Normothermic ex vivo perfusion prevents lung injury compared to extended cold preservation for transplantation.

Treatment of injured donor lungs ex vivo to accelerate organ recovery and ameliorate reperfusion injury could have a major impact in lung transplantation. We have recently demonstrated a feasible technique for prolonged (12 h) normothermic ex vivo lung perfusion (EVLP). This study was performed to examine the impact of prolonged EVLP on ischemic injury. Pig donor lungs were cold preserved in Perfadex for 12 h and subsequently divided into two groups: cold static preservation (CSP) or EVLP at 37 degrees C with Steen solution for a further 12 h (total 24 h preservation). Lungs were then transplanted and reperfused for 4 h. EVLP preservation resulted in significantly better lung oxygenation (PaO(2) 531 +/- 43 vs. 244 +/- 49 mmHg, p < 0.01) and lower edema formation rates after transplantation. Alveolar epithelial cell tight junction integrity, evaluated by zona occludens-1 protein staining, was disrupted in the cell membranes after prolonged CSP but not after EVLP. The maintenance of integrity of barrier function during EVLP translates into significant attenuation of reperfusion injury and improved graft performance after transplantation. Integrity of functional metabolic pathways during normothermic perfusion was confirmed by effective gene transfer and GFP protein synthesis by lung alveolar cells. In conclusion, EVLP prevents ongoing injury associated with prolonged ischemia and accelerates lung recovery.

Prolonged hypothermic cardiac storage for transplantation. The effects on myocardial metabolism and mitochondrial function.

Cardiac storage for transplantation is currently limited to 6 hours. To better understand the metabolic changes that occur during hypothermic (4 degrees C) storage, we monitored the morphologic and metabolic changes in the canine myocardium at 0, 12, and 24 hours of storage in University of Wisconsin solution. Attempts to isolate cardiac mitochondria resulted in a progressive decline in the yield (milligrams of mitochondria per gram of heart tissue), which decreased (p less than 0.05) from 9.2 +/- 0.4 at 0 hours (control) to 4.0 +/- 0.3 after 12 hours and further decreased (p less than 0.05) to 1.9 +/- 0.2 after 24 hours of cold storage. Mitochondrial state 3 respiration fell to 64% of control after 12 hours and 28% of control after 24 hours of cold storage (p less than 0.05). Citrate synthetase activity, but not cytochrome C oxidase activity, was significantly depressed after 12 and 24 hours of cold storage. Adenosine triphosphate content decreased to 67% of control after 12 hours and 50% of control after 24 hours. After 12 hours of storage, sufficient adenosine diphosphate and monophosphate were present to permit some restoration of adenosine triphosphate, provided mitochondrial function was normal after transplantation. However, restoration of mitochondrial function and adenosine triphosphate levels sufficient to support myocardial contractility was unlikely after 24 hours of storage. This study suggests that a return of adequate cardiac function after transplantation may be possible after 12 hours of cold storage in University of Wisconsin solution but not after 24 hours of cold storage.

Right ventricular function and metabolism.

Right ventricular protection may be limited with current methods of cardioplegic delivery. Sensitive measurements of right and left ventricular function and metabolism were made in 30 patients undergoing elective coronary artery bypass surgery with cold cardioplegic arrest. Myocardial adenine nucleotide concentrations decreased with cardioplegia and reperfusion in both the right and left ventricles despite adequate levels of precursors, suggesting perioperative mitochondrial dysfunction. Postoperatively, right and left ventricular pressures were measured with micromanometer catheters and volumes were measured by nuclear ventriculography. Right and left ventricular systolic elastance was calculated by the isochronic method and by the end-systolic method. Both methods provided sensitive indexes of end-systolic elastance. This study demonstrated that right ventricular function and metabolism can be evaluated by methods analogous to methods used in the left ventricle. These results suggest that right ventricular functional and metabolic recovery are delayed despite apparently adequate myocardial protection. Sensitive measurements may permit improved assessment of alternative methods of right ventricular protection.

The effect of lactate infusion on myocardial metabolism and ventricular function following ischemia and cardioplegia.

Impaired myocardial fatty acid and glucose metabolism following ischemia and cardioplegia may limit the recovery of myocardial oxidative metabolism and ventricular function. Lactate, a simple three carbon compound, can be readily metabolized to pyruvate and is possibly the preferred substrate for aerobic metabolism. Therefore, increasing arterial lactate concentrations may improve myocardial metabolic recovery after ischemia and cardioplegia. Myocardial lactate metabolism and ventricular function were assessed in a canine model of 45 mins of global normothermic ischemia followed by 60 mins of cold potassium cardioplegic arrest. Thirteen dogs received a perioperative infusion of sodium lactate to elevate arterial concentrations (from 6 to 12 mmol/L) and 12 dogs received an equivalent amount of saline. The high arterial lactate concentrations were associated with an increased myocardial lactate consumption and oxidation (as assessed by 14C-labelled lactate) during reperfusion. Myocardial ATP concentrations fell during reperfusion despite improved myocardial oxidation. The recovery of ventricular function (as assessed by a compliant intraventricular balloon) was incomplete and only marginally better with the high arterial lactate concentrations. An infusion of lactate improved myocardial oxidative metabolism following ischemia and cardioplegia. However, the recovery of ventricular function was incomplete perhaps because of inadequate preservation of myocardial ATP.

Myocardial free-radical injury after cardioplegia.

Although cold blood cardioplegia provides excellent myocardial protection for elective coronary bypass surgery, myocardial metabolic recovery is delayed postoperatively, perhaps because of free-radical injury during reperfusion. To assess free-radical reperfusion injury, we measured the products of lipid peroxidation and the cardiac concentrations of alpha tocopherol in 10 patients undergoing elective surgical revascularization. Arterial and coronary sinus blood measurements revealed a delayed recovery of myocardial oxygen consumption and lactate utilization and the myocardial release of conjugated dienes (chemical signatures of free-radical injury) at 3 and 60 minutes after reperfusion. In addition, myocardial concentrations of alpha tocopherol decreased after reperfusion, suggesting consumption of the major membrane antioxidant. These results support the hypothesis that oxygen-derived free radicals contribute to myocardial injury after cardioplegic arrest and that antioxidant therapy should improve myocardial protection.

Delayed myocardial metabolic recovery after blood cardioplegia.

Previous studies have demonstrated that both myocardial metabolism and ventricular function were depressed after blood cardioplegic arrest for elective coronary artery bypass grafting. To evaluate the etiology of this metabolic defect, we measured the levels of adenine nucleotides and their precursors in 29 patients undergoing elective coronary revascularization. Myocardial biopsy specimens were obtained at 37 degrees C before cardioplegic arrest, immediately after 74 +/- 4 minutes of cardioplegic arrest, and after 30 minutes of reperfusion. Biopsy specimens were analyzed for levels of adenine nucleotides and their precursors by high-performance liquid chromatography. Adenosine triphosphate concentrations decreased with cardioplegic arrest and with reperfusion. Adenosine monophosphate concentrations increased after cardioplegic arrest and remained nearly twice the initial values after reperfusion. The ratio of adenosine monophosphate to adenosine triphosphate doubled after reperfusion, suggesting defective conversion of adenosine monophosphate to adenosine triphosphate. Levels of adenine nucleotide degradation products (adenosine, inosine, and hypoxanthine) increased after cardioplegia and decreased with reperfusion, suggesting a washout of soluble precursors. This study suggests that improvements in myocardial protection should attempt to stimulate mitochondrial energy production and preserve adenine nucleotide precursors.

Myocardial salvage with trolox and ascorbic acid for an acute evolving infarction.

Both Trolox (a water-soluble analogue of alpha-tocopherol) and ascorbic acid were more effective than superoxide dismutase or catalase in protecting myocyte cell cultures from free radical attack (induced by hypoxanthine and xanthine oxidase). In a canine model of two hours of left anterior descending coronary artery occlusion followed by four hours of reperfusion, Trolox and ascorbic acid reduced the area of infarction within the area at risk. The Trolox group received 500 mL of deoxygenated saline solution containing 2.0 g of Trolox, 3.0 g of ascorbic acid, and 18 mg of EDTA (ethylenediaminetetraacetic acid) infused into the ascending aorta 30 seconds before and four minutes after reperfusion. Saline controls received 500 mL of deoxygenated saline solution containing 18 mg of EDTA. The angioplasty group had unmodified reperfusion by simple release of the occlusion. The area at risk and the area infarcted were estimated with Evans blue and triphenyl tetrazolium hydrochloride stains, respectively. The ratio of the area infarcted to the area at risk was significantly lower with Trolox (angioplasty, 30.4% +/- 5.1%; saline, 20.8% +/- 2.9%; and Trolox, 8.7% +/- 4.0%; p less than 0.01). In summary, the antioxidants Trolox and ascorbic acid effectively reduced myocardial necrosis after ischemia.

Right and left ventricular metabolites.

Current methods of cardioplegic delivery may delay the recovery of right ventricular metabolism and function. To evaluate right and left ventricular metabolism, we performed biopsies in 37 patients undergoing elective coronary bypass operation with aortic root blood cardioplegia. Right ventricular temperatures were warmer than left ventricular temperatures during cardioplegic arrest (right ventricle: 16.8 degrees +/- 3.8 degrees C, left ventricle: 14.3 degrees +/- 3.7 degrees C, p = 0.02). Adenosine triphosphate concentrations were lower in the right ventricle than in the left ventricle before cardioplegic arrest (right ventricle: 13.8 +/- 7.8 mmol/kg, left ventricle: 21.5 +/- 8.7 mmol/kg, p = 0.02). After reperfusion, right ventricular adenosine triphosphate concentrations fell to low levels (10 +/- 6 mmol/kg). Postoperative left and right ventricular high energy phosphate concentrations (the sum of adenosine triphosphate and creatine phosphate levels) correlated inversely with myocardial temperatures during cardioplegia (r = -0.29, p = 0.048). Aortic root cardioplegia did not cool the right ventricle as well as it did the left ventricle. The lower preoperative high energy phosphate concentrations may have increased the susceptibility of the right ventricle to ischemic injury. Alternative methods of myocardial preservation may improve right ventricular cooling and protection.

Dipyridamole preserved platelets and reduced blood loss after cardiopulmonary bypass.

Cardiopulmonary bypass activates and depletes platelets, which may contribute to postoperative bleeding. In addition, activated platelets may be deposited in the coronary vasculature after ischemia and cardioplegia, which may delay recovery of cardiac function and metabolism and may contribute to early bypass graft occlusion. The antiplatelet agent dipyridamole reduces platelet activation and depletion and may decrease postoperative bleeding and transfusion requirements. A prospective randomized trial was conducted in 58 patients undergoing elective coronary bypass operations to compare the effects of oral (19 patients) and intravenous (21 patients) dipyridamole to the results obtained in a control group (18 patients) who received no dipyridamole. Preoperative oral administration of dipyridamole resulted in lower plasma drug concentrations in the early postoperative period than perioperative intravenous administration (p = 0.0001 by analysis of variance). Postoperative arterial platelet counts were highest in the patients receiving intravenous dipyridamole, intermediate in those receiving oral dipyridamole, and lowest in the control group (p = 0.03 by analysis of variance). Postoperative blood loss and blood product transfusions were significantly reduced with both oral and intravenous dipyridamole (p = 0.04 by analysis of variance). Dipyridamole preserved platelets and reduced postoperative bleeding. Intravenous dipyridamole resulted in higher platelet counts than oral dipyridamole and may be required to reduce postoperative bleeding in high-risk patients.

Postoperative hypertension: a comparison of diltiazem, nifedipine, and nitroprusside.

In previous studies, the treatment of postoperative hypertension with sodium nitroprusside induced ischemic metabolism without a decrease in coronary sinus blood flow. In contrast, the calcium antagonists diltiazem and nifedipine reduce blood pressure and may improve myocardial metabolism. A prospective randomized trial was performed in 62 patients, in whom hypertension developed (mean arterial pressure greater than 95 mm Hg) after coronary bypass procedures, to compare diltiazem (n = 22), nifedipine (n = 20), and nitroprusside (n = 20). All three agents reduced blood pressure equally (p less than 0.0001, by analysis of variance). Heart rate decreased with diltiazem (p = 0.006) but increased with nifedipine and nitroprusside (p less than 0.05). Left ventricular diastolic function (the relation between left atrial pressure and left ventricular end-diastolic volume) was not changed with the three drugs. Systolic function (the relation between systolic blood pressure and left ventricular end-systolic volume) was depressed with diltiazem (p = 0.05 by analysis of covariance) and nifedipine (p = 0.05) but not with nitroprusside. Myocardial performance (the relation between left ventricular stroke work index and end-diastolic volume) was depressed most by diltiazem (p = 0.001 by analysis of covariance), and to a lesser extent with nifedipine (p = 0.03), but not with nitroprusside. Myocardial lactate flux in response to the stress of atrial pacing decreased with nitroprusside but not with diltiazem or nifedipine (p = 0.03 by analysis of variance). Diltiazem and nifedipine are effective agents for treating postoperative hypertension after coronary artery bypass operations.

Improving myocardial metabolic and functional recovery after cardioplegic arrest.

The myocardial oxidation of fatty acids and glucose, the predominant substrates for aerobic metabolism, is impaired after cardioplegic arrest for coronary revascularization. Because lactate can be readily metabolized to pyruvate, it may be the preferred substrate for aerobic metabolism after cardioplegic arrest when arterial concentrations are elevated. Nineteen patients undergoing elective coronary revascularization with blood cardioplegia were randomized to receive LOW (nine patients, no exogenous lactate) or HIGH (10 patients, a perioperative infusion of Ringer's lactate) arterial lactate concentrations. Coronary sinus catheterization and lactate labeled with carbon 14 permitted calculation of myocardial oxygen consumption and lactate oxidation which were significantly increased during reperfusion in the group with HIGH arterial lactate concentrations. Atrial pacing at 110 beats/min on cardiopulmonary bypass resulted in myocardial lactate production (suggesting ischemic anaerobic metabolism) in the LOW lactate group, but atrial pacing increased lactate consumption and oxidation in the HIGH lactate group (suggesting increased aerobic metabolism). Systolic function (the relation between end-systolic pressure and volume) as assessed by nuclear ventriculography 3 hours postoperatively was significantly better (p less than 0.05 by analysis of covariance) in the HIGH lactate group. Postoperative myocardial creatine kinase release was significantly lower in the HIGH lactate group, which suggested less perioperative ischemic injury. Lactate was the preferred substrate for myocardial oxidative metabolism after cardioplegic arrest, and the higher arterial lactate concentrations improved myocardial metabolic and functional recovery and reduced perioperative ischemic injury.

Effects of anesthetic induction on myocardial function and metabolism: a comparison of fentanyl, sufentanil and alfentanil.

Anaesthetic induction may induce myocardial ischaemia. A prospective randomized trial was instituted to compare the effect on ventricular function and myocardial metabolism of induction with fentanyl (FEN) or its analogues sufentanil (SUF) or alfentanil (ALF) in 96 patients undergoing elective coronary artery bypass grafting (CABG). Haemodynamic, metabolic (coronary sinus oxygen and lactate extraction) and gated ventriculographic measurements were made awake pre-induction (PRE), after induction (IND) and after intubation (INT). Induction was performed with FEN 75 micrograms.kg-1, SUF 15 micrograms.kg-1 or ALF 125 micrograms.kg-1 and metocurine. Fentanyl induction was associated with the greatest stability of mean arterial pressure (MAP), cardiac performance, and systolic function without associated myocardial lactate production. SUF produced the greatest depression of systolic function (p less than 0.05) but without haemodynamic instability or myocardial lactate production in all but one patient. Induction with ALF produced the greatest reduction in MAP (p less than 0.05) associated with the greatest decrease in diastolic compliance (p less than 0.05) and 50 per cent incidence of myocardial lactate production (p less than 0.05) with no significant change in coronary blood flow or myocardial oxygen consumption.

Decreased postoperative myocardial fatty acid oxidation.

Myocardial substrate preferences following cardioplegic arrest for coronary bypass surgery have not been established. Fatty acids are believed to be the major fuel source for aerobic metabolism. Following cardioplegic arrest arterial fatty acid levels are elevated and myocardial fatty acid accumulation without oxidation may contribute to reperfusion injury. Perioperative fatty acid metabolism was evaluated in 18 patients undergoing elective coronary bypass surgery who were randomized to receive either blood (n = 11) or crystalloid (n = 7) cardioplegia. Palmitate labeled with 14carbon was infused perioperatively and arterial and coronary sinus blood samples were obtained to calculate myocardial fatty acid extraction and oxidation before and after cardioplegic arrest. Lactate and glycerol were released from the heart during both blood and crystalloid cardioplegia, suggesting ischemic glycolysis and lipolysis. Myocardial oxygen consumption was depressed and the myocardial consumptions of lactate, glucose, and fatty acids were minimal during the first 60 min after aortic clamp removal in both groups despite high arterial concentrations. Fatty acid oxidation was minimal after blood cardioplegia and was not found after crystalloid cardioplegia. Fatty acids were extracted by the heart, but were not aerobically metabolized following cardioplegic arrest. Myocardial fatty acid accumulation without oxidation may have been deleterious. The inability of the heart to oxidize exogenous fatty acids may reflect altered myocardial exogenous substrate preferences during reperfusion following coronary bypass surgery.

Atrial activity during cardioplegia and postoperative arrhythmias.

Cardioplegia provides excellent protection for the left ventricle, but the right atrium may be poorly protected. Myocardial temperatures, right atrial electrical activity, and postoperative arrhythmias were assessed in 103 patients participating in two consecutive randomized trials comparing blood cardioplegia (n = 36), crystalloid cardioplegia (n = 38), and diltiazem crystalloid cardioplegia (n = 29). Both right atrial and right ventricular temperatures were significantly warmer (p less than 0.05) during delivery of the blood cardioplegic solution than during delivery of either the crystalloid or the diltiazem crystalloid cardioplegic solutions; the aortic root temperatures were 9 degrees +/- 2 degrees C with blood cardioplegia and 5 degrees + 1 degrees C with both crystalloid and diltiazem crystalloid cardioplegia. Atrial activity during cardioplegic arrest was greatest with blood cardioplegia (12 +/- 3 beats/min), lower with crystalloid cardioplegia (10 +/- 2 beats/min), and minimal with diltiazem crystalloid cardioplegia (5 +/- 1 beats/min, p less than 0.05). Perioperative ischemic injury (by creatine kinase MB isoenzyme analysis) was greatest with crystalloid cardioplegia (p less than 0.05). Postoperative supraventricular arrhythmias (both treated and untreated) were more frequent after crystalloid cardioplegia (crystalloid, 63%; blood, 40%; diltiazem, 47%; p less than 0.05). Patients in whom supraventricular arrhythmias developed had significantly more postoperative ischemic injury (by creatinine kinase MB isoenzyme analysis, p less than 0.05). Blood cardioplegia reduced supraventricular arrhythmias by reducing ischemic injury despite warmer intraoperative temperatures and more right atrial activity. Diltiazem crystalloid cardioplegia reduced postoperative arrhythmias by improving intraoperative myocardial protection and suppressing intraoperative and postoperative atrial activity. Crystalloid cardioplegia cooled but did not arrest the right atrium intraoperatively, resulted in the most perioperative ischemic injury, and yielded the highest incidence of postoperative supraventricular arrhythmias.

Blood conservation with membrane oxygenators and dipyridamole.

Cardiopulmonary bypass induces platelet activation and dysfunction, which result in platelet deposition and depletion. Reduced platelet numbers and abnormal platelet function may contribute to postoperative bleeding. A membrane oxygenator may preserve platelets and reduce bleeding more than a bubble oxygenator, and the antiplatelet agent dipyridamole may protect platelets intraoperatively and reduce bleeding postoperatively. A prospective randomized trial was performed in 44 patients undergoing elective coronary artery bypass grafting to assess the effects of the membrane oxygenator and dipyridamole on platelet counts, platelet activation products, and postoperative bleeding. Patients who were randomized to receive a bubble oxygenator and no dipyridamole had the lowest postoperative platelet counts, the greatest blood loss, and the most blood products transfused. Platelet counts were highest and blood loss was least in patients randomized to receive a membrane oxygenator and dipyridamole (p less than .05). A bubble oxygenator with dipyridamole and a membrane oxygenator without dipyridamole resulted in intermediate postoperative platelet counts and blood loss. Arterial thromboxane B2 and platelet factor 4 concentrations were elevated on cardiopulmonary bypass in all groups. Both the membrane oxygenator and dipyridamole were independently effective (by multivariate analysis) in preserving platelets. Optimal blood conservation was achieved with a membrane oxygenator and dipyridamole.

Dipyridamole reduced myocardial platelet and leukocyte deposition following ischemia and cardioplegia.

Urgent coronary revascularization for acute myocardial ischemia results in an increased mortality and morbidity. Deposition of activated platelets and leukocytes into the ischemic myocardium during reperfusion may augment perioperative ischemic injury. Dipyridamole reduces platelet activation and may reduce myocardial deposition and prevent ischemic injury during reperfusion. The effects of dipyridamole on myocardial platelet and leukocyte deposition were evaluated in a canine model of acute regional myocardial ischemia with reperfusion during cardioplegia on cardiopulmonary bypass. Eight dogs underwent left anterior descending (LAD) coronary artery ligation for 45 min followed by cardiopulmonary bypass and release of the ligature during 60 min of cold crystalloid cardioplegic arrest to simulate urgent revascularization. Four dogs were randomized to receive an infusion of dipyridamole perioperatively (50 mg/hr) and 4 dogs served as controls. Autologous platelets were labeled with 111In, leukocytes with 99mTc, and erythrocytes with 51Cr. The labeled cells were infused immediately after cross-clamp release and myocardial biopsies were obtained at 10, 20, 30, and 60 min of reperfusion. Platelets were deposited in the myocardium during reperfusion and four times more platelets were found in the LAD region than the circumflex region. Leukocyte deposition was similar in the LAD and circumflex regions. Dipyridamole reduced both platelet and leukocyte deposition and the reduction was greater in the LAD than in the circumflex region. Myocardial platelet and leukocyte deposition was found after regional ischemia, cardioplegia, and cardiopulmonary bypass. Dipyridamole reduced myocardial platelet and leukocyte deposition and may reduce perioperative ischemic injury.

Transient biventricular dysfunction following coronary bypass surgery with potassium cardioplegia.

Although myocardial revascularization relieves anginal symptoms, the effect on ventricular function remains controversial. Sixty-six patients undergoing elective coronary bypass surgery with normal right and left ventricular function were studied 1 month preoperatively (PRE), 3-5 hours perioperatively (PERI) and 3-5 months postoperatively (POST). Nuclear ventriculograms were employed to calculate right and left ventricular ejection fractions (RVEF, LVEF), end diastolic volume indices (RVEDVI, LVEDVI) and end systolic volume indices (RVESVI, LVESVI). Cardiac index (CI), stroke index (SI) and an approximation of left ventricular stroke work index (LVSWI) were also calculated from the scintigraphic data. Right and left ventricular ejection fractions were lower perioperatively (PRE:RVEF 37 +/- 2.5, LVEF 61 +/- 3; PERI:RVEF 32 +/- 3, LVEF 51 +/- 4; POST:RVEF 35 +/- 3, LVEF 56 +/- 4%, p less than 0.01 by analysis of variance, ANOVA) despite lower end diastolic volume indices perioperatively, (p less than 0.05 by ANOVA). The ratio of systolic blood pressure to LVESVI was significantly lower PERI than PRE or POST, (p less than 0.01 by ANOVA). SI, LVSWI, LVEF and RVEF were lower perioperatively at any level of LVEDVI or RVEDVI (p less than 0.01 by paired analyses of covariance), suggesting transient depression of right and left ventricular performance perioperatively. Right ventricular recovery was incomplete 4 months postoperatively. The patients were able to exercise longer at higher workloads postoperatively (p less than 0.01 by ANOVA). Chest pain resulted in discontinuation of exercise in 57% of patients PRE but only 5% POST (p less than 0.01), even though all patients were receiving full medical therapy preoperatively and no therapy postoperatively. Myocardial revascularization provided symptomatic relief and increased work capacity. However, right and left ventricular function were transiently depressed in the early perioperative period.