angled tip cannulae is suggested because the force exerted on the aortic wall decreases the more the angle of incidence of the jet deviates from 90°. Pressure drop is the lowest for the 4 side hole design and highest for the open tip and increases when an angled tip is used.

Clinical experience with the first 100 ATS heart valve implants

Abstract Between May 1992 and March 1994, 100 consecutive patients had 119 new ATS mechanical bileaflet valves inserted (61 aortic, 50 mitral, eight tricuspid). The mean age of the patients was 63.7 (range 13–82) years. The follow-up period ranged from 5 to 27 months and was complete in all cases. Before surgery, 53 aortic valve patients were in New York Heart Association functional class III or higher. This improved to a mean of 1.3 postoperatively, all patients being in classes I or II. One patient died in hospital, and another 3 months after implantation (actuarial survival rate 98%). One patient had an embolic event 9 days after an aortic valve reoperation which caused a parietal infarction. One tricuspid valve blocked in the open position 6 weeks after implantation as a result of inadequate anticoagulation and was successfully unblocked after 2 days of intensive thrombolytic therapy. Patients were treated by mild anticoagulation without developing bleeding complications. Echocardiographic, transoesophageal and transthoracic valvular gradients compared favourably with the gradients reported in other mechanical valves (including small aortic valves). The haemodynamics were excellent without evidence of significant regurgitation. This was confirmed by an in vitro hydrodynamic evaluation of the valve using a pulse duplicator system. The valve closure caused little noise and was as a result well tolerated.

Off-pump coronary surgery : surgical strategy for the high-risk patient

OBJECTIVE In a retrospective study, we compared two groups of consecutive patients operated by the same team during the year 2000 for coronary artery disease with the use of extracorporeal circulation (group 1, n=230) or on the beating heart using the Octopus II plus stabiliser (group 2, n=228). High-risk patients were identified by a EuroSCORE plus 6. EuroSCORE definitions and predicted risk models were utilized to compare the variables of the groups. METHODS There were no significant differences between the preoperative variables of the groups in age, gender, left ventricular function, diabetes and peripheral vascular and renal disease as is indicated by the Euroscore (resp. 4.7/5.1 p=0.107). Calcification of the ascending aorta and chronic obstructive lung disease were statistically significant more prevalent in the beating heart group. No differences in preoperative variables in the high-risk patients group (Euroscore 8.5/8.1 p=0.356) except for calcification of the ascending aorta. RESULTS All patients underwent a full revascularisation through a midline sternotomy. Significant more distal anastomoses were performed in group 1 (3.7 per patient (1-6)) with regard to group 2 (2.9 per patient (1-6)). Anesthesia, postoperative treatment and follow up were equal for both groups. A significant lower incidence of atrial fibrillation (p=0.010), shorter ICU stay (p=0.031) and renal insufficiency (p=0.033) was reported in group 2. In the low risk group, we could not diagnose any difference between the two groups, except for atrial fibrillation. The benefits of the beating heart surgery however were more pronounced in the high-risk patient as is indicated by a significant reduction of the ICU stay by 1 day (3.5d/2.5d (p=0.028)), better preservation of the renal function (p=0.017) and a significant reduction of the length of hospital stay by more than two days (p=0.040). A lower incidence of atrial fibrillation, however not significant. CONCLUSION In our experience, beating heart surgery is a safe alternative for conventional coronary heart surgery. High-risk patients do benefit most from this technique. It became our first choice in the elderly patient and patients presenting with higher co-morbidities.

Low extracorporeal priming volumes for infants: a benefit?

An extracorporeal circuit consisting of an oxygenator especially designed for neonatal use and appropriately sized tubing, with an average total priming volume of 205 ml, was used on 80 infants undergoing cardiac surgery for congenital heart-disease. The priming volume and foreign surface area of the circuit were determined. The influence of low priming volumes on the use of blood products and the management of cardiopulmonary bypass was studied. No whole blood or platelets were used in this study. The mean volume of packed red blood cells used over the hospital stay was 202 ± 67 ml. The mean volume of fresh frozen plasma (FFP) used until the second postoperative day was 62 ± 72 ml. The mean total blood loss until the second postoperative day was 15.8 ± 9.2 ml/kg. The priming volume of the extracorporeal circuit was 62% lower than values commonly reported in the literature. The low priming volume had a strong influence on the use of platelets and FFP and to a lesser extent on the use of packed red blood cells.

Can an oxygenator design potentially contribute to air embolism in cardiopulmonary bypass? A novel method for the determination of the air removal capabilities of neonatal membrane oxygenators.

At present, air handling of a membrane oxygenator is generally studied by using an ultrasonic sound bubble counter. However, this is not a quantitative method and it does not give any information on where air was entrapped in the oxygenator and if it eventually was removed through the membrane for gas exchange. The study presented here gives a novel technique for the determination of the air-handling characteristics of a membrane oxygenator. The study aimed at defining not only the amount of air released by the oxygenator, but also the amount of air trapped within the oxygenator and/or removed through the gas exchange membrane. Two neonatal membrane oxygenators without the use of an arterial filter were investigated: the Polystan Microsafe and the Dideco Lilliput. Although the air trap function of both oxygenators when challenged with a bolus of air was similar, the Microsafe obtained this effect mainly by capturing the air in the heat exchanger compartment while the Lilliput did remove a large amount of air through the membrane. In conclusion, the difference in trap function was most striking during continuous infusion of air. Immediate contact with a microporous membrane, avoidance of high velocities within the oxygenator, pressure drop, transit time and construction of the fibre mat all contribute to the air-handling characteristics of a membrane oxygenator.