Changing patterns of patients undergoing emergency surgical revascularization for acute coronary occlusion

The use of controlled reperfusion strategies in cardiac surgery to minimize ischaemia/reperfusion damage

Ischaemia and reperfusion occur during almost every cardiac operation, and one of the key elements to achieve a successful operation is to counteract the detrimental effects of induced ischaemia and reperfusion during the operation. The cardiac surgeon is in a unique position to protect the heart before ischaemia is induced and to avoid further damage during the reperfusion period. The surgeon can alter the composition of the reperfusate and the conditions of reperfusion so that the ischaemia/reperfusion injury is minimal, even after very complex procedures that require long aortic cross-clamp periods. This in turn allows him to perform a near-perfect surgical repair of the underlying disease without the pressure of time. The vast knowledge gained in this field over the years has led to application in other organs, such as the limbs (acute limb ischaemia), lungs (lung transplantation), kidney and liver (kidney and liver transplantation), and more recently even for the brain [acute cerebral artery occlusion (stroke)] and the whole body (cardiopulmonary resuscitation). Further improvements in reperfusion strategies will allow salvage of tissue and even whole body after ischaemic periods thought previously to be irreversibly damaged.

Metabolic changes induced by ischemia and cardioplegia: a study employing cardiac microdialysis in pigs

OBJECTIVE

The present study investigates dynamic changes of myocardial metabolism in response to ischemia, cardioplegia, and extracorporeal circulation (ECC) in order to differentiate between the contributing effects of each of these interventions. Furthermore, warm blood cardioplegia versus empty beating of the heart were compared as methods to resuscitate the ischemic myocardial metabolism.

METHODS

Swedish Landrace pigs on ECC (ECC) were compared with pigs on ECC with warm ischemic cardiac arrest (ischemia) or on ECC with warm ischemic arrest followed by warm blood cardioplegia (ischemia-cardioplegia), using sham-operated pigs as controls (n=7 in each group). Microdialysis probes were placed on the surface of the left ventricle and in the femoral artery for serial evaluation of metabolites in the intracardiac extracellular fluid and arterial blood. When hearts started in ventricular fibrillation (VF), it was electroconverted after 10 min of normal blood reperfusion. If VF started after 10 min of reperfusion electroconversion was immediately performed.

RESULTS

There were no differences between groups in arterial contents of serine, citrulline, arginine, inosine, hypoxanthine, guanosine, aspartate, glutamate, pyruvate, or asparagine throughout the observation period. Systemic lactate increased in pigs subjected to ischemia (P<0.001) or ischemia and cardioplegia (P=0.002), highest in the ischemia only group (P=0.002). In left ventricular microdialysates, lactate increased in pigs subjected to ischemia alone (P<0.001 vs. ECC) and ischemia and cardioplegia (P=0.004 vs. ECC). Guanosine increased in ischemia versus ECC (P=0.002), while hypoxanthine was increased in microdialysates of both ischemic (P=0.002) and ischemic-cardioplegic (P=0.001) pig hearts. Inosine was increased in pigs subjected to ischemia and cardioplegia (P<0.001 vs. ECC). All ischemic hearts started with VF, but while in the warm ischemia group VF started within 10 min of reperfusion, the ischemia-cardioplegia group had a longer asystolia with VF starting 11-22 min of blood reperfusion.

CONCLUSION

The heart should be allowed to start empty beating rather than by the use of warm continuous blood cardioplegia. Microdialysis and sampling of interstitial metabolites may be advantageous when an increased sensitivity is needed or when repeated blood sampling is difficult or contraindicated in monitoring of the myocardium.

Myocardial protection with high-dose beta-blockade in acute myocardial ischemia

OBJECTIVE

The risk of postoperative cardiac dysfunction is markedly increased by emergency coronary artery bypass grafting in the presence of acute myocardial ischemia. High dose beta-blockade during continuous coronary perfusion has been suggested as an alternative to conventional cardioplegia and this technique has been applied successfully in high risk patients for coronary artery bypass grafting (CABG) surgery. This study compared high dose beta-blockade with esmolol to continuous warm blood cardioplegia in a clinically oriented model of acute left ventricular (LV) ischemia and reperfusion.

METHODS

Twelve dogs were subjected to 60 min of regional LV ischemia by left anterior descending branch (LAD) ligation. Cardiopulmonary bypass (CPB) and aortic crossclamp were applied after 45 min of ischemia. Thereafter, high dose beta-blockade during continuous coronary perfusion (ESMO, n = 6) or antegrade continuous warm blood cardioplegia (WBC, n = 6) were maintained for 60 min. Myocardial water content (measured from endomyocardial biopsies using a microgravimetric technique), global LV function (preload recruitable stroke work: PRSW), and regional LV function (echocardiographic wall motion score) were determined at baseline and after weaning from CPB.

RESULTS

During aortic crossclamp interstitial edema formation was significantly higher in the WBC group with an average water gain of 2.2 +/- 0.49 vs. 0.76 +/- 0.12% in the ESMO group. Thereafter, edema resolved in both groups, but myocardial water gain remained significantly higher in the WBC group at 60 and 120 min post CPB (0.98 +/- 0.19 and 1.13 +/- 0.32% vs. 0.07 +/- 0.25 and 0.04 +/- 0.08%). Global LV function was significantly higher in the ESMO group at 60 and 120 min post CPB (PRSW 103 +/- 6 and 94.7 +/- 4.6% of baseline vs. 85.3 +/- 4.9 and 74.7 +/- 7.6% of baseline). However, regional LV function showed no significant difference between groups.

CONCLUSIONS

High-dose beta-blockade during continuous coronary perfusion may allow the surgeon to utilize the advantages of warm heart surgery, while avoiding the interstitial edema formation and temporary cardiac dysfunction associated with continuous warm blood cardioplegia. In high risk patients such as patients with unstable angina or after failed PTCA, high-dose beta-blockade may be an applicable alternative to cardioplegic arrest.

Protection of acutely ischemic myocardium by controlled reperfusion

The goal of revascularization after acute occlusion of a coronary artery is the return of contractile function and the reduction of mortality. Although reperfusion of ischemic myocardium is a prerequisite for return of function, it may, in itself, cause further injury. Controlled blood cardioplegic reperfusion reduces this "reperfusion injury" and provides maximal myocardial protection. In this article, we review recent advances in surgically controlled reperfusion and speculate on future prospects for myocardial protective techniques in patients with acute coronary artery occlusion.

Beta-blockade versus Buckberg blood-cardioplegia in coronary bypass operation

OBJECTIVE

Continuous perfusion of the coronary arteries with beta-blocker (esmolol)-enriched normothermic blood during cardiac surgery has been suggested as an alternative technique for myocardial protection. The aim of the present study was to compare the beta-blocker technique to Buckberg's blood cardioplegia during coronary artery bypass grafting (CABG).

METHODS

Sixty patients with coronary artery disease were randomly assigned to either the esmolol group (ES, n = 30) or the blood cardioplegia group (BC, n = 30). During aortic crossclamp ES patients received continuous normothermic coronary perfusion with esmolol-enriched blood. Hearts of the BC group were protected by antegrade cold blood cardioplegia according to Buckberg. We measured left ventricular (LV) contractility using TEE (fractional area of contraction, FAC) and hemodynamic parameters prior to cannulation for cardiopulmonary bypass (CPB), after decannulation, and 4 h postoperatively. Myocardial lactate release was measured prior to aortic cross-clamp, during cross-clamp, and after decannulation. LV biopsies for determination of heat-shock protein (HSP-70), actin pattern and intercellular adhesion-molecule (ICAM-I) as indicators for structural changes were collected prior CPB, at the end of the aortic cross-clamp period, and prior to weaning off CPB.

RESULTS

There was no significant difference between both groups with respect to grafts and cross-clamp time. ES hearts did not release lactate during cross-clamp. In contrast, BC hearts released significant amounts of lactate. Post CPB FAC and hemodynamics under similar inotropic stimulation showed no difference between groups, whereas at 4 h post CPB measurements showed slightly better values in the ES group: cardiac index: ES: 2.9+/-0.1 (SEM) versus BC: 2.6+/-0.1 L/min per m2 (P < 0.05); FAC: ES: 55+/-3 versus BC: 48+/-3% (P < 0.05). HSP-70 and actin pattern showed no difference between groups; however, ICAM-I showed a significantly higher degree of structural changes in BC hearts: 18+/-2 versus ES: 11+/-1% (P < 0.05).

CONCLUSION

Our data demonstrate that application of the beta-blocker technique during routine CABG was associated with slightly better functional recovery and less structural myocardial alteration as compared with intermittent cold blood cardioplegia, however, both techniques provided equivalent myocardial protection in terms of patient outcome. Future studies are required to investigate if myocardial ischemia minimization by use of the beta-blocker technique may be beneficial in compromized hearts.

Orthotopic transplantation of pig hearts harvested after 30 min of normothermic ischemia: controlled reperfusion with blood cardioplegia containing the Na+-H+-exchange inhibitor HOE 642

OBJECTIVES

The aim of our study was to develop a surgical technique for a successful transplantation of hearts harvested after 30 min of normothermic ischemia without donor pretreatment. Successful transplantation of ischemic compromised hearts could help to expand the severely limited donor pool. We used the pig model because this species is very susceptible to myocardial ischemia. Na+-H+-exchange (NHE) inhibitors have shown excellent protective properties in several in vitro and in vivo models of myocardial ischemia and reperfusion.

METHODS

In group I (n=12) hearts were harvested after 30 min of normothermic ischemia following cardiac arrest induced by exsanguination. Hearts were perfused with warm blood cardioplegia and transplanted orthotopically. In group II (n=9) controlled reperfusion with cold leucocyte-depleted blood cardioplegia was performed after 30 min of normothermic ischemia. In group III (n=8) the same procedure was performed as in group II but blood cardioplegia contained 1 mmol/l HOE 642.

RESULTS

In group I massive myocardial oedema was observed and none of the animals could be weaned from cardiopulmonary bypass (CPB). In contrast, all animals in groups II and III could be weaned from CPB with low dose inotropic support. In groups II and III the contractility of the hearts, expressed as maximal left and right ventricular stroke work index was significantly impaired after transplantation as compared with the preoperative value. Supplementation of blood cardioplegia with HOE 642 resulted in a significantly better recovery of the LVSWImax (Group II vs. III).

CONCLUSIONS

Successful transplantation of pig hearts is possible after 30 min of normothermic ischemia without donor pretreatment if a controlled reperfusion with cold leucocyte-depleted blood cardioplegia is performed. HOE 642 given during reperfusion only improves posttransplant left ventricular function.

[Animal experiment study of the design of microelectrodes for selective detection of epicardial potassium ion activities]

Early detection of myocardial ischaemia following cardiac surgery remains a central problem of intensive care medicine. On the basis of the observation in the epicardium that an elevated potassium activity accompanies myocardial ischaemia, a miniaturized electrode system for the measurement of epicardial potassium concentration was constructed and tested. Different types of electrode were implanted in two groups of rabbits. The electrode parameters were satisfactory (slope, screening) and it proved possible to record interference-free myocardial ion potentials, which with regard to the ionophores used is selective for potassium ion activity in the solid phase electrode. The system thus meets the prerequisites for further investigations into its suitability for early diagnosis of ischaemia.

Effect of cardiac surgery patient characteristics on patient outcomes from 1981 through 1995

BACKGROUND

Previous studies have demonstrated increased risk in patients undergoing coronary artery bypass surgery (CABG), but the effect of this increasing risk on outcomes has not been well documented. The purposes of this study were (1) to evaluate patients who had CABG from 1993 to 1995 (group III) and compare them with patients from 1981 through 1987 (group I) and 1988 through 1992 (group II) to determine if the trend toward higher-risk patients continued and (2) to evaluate what effect risk had on in-hospital outcomes.

METHODS AND RESULTS

Data were collected prospectively on patients undergoing CABG. Patients from the three time periods were compared by use of univariate and multivariate statistics. Risk models for mortality were developed by use of logistic regression. Significant changes were noted in the three time periods, with risk increasing over time. Increased risk was associated with increased mortality in group II, but mortality declined in group III despite the continued increase in patient risk. Group II had an increase in complications, with little change in group III. The actual mortality rate was lower than predicted in group III.

CONCLUSIONS

Patients undergoing CABG are increasingly high risk. In-hospital mortality rates declined during the period from 1993 through 1995 and were lower than predicted despite the increase in risk. This decreased mortality rate may reflect greater experience in providing care to high-risk patients and improved myocardial protection and surgical and anesthetic techniques. Although continued analysis of patient risk and benefit is needed, researchers must be cognizant of the rapid changes in technology and knowledge and should correlate changes in the process of care with outcomes.

Surgical revascularization for acute coronary insufficiency: analysis of risk factors for hospital mortality

BACKGROUND

A retrospective study of 444 patients undergoing urgent and emergent coronary artery bypass grafting for acute coronary insufficiency was performed to identify the risk factors for hospital death specifically associated with the clinical severity of the acute coronary insufficiency syndrome.

METHODS

The patients were divided into three groups-urgent, emergent A, and emergent B-on the basis of the evolution of the clinical pattern of the acute coronary insufficiency syndrome on full medical treatment. The three categories were defined as follows: urgent (257 patients), surgical revascularization could be delayed for 24 to 36 hours after surgical consultation because of adequate control of ischemia; emergent A (127 patients), prompt myocardial revascularization was required because medical treatment achieved only transient regression of an unrelenting ischemic pattern; and emergent B (60 patients), prompt myocardial revascularization was required because the acute coronary insufficiency was entirely refractory to medical treatment.

RESULTS

Mortality rates were 7.4% for the urgent group, 13.4% for the emergent A group, and 31.7% for the emergent B group. Multivariate analysis identified the following as risk factors for hospital mortality: ejection fraction (p = 0.023) and aortic cross-clamp time (p = 0.10) for the urgent group; aortic cross-clamp time (p = 0.017), ejection fraction (p = 0.03), and nonuse of blood cardioplegia (p = 0.04) for the emergent A group; and cardiogenic shock (p = 0.00), preoperative ischemic interval (p = 0.00), aortic cross-clamp time (p = 0.018), and nonuse of blood cardioplegia (p = 0.012) for the emergent B group.

CONCLUSIONS

A more exact definition of patient risk can be achieved when predictive outcome models are constructed using the risk factors specifically related to each level of clinical severity of the ischemic syndrome.

Controlled limb reperfusion in patients having cardiac operations

HYPOTHESIS

Severe limb ischemia in patients having cardiac operations may occur after intraaortic balloon pump insertion, prolonged femoral vessel cannulation, percutaneous cardiopulmonary bypass, dissecting aneurysms, or emboli. Normal blood reperfusion can cause a postischemic syndrome that increases morbidity and mortality. This clinical study is based on an experimental infrastructure patterned after controlled cardiac reperfusion. (1) It tests the hypothesis that controlled limb reperfusion (i.e., modifying the composition of the initial reperfusate and the conditions of reperfusion) reduces the local and systemic complications seen after normal blood reperfusion. (2) It reports initial clinical application of this strategy in three cardiac surgery centers.

METHODS

Controlled limb reperfusion was applied to 19 patients with signs of severe prolonged unilateral or bilateral ischemia (including paralysis, anesthesia, and muscle contracture); six patients (32%) were in cardiogenic shock. The mean ischemic duration was 26 +/- 6 hours. The reperfusion method includes a 30-minute infusion into the distal vessels of a normothermic reperfusate solution mixed with the patient's arterial blood (obtained proximal to the obstruction) in a 6:1 blood/reperfusate ratio. Data are mean +/- standard error of the mean.

RESULTS

Sixteen patients (84%) survived with salvaged and functional limbs at the time of discharge. No renal, cardiac, pulmonary, cerebral, or hemodynamic complications developed in the survivors. The three deaths occurred in patients undergoing controlled limb reperfusion while in profound postoperative cardiogenic shock; neither postischemic edema nor contracture developed in any of them.

CONCLUSIONS

These findings show that controlled limb reperfusion can be applied readily with standard equipment that is used for cardiac surgery and may salvage limbs while reducing postreperfusion morbidity and mortality.

Substrate enhancement of cardioplegic solution: experimental studies and clinical evaluation

BACKGROUND

The development of myocardial protective strategies depends on a complete understanding of the pathophysiology of myocardial ischemia and reperfusion. This article reviews the rationale for inclusion of metabolic substrates in cardioplegic solutions on the basis of our current understanding of the underlying pathophysiologic pathways and speculates on the inclusion of future additives that await further investigation.

METHODS

The pathophysiology of myocardial ischemia and reperfusion was evaluated from an extensive review of the pertinent literature. Experimental and clinical studies supporting the inclusion of metabolic substrates in clinical cardioplegic solutions were reviewed and summarized. Speculation on possible future additives to these formulas was made on the basis of encouraging, albeit preliminary, experimental data.

RESULTS

Sound experimental and clinical evidence supports the inclusion of glucose, amino acids, calcium chelators, and oxygen as fundamental substrate additives to current cardioplegic solutions. Antioxidants, calcium-channel blockers, and tricarboxylic acid cycle intermediates may be of value. Adenosine, potassium-adenosine triphosphate channel modulators, and nitric oxide may join these lists after further research.

CONCLUSIONS

Substrate enhancement of clinical cardioplegic solutions is based on physiologic principles that have been confirmed in the clinical setting. Further definition of the intricacies of myocardial ischemia and reperfusion promises to expand the current list of additives.

Protection of evolving myocardial infarction and failed PTCA

Acute myocardial infarction is caused by acute coronary occlusion and is the major cause of death in Europe and the United States. In-hospital mortality is due principally to cardiogenic shock because of extensive ischemic muscle damage. Previous surgical results of coronary artery bypass grafting for left ventricular power failure have been disappointing because intraoperative ischemic injury is superimposed on severe damage already sustained by the myocardium. Surgical revascularization has, in general, been restricted to patients with acute occlusion after elective percutaneous transluminal coronary angioplasty with or without thrombolytic therapy. During the last years new knowledge has been gained in the pathophysiology of acute coronary occlusion on ischemic and nonischemic (remote) myocardium that has evolved in a new surgical strategy for revascularization of patients with evolving myocardial infarctions and failed percutaneous transluminal coronary angioplasty. Studies of the natural history of acute regional ischemia have shown that acute occlusion of a coronary artery not only affects the ischemic myocardium but causes structural, functional, and metabolic alterations in the remote and adjacent myocardium. These changes in the remote myocardium are even more severe if the remote myocardium is supplied by a stenotic coronary artery. Furthermore, many experimental and clinical studies have shown that normal blood reperfusion of myocardium injured previously by ischemia leads to additional damage (reperfusion injury).(ABSTRACT TRUNCATED AT 250 WORDS)

Perfusion therapy to reduce myocardial ischemia en route to emergency coronary artery bypass grafting for failed percutaneous transluminal coronary angioplasty

Despite improvements in operator technique, catheter technology, and the development of new devices, emergency coronary artery bypass grafting (CABG) is still required in 1%-4% of attempted catheter based revascularization procedures. Patients who require such emergency CABG after failed percutaneous transluminal coronary angioplasty (PTCA) have worse acute outcomes than those undergoing elective CABG, with a higher incidence of Q wave myocardial infarction (MI) and a higher operative mortality. In patients with otherwise refractory abrupt closure, maintenance of antegrade coronary blood flow using perfusion catheters lessens the incidence of Q wave MI and lowers peak creatinine phosphokinase. Direct maintenance of coronary flow thus appears to provide more definitive control of myocardial ischemia than purely adjunctive measures, such as intra-aortic balloon pumping, cardiopulmonary support, or coronary sinus retroperfusion. Although the recent introduction of coronary stents holds great promise for definitive percutaneous reversal of abrupt closure and a dramatic decrease in the incidence of emergency CABG for failed PTCA, maintenance of antegrade flow via perfusion technology remains the cornerstone of management in reducing the perioperative mortality and morbidity of patients who still require emergency bypass surgery after failed PTCA.

Operation for unstable angina pectoris: factors influencing adverse in-hospital outcome

Coronary artery bypass grafting for the treatment of unstable angina is still associated with increased operative risk and postoperative morbidity. The impact of the extended use of arterial grafts on early results is incompletely defined. In a 7-year period (1986 to 1993), 474 patients (average age, 65 years; range, 34 to 85 years) underwent coronary artery bypass grafting for the treatment of unstable angina. Sixty-eight patients were operated on emergently and 406 urgently. They received an average of 3.0 distal anastomoses (range, 1 to 6). Seventy-nine patients had exclusively venous grafts, 316 had one internal thoracic artery graft, 79 had bilateral internal thoracic artery grafts, and 20 had inferior epigastric artery grafts. Sequential internal thoracic artery grafting was performed in 70 patients. Redo operations were performed in 26 patients. Thirty-four patients (7.2%) experienced a new myocardial infarction. Eighty-nine patients (18.8%) had an intraaortic balloon pump inserted preoperatively, intraoperatively, or postoperatively. Eight patients (1.7%) died intraoperatively and 24 patients (5.1%) died postoperatively. Seventy-seven patients (16.2%) had an adverse outcome, as shown by the need for an intraaortic balloon pump (intraoperatively or postoperatively) or hospital death, or by both. Forty variables were examined by multivariate analysis for their influence on the occurrence of an adverse outcome. Aortic cross-clamp time (p = 0.0004), transfer from the intensive care unit (p = 0.0023), female sex (p = 0.0023), operation performed in early years (p = 0.0041), left ventricular aneurysm (p = 0.0068), the number of diseased coronary vessels (p = 0.0312), and reoperation (p = 0.0318) were all found to be significant independent predictors of increased risk.(ABSTRACT TRUNCATED AT 250 WORDS)

Arterial conduits in emergency coronary artery surgery

The internal thoracic artery (ITA) is considered to be the conduit of choice for coronary bypass (CABG), but there has been some reluctance to utilize the ITA for revascularization in emergency situations. In a 9-year retrospective analysis from 1986 through 1993, 484 patients had emergency CABG, 237 were not associated with failed PTCA (noninstrumented) and 247 were within 24 hours of PTCA (instrumented). About 62% of noninstrumented and 49.3% of instrumented patients received one or more ITA grafts, the others receiving only saphenous vein grafts (SVGs). Those who received an ITA graft tended toward male sex, better ejection fraction, and a generally lower clinical risk score. Instrumented patients tended toward a lower incidence of diabetes and left main coronary disease, higher ejection fraction, and lower clinical risk score than noninstrumented patients. The postoperative results were not significantly different between ITA and SVG groups with respect to new Q waves, need for reexploration, sternal wound infection, respiratory complications, or stroke. However, ITA patients more often had an event-free postoperative course, received fewer blood transfusions, and experienced fewer cardiac deaths (2.7% vs 9.4%, p < 0.01). There were few obvious differences in postoperative results between instrumented and noninstrumented patients. These results indicate that the ITA can be used for emergency CABG in selected patients with good results.