Cerebral protection during controlled hypoperfusion in a piglet model: comparison of moderate (25°C) versus deep (18°C) hypothermia at various flow rates using intraoperative measurements and ex vivo investigation.

BACKGROUND: During surgical correction of complex cardiac anomalies, some degree of hypoperfusion may be required. The aim of this study was to evaluate the effectiveness and safety of controlled cerebral hypoperfusion at moderate (25°C) versus deep (18°C) hypothermia. METHODS: In this study, 56 female piglets (9.4 ± 0.8 kg, 3-4 weeks old) received cardiopulmonary bypass (CPB) at 25, 50, or 100% of the standard flow rate for 60 minutes of cardioplegic cardiac arrest. Body temperature was kept at 18, 25, and 37°C. Routine hemodynamic and functional parameters were measured online until 4 hours of reperfusion. Immunohistology was used to quantify heat shock protein 70 (HSP70) and nitrotyrosine (NO-Tyr) levels in the hippocampus; high-performance liquid chromatography was used to quantify jugular venous blood malondialdehyde (MDA) levels. RESULTS: Reduced CPB flow led to significant reduction of mean arterial pressure by 79%, reduction of jugular venous oxygen saturation (SvO2) by 47%, reduction of carotid blood flow by 92%, and increase of serum lactate by 350%. All these changes were significantly enhanced in the 37°C versus the 25 and the 18°C groups. Regional oxygen saturation (rSO2) was significantly reduced in the 37°C low flow groups. HSP70, NO-Tyr, and MDA were increased in the 25 and 50% flow groups (p < 0.05). There was a significant correlation between rSO2 and SvO2 (r = 0.61) and between SvO2 and HSP70 (r = - 0.72). CONCLUSIONS: Reduction in global blood flow during CPB leads to comparable biochemical changes in the hippocampus at 25 and 18°C. Regional oxygenation saturation, SvO2, and HSP70 are important parameters to evaluate the efficacy of further anti-ischemic therapies during surgical corrections.

Selective cerebral perfusion using moderate flow in complex cardiac surgery provides sufficient neuroprotection. Are children young adults?

OBJECTIVE: Selective cerebral perfusion (SCP) is commonly applied during the correction of complex congenital cardiac defects. In this study, we assessed the impact of different flow levels of SCP on potential brain ischaemia. METHODS: Fifteen piglets (7-10 kg, age 3-4 weeks) received SCP via the right common carotid artery during cardiopulmonary bypass at 25°C for 90 min. Regular brain perfusion (1 ml/g brain weight/min), moderate hypoperfusion (0.5 ml/g/min) and extensive hypoperfusion (0.25 ml/g/min) were evaluated. Clinical parameters and tissue oxygenation index (TOI) were registered online until 3 h of reperfusion. Hematoxylin and eosin (HE) staining and immunohistological analyses for apoptosis inducing factor (AIF) and nitrotyrosine (NO-Tyr) were performed on sections of the hippocampus. RESULTS: Intracerebral pressure remained stable throughout the study. Haemodynamic parameters, blood gas and lactate measurements were stable until the end of the study. Extensive hypoperfusion led to a moderate reduction of TOI. NO-Tyr immuno-positive cells were 15.7% at regular cerebral perfusion, 23.9% at moderate hypoperfusion (P = n.s.) and 46.1% at extensive hypoperfusion (P < 0.05). AIF immuno-positive nuclei were present in 8.3% of the hippocampus cells after regular perfusion, in 10.8% after moderate hypoperfusion (P = n.s.) and in 17.9% after extensive hypoperfusion (P < 0.05). CONCLUSIONS: SCP using a moderate SCP flow regime demonstrates comparable results to normal brain perfusion while after extensive hypoperfusion significant morphological brain injury could be found. Thus moderate, but not extensive, hypoperfusion might have the potential to prevent perfusion-related cerebral oedema and an increasing risk of brain injury.

Functional, metabolic, and morphological aspects of continuous, normothermic heart preservation: effects of different preparation and perfusion techniques.

Continuous blood perfusion of donor hearts for transplantation has been the focus of an increasing amount of research, but the optimal preparation and perfusion techniques have not been clearly defined. Therefore, we investigated the effectiveness of different preservation strategies using continuous, normothermic heart perfusion after donor heart harvesting. Hearts of 12 pigs were randomly assigned to two groups receiving a constant pressure perfusion in a modified Langendorff system after different preparation techniques. In Group 1, six hearts were arrested with Bretschneider HTK cardioplegia (4 degrees C) and then reperfused with a circulating pressure of 80 to 90 mmHg using leukocyte depleted autologous blood. In Group 2, beating hearts of six pigs were explanted while being perfused, without cardioplegic arrest. Post-harvesting perfusion was similar to Group 1 except for a lower circulating pressure (40-50 mm Hg). At different time points (baseline and 1, 6, and 12 h after reperfusion), myocardial biopsies were taken, and contractility was assessed by measuring the maximum rate of left ventricular pressure rise (Deltap/Deltat (max)). Adenosine triphosphate (ATP) concentration was measured in all biopsies using a bioluminescence technique. Additionally, ultrastructural alterations were investigated using electron microscopy. Hypothermic cardioplegia and a higher reperfusion pressure (Group 1) were associated with an earlier and sharper decline in contractile function and intracellular ATP concentration. Ultrastructural alterations in Group 1 appeared earlier and were more distinctive than in Group 2. Endothelial ultrastructure, in particular, was better preserved in Group 2. Significant alterations were present in both groups after 12 h of perfusion but were more severe in Group 1. Blood perfusion provides protection against severe ischemic damage for a limited time. The use of a lower perfusion pressure, as well as avoiding cardioplegia and hypothermia, led to significantly better and longer preservation of perfused hearts.

Selective arterialization of a cardiac vein in a model of cardiac microangiopathy and macroangiopathy in sheep.

OBJECTIVE: Some patients with significant arteriosclerosis of the heart are not amenable to revascularization of a coronary artery because they have a combination of microangiopathy and significant macroangiopathy. We investigated the benefit of arterialization of a cardiac vein under these circumstances in an acute animal model. METHODS: In the hearts of 8 sheep, microspheres were injected into the left coronary artery; 60 minutes later, a stenosis of the left anterior descending artery was performed. After 45 minutes, retrograde venous revascularization was performed by sewing the left internal thoracic artery to the concomitant vein of the left anterior descending artery in a beating-heart technique. For flow reversal, the vein was ligated proximally to the anastomosis. The efficiency of the bypass graft was evaluated by coronary angiography and flow measurement. Cardiac output, electrocardiography, and mean arterial blood pressure were assessed in each phase of the experiment. RESULTS: The ischemic state of the myocardium was confirmed by a significant decrease of cardiac output, stroke volume, and mean arterial blood pressure, and a significant elevation of the ST segment in the electrocardiography. After retrograde venous revascularization was established, cardiac output and stroke volume increased and ST elevations decreased. The grafts showed adequate flow (26.15 +/- 2.08 mL/min), and reversed blood flow in the grafted vein was proved by coronary angiography. CONCLUSION: Retrograde venous revascularization is possible and improves cardiac function in a state of acute ischemia caused by a combination of microangiopathy and macroangiopathy.

Effects of autologous bone marrow stem cell transplantation on beta-adrenoceptor density and electrical activation pattern in a rabbit model of non-ischemic heart failure.

BACKGROUND: Since only little is known on stem cell therapy in non-ischemic heart failure we wanted to know whether a long-term improvement of cardiac function in non-ischemic heart failure can be achieved by stem cell transplantation. METHODS: White male New Zealand rabbits were treated with doxorubicin (3 mg/kg/week; 6 weeks) to induce dilative non-ischemic cardiomyopathy. Thereafter, we obtained autologous bone marrow stem cells (BMSC) and injected 1.5-2.0 Mio cells in 1 ml medium by infiltrating the myocardium via a left anterolateral thoracotomy in comparison to sham-operated rabbits. 4 weeks later intracardiac contractility was determined in-vivo using a Millar catheter. Thereafter, the heart was excised and processed for radioligand binding assays to detect beta1- and beta2-adrenoceptor density. In addition, catecholamine plasma levels were determined via HPLC. In a subgroup we investigated cardiac electrophysiology by use of 256 channel mapping. RESULTS: In doxorubicin-treated animals beta-adrenoceptor density was significantly down-regulated in left ventricle and septum, but not in right ventricle, thereby indicating a typical left ventricular heart failure. Sham-operated rabbits exhibited the same down-regulation. In contrast, BMSC transplantation led to significantly less beta-adrenoceptor down-regulation in septum and left ventricle. Cardiac contractility was significantly decreased in heart failure and sham-operated rabbits, but was significantly higher in BMSC-transplanted hearts. Norepinephrine and epinephrine plasma levels were enhanced in heart failure and sham-operated animals, while these were not different from normal in BMSC-transplanted animals. Electrophysiological mapping revealed unaltered electrophysiology and did not show signs of arrhythmogeneity. CONCLUSION: BMSC transplantation improves sympathoadrenal dysregulation in non-ischemic heart failure.

Modeling of temperature mapping for quantitative dynamic infrared coronary angiography for intraoperative graft patency control.

OBJECTIVES: Intraoperative application of thermal coronary angiography based on dynamic infrared imaging leads to useful qualitative information concerning coronary artery bypass graft flow and anatomy. Additional quantitative flow estimation is desirable to detect graft failures. The aim of this study was to develop a heat-transfer model for quantitative flow estimation in an experimental setup. The first clinical results in coronary artery bypass grafting are reported. METHODS: Dynamic infrared imaging was applied in pig hearts to collect video data of the rewarming process of the left anterior descending artery supplied by antegrade perfusion. For mathematic description, we used the dynamic enthalpy balance for open systems, and a Laplace transformation was carried out. Therefore the time constant tau was calculated by performing a nonlinear fit procedure on the averaged dynamic temperature curves recorded over a left anterior descending artery segment. Subsequently, left internal thoracic artery-left anterior descending artery bypass graft flow was assessed intraoperatively. Effective left anterior descending artery flow was determined by using a transit-time flowmeter. RESULTS: Tau is a system constant and changes depending on the flow and the system capacity. Assuming system capacity to be constant, tau only depends on the flow. It follows from the differential equation that there is a potential relation between tau and the flow. An excellent comparison (R2 = 0.968, P <.005) was demonstrated. By using the algorithms, quantitative flow estimation in pig hearts was possible. For clinical application, the formulas were applied to intraoperatively derived dynamic temperature curves with a good comparison to the actual left internal thoracic artery-left anterior descending artery flow. CONCLUSION: The developed heat-transfer model allows for precise measurement of graft flow by using dynamic infrared imaging and can be applied for noninvasive graft flow estimation in beating-heart surgery.

Ablation of atrial fibrillation and esophageal injury: effects of energy source and ablation technique.

OBJECTIVE: The aim of this study was the evaluation of histologic changes induced on the esophagus by surgical ablation therapy for atrial fibrillation. METHODS: Experiments were performed on 39 sheep. Circular lesions were created endocardially or epicardially in the left atrium and at the pulmonary veins by using different energy sources: cryoablation, microwave, laser, and unipolar or bipolar radiofrequency. Temperatures inside the esophagus were measured, and esophageal tissue was investigated macroscopically and histopathologically. RESULTS: Esophageal damage was seen histologically in 24 of 39 cases. The epithelium was intact in all cases. Unipolar radiofrequency induced the most intensive esophageal lesions in 4 of 6 cases. The affected areas were small (1.56-3.01 mm) but reached deep into the tissue. Endocardial cryoablation resulted in wider lesions (2.01-8.54 mm), which were intensive in only 2 of 6 cases. Epicardial cryoablation and bipolar radiofrequency induced wide (1.11-6.8 mm) but mainly mild alterations. Endocardial and epicardial microwave energy affected the esophagus in single cases, and lesions were small (0.97-2.81 mm). Only in 1 case did laser energy induce a moderate alteration (5.30 mm) of the esophageal wall. CONCLUSIONS: Esophageal alterations were found in numerous cases. However, marked lesions were especially induced by endocardial unipolar radiofrequency and cryoablation.

Histological findings induced by different energy sources in experimental atrial ablation in sheep.

The aim of this study was a detailed comparative investigation of acute cardiac alterations induced by different energy sources and approaches in a sheep model. Experiments were performed on 39 sheep. Circular lesions were created endo- or epicardially in the left atrium and at the pulmonary veins using different energy sources: cryo, microwave, laser and unipolar or bipolar radiofrequency (RF). Electrophysiological examinations were performed immediately post treatment and 2 h after ablation to prove conduction block. Altered areas of the atria and pulmonary veins were investigated histopathologically. Endocardial ablation resulted in transmural lesions, confirmed by electrophysiological examinations. However, endocardial microwave and laser induced intensive thrombus formation, whereas radiofrequency and cryoablation induced more circumscribed necrosis and led to little endocardial thrombi. Epicardial cryoablation and microwave energy were not successful in acute phase in 8 of 9 animals. In contrast, epicardial bipolar RF was efficient and resulted in well demarcated slim lesion lines but induced marked thrombus formation. It can be summarized that surgical ablation techniques using different energy sources and approaches in this acute animal model resulted in different electrophysiological effectiveness and histomorphological lesions. Further mid and long term studies are necessary to confirm these results.