ISSN:0886-0440    

DOI:10.1111/j.1540-8191.1993.tb01307.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractOver the past two decades, we have challenged the belief that transient ischemia is benign with little functional sequelae following resolution of ischemia. The phenomenon of prolonged postischemic contractile dysfunction, or of myocardial stunning, has been developed and is under investigation using multiple experimental and clinical models. Classifications of myocardial stunning have been suggested and include single and multiple reversible ischemic episodes, partially reversible episodes, and global ischemia. More challenging is the understanding of the mechanisms of myocardial stunning, including free radical protection, excitation‐contraction uncoupling, altered calcium flux, microvascular dysfunction, and impaired energy production and use. Finally, advances have been made in the clinical arena, including development of new more sensitive technologies to detect dysfunction, and development of potentially important therapies, including free radical scavengers, adenosine‐regulating agents, and calcium channel blockers. In this brief overview, we focus on myocardial stunning, including a historical perspective of coronary occlusion, and definition, classification, and clinical implications of myocardial stunn

ISSN:0886-0440    

DOI:10.1111/j.1540-8191.1993.tb01308.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractMyocardial stunning can follow regional or global ischemia in the adult or immature heart. This report reviews some of our studies of the protean causes of stunning including energy and substrate depletion, inefficient oxygen utilization, calcium loading, acidosis, oxyradical damage, and summarizes studies and strategies to limit its occurrence. Data showing that reintroduction of molecular oxygen during reoxygenation of immature cyanotic hearts can cause stunning via a newly described biochemical pathway involving superoxide anion and nitric oxide are also included.

ISSN:0886-0440    

DOI:10.1111/j.1540-8191.1993.tb01309.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractAlthough patients who have undergone coronary artery bypass graft (CABG) surgery frequently present with symptoms suggesting that myocardial stunning has occurred, measurements of regional myocardial function and perfusion are difficult in clinical settings. Several studies have used left ventricular function indices (i.e., cardiac index, left ventricular stroke work index, ejection fraction) to assess myocardial stunning immediately following CABG surgery. These changes in ventricular function have been found to be reversible and the clinical data are consistent with the occurrence of myocardial stunning. Myocardial metabolism is also reportedly depressed following CABG surgery. Decreases in myocardial oxygen extraction, consumption, and lactate utilization all point to the presence of myocardial stunning, as do abnormalities in regional wall‐motion and electrocardiographic changes (i.e., transient Q waves) described in patients who have undergone CABG surgery. New approaches to differentiating viable from nonviable myocardial tissue will likely include stress echocardiography using new stress agents, ultrasound contrast agents, and high frequency ultrasoun

ISSN:0886-0440    

DOI:10.1111/j.1540-8191.1993.tb01310.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractDifferentiation of reversibly stunned myocardium from irreversibly damaged (infarcted) myocardium is critically important in patient management. Current methods for monitoring myocardial function yield only nonspecific assessments of myocardial viability. On the other hand, myocardial contrast echocardiography (MCE) can be used to evaluate the extent of myocardial perfusion as well as the efficacy of myocardial protection in patients undergoing coronary artery bypass graft (CABG). This system includes an external ultrasound unit and an internal tracer, usually gaseous microbubbles, which reflect the ultrasonic beam. Previous studies have shown that myocardial risk areas identified with MCE correlate with areas defined by technetium autoradiography and infarction size. We have used MCE to evaluate coronary artery bypass patients (N = 21) with regard to myocardial function and cardioplegia perfusion patterns. A significant correlation (p<0.01) was found between abnormal contrast enhanced cardioplegia patterns and depression of left ventricular function. Refinements to ultrasound technology and contrast agents will further enhance the diagnostic power of MCE for the quantification of myocardial blood flow.

ISSN:0886-0440    

DOI:10.1111/j.1540-8191.1993.tb01311.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThe effects of nitroglycerin (NTG) on regional wall‐motion abnormalities, ST segment changes, and the incidence of myocardial infarction (MI), cardiac failure, and mortality were studied in 30 patients undergoing coronary artery bypass. Patients received continuous infusions of either normal saline or NTG (1 μg/kg per min [low dose] or 2 μg/kg per min [high dose]) beginning at anesthesia and continuing for 4 hours postoperatively. The occurrence of wall‐motion abnormalities as detected by transesophageal echocardiography was 38 events in the normal saline group (N = 10). Significantly fewer events (p<0.05) were recorded in the low dose and high dose NTG groups (20 events and 15 events, respectively) compared to controls. There were no significant differences between the control and NTG groups with regard to the incidence of Holter ST segment events or the incidence of MI, cardiac failure, or cardiac death. NTG reduced the incidence of echocardiographic wall‐motion abnormalities in a dose dependent manner while having no significant effect on other parameters e

ISSN:0886-0440    

DOI:10.1111/j.1540-8191.1993.tb01312.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractClinical markers must be identified to distinguish between stunned and acutely ischemic myocardial tissue, as well as to assess the viability of myocardium. Evaluation of electrocardiographic ST segment abnormalities can distinguish transmural oxygen deprivation from subendocardial oxygen declines, but stunned myocardium may have normal ST segments. Myocardial contrast echocardiography can estimate regional myocardial blood flow but ultrasound measurement of blood flow is not always able to discern stunned from nonviable myocardium. Change in extracellular pH has been used to study ischemia, but has not yet been shown to reflect differences between stunned and ischemic myocardium. A combination of clinical markers of flow, delivery, and oxygen consumption may be necessary in order to differentiate between stunned and ischemic regions. This distinction can have important therapeutic consequences because patients with acutely ischemic but viable myocardium may be ultimately harmed by inotropic drugs that increase myocardial oxygen demand. In contrast, inotropes may be indicated for stunned myocardial tissue. The determination of the reversibility of myocardial dysfunction can also impact on decisions to use mechanical cardiocirculatory support. Differentiation of stunned and ischemic myocardium might also streamline ICU assignments and lead to more effective use of high technology resources.

ISSN:0886-0440    

DOI:10.1111/j.1540-8191.1993.tb01313.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractIt has been suggested that cardioplegic arrest during cardiopulmonary bypass (CPB) produces global myocardial ischemia with a risk of myocardial stunning. It has also been postulated that anesthetic technique may affect the course of post‐CPB myocardial stunning via exaggerated myocardial depression. However, we have previously found that global ventricular and regional myocardial responses to halothane do not differ in post‐CPB and pre‐CPB dogs. Our examination of the effects of CPB on the beta‐adrenergic function revealed that beta‐adrenergic receptor function is only slightly decreased immediately following (i.e., 1 min) and 30 minutes post‐CPB. A dose‐response relationship was established for dobutamine, with decreased responsiveness noted at both times. Since other data show normal inotropic stimulation of stunned myocardium, decreases in dobutamine responsiveness cannot be explained by beta‐receptor desensitization. Overall, these data indicate that CPB does not result in myocardial stunning. The differences between these data and others showing myocardial stunning following CPB may be due to several factors, such as anesthetic regimen, lack of coronary blood flow abnormalities, and a reduction in sarcoplasmic reticular damage due to the hypothermic

ISSN:0886-0440    

DOI:10.1111/j.1540-8191.1993.tb01314.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractMyocardial stunning commonly occurs after cardiopulmonary bypass (CPB). Myocardial stunning can be cardioprotective under some conditions, but in other situations may actually contribute to myocardial infarction (MI). Vascular endothelial stunning may be one of the mechanisms by which myocardial stunning can cause MI. It has been found that 15 minutes of reversible ischemia is enough to cause elevations in vascular resistance and impairment of vasodilator responsiveness. However, no correlation between contractile dysfunction and microvascular stunning has been observed. Transduction defects (increased oxygen extraction and consumption despite normal regional oxygen blood flow and delivery) may be another mechanism by which stunning predisposes to MI, indicating uncoupling of substrate utilization from energy production. In addition, abnormalities in wall motion, oxygen free radical toxicity, hypotension, use of inotropic agents (leading to increased oxygen consumption, high heart rates, and arrhythmias) increase the risk of cellular necrosis. Following CPB, flow limitations due to diffuse atherosclerosis in some areas may result in poor contractility, and newly grafted areas have a high probability of becoming ischemic and stunned. These areas are likely to contribute to MI.

ISSN:0886-0440    

DOI:10.1111/j.1540-8191.1993.tb01315.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractAt the Toronto Hospital, 2,510 patients received isolated coronary bypass grafts (CABG). Overall mortality was 2.3%, the incidence of low output syndrome (as defined by need for inotropic agents or intraaortic balloon pump) was 9.2%, and mortality among low output syndrome patients was 16%. We have attempted to identify factors that minimize cardiac injury. We have previously shown that free radical injury occurs during CABG: coronary blood contains increased levels of conjugated dienes after cross‐clamp release; and, there is a reduction in the antioxidant, α‐tocopherol. In vitro studies revealed that ascorbic acid and α‐tocopherol protect cardiac myocytes, while endothelial cells are protected from free radical injury by superoxide dismutase and catalase. To test the former two antioxidants in vivo, we used left anterior descending artery (LAD) occlusion in the dog followed by 2 to 4 hours of reperfusion. When administered in deoxygenated saline at 30 seconds prior to reperfusion and 4 minutes after release of LAD occlusion, both agents significantly reduced the infarction area compared to simple reperfusion or deoxygenated saline alone. Antioxidants therefore have the potential to reduce the ischemic injury and myocardial stunning that accompa

ISSN:0886-0440    

DOI:10.1111/j.1540-8191.1993.tb01316.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY