Pre-filling of the extracorporeal circuit with autologous blood is safe, but not effective in optimizing biocompatibility in high-risk patients

OBJECTIVES

Haemodilution resulting from crystalloid priming of the cardiopulmonary bypass circuit represents a major risk factor for blood transfusions in high-risk cardiac surgery patients. We designed this study to evaluate the effects of antegrade autologous priming (AAP) on reducing perioperative blood transfusion and markers of the inflammatory response in older patients (>75 years).

METHODS

Seventy-two patients undergoing first-time coronary bypass and/or aortic valve replacement were prospectively randomised to a cardiopulmonary bypass (CPB) with or without AAP. AAP was performed by adding the patient's own blood to the prime solution (mean 280 ml). Perfusion and anaesthetic techniques were as usual. The haematocrit was maintained at a minimum of 21% during CPB. Patients were well matched for all preoperative variables, including established transfusion risk factors. The primary endpoint was the requirement of red cell transfusion. The surrogate endpoints were renal function, inflammatory response and ischaemic parameters. Blood samples were drawn pre- and intraoperatively and at intervals of 6 hours till POD 6.

RESULTS

Current analysis shows no differences in patients receiving homologous packed red cell transfusions. Also, markers of the inflammatory response (IL6, IL8), renal function (cystatin C, creatinine) and myocardial ischaemia (troponin T, CK-MB) were comparable in both groups (p>0.05). Clinical outcomes were similar with respect to pulmonary, renal and hepatic function, length of ICU stay and hospital stay.

CONCLUSION

These data suggest that antegrade autologous priming is a safe procedure, but an ineffective way for improving biocompatibility and reducing the need for blood transfusion in older patients.

Regulation of endothelial nitric oxide synthase (eNOS) in myocardium subjected to cardioplegic arrest

BACKGROUND

Nitric oxide (NO) production by both coronary endothelial cells and cardiomyocytes is thought to play a significant role in myocardial pathophysiology following ischemia/reperfusion (I/R).

METHODS

In thirteen pigs subjected to 1 hour cardioplegic arrest (CA) on CPB, left ventricular (LV) biopsies were collected prior to CPB (baseline), at 60 min CPA, at 15 and 30 min reperfusion on CPB, and at 120 min post CPB. LV specimens were immunocytochemically stained against phospho-eNOS (Ser1177), phospho-eNOS (Thr495), phosphorylated ERK1/2, and AKT/PKB. Four additional pigs without CA served as controls. Cardiomyocytes were quantitatively investigated using TV densitometry (gray units: U).

RESULTS

After 60 min CA phosphorylation of eNOS (Ser1177) increased significantly and remained elevated until 30 min of reperfusion. In contrast, eNOS (Thr495) phosphorylation remained unchanged during CA and throughout reperfusion. In control animals, eNOS phosphorylation remained unchanged. Akt/PKB activity significantly increased after 60 min CA and decreased thereafter. ERK1/2 activity remained unchanged during ischemia but increased during reperfusion.

CONCLUSIONS

ENOS activation during ischemia occurs through phosphorylation at Ser1177 mediated by Akt/PKB. ERK1/2 does not seem to be involved in myocardial eNOS regulation especially not via phosphorylation at eNOS (Thr495).

Endovascular repair of infrarenal abdominal aortic aneurysm associated with a horseshoe kidney and graft thrombosis in early follow-up

Endovascular aneurysm repair (EVAR) is a well-established alternative to open surgery. The presented case underwent endovascular therapy of an abdominal aortic aneurysm (AAA) with the anatomical prerequisite of a horseshoe kidney. We describe the technique used, including the embolization of aortic side branches, to avoid endoleaks, and the management of thrombotic complications during follow-up.

Extravasale Lage von zentralen Venenkathetern bei korrekter EKG-Ableitung

OBJECTIVE

Does the electrocardiographic method for central venous catheter positioning distinguish between a correct intravasal and a malpositioned extravasal position?

METHODS

24 cardiac surgical patients were enrolled in this prospective observational study. In 18 patients the left, in another 6 patients the right internal jugular vein was cannulated. Using a J-wire within a triple-lumen catheter the amplitude of the P-wave was measured at 3 different intravasal sites: Intra-1: (intravasal baseline electrocardiogram), i. e. 10 cm marking of the catheter on skin level; Intra-2: clear rise of the P-wave amplitude upon further insertion of the catheter; Intra-3: maximum P-wave amplitude. At this position the control of the catheter tip was achieved by means of transoesophageal echocardiography (TOE). Intraoperatively, another J-wire within a triple-lumen catheter was placed by the heart surgeon on 3 extravasal sites and the ECG was recorded: Extra-1: extravasal at the left innominate vein above the pericardial reflection; Extra-2: extravasal on the superior vena cava below the pericardial reflection; Extra-A: extravasal on ascending aorta below the pericardial reflection. The catheter was suture fixed with its tip in position Intra-3. Post surgery a chest radiograph was taken.

RESULTS

All catheter tips were visualised at the basis of the Crista terminals (border between right atrium and superior vena cava) by TOE control. The rise of the P wave amplitude at Intra-2, Extra-2 and Extra-A was highly significant compared to the base line at Intra-1 (Intra-1/Intra-2, Intra-1/Extra-2, Intra-1/Extra-A: p in each case < 0.001). The P wave amplitudes of the corresponding intra- and extravasal positions of the left innominate vein (Intra-1/Extra-1, n = 18, p = 0.096)) as well as those of the superior vena cava (Intra-2/Extra-2, n = 24, p = 0.859) did not differ.

CONCLUSION

The electrocardiographic method can not differentiate between intra- and extravasal position of a central venous catheter, and thus, presumably fails to identify malpositioning as a result of vascular perforation.

Central venous catheters—the inability of ‘intra-atrial ECG’ to prove adequate positioning

BACKGROUND

The classic increase in P wave size, known as 'P-atriale', is a widely accepted criterion for determination of proper positioning of central venous catheter tips. Recent transoesophageal echocardiography (TOE) studies did not confirm intra-atrial position despite advancing the central venous catheter further than indicated by ECG guidance. We postulate that the pericardial reflection rather than the entry into the right atrium corresponds to the ECG changes. In order to test our hypothesis we sought to determine the anatomical substrate for the electrical changes in an animal study. Subsequently, a modified version of the study was undertaken in man and is also reported.

METHODS

In six juvenile pigs the left external jugular vein and right carotid artery were cannulated. A triple-lumen central venous catheter was positioned by ECG guidance using a Seldinger wire as an exploring electrode. The venous and arterial catheters were suture fixed 2 cm beyond the onset of an increase in P wave size. The corresponding anatomical catheter tip position was determined by open exploration of the vessels and the heart. Subsequently the catheter tip position (during advancement) of a pulmonary artery catheter and the corresponding electrical ECG changes were examined in 10 patients during open chest cardiac surgery.

RESULTS

All catheters-arterial and venous, in animals and humans-revealed an increase in size of the P wave as well as the QRS complex. All venous catheters were positioned in the superior vena cava, beyond the pericardial reflection but outside the right atrium. All arterial catheters were positioned in the ascending aorta thus also beyond the pericardial reflection.

CONCLUSIONS

The start of an increase in P wave size does not correspond with the entrance of the right atrium. The anatomic equivalent for the electrophysiological changes of the ECG is the pericardial reflection. ECG guidance is unable to distinguish between venous and arterial catheter position.

Evaluation of different minimally invasive techniques in pediatric cardiac surgery: is a full sternotomy always a necessity?

STUDY OBJECTIVES

A variety of minimally invasive techniques have been recently introduced in adult cardiac surgery. Experiences with children and newborns are, however, limited. In this report, we present our first experiences with different methods of ministernotomies for closure of atrial septum defect (ASD) and ventricular septum defect (VSD) in pediatric cardiac patients. Also, the current literature for different surgical approaches is reviewed.

PATIENTS AND METHODS

Twenty-five pediatric patients (range, 4 months to 12 years old) underwent elective ASD or VSD closure. Surgical access was either without division of the sternum (group A, n = 5), with partial inferior sternotomy (group B, n = 5), total sternotomy with limited skin incision (group C, n = 5), or total sternotomy with full skin incision (group D, n = 10).

RESULTS

There were no severe intraoperative complications regarding exposure, cannulation, or bleeding. Conversion to full sternotomy was not necessary in any patient. Bypass time and cross-clamp time in groups A, B, and C were comparable to the standard operation (group D). However, preparation time was significantly increased in one minimally invasive group (group A vs group D, p<0.05). Despite general feasibility, the transxiphoidal access without sternotomy compromises exposure of the ascending aorta, resulting in impaired administration of cross-clamping, cardioplegia, and especially de-airing.

CONCLUSIONS

Transatrial pediatric cardiac operations can be performed without or with limited sternotomy. The partial sternotomy allows uncompromised exposure of the great vessels and should be favored over the transxiphoidal approach. The operative access and perioperative risk is comparable to a classical standard surgical approach. Advantages include improved cosmetic results in combination with a high degree of safety.

Tissue engineering of pulmonary heart valves on allogenic acellular matrix conduits: in vivo restoration of valve tissue

BACKGROUND

Tissue engineering using in vitro-cultivated autologous vascular wall cells is a new approach to biological heart valve replacement. In the present study, we analyzed a new concept to process allogenic acellular matrix scaffolds of pulmonary heart valves after in vitro seeding with the use of autologous cells in a sheep model.

METHODS AND RESULTS

Allogenic heart valve conduits were acellularized by a 48-hour trypsin/EDTA incubation to extract endothelial cells and myofibroblasts. The acellularization procedure resulted in an almost complete removal of cells. After that procedure, a static reseeding of the upper surface of the valve was performed sequentially with autologous myofibroblasts for 6 days and endothelial cells for 2 days, resulting in a patchy cellular restitution on the valve surface. The in vivo function was tested in a sheep model of orthotopic pulmonary valve conduit transplantation. Three of 4 unseeded control valves and 5 of 6 tissue-engineered valves showed normal function up to 3 months. Unseeded allogenic acellular control valves showed partial degeneration (2 of 4 valves) and no interstitial valve tissue reconstitution. Tissue-engineered valves showed complete histological restitution of valve tissue and confluent endothelial surface coverage in all cases. Immunohistological analysis revealed cellular reconstitution of endothelial cells (von Willebrand factor), myofibroblasts (alpha-actin), and matrix synthesis (procollagen I). There were histological signs of inflammatory reactions to subvalvar muscle leading to calcifications, but these were not found in valve and pulmonary artery tissue.

CONCLUSIONS

The in vitro tissue-engineering approach using acellular matrix conduits leads to the in vivo reconstitution of viable heart valve tissue.

Cardiac performance after deep hypothermic circulatory arrest in chronically cyanotic neonatal lambs

OBJECTIVES

It is controversial whether immature cyanotic hearts are more susceptible to ischemic injury than normoxemic hearts. Acutely induced alveolar hypoxic stress before cardiopulmonary bypass has been used as a model of cyanosis and is reported to worsen recovery of immature hearts after subsequent ischemic insult by means of a free radical injury mechanism. Because of concerns about the relevance of acute alveolar repair to the chronic cyanosis encountered clinically, we assessed the effects of chronic cyanosis without alveolar hypoxia, acute alveolar hypoxia, and normoxemia on recovery of cardiac function after deep hypothermic circulatory arrest.

METHODS

A chronic cyanosis model was created in 8 lambs by an anastomosis between the pulmonary artery and the left atrium (cyanosis group). Eight lambs underwent sham operation (control). One week later, the animals underwent cardiopulmonary bypass with 90 minutes of deep hypothermic circulatory arrest at 18 degrees C. Another 8 lambs underwent 45 minutes of hypoxic ventilation before bypass, with arterial oxygen tension being maintained at 30 mm Hg (acute hypoxia group). Cardiac index, preload recruitable stroke work, and tau were measured. Malondialdehyde and nitrate-nitrite, nitric oxide metabolites, were also measured in the coronary sinus. Myocardial antioxidant reserve capacity at 2 hours of reperfusion was assessed by measuring lipid peroxidation in left ventricular tissue samples incubated with t-butylhydroperoxide at 37 degrees C.

RESULTS

Oxygen tension was 35 +/- 3 mm Hg in the acute hypoxia group versus 93 +/- 7 mm Hg in the control group. In the acute hypoxia group the recovery of cardiac index, preload recruitable stroke work, and tau were significantly worse than that found in both the control and cyanosis groups. Preload recruitable stroke work at 2 hours of reperfusion was slightly but significantly lower in the cyanosis group than in the control group. The postischemic level of nitric oxide metabolites was significantly lower in the acute hypoxia group than in the cyanosis and control groups. However, malondialdehyde levels in the coronary sinus and myocardial antioxidant reserve capacity were not significantly different among the groups.

CONCLUSION

Recovery of left ventricular function after deep hypothermic circulatory arrest in neonatal lambs with chronic cyanosis was slightly worse than that found in acyanotic animals. Acute hypoxia before bypass was associated with significantly worse recovery of left ventricular function, and the mechanism of injury may be related to an impairment of nitric oxide production. Free radical injury does not appear to explain any differences among cyanotic, acyanotic, and acutely hypoxic animals in recovery of left ventricular function after ischemia.

Fabrication of a trileaflet heart valve scaffold from a polyhydroxyalkanoate biopolyester for use in tissue engineering

Previously, we reported the implantation of a single tissue engineered leaflet in the posterior position of the pulmonary valve in a lamb model. The major problems with this leaflet replacement were the scaffold's inherent stiffness, thickness, and nonpliability. We have now created a scaffold for a trileaflet heart valve using a thermoplastic polyester. In this experiment, we show the suitability of this material in the production of a biodegradable, biocompatible scaffold for tissue engineered heart valves. A heart valve scaffold was constructed from a thermoplastic elastomer. The elastomer belongs to a class of biodegradable, biocompatible polyesters known as polyhydroxyalkanoates (PHAs) and is produced by fermentation (Metabolix Inc., Cambridge, MA). It was modified by a salt leaching technique to create a porous, three-dimensional structure, suitable for tissue engineering. The trileaflet heart valve scaffold consisted of a cylindrical stent (1 mm X 15 mm X 20 mm I.D.) containing three valve leaflets. The leaflets were formed from a single piece of PHA (0.3 mm thick), and were attached to the outside of the stent by thermal processing techniques, which required no suturing. After fabrication, the heart valve construct was allowed to crystallize (4 degrees C for 24 h), and salt particles were leached into doubly distilled water over a period of 5 days to yield pore sizes ranging from 80 to 200 microns. Ten heart valve scaffolds were fabricated and seeded with vascular cells from an ovine carotid artery. After 4 days of incubation, the constructs were examined by scanning electron microscopy. The heart valve scaffold was tested in a pulsatile flow bioreactor and it was noted that the leaflets opened and closed. Cells attached to the polymer and formed a confluent layer after incubation. One advantage of this material is the ability to mold a complete trileaflet heart valve scaffold without the need for suturing leaflets to the conduit. Second advantage is the use of only one polymer material (PHA) as opposed to hybridized polymer scaffolds. Furthermore, the mechanical properties of PHA, such as elasticity and mechanical strength, exceed those of the previously utilized material. This experiment shows that PHAs can be used to fabricate a three-dimensional, biodegradable heart valve scaffold.

Tissue engineering of autologous aorta using a new biodegradable polymer

BACKGROUND

Ovine pulmonary valve leaflets and pulmonary arteries have been tissue-engineered (TE) from autologous cells and biodegradable polyglycolic acid (PGA)-polyglactin copolymers. Use of this cell-polymer construct in the systemic circulation resulted in aneurysm formation. This study evaluates a TE vascular graft in the systemic circulation which is based on a new copolymer of PGA and polyhydroxyalkanoate (PHA).

METHODS

Ovine carotid arteries were harvested, expanded in vitro, and seeded onto 7-mm diameter PHA-PGA tubular scaffolds. The autologous cell-polymer vascular constructs were used to replace 3-4 cm abdominal aortic segments in lambs (group TE, n = 7). In a control group (n = 4), aortic segments were replaced with acellular polymer tubes. Vascular patency was evaluated with echography. All control animals were sacrificed when the grafts became occluded. Animals in TE group were sacrificed at 10 days (n = 1), 3 (n = 3), and 5 months (n = 3). Explanted TE conduits were evaluated for collagen content, deoxyribonucleic acid (DNA) content, structural and ultrastructural examination, mechanical strength, and matrix metalloproteinase (MMP) activity.

RESULTS

The 4 control conduits became occluded at 1, 2, 55, and 101 days. All TE grafts remained patent, and no aneurysms developed by the time of sacrifice. There was one mild stenosis at the anastomotic site after 5 months postoperatively. The percent collagen and DNA contents approached the native aorta over time (% collagen = 25.7%+/-3.4 [3 months] vs 99.6%+/-11.7 [5 months], p < 0.05; and % DNA = 30.8%+/-6.0 [3 months] vs 150.5%+/-16.9 [5 months], p < 0.05). Histology demonstrated elastic fibers in the medial layer and endothelial specific von Willebrand factor on the luminal surface. The mechanical strain-stress curve of the TE aorta approached that of the native vessel. A 66 kDa MMP-2 was found in the TE and native aorta but not in control group.

CONCLUSIONS

Autologous aortic grafts with biological characteristics resembling the native aorta can be created using TE approach. This may allow the development of "live" vascular grafts.