Fellery de Lange

A novel survival model of cardioplegic arrest and cardiopulmonary bypass in rats: a methodology paper

BackgroundGiven the growing population of cardiac surgery patients with impaired preoperative cardiac function and rapidly expanding surgical techniques, continued efforts to improve myocardial protection strategies are warranted. Prior research is mostly limited to either large animal models or ex vivo preparations. We developed a new in vivo survival model that combines administration of antegrade cardioplegia with endoaortic crossclamping during cardiopulmonary bypass (CPB) in the rat.MethodsSprague-Dawley rats were cannulated for CPB (n = 10). With ultrasound guidance, a 3.5 mm balloon angioplasty catheter was positioned via the right common carotid artery with its tip proximal to the aortic valve. To initiate cardioplegic arrest, the balloon was inflated and cardioplegia solution injected. After 30 min of cardioplegic arrest, the balloon was deflated, ventilation resumed, and rats were weaned from CPB and recovered. To rule out any evidence of cerebral ischemia due to right carotid artery ligation, animals were neurologically tested on postoperative day 14, and their brains histologically assessed.ResultsThirty minutes of cardioplegic arrest was successfully established in all animals. Functional assessment revealed no neurologic deficits, and histology demonstrated no gross neuronal damage.ConclusionThis novel small animal CPB model with cardioplegic arrest allows for both the study of myocardial ischemia-reperfusion injury as well as new cardioprotective strategies. Major advantages of this model include its overall feasibility and cost effectiveness. In future experiments long-term echocardiographic outcomes as well as enzymatic, genetic, and histologic characterization of myocardial injury can be assessed. In the field of myocardial protection, rodent models will be an important avenue of research.

Three-Dimensional Transesophageal Echocardiography for Perioperative Right Ventricular Assessment

BACKGROUND In high-risk cardiac procedures, dynamic analysis of right ventricular (RV) performance is desirable, but the geometric complexity of the RV limits the applicability of current two-dimensional echocardiographic imaging techniques. This study aimed to evaluate the utility of three-dimensional transesophageal echocardiography (TEE) for the perioperative assessment of RV function and dimensions. METHODS Patients undergoing cardiac surgical procedures with complete TEE examinations were identified and reviewed according to current guidelines to exclude patients with significant coexisting valvular regurgitation. Full-volume, three-dimensional datasets were analyzed by two independent investigators using stand-alone software, and left ventricular and RV dimensions were recorded. RESULTS Datasets from 50 patients undergoing cardiac surgical procedures were evaluated for this study. The mean RV volume was 111.7 mL (range, 37.5 to 349.7 mL) at end diastole and 67.6 mL (range, 25.5 to 274.4 mL) at end systole. Intraobserver reliability was 0.93 and 0.90 for end diastolic and 0.77 and 0.87 for end systolic volumes. The interobserver reliability for RV volumes was 0.83 at end diastole and 0.86 at end systole. The mean stroke volume was 43.6 mL (range, 12 to 111.2 mL) for the RV and 49.1 mL (range, 19.9 to 102.8 mL) for the left ventricle; the correlation coefficient between the two was 0.85. CONCLUSIONS Three-dimensional TEE volumetric measurements were reproducible across a wide range of RV dimensions. As postulated by the continuity principle, stroke volume measurements between both ventricles correlated well, supporting the validity of this approach. Therefore, our work provides preliminary evidence that three-dimensional TEE offers reproducible information about RV function and size in the dynamic and complex perioperative setting of cardiac surgical procedures.

Effect of combined anticoagulation using heparin and bivalirudin on the hemostatic and inflammatory responses to cardiopulmonary bypass in the rat.

Background:Despite high-dose heparin anticoagulation, cardiopulmonary bypass (CPB) is still associated with marked hemostatic activation. The purpose of this study was to determine whether a reduced dose of bivalirudin, added as an adjunct to heparin, would reduce thrombin generation and circulating markers of inflammatory system activation during CPB as effectively as full-dose bivalirudin, without adversely affecting postoperative hemostasis. Methods:Using a model of normothermic CPB in rats, the authors prospectively compared markers of thrombin generation (thrombin–antithrombin complexes) and inflammatory markers (tumor necrosis factor α, interleukin 1β, interleukin 6, and interleukin 10) in three groups: conventional high-dose heparin (H), full-dose bivalirudin (B), and a combined group (standard high-dose heparin with the addition of reduced dose bivalirudin or H&B), at baseline, after 60 min of CPB, and 60 min after CPB. Postoperative hemostasis was also assessed. Results:Groups H&B and B showed reduced thrombin–antithrombin complex formation during CPB compared with group H (P = 0.0003), and this persisted after CPB for group B (P = 0.009). Perioperative increases in interleukin 6 and interleukin 10 showed a trend toward being reduced in animals receiving bivalirudin (P = 0.06). Evidence of residual anticoagulation was found in group H&B as measured by activated clotting time (P = 0.04) and activated partial thromboplastin time (P = 0.02), but no intergroup difference in primary hemostasis was found. Conclusions:Bivalirudin attenuates hemostatic activation during experimental CPB with potential effects on markers of the inflammatory response. However, with this dosing regimen, the combination of heparin and bivalirudin does not seem to confer any measurable advantages over full-dose bivalirudin anticoagulation.

Intraoperative High-Dose Dexamethasone and Severe AKI after Cardiac Surgery

Administration of prophylactic glucocorticoids has been suggested as a strategy to reduce postoperative AKI and other adverse events after cardiac surgery requiring cardiopulmonary bypass. In this post hoc analysis of a large placebo-controlled randomized trial of dexamethasone in 4465 adult patients undergoing cardiac surgery, we examined severe AKI, defined as use of RRT, as a primary outcome. Secondary outcomes were doubling of serum creatinine level or AKI-RRT, as well as AKI-RRT or in-hospital mortality (RRT/death). The primary outcome occurred in ten patients (0.4%) in the dexamethasone group and in 23 patients (1.0%) in the placebo group (relative risk, 0.44; 95% confidence interval, 0.19 to 0.96). In stratified analyses, the strongest signal for potential benefit of dexamethasone was in patients with an eGFR<15 ml/min per 1.73 m(2). In conclusion, compared with placebo, intraoperative dexamethasone appeared to reduce the incidence of severe AKI after cardiac surgery in those with advanced CKD.

Dexamethasone for the prevention of postoperative atrial fibrillation

BACKGROUND Postoperative atrial fibrillation (AF) is a common complication after cardiac surgery. Inflammation is believed to play a pivotal role in the etiology of postoperative AF. There is a suggestion from small studies that perioperative treatment with corticosteroids may reduce postoperative AF. The DExamethasone for Cardiac Surgery (DECS) study was a large randomized trial showing no protective effect of dexamethasone on major adverse events. The aim of this study was to investigate the effect of dexamethasone treatment on the occurrence of AF after cardiac surgery. METHODS The DECS study compared intra-operative dexamethasone (1mg/kg) or placebo treatment in 4494 adult patients undergoing cardiac surgery. AF was defined by the occurrence of any reported AF within 30days after surgery. We also performed an in-depth analysis of a subset of 1565 patients on new-onset AF. Relative risks (RRs) with 95% confidence intervals (CIs) were calculated. RESULTS The incidence of any AF in the main study of 4494 patients was 33.1% in the dexamethasone and 35.2% in the placebo group (RR 0.94, 95% CI: 0.87-1.02, p=0.14). In the substudy of 1565 patients, the incidence of new-onset AF was 33.0% vs. 35.5% (RR 0.93, 95% CI: 0.81-1.07, p=0.31), respectively. There was no protective effect of dexamethasone across clinically important patient subgroups. CONCLUSION Intraoperative administration of dexamethasone had no protective effect on the occurrence of any or new-onset atrial fibrillation after cardiac surgery. Therefore, the use of dexamethasone for the reduction of postoperative AF should not be recommended.

Reduction in air bubble size using perfluorocarbons during cardiopulmonary bypass in the rat.

BACKGROUND: Perfluorocarbon (PFC) emulsions are artificial oxygen-carrying compounds with a high solubility for gases that have experimentally been shown to ameliorate cerebral air embolism. Cerebral air embolism has been associated with adverse cerebral outcomes after cardiac surgery using cardiopulmonary bypass (CPB). We designed this study to test whether PFC emulsions could reduce the volume of bubbles within the CPB circuit. METHODS: Male Sprague-Dawley rats undergoing 60 min of normothermic nonpulsatile CPB were randomized to one of the three groups. The PFC group (n = 10) received 60% O2/36% N2/4% CO2 via the membrane oxygenator and 2.7 g/kg (4.5 mL/kg) of PFC into the venous reservoir; the control group (n = 10) received the same gas mixture and 4.5 mL/kg of saline; the N2O group (n = 6) was exposed to 36% N2O/60% O2/4% CO2 and received 4.5 mL/kg of saline. After 10 min and 35 min of CPB, 400 &mgr;L of air was injected into a bubble chamber in the CPB circuit. After 20 min, the bubble was removed for volumetric analysis. RESULTS: Compared with baseline, the bubble decreased 13% ± 5% in size in the PFC group and increased 46% ± 9% in the nitrous oxide group, both of these changes significantly different from the control group (P < 0.0001). CONCLUSION: The results suggest that PFC administration may be useful in reducing the volume of gaseous bubbles present during CPB.

Perfluorocarbon administration during cardiopulmonary bypass in rats: an inflammatory link to adverse outcome?

BACKGROUND:Perfluorocarbon (PFC) emulsions are artificial oxygen carriers that have been shown to attenuate the effects of air embolism. Cerebral air embolism, known to occur during cardiopulmonary bypass (CPB), may contribute to adverse cerebral outcomes after cardiac surgery. We designed this study to evaluate the effect of a 60% PFC emulsion (perfluoro-tert-butylcyclohexane; PTBCH) on the inflammatory response and neurocognitive outcome of rats after CPB. METHODS:Twenty-eight Sprague Dawley rats subjected to 60 min of CPB were randomly divided into two groups: PTBCH CPB animals receiving 3 mL/kg of PTBCH into the venous reservoir and control CPB animals receiving 3 mL/kg of 0.9% saline. At several time points, the cytokines interleukin (IL)-1&bgr;, IL-6, IL-10, and tumor necrosis factor (TNF)-&agr; were measured. Neurocognitive testing was planned postoperatively using the Morris water maze. Histologic samples were obtained in a separate series of experiments. RESULTS:Physiologic variables were comparable between groups, but the PTBCH CPB animals required more phenylephrine compared with the controls. Cytokine levels in the PTBCH CPB group were significantly higher than in the control group at 2 and 4 h after CPB (P < 0.05). Neurocognitive outcome could not be evaluated as none of the animals in the PTBCH CPB group survived. Myocardial histological analysis revealed increased areas of contraction band necrosis in the PTBCH CPB animals (P = 0.034). CONCLUSIONS:Administration of PTBCH during CPB was associated with an excessive release of cytokines. This enhanced inflammatory response with subsequent hypotension may have contributed to mortality in rats receiving PTBCH. The observed patterns of myocardial injury indicate global hypoperfusion and catecholamine excess.

Impaired microcirculatory perfusion in a rat model of cardiopulmonary bypass: the role of hemodilution

Although hemodilution is attributed as the main cause of microcirculatory impairment during cardiopulmonary bypass (CPB), this relationship has never been investigated. We investigated the distinct effects of hemodilution with or without CPB on microvascular perfusion and subsequent renal tissue injury in a rat model. Male Wistar rats (375-425 g) were anesthetized, prepared for cremaster muscle intravital microscopy, and subjected to CPB (n = 9), hemodilution alone (n = 9), or a sham procedure (n = 6). Microcirculatory recordings were performed at multiple time points and analyzed for perfusion characteristics. Kidney and lung tissue were investigated for mRNA expression for genes regulating inflammation and endothelial adhesion molecule expression. Renal injury was assessed with immunohistochemistry. Hematocrit levels dropped to 0.24 ± 0.03 l/l and 0.22 ± 0.02 l/l after onset of hemodilution with or without CPB. Microcirculatory perfusion remained unaltered in sham rats. Hemodilution alone induced a 13% decrease in perfused capillaries, after which recovery was observed. Onset of CPB reduced the perfused capillaries by 40% (9.2 ± 0.9 to 5.5 ± 1.5 perfused capillaries per microscope field; P < 0.001), and this reduction persisted throughout the experiment. Endothelial and inflammatory activation and renal histological injury were increased after CPB compared with hemodilution or sham procedure. Hemodilution leads to minor and transient disturbances in microcirculatory perfusion, which cannot fully explain impaired microcirculation following cardiopulmonary bypass. CPB led to increased renal injury and endothelial adhesion molecule expression in the kidney and lung compared with hemodilution. Our findings suggest that microcirculatory impairment during CPB may play a role in the development of kidney injury.

Exacerbation of systemic inflammation and increased cerebral infarct volume with cardiopulmonary bypass after focal cerebral ischemia in the rat

OBJECTIVE Stroke remains a significant contributor to morbidity and mortality after cardiac surgery. Cardiopulmonary bypass is known to induce a significant inflammatory response, which could adversely influence outcomes. We hypothesized that cardiopulmonary bypass, through an enhanced systemic inflammatory response, might affect outcomes after focal cerebral ischemia. METHODS Wistar rats (275-300 g) were anesthetized, surgically prepared for cardiopulmonary bypass and right middle cerebral artery occlusion, and randomly allocated to 2 groups: focal cerebral ischemia alone (n = 9) and focal cerebral ischemia combined with normothermic cardiopulmonary bypass (n = 8). Serum cytokines (tumor necrosis factor alpha and interleukins 1beta, 6, and 10) were measured at baseline, at end of bypass, and at 2, 6, and 24 hours after bypass. On postoperative day 3, animals underwent neurologic testing, after which the brains were prepared for assessment of cerebral infarct volume. Data were compared between groups by Mann-Whitney U test. RESULTS Compared with the ischemia-alone group, the ischemia plus bypass group had significantly higher levels of circulating tumor necrosis factor alpha and interleukins 1beta and 10 at the end of bypass and 2 hours after bypass. In addition, the ischemia plus bypass animals had larger total cerebral infarct volumes (286 +/- 125 mm(3)) than did those with ischemia alone (144 +/- 85 mm(3), P = .0124). CONCLUSIONS Cardiopulmonary bypass increased cerebral infarct size after focal cerebral ischemia in rats. This worsening of outcome may in part be related to an augmented inflammatory response that accompanies cardiopulmonary bypass.

Right Ventricular Function After Cardiac Surgery Is a Strong Independent Predictor for Long-Term Mortality

OBJECTIVE To establish the all-cause mortality of right ventricular dysfunction after cardiac surgery in a heterogeneous group of cardiac surgery patients. DESIGN Retrospective analysis of a heterogeneous group of 1,109 cardiac surgery patients in a 4-year period. SETTING Single-center study in a tertiary teaching hospital. PARTICIPANTS One thousand one hundred nine cardiac surgery patients. By protocol, patients were monitored with a pulmonary artery catheter, enabling continuous right ventricular ejection fraction (RVEF) measurements. INTERVENTIONS None. MEASUREMENTS AND MAIN RESULTS Measurements were performed once per minute for the first 24 postoperative hours and expressed as average over the complete period. Primary outcome was 2-year all-cause mortality. RVEF was categorized into 3 subgroups: <20%, 20-30%, and >30%. Median follow-up time was 739 days. Two-year mortality was significantly different across groups: 4.1% for patients with RVEF >30%, 8.2% in the group with RVEF 20-30%, and 16.7% for patients with RVEF <20%, p < 0.001. Additional risk factors for a poor RVEF were age, body weight, New York Heart Association class, chronic obstructive pulmonary disease, poor left ventricular function, and higher risk scores (Acute Physiology and Chronic Health Evaluation and European System for Cardiac Operative Risk Evaluation). In a multivariate analysis, RVEF as a continuous variable was associated independently with the primary outcome (odds ratio 0.95 confidence interval 0.91-0.99, p = 0.011.) Odds ratios for RVEF <20% were 1.88 (confidence interval 1.18-3.00, p = 0.008). CONCLUSIONS Right ventricular function is associated independently with 2-year all-cause mortality in a heterogenic cardiac surgery population.