Postischemic myocardial "stunning": a clinically relevant phenomenon

Myocardial stunning and hibernation revisited

Unlike acute myocardial infarction with reperfusion, in which infarct size is the end point reflecting irreversible injury, myocardial stunning and hibernation result from reversible myocardial ischaemia-reperfusion injury, and contractile dysfunction is the obvious end point. Stunned myocardium is characterized by a disproportionately long-lasting, yet fully reversible, contractile dysfunction that follows brief bouts of myocardial ischaemia. Reperfusion precipitates a burst of reactive oxygen species formation and alterations in excitation-contraction coupling, which interact and cause the contractile dysfunction. Hibernating myocardium is characterized by reduced regional contractile function and blood flow, which both recover after reperfusion or revascularization. Short-term myocardial hibernation is an adaptation of contractile function to the reduced blood flow such that energy and substrate metabolism recover during the ongoing ischaemia. Chronic myocardial hibernation is characterized by severe morphological alterations and altered expression of metabolic and pro-survival proteins. Myocardial stunning is observed clinically and must be recognized but is rarely haemodynamically compromising and does not require treatment. Myocardial hibernation is clinically identified with the use of imaging techniques, and the myocardium recovers after revascularization. Several trials in the past two decades have challenged the superiority of revascularization over medical therapy for symptomatic relief and prognosis in patients with chronic coronary syndromes. A better understanding of the pathophysiology of myocardial stunning and hibernation is important for a more precise indication of revascularization and its consequences. Therefore, this Review summarizes the current knowledge of the pathophysiology of these characteristic reperfusion phenomena and highlights their clinical implications.

The Oxygen Paradox, the French Paradox, and age-related diseases

A paradox is a seemingly absurd or impossible concept, proposition, or theory that is often difficult to understand or explain, sometimes apparently self-contradictory, and yet ultimately correct or true. How is it possible, for example, that oxygen "a toxic environmental poison" could be also indispensable for life (Beckman and Ames Physiol Rev 78(2):547-81, 1998; Stadtman and Berlett Chem Res Toxicol 10(5):485-94, 1997)?: the so-called Oxygen Paradox (Davies and Ursini 1995; Davies Biochem Soc Symp 61:1-31, 1995). How can French people apparently disregard the rule that high dietary intakes of cholesterol and saturated fats (e.g., cheese and paté) will result in an early death from cardiovascular diseases (Renaud and de Lorgeril Lancet 339(8808):1523-6, 1992; Catalgol et al. Front Pharmacol 3:141, 2012; Eisenberg et al. Nat Med 22(12):1428-1438, 2016)?: the so-called, French Paradox. Doubtless, the truth is not a duality and epistemological bias probably generates apparently self-contradictory conclusions. Perhaps nowhere in biology are there so many apparently contradictory views, and even experimental results, affecting human physiology and pathology as in the fields of free radicals and oxidative stress, antioxidants, foods and drinks, and dietary recommendations; this is particularly true when issues such as disease-susceptibility or avoidance, "healthspan," "lifespan," and ageing are involved. Consider, for example, the apparently paradoxical observation that treatment with low doses of a substance that is toxic at high concentrations may actually induce transient adaptations that protect against a subsequent exposure to the same (or similar) toxin. This particular paradox is now mechanistically explained as "Adaptive Homeostasis" (Davies Mol Asp Med 49:1-7, 2016; Pomatto et al. 2017a; Lomeli et al. Clin Sci (Lond) 131(21):2573-2599, 2017; Pomatto and Davies 2017); the non-damaging process by which an apparent toxicant can activate biological signal transduction pathways to increase expression of protective genes, by mechanisms that are completely different from those by which the same agent induces toxicity at high concentrations. In this review, we explore the influences and effects of paradoxes such as the Oxygen Paradox and the French Paradox on the etiology, progression, and outcomes of many of the major human age-related diseases, as well as the basic biological phenomenon of ageing itself.

Pathobiology of Ischemic Heart Disease: Past, Present and Future

This review provides a perspective on knowledge of ischemic heart disease (IHD) obtained from the contemporary era of research which began in the 1960s and has continued to the present day. Important discoveries have been made by basic and translational scientists and clinicians. Pathologists have contributed significantly to insights obtained from experimental studies and clinicopathological studies in humans. The review also provides a perspective for future directions in research in IHD aimed at increasing basic knowledge and developing additional therapeutic options for patients with IHD.

Severe stunned myocardium after lightning strike

OBJECTIVE

To report the development of myocardial stunning and severe heart failure after lightning strike with total recovery of function.

DESIGN

Case report.

SETTING

Coronary care unit at Medica Sur Clinic, Mexico.

PATIENT

A 42-yr-old woman who was hit by lightning developed rapid and progressive hemodynamic deterioration manifested by cardiogenic shock that required invasive monitoring. Twenty-four hours after the strike, intravenous levosimendan and intra-aortic balloon pump were initiated because the patient demonstrated no significant response to management with conventional inotropic agents. Two days later, echocardiographic signs of systolic and diastolic dysfunction improved markedly. Dual-isotope-imaging myocardial perfusion testing with technetium-99m-sestamibi and thallium-201, performed 9 days after admission, showed normal perfusion and normal left ventricular systolic function. The patient exhibited complete recovery of function. The exact mechanism of abnormal contractility in the absence of direct electrofulguration is unknown but may be explained by release of oxygen free radicals, proteolysis of the contractile apparatus, and cytosolic overload of intracellular calcium, followed by reduced myofilament sensitivity to calcium. These abnormalities are consistent with stunned myocardium.

CONCLUSIONS

Lightning strike may cause serious contractile dysfunction in the absence of irreversible myocardial injury, but the exact mechanism of this phenomenon remains unknown. We propose that lighting strike can cause myocardial stunning resulting in severe but reversible left ventricular dysfunction. The patient's recovery was facilitated by support treatment including administration of levosimendan, which increases the intracellular sensitivity to calcium, a mechanism disturbed in patients with myocardial stunning.

Mechanisms leading to reversible mechanical dysfunction in severe CAD: alternatives to myocardial stunning

Patients with severe chronic coronary artery disease (CAD) exhibit a highly altered myocardial pattern of perfusion, metabolism, and mechanical performance. In this context, the diagnosis of stunning remains elusive not only because of methodological and logistic considerations, but also because of the pathophysiological characteristics of the myocardium of these patients. In addition, a number of alternative pathophysiological mechanisms may act by mimicking the functional manifestations usually attributed to stunning. The present review describes three mechanisms that could theoretically lead to reversible mechanical dysfunction in these patients: myocardial wall stress, the tethering effect, and myocardial expression and release of auto- and paracrine agents. Attention is focused on the role of these mechanisms in scintigraphically “normal” regions (i.e., regions usually showing normal perfusion, glucose metabolism, and cellular integrity as assessed by nuclear imaging techniques), in which stunning is usually considered, but these mechanisms could also operate throughout the viable myocardium. We hypothesize that reversion of these three mechanisms could partially explain the unexpected functional benefit after reperfusion recently highlighted by high-spatial-resolution imaging techniques.

ECG changes after CABG: the role of the surgical technique

OBJECTIVE

The purpose of this study was to determine whether coronary artery bypass grafting (CABG) surgery on the beating heart (BH) is associated with reduction of R-wave potentials on the precordial leads on the surface electrocardiogram (ECG) as previously shown for CABG with cardiopulmonary bypass.

METHODS

Fifty-four patients undergoing CABG surgery at a single tertiary care university hospital were analyzed. Patients suffering a postoperative cardiac event (myocardial infarction) or nonspecific ECG changes were excluded. ECG results were recorded at arrival in the intensive care unit, after 4 and 18 hours postoperatively; simultaneously, myocardial cell damage biomarkers (CK-MB and cTnI) were assayed. A control group of 31 patients undergoing mitral valve repair was also evaluated.

RESULTS

Patients operated with the BH (OPCABG) technique did not show any decrease of R-wave amplitude at 0, 4, and 18 hours postoperatively; whereas those operated with CPB, both for coronary artery surgery and for mitral repair, had a similar extent and pattern of R-wave reduction. The release of myocardial necrosis markers was significantly lower in coronary artery patients operated with BH than in those operated with CPB; however, no statistically significant correlation between the ECG changes and release of myocardial cell damage markers was observed in any of the groups.

CONCLUSIONS

The findings indicate, for the first time, that CABG surgery on the BH is not followed by any reduction of R-wave amplitude on precordial leads and confirms that the BH technique is associated with a lower release of myocardial cell damage markers.

Computed tomography assessment of myocardial perfusion, viability, and function

In addition to coronary artery assessment, contrast-enhanced multidetector spiral computed tomography (CE-MDCT) can provide valuable information about myocardial perfusion. Using CE-MDCT, myocardial perfusion defects are often observed in the early phase of the contrast bolus (early defect (ED)), with residual defects (RDs) and late enhancement (LE) observed in the late phase in myocardial infarction (MI). However, the clinical significance of EDs, RDs, and LE has not yet been fully described. This work reviews myocardial viability and function by CE-MDCT based on our prior data by including contrast-enhanced single-slice (detector) CT (CE-SSCT) and CE-MDCT. Recently, equivalent results were obtained, as seen in CE-SSCT with images by CE-MDCT. In this review, images that were acquired by MDCT will be presented. In this work, the following items will be the focus: myocardial enhancement patterns (EDs, LE, and RDs), early perfusion defects and their relationship to wall thickness (WT) and wall motion, early CT perfusion defects vs. Tl-201 single photon emission CT (SPECT), the protocol for performing dual-phase contrast CT, classification of enhancement patterns, enhancement patterns on dual-phase CE-MDCT vs. left ventricular functional recovery and WT, changes in enhancement patterns in conjunction with healing stage, enhancement patterns on dual-phase CE-MDCT vs. 201Tl/99mTc-pyrophosphate (dual-isotope SPECT), the clinical meaning of each enhancement pattern, pitfalls of enhancement patterns and other diseases, and study limitations and the future of MDCT.

Hibernation, Stunning, and Preconditioning: Historical Perspective, Current Concepts, Clinical Applications, and Future Implications

Despite considerable advances, coronary artery disease is the leading cause of morbidity and mortality in the Western world. The development of effective therapeutic strategies for protecting the myocardium from ischemia would have major impact on patients with coronary artery disease. It is now accepted that patients with coronary artery disease can experience prolonged regional ischemic dysfunction that does not necessarily arise from irreversible tissue damage, and to some extent, can be reversed by restoration of blood flow. The initial stages of dysfunction are probably caused by chronic stunning that can be reversed after revascularization, resulting in rapid and complete functional recovery. On the other hand, the more advanced stages of dysfunction likely correspond to chronic hibernation. After revascularization, functional recovery will probably be quite delayed and mostly incomplete. Over the past decade, the possibility that an innate mechanism of myocardial protection might be inducible in the human heart has generated considerable excitement. In the last two decades, there was phenomenal growth in the understanding of the mechanism known as ischemic preconditioning that is responsible for the innate myocardial protection. Continued research and progress in this area may soon lead to the availability of preconditioning-mimetic treatments. The current concepts, mechanisms, and potential clinical applications of myocardial hibernation, stunning, and ischemic preconditioning are reviewed.

Relationship between T-wave normalization on exercise ECG and myocardial functional recovery in patients with acute myocardial infarction

BACKGROUND

Several studies suggested that T-wave normalization (TWN) in exercise ECG indicates the presence of viable myocardium. But the clinical implication of this phenomenon in patients with acute myocardial infarction who received proper revascularization therapy was not determined. Precisely the aim of this study was to investigate the relationship between TWN in exercise ECG and myocardial functional recovery after acute myocardial infarction.

METHODS

We studied 30 acute myocardial infarction patients with negative T waves in infarct related electrocardiographic leads and who had received successful revascularization therapy. Exercise ECG was performed 10-14 days after infarct onset using Naughton protocol. Patients were divided into 2 groups according to presence (group I; n = 14) or not (group II; n = 16) of TWN in exercise ECG. Exercise parameters and coronary angiographic findings were compared between groups. Baseline and follow-up (mean 11 months) regional and global left ventricular function was analyzed by echocardiography.

RESULTS

Exercise parameters were similar between groups. There was no difference in baseline ejection fraction and wall motion score between group I and II (EF; 56 +/- 12% vs 52 +/- 11%, p = ns. WMS; 21 +/- 3 vs 23 +/- 4, p = ns) and it was improved at the tenth month by similar magnitude (group I/group II, EF% change = 12 +/- 12% vs 7 +/- 6%, p = ns, WMS% change = 6 +/- 6% vs 7 +/- 5%, p = ns). The finding of no relation between TWN and functional recovery was observed also when the patients were analysed according to infarct location and presence or absence of Q-waves.

CONCLUSION

As the exercise-induced TWN in patients with acute myocardial infarction was not related with better functional recovery of dysfunctional regional wall motion and ejection fraction, TWN does not appear to be an indicator of myocardial viability.

Cardioprotective effects of 9-hydroxyellipticine on ischemia and reperfusion in isolated rat heart

We determined the effect of 9-hydroxyellipticine (9HE) on ryanodine receptor (RyR) and cardiac function after global ischemia in isolated rat hearts. The binding of [3H]-ryanodine in rabbit cardiac sarcoplasmic reticulum was displaced by 9HE in a biphasic manner corresponding to the two sites model with IC50 values of 6.1 microM and 55 mM. The increase of the intracellular Ca2+ concentration induced by caffeine in CHO cells expressing cardiac-type RyR was suppressed by 9HE in a concentration-dependent manner. Pretreatment of the heart with 9HE decreased the total duration of reperfusion-induced ventricular fibrillation (VF) and delayed the onset of VF. There was also a significant recovery of contractile force of ischemic hearts following 9HE. Unlike nifedipine, an L-type Ca2+-channel blocker, 9HE did not suppress the contraction of rat papillary muscles. Thus, 9HE exerts the cardioprotective effects against ischemia /reperfusion injury without changing hemodynamic indices.

Effects of intracoronary calcium chloride on regional oxygen balance and mechanical function in normal and stunned myocardium in dogs

BACKGROUND

Brief myocardial ischaemia has been demonstrated to result in mechanical and coronary endothelial dysfunction, in which calcium may play a role. We examined whether the mechanical and vascular responses to calcium are altered in postischaemic, reperfused myocardium.

METHODS

Regional myocardial oxygen consumption (MVO2), mechanical function and coronary blood flow (CBF) in response to calcium chloride (0.10, 0.25, 0.50 and 0.75 mg ml(-1) of CBF) directly infused into the left anterior descending (LAD) artery were determined before (normal) and 30 min after a 15-min-period of LAD occlusion (stunned) in an open-chest canine model. Percentage segment shortening (%SS) and percentage postsystolic shortening (%PSS) in the LAD territory were determined using ultrasonic crystals and CBF using a Doppler transducer. Myocardial extraction of oxygen (EO2) and lactate (Elac) was calculated.

RESULTS

The infusion of calcium chloride resulted in dose-dependent increases in %SS and MVO2 but did not affect %PSS in normal myocardium. These changes were accompanied by parallel increases in CBF, resulting in no change in EO2. In stunned myocardium, the responses to calcium chloride were not significantly altered, with the exception of a reduction in %PSS. However, ischaemia and reperfusion itself significantly reduced %SS and Elac and increased %PSS.

CONCLUSIONS

These data suggest that calcium chloride improves regional systolic and diastolic function both in normal and stunned myocardium. Calcium chloride is unlikely to cause direct coronary vasoconstriction or to deteriorate regional mechanical function in postischaemic myocardium.

Consequences of brief ischemia: stunning, preconditioning, and their clinical implications: part 1

In experimental studies in the dog, total proximal coronary artery occlusions of up to 15 minutes result in reversible injury, meaning that the myocytes survive this insult. The 15 minutes of ischemia, however, induce numerous changes in the myocardium, including certain monuments to the brief episode of ischemia that may persist for days. One of these monuments is stunned myocardium, which represents "prolonged postischemic contractile dysfunction of myocardium salvaged by reperfusion." The mechanism of stunning involves generation of oxygen radicals as well as alteration in calcium homeostasis and possibly alteration in contractile protein structure. Stunning has been observed in several clinical scenarios, including after percutaneous transluminal coronary angioplasty, unstable angina, stress-induced ischemia, after thrombolysis, and after cardiopulmonary bypass. Oxygen radical scavengers and calcium channel blockers have been shown to enhance function of stunned myocardium in experimental studies, and in a few clinical studies, calcium channel blockers have been shown to ameliorate stunning. Although brief periods of ischemia can contribute to prolonged left ventricular dysfunction and even heart failure, they paradoxically play a cardioprotective role. Episodes of ischemia as short as 5 minutes, followed by reperfusion, protect the heart from a subsequent longer coronary artery occlusion by markedly reducing the amount of necrosis that results from the test episode of ischemia. This phenomenon, called ischemic preconditioning, has been observed in virtually every species in which it has been studied and is a powerful cardioprotective effect. The mechanism of ischemic preconditioning involves both triggers and mediators and involves complex second messenger pathways that appear to involve such components as adenosine, adenosine receptors, the epsilon isoform of protein kinase C, the ATP-dependent potassium channels, as well as others, including a paradoxical protective role of oxygen radicals. Both an early and a late phase of preconditioning have been described, and the mechanisms underlying their induction are under investigation. That preconditioning may occur in humans is suggested by the observations that repetitive balloon inflations in the coronary artery are associated with progressively less chest pain, ST-segment elevation, lactate production, the protective effects of preinfarction angina, the anginal "warm-up phenomenon," and studies performed on human cardiac biopsies that show metabolic properties suggesting preconditioning. Development of pharmacological agents that stimulate second messenger pathways thought to be involved in preconditioning, but without causing ischemia, could result in novel approaches to treating ischemia. Hence, on one hand, brief episodes of ischemia can have a negative effect on the heart: stunning; and on the other hand, they have a protective effect: preconditioning. The future challenge is how to minimize the stunning phenomenon and maximize the preconditioning phenomenon in clinical practice.

Patient outcomes in the assessment of myocardial injury following cardiac surgery

In the absence of online methods for the intraoperative assessment of the adequacy of myocardial protection, patient outcomes remain the gold standard for determining whether a patient has sustained injury in the course of a cardiac operation. Properly risk-adjusted 30-day postoperative mortality and myocardial infarction are the most definitive indicators of perioperative injury. The definition and clinical assessment of irreversible ischemic myocardial injury continues to be problematic postoperatively. In most instances, deterioration in postoperative cardiac function and performance is indicative of intraoperative injury. Late postoperative mortality and long-term survival may be affected by intraoperative myocardial injury. Likewise, long-term graft patency may be affected by intraoperative injury to the conduit vascular endothelium. Proper assessment of outcomes, although it may not change the intraoperative course of an operation, can be useful in the comparative assessment of the efficacy of various operations, methods, and techniques.

Evidence for stunned myocardium in humans: a 2001 update

This article describes clinical situations in which stunning occurs and updates previous reviews on the topic. Stunning following angioplasty, angina and exercise-induced ischemia, infarction, and after cardiac surgery are described. In addition, newer concepts regarding stunning, including neurogenic stunned myocardium, are discussed. Left atrial stunning following cardioversion is a recently recognized phenomenon with important clinical implications, but differs from the original concept of post-ischemic stunning.

Translocation of S100A1(1) calcium binding protein during heart surgery

Myocardial ischemia during cardiopulmonary bypass terminated by reperfusion generally leads to different degrees of damage of the cardiomyocytes induced by transient cytosolic Ca(2+) overload. Recently, much attention has been paid to the role of heart-specific Ca(2+)-binding proteins in the pathogenesis of myocardial ischemia-reperfusion injury. S100A1 is a heart-specific EF-hand Ca(2+)-binding protein that is directly involved in a variety of Ca(2+)-mediated functions in myocytes. The aim of our study was to investigate the localization and translocation of S100A1 in the human heart under normal (baseline) conditions and after prolonged ischemia and reperfusion of the myocardium. Our data suggest that S100A1 is directly involved in the transient perioperative myocardial damage caused by ischemia during open heart surgery in humans. Given its role in the contractile function of muscle cells, this S100 protein could be an important "intracellular link" in ischemia-reperfusion injury of the heart.

Effects of exercise training on myocardial fatty acid metabolism in rats with depressed cardiac function induced by transient ischemia

The effects of exercise training on metabolic and functional recovery after myocardial transient ischemia were investigated in a rat model. Male Wistar Kyoto rats were subjected either to a 30-min left coronary artery occlusion followed by reperfusion or to a sham operation. At 4 weeks after operation, the rats were randomly assigned either to sedentary conditions or to exercise training for 6 weeks. In the ischemic rats, pinhole SPECT (single photon emission computed tomography) imaging with thallium-201 (201Tl) and 123I-(rho-iodophenyl)-3-R,S-methylpentadecanoic acid (BMIPP) showed a reduction of both myocardial perfusion and fatty acid metabolism in the risk zone of the left ventricle (LV). The LV was dilated and the ejection fraction was decreased after ischemic injury. The severity score showed a significant decrease on both 201Tl and BMIPP (201Tl, from 19.9+/-2.7 to 17.0+/-2.2, p<0.05; BMIPP, from 21.5+/-2.4 to 18.6+/-1.9, p<0.05) after exercise training in the ischemic trained rats, but did not change significantly in their sedentary counterparts. Plasma levels of free fatty acids normalized in the ischemic trained rats, but elevated in the ischemic sedentary rats (0.53+/-0.05 vs 0.73+/-0.06 mmol/L, p<0.05). Furthermore, the trained rats had a significant increase in LV stroke volume (0.25+/-0.02 vs 0.21+/-0.01 ml/beat, p<0.05) and adaptive cardiac hypertrophy. These findings demonstrate that adaptive improvements in myocardial perfusion, fatty-acid metabolism and LV function were induced by exercise training after transient ischemia.

Morphometric identification of luminal narrowing of myocardial capillaries after cardioplegic arrest

BACKGROUND

Because there is no smooth muscle cell surrounding the capillary endothelial cells, the effect of coronary microcirculation at the capillary level following cardioplegic arrest and reperfusion would be much different from that of resistant arterioles. We therefore studied the effect of hypothermic blood cardioplegic arrest and subsequent reperfusion on the myocardial capillaries in cardiac operation patients.

METHODS

Twenty-seven patients who underwent cardiac operations were included in this study. Three sequential biopsies (preischemia, ischemia, and reperfusion) were obtained from the right atrium. This study was restricted to blood vessels with a diameter of less than 8 microns. Ten randomly selected capillaries from each biopsy were measured for luminal surface area, endothelial cytoplasmic surface area, and total cross-sectional surface area of capillaries.

RESULTS

From stereologic morphometric studies, the serial changes in total cross-sectional surface area were not statistically significant (p = 0.152). However, there was a significant swelling of endothelial cytoplasm following ischemia and reperfusion (p = 0.0007). Meanwhile, changes in luminal surface area of capillaries following ischemia and reperfusion were also remarkable (p = 0.0008).

CONCLUSIONS

The most striking finding of this study was the progressive decrease in capillary lumen during ischemia and after reperfusion. The swelling of endothelial cells is a major determinant of luminal narrowing of capillaries in patients receiving cardioplegic arrest.

Severe transmyocardial ischemia in a patient with tension pneumothorax

OBJECTIVE

To report tension pneumothorax (TP) as a cause of severe myocardial ischemia.

DESIGN

Clinical case report.

SETTING

Medical intensive care unit of a university hospital.

PATIENTS

One patient with severe shock attributable to right TP after unsuccessful percutaneous central venous catheterization.

INTERVENTIONS

Blood pressure, electrocardiogram (ECG), chest radiograph, and echocardiography during and after shock.

MEASUREMENTS AND MAIN RESULTS

On admission the patient was in profound state of shock (heart rate 140 beats/min, blood pressure 65/30 mm Hg). Twelve-lead ECG showed pronounced ST segment elevation in leads II, III, aVF, and V4-V6. Chest radiograph revealed right TP with complete displacement of the mediastinum and the heart to the left side. Immediate right-sided tube thoracostomy resulted in reexpansion of the lung followed by instantaneous hemodynamic and respiratory improvement as well as nearly complete resolution of the ECG changes. Peak value of the creatine phosphokinase was 4140 U/L without significant elevation of the MB isoenzyme at any time. Moreover, the initial hypokinesia of the posterior and lateral left ventricular wall resolved completely, as demonstrated by echocardiography.

CONCLUSION

The specific condition of TP may lead to impaired systolic and diastolic coronary artery blood flow affecting ventricular repolarization and T-wave configuration in ECG indicative of transmyocardial ischemia. General symptoms, namely hypotension, tachycardia, and hypoxemia, are likewise typical for cardiogenic shock attributable to myocardial infarction. Yet any therapeutic measure directed toward revascularization, such as thrombolysis or even percutaneous transluminal coronary angioplasty, would have had devastating consequences. Therefore, thorough physical examination of our patient was pivotal in disclosing the true origin of profound shock.

Cardioprotective effects of YM934, an ATP-sensitive potassium channel opener, on stunned myocardium in anesthetized dogs

The effects of YM934 [2-(3,4-dihydro-2,2-dimethyl-6-nitro-2H-1,4-benzoxazin-4-yl) pyridine N-oxide], an adenosine triphosphate (ATP)-sensitive potassium channel opener, on stunned myocardium were examined. Forty eight anesthetized dogs were subjected to 15 min of left anterior descending (LAD) coronary artery occlusion followed by 3 hours of reperfusion. To elucidate the possible contribution of the cardioprotective property of YM934 to stunned myocardium, a nonhypotensive dose of YM934 was directly injected into the LAD coronary artery before the ischemic insults. Intracoronary artery infusion (i.c.) of YM934 (0.1 microg/kg/min) produced a marked improvement in post-ischemic regional contractile dysfunction. The effects were not associated with improvement of hemodynamics, including regional myocardial blood flow during ischemia, heart rate and mean arterial blood pressure. The anatomic areas at risk expressed as a percentage of the left ventricle and regional myocardial blood flow were not significantly different between groups. The cardioprotective effect of YM934 was completely blocked by pretreatment with an ATP-sensitive potassium channel blocker, glibenclamide (1.0 mg/kg i.v. bolus). These results suggest that YM934 exerts cardioprotective effect on stunned myocardium through opening myocardial ATP-sensitive potassium channels.

Randomized, double-blind crossover study to investigate the effects of amlodipine and isosorbide mononitrate on the time course and severity of exercise-induced myocardial stunning

BACKGROUND

Myocardial stunning may cause prolonged left ventricular dysfunction after exercise-induced ischemia that can be attenuated by calcium antagonists in animal models. To assess their effects in humans, we performed a randomized, double-blind crossover study comparing the calcium antagonist amlodipine (10 mg once daily) versus isosorbide mononitrate (ISMN, 50 mg once daily) on postexercise stunning.

METHODS AND RESULTS

Twenty-four men with chronic stable angina and normal left ventricular function underwent serial quantitative exercise stress echocardiography after 3 weeks on each treatment to assess the degree of postexercise stunning with simultaneous sestamibi single-photon emission computed tomography perfusion scans at peak stress to quantify the ischemic burden. Exercise time (P=1), maximum ST depression (P=0.48), and sestamibi single-photon emission computed tomography scores (P=0.17) were unchanged between treatments. Stunning occurred more often with ISMN than amlodipine (82% versus 48%). The global and segmental stress echocardiography parameters of stunning were attenuated in patients while taking amlodipine compared with ISMN. Shortening fractions and ejection fractions were less impaired 30 minutes after exercise in patients receiving amlodipine (3.5+/-1.4% versus 2.5+/-1.4%, P=0.014, and 59.7+/-5.4% versus 54.5+/-8%, P<0.001); similarly, the isovolumic relaxation period was less prolonged with amlodipine (93+/-15.5 versus 106.3+/-14.9 ms, P=0.018).

CONCLUSIONS

Despite comparable levels of ischemia, amlodipine attenuated stunning when compared with ISMN. This beneficial effect may relate to a prevention of the calcium overload implicated in the pathogenesis of stunning.

Different outcomes of the reperfused myocardium: insights into the comments of stunning and hibernation

There are several potential outcomes of myocardial ischaemia. When ischaemia is severe and prolonged, irreversible damage occurs and there is no recovery of contractile function. Interventions aimed at reducing mechanical activity and oxygen demand either before ischaemia or during reperfusion have been shown to delay the onset of ischaemic damage and to improve recovery during reperfusion. When myocardial ischaemia is less severe but still prolonged, myocytes may remain viable but exhibit depressed contractile function. Under these conditions, reperfusion restores complete contractile performance. This type of ischaemia leading to a reversible, chronic left ventricular dysfunction has been termed 'hibernating myocardium'. It is important clinically recognize hibernation as reperfusion of hibernating myocardium by angioplasty or heart surgery restores contraction and this correlates with long term survival. A third possible outcome after a short period of myocardial ischaemia is a transient post-ischaemic ventricular dysfunction, a situation termed 'stunned myocardium'.

Functional and ultrastructural evidence of myocardial stunning after acute carbon monoxide poisoning

OBJECTIVE

To study human myocardial ultrastructural changes after carbon monoxide (CO) poisoning inducing reversible cardiac failure.

DESIGN

CASE REPORT

clinical, functional and morphologic findings.

SETTINGS

Public university-affiliated hospital and electron microscopy laboratory.

PATIENT

A 25-yr-old woman with functional evidence of cardiac failure after acute CO poisoning.

INTERVENTIONS

Hyperbaric and intensive care treatment over 10 days. Scintigraphic and cardiac angiography with endomyocardial biopsy.

MEASUREMENTS AND MAIN RESULTS

Scintigraphy with 99mTc hexakis 2-methoxy-2-isobutyl isonitrile (sestaMIBI) showed an uptake defect in the left anterior descending artery territory. The cardiac angiography demonstrated a slight hypokinesis of the superior two thirds of the anterior wall and of the septal region with completely normal coronary angiograms. Electron microscopy of left ventricular biopsies showed slight ultrastructural changes in the myocytes. In addition, large glycogen deposits were mostly associated with swollen mitochondria. The patient was discharged in good clinical condition on day 10.

CONCLUSIONS

Presence of glycogen deposits associated with abnormal mitochondria may be signs of the incapability of myocardial cells in utilizing energy substrata. In the presence of normal myocardial perfusion, our findings are consistent with the presence of a stunned myocardium-like syndrome. Early recognition and treatment of this clinical syndrome allow the prevention of myocardial infarction.

Protection against myocardial dysfunction after a brief ischemic period in transgenic mice expressing inducible heat shock protein 70

Brief ischemic periods lead to myocardial dysfunction without myocardial infarction. It has been shown that expression of inducible HSP70 in hearts of transgenic mice leads to decreased infarct size, but it remains unclear if HSP70 can also protect against myocardial dysfunction after brief ischemia. To investigate this question, we developed a mouse model in which regional myocardial function can be measured before and after a temporary ischemic event in vivo. In addition, myocardial function was determined after brief episodes of global ischemia in an isolated Langendorff heart. HSP70-positive mice and transgene negative littermates underwent 8 min of regional myocardial ischemia created by occlusion of the left descending coronary artery, followed by 60 min of reperfusion. This procedure did not result in a myocardial infarction. Regional epicardial strain was used as a sensitive indicator for changes in myocardial function after cardiac ischemia. Maximum principal strain was significantly greater in HSP70-positive mice with 88+/-6% of preischemic values vs. 58+/-6% in transgene-negative mice (P < 0.05). Similarly, in isolated Langendorff perfused hearts of HSP70-positive and transgene-negative littermates exposed to 10 min of global ischemia and 90 min of reperfusion, HSP70 transgenic hearts showed a better-preserved ventricular peak systolic pressure. Thus, we conclude that expression of HSP70 protects against postischemic myocardial dysfunction as shown by better preserved myocardial function.

Angiotensin converting enzyme inhibitor therapy in severe postcardiotomy dysfunction: a prospective randomized study

BACKGROUND

Occurrence of severe postcardiotomy dysfunction requiring prolonged postoperative support with intra-aortic balloon counterpulsation (IABP) and inotropes, complicating surgery for coronary artery disease and valvular heart disease carries important hospital morbidity and mortality. This study evaluated the impact of angiotensin converting enzyme inhibitor (captopril) therapy in these patients in the early postoperative period.

METHODS

During a 5-year period, 298 patients with prolonged diminished cardiac output required support (> 48 to 72 hours) with IABP plus two or three inotropes. This cohort was randomized to two groups, group A (195 patients) who were continued on IABP and inotropes alone and group B (103 patients) who were given an angiotensin converting enzyme (ACE) inhibitor, captopril 48 to 72 hours postoperatively and continued on IABP and inotropes.

RESULTS

Tissue perfusion and hemodynamic parameters improved (p < 0.0001) in group B with early termination of IABP (duration of support mean 86 hours in group B vs 169 hours in group A) and inotropes. Peak improvement in tissue perfusion and hemodynamic parameters correlated with decreased serum angiotensin converting enzyme levels. Hospital mortality occurred in 31% of patients in group A and 14.5% in group B. Morbidity complications developed in 37% of patients in group A and 20% in group B. The average length of hospital stay in group A was 27 days and 17 days in group B. Cardiac, pulmonary, infective, gastrointestinal, renal, and neurological complications were common in both groups.

CONCLUSION

Administration of ACE inhibitors in the early postoperative period to patients with severe postcardiotomy dysfunction caused improvement in tissue perfusion with decreases in mortality, morbidity, and length of hospital stay. These drugs, by effectively limiting physiological effects induced by renin angiotensin-aldosterone axis and other mechanisms, caused recovery of stunned myocardium. More randomized trials are needed before recommending these drugs for routine use in similar patients.

Reduction of oxidative stress does not affect recovery of myocardial function: warm continuous versus cold intermittent blood cardioplegia

OBJECTIVE

To compare oxidative stress after cardiac surgery in patients treated with two different methods of myocardial protection: warm continuous versus cold intermittent blood cardioplegia. To correlate oxidative stress with postoperative myocardial dysfunction.

DESIGN

Prospective, randomised, double blind, trial.

SETTING

Institutional centre of cardiovascular surgery.

PATIENTS

20 patients were selected for coronary artery bypass surgery (CABG) on the following basis: stable angina, ejection fraction > 50%, double or triple vessel disease, no previous CABG or associated disease. Patients were randomised to two groups of 10 patients each.

INTERVENTIONS

Patients underwent CABG with one of two different methods of myocardial protection and cardiopulmonary bypass. CBC group: intermittent cold blood antegrade-retrograde cardioplegia with moderate hypothermic cardiopulmonary bypass; WBC group: continuous warm blood antegrade-retrograde cardioplegia with mild hypothermic cardiopulmonary bypass.

MAIN OUTCOME MEASURE

The index of oxidative stress used was the alteration of whole blood and plasma glutathione redox status. Samples were collected from the coronary sinus and peripheral vein before anaesthesia (T1), before aortic unclamping (T2), 15 minutes (T3), and 30 minutes (T4) after unclamping. Haemodynamic parameters were measured with thermodilution techniques.

RESULTS

Oxidised glutathione and glutathione-cysteine mixed disulphide significantly increased in the coronary sinus plasma in the CBC group, and the overall redox balance of glutathione was decreased (P < 0.01) at T2-T4 versus T1, and compared with the WBC group. Comparable results were obtained for coronary sinus blood. There was no correlation between postoperative haemodynamic measurements and oxidative stress markers.

CONCLUSIONS

Oxidative stress was significant in patients undergoing CABG using cold blood cardioplegia, while the warm technique minimised the effects of ischaemia. However, oxidative stress was not correlated with myocardial dysfunction following CABG.

Reperfusion Injury: Basic Concepts and Protection Strategies

Prolonged ischemia such as that following myocardial infarction or occurring during long-term coronary bypass procedures causes serious damage to the myocardium. Early reperfusion is an absolute prerequisite for the survival of ischemic tissue. However, reperfusion has been referred to as the "double edged sword" because reperfusing ischemic myocardium carries with it a component of injury known as reperfusion injury. Reperfusion injury includes a number of events, such as reperfusion arrhythmias, myocardial infarction, stunning, vascular damage, and endothelial dysfunction. The underlying mechanism of reperfusion injury is not entirely known, but the existing evidence suggests that oxygen free radicals generated during the first few minutes of reflow lead to damage of cellular membranes, intracellular calcium overload, and uncoupling of excitation-contraction coupling. Although controversial, free radical scavengers, in general, are highly effective in the attenuation of reperfusion injury in animal models. Newer endogenous protection strategies, which include ischemic and heat shock preconditioning, are known to reduce reperfusion injury following ischemia.

Complete stunning in hypertrophied guinea pig heart. Defects in sarcolemmal calcium influx

Isolated sham control as well as hypertrophied guinea pig hearts were subjected to global ischemia and reperfusion. Developed force declined to zero during 5 min of ischemia without any significant change in resting tension in both sham control and hypertrophied hearts. Upon reperfusion, control hearts showed nearly complete recovery of developed force within 20 min, whereas hypertrophied hearts during this time showed no contractile function, i.e., "a complete stunning" was observed. A continued reperfusion of the stunned hypertrophied hearts ultimately resulted in complete recovery of force within 40-60 min. Data on myocardial cation content showed a relative calcium deficiency in the stunned hearts (3.4 mumol/gm dry wt) as compared to sham control hearts (5.3 mumol/gm dry wt). Stunning could be reversed sooner by isoproterenol (100 microns), and low Na+ (35 and 60 mM) perfusion. Recovery of contractile function by low Na+ was blocked by amiloride (0.17-1.2 mM) in a dose-dependent manner. Perfusion with Bay K8644 (0.1-10 microM) as well as low (0.62 mM) and high (2.5 mM) extracellular calcium concentrations failed to reverse stunning. The pharmacological interventions that were able to reverse the stunning condition also increased the myocardial calcium content. Although the possibilities of a sarcoplasmic reticular dysfunction and/or reduced sensitivity of myofilaments are not excluded, data suggest that a defect in calcium influx across the sarcolemma is an important factor in "complete stunning." It is suggested that this "potential sarcolemmal defect" in the hypertrophied heart, which is unmasked by the ischemic stress, may also represent an early abnormality in the pathogenesis of heart failure.

Stress radionuclide studies after acute myocardial infarction: changes with revascularization

BACKGROUND

Successful revascularization of ischemic asynergic myocardium should be followed by improvement in contractile function. However, a clear improvement is not always observed. Assessment of contractile reserve may allow a better evaluation of procedural results.

METHODS AND RESULTS

To assess the changes in global and regional left ventricular ejection fraction (EF), as well as the contractile reserve after revascularization, equilibrium radionuclide angiography was performed in 16 patients with acute myocardial infarction who had periinfarct redistribution (observed in stress-rest-reinjection thallium single-photon emission computed tomography). Regional EF was defined in the asynergic region at rest, which corresponded to the infarct plus periinfarct areas. Both thallium single-photon emission computed tomography and equilibrium radionuclide angiography were performed at rest and during stress with dobutamine, up to a maximal dose of 40 micrograms/kg/min. The same studies were repeated 8 +/- 6 months after successful revascularization (nine coronary angioplasties and seven bypass procedures). After intervention, the thallium defect score decreased significantly at rest and during stress. Global EF changed from 45% +/- 10% to 47% +/- 11% (difference not significant) at rest and from 49% +/- 12% to 63% +/- 13% (p = 0.0001) at peak stress. Regional EF changed from 27% +/- 8% to 35% +/- 18% (p = 0.03) at rest and from 29% +/- 10% to 56% +/- 21% (p = 0.0001) at peak stress.

CONCLUSIONS

In patients with asynergy caused by periinfarct ischemia, there can be an increase in regional but not global EF at rest after revascularization. However, both parameters improve at peak dobutamine dose. This indicates an improvement in contractile reserve.

Analysis of P50 and oxygen transport in patients after cardiac surgery

OBJECTIVE

To determine whether standard P50 after cardiac surgery decreases and whether decreased P50 is related to the transfusion of red blood cells (RBCs), acid-base changes, body temperature, oxygen parameters and/or duration of cardiopulmonary bypass (CPB).

DESIGN

Pilot study in cardiac surgery patients.

SETTING

University hospital.

PATIENTS

12 Consecutive elective cardiac surgery patients.

INTERVENTIONS

Blood was taken before surgery, after CPB and in the intensive care unit until 18 h post-operatively. Cardiac output and oxygen consumption were measured. Buffy coat-poor RBCs were transfused, anticoagulated with citrate-phosphate-dextrose buffer and stored in saline-adenine-glucose-mannitol at 4 degrees C, when haemoglobin was < 5.6 mmol.l-1.

MEASUREMENTS AND RESULTS

Standard P50 was calculated from measured partial pressure of oxygen and of carbon dioxide, pH and oxygen saturation in mixed venous blood (SvO2) using the Severinghaus formula. Median length of RBC storage was 25 days. Standard P50 after surgery was significantly lower than baseline value (p = 0.0001). The number of RBC units transfused and duration of CPB were conjointly associated with P50 (R2 = 0.72). Patients who received more RBCs consumed more oxygen.

CONCLUSION

Cardiac surgery patients receiving more RBC units have lower standard P50 and consume more oxygen. P50 decreased more when the CPB took longer. Because a decrease in P50 implies a low ratio of mixed venous oxygen tension (PvO2) to SvO2, a shift in P50 should be taken into account when using SvO2 as a measure of global oxygen availability. When a direct measurement of SvO2 is not available, PvO2 should be used instead of calculated SvO2.

Increased oxygen consumption after cardiac surgery is associated with the inflammatory response to endotoxemia

OBJECTIVE

The aim of this study was to determine whether the increase in post-operative oxygen consumption (delta VO2) in cardiac surgery patients is related to endotoxemia and subsequent cytokine release and whether delta VO2 can be used as a parameter of post-perfusion syndrome.

DESIGN

Prospective study.

SETTING

Operating room and intensive care unit of a university hospital.

PATIENTS

Twenty-one consecutive male patients undergoing elective coronary artery bypass surgery without major organ dysfunction and not receiving corticosteroids.

MEASUREMENTS AND RESULTS

Plasma levels of endotoxin, tumor necrosis factor (TNF) and interleukin-6 (IL-6) were measured before, during and for 18 h after cardiac surgery. Oxygen consumption, haemodynamics, the use of IV fluids and dopamine, body temperature and the time of extubation were also measured. Measurements from patients with high delta VO2 (> or = median value of the entire group) were compared with measurements from patients with low delta VO2 (< median). Patients with high delta VO2 had higher levels of circulating endotoxin (P = 0.004), TNF (P = 0.04) and IL-6 (P = 0.009) received more IV fluids and dopamine while in the ICU, and were extubated later than patients with low delta VO2. Several hours after delta VO2 the patient's body temperature rose. Forward stepwise regression analysis showed that circulating endotoxin and TNF explained 50% of the variability of delta VO2.

CONCLUSIONS

This study demonstrates that patients with high post operative oxygen consumption after elective cardiac surgery have higher circulating levels of endotoxin, TNF and IL-6 and also have more symptoms of post-perfusion syndrome. Early detection of high VO2 might be used as a clinical signal to improve circulation in order to meet the high oxygen demand of inflammation. In addition, continuous measurement of VO2 provides us with a clinical parameter of inflammation in interventional studies aiming at a reduction of endotoxemia or circulating cytokines.

Ischemic event characteristics determine the extent of myocardial stunning in conscious dogs

Both the severity and duration of postischemic myocardial dysfunction ("stunned" myocardium) are unpredictable and may vary considerably between subjects that underwent apparently similar ischemic insults. To explain this heterogeneous response of the heart to ischemia and reperfusion, we investigated the determinants of stunning in conscious dogs. Twenty-five dogs were chronically instrumented for measurement of global and regional myocardial performance (wall thickening) and myocardial perfusion (coloured microspheres). A hydraulic occluder was positioned around the LAD coronary artery. Conscious dogs were subjected to acute coronary artery occlusions of predetermined duration (2, 5 and 10 min), followed by complete reperfusion. Multiple regression analysis identified the following variables as determinants of postischemic contractile recovery: 1) the duration of ischemia (p < 0.01),2) the amount of collateral perfusion (p = 0.01) and 3) left ventricular end-diastolic pressure during ischemia (p < 0.01). Neither the severity of regional dyskinesia during ischemia nor indices of global systolic hemodynamic performance correlated with the rate of recovery. Our data confirm that myocardial stunning relates primarily to the intensity of preceding ischemia. Variations in the preexisting level of collateral perfusion may result in markedly different recovery profiles. Except for LV end-diastolic pressure during ischemia, indices of global and regional cardiac performance fail to predict the severity of postischemic contractile failure.

Postischemic functional recovery and BMIPP uptake after primary percutaneous transluminal coronary angioplasty in acute myocardial infarction

To correlate asynergic wall motion after primary percutaneous transluminal coronary angioplasty with myocardial perfusion and fatty acid metabolism, quantitative tomographies using thallium and radioiodinated 15-(p-iodophenyl)-3-R,S-methylpentadecanoic acid (BMIPP) were performed during the acute and recovery stages in 56 consecutive patients with acute myocardial infarction, of whom 32 underwent primary percutaneous transluminal coronary angioplasty (group A) and 24 were conservatively treated (group B); 44 patients (79%) had 1-vessel disease. Reduced myocardial uptakes of thallium and BMIPP and regional wall motion were quantified with a bull's eye technique and a centerline method using contrast left ventriculography, respectively. BMIPP activity was significantly lower than that of thallium at an acute stage in both groups. Abnormal BMIPP activities and the difference in thallium and BMIPP abnormalities (perfusion metabolism mismatch) at an acute stage decreased significantly during follow-up in group A (111 +/- 13 to 99 +/- 12 and 30 +/- 10 to 15 +/- 10, respectively), and not in group B (129 +/- 31 vs 118 +/- 29 and 29 +/- 13 vs 30 +/- 10, respectively). Improvement in regional wall motion abnormality correlated closely with the improved uptakes of thallium and BMIPP (y = 0.64x + 26.4, r = 0.56, p < 0.05; y = 1.1x + 11.1, r = 0.81, p < 0.001; respectively). The mismatched uptake of both tracers at an acute stage was significantly related to recovery from asynergic wall motion during follow-up in group A (y = 0.45x + 13.9, r = 0.65, p < 0.005). In conclusion, despite restored myocardial perfusion by primary coronary angioplasty, BMIPP uptake is impaired in salvaged myocardium at an acute stage of infarction. However, the degree and improvement of perfusion metabolism mismatch in acute myocardial infarction may reflect subsequent recovery from postischemic wall motion abnormality in metabolically impaired but viable myocardium after coronary reperfusion.

Isoflurane-induced coronary vasodilation is preserved in reperfused myocardium

Isoflurane causes vasodilation in the coronary circulation. The present study evaluated whether this action is preserved after a brief coronary occlusion followed by reperfusion. Fourteen open-chest dogs anesthetized with fentanyl and midazolam were studied. The left anterior descending coronary artery was perfused via an extracorporeal system with normal arterial blood or with arterial blood equilibrated with 1.4% (1 minimum alveolar anesthetic concentration [MAC]) isoflurane. Coronary perfusion pressure was maintained at 90 mm Hg. Coronary blood flow (CBF) was measured with a Doppler flow transducer. Steady-state changes in CBF during isoflurane, and during intracoronary infusions of acetylcholine (Ach; 20 micrograms/min), an endothelium-dependent vasodilator, and sodium nitroprusside (SNP; 80 micrograms/min), an endothelium-independent vasodilator, were compared in normal myocardium and in myocardium subjected to 15 min of ischemia (due to cessation of perfusion) followed by 30 min of reperfusion. Ischemia-reperfusion had no significant effect on the increases in CBF by isoflurane (421% +/- 88% vs 388% +/- 84%) or SNP (115% +/- 18% vs 135% +/- 19%), whereas it attenuated these increases in CBF by Ach (232% +/- 38% vs 143% +/- 21%). In conclusion, a brief period of myocardial ischemia followed by reperfusion did not affect the coronary vasodilating effects of isoflurane and SNP, although it blunted these effects of Ach. The present findings provide further evidence suggesting that the ability of isoflurane to relax coronary vascular smooth muscle is independent of the nitric oxide-cyclic guanosine monophosphate pathway.

Left ventricular dysfunction due to the new ischemic outcomes: stunning and hibernation

Several potential manifestations and outcomes are associated with myocardial ischemia and reperfusion. When ischemia is severe and prolonged, irreversible damage occurs and there is no recovery of contractile function. When ischemia is less severe or shorter in duration, recovery of contraction may occur instantaneously or more commonly, after considerable delay, which is the condition recognized as "stunned myocardium." Stunning is defined as a transient left ventricular dysfunction that persists after reperfusion despite the absence of irreversible damage and restoration of normal or near-normal coronary flow. Oxidative stress and alteration of calcium homeostasis during reperfusion are the probable causes of stunning. Clinically, stunning may occur after acute infarction, successful thrombolysis, unstable angina, angioplasty, resolution of coronary spasm, open-heart surgery, or transplantation. It can be treated with interventions aimed at prevention or reversal. When ischemia is prolonged but less severe, myocytes may remain viable but exhibit depressed contraction. Under these conditions, reperfusion restores normal contractile performance. This type of ischemia, leading to a reversible, chronic left ventricular dysfunction, has been termed "hibernating myocardium." The intrinsic mechanisms of this condition are unknown. Clinically, it is very important to diagnose hibernation because reperfusion of the hibernating myocardium by angioplasty or heart surgery restores contraction, and this correlates with long-term survival. A number of methods are available to access the hibernating myocardium. These include cardiac imaging techniques that evaluate myocardial viability, such as positron emission tomography and thallium myocardial imaging, or methods that evaluate contractile reserve, such as low-dose dobutamine echocardiography. Interestingly, reperfusion of patients with end-stage ischemic cardiomyopathy and hibernating myocardium can be considered an alternative to transplantation.

Myocardial stunning: a therapeutic conundrum

Dobutamine and pyruvate are two inotropic agents with different mechanisms of action. Although both agents alter postischemic myocardial dysfunction, their potential metabolic effects in the setting of in vivo myocardial stunning have not been addressed. In this study, the effects of dobutamine and pyruvate on systolic wall thickening, myocardial phosphorylation potential index, interstitial fluid adenosine level, and myocardial oxygen consumption in in vivo stunned porcine myocardium were assessed. Stunning was induced with a 10-minute occlusion of the left anterior descending coronary artery. After 30 minutes of reperfusion, pigs were treated with either intravenous dobutamine (10 micrograms/kg per minute) or intracoronary pyruvate (1 ml/min, 150 mmol/L solution, pH 7.4). Infusion of both agents resulted in a marked improvement in regional systolic wall thickening. The dobutamine effect, however, produced a marked increase in myocardial oxygen consumption and was associated with an increase in interstitial adenosine caused by myocardial de-energization, because the myocardial phosphorylation potential index ratio decreased from 0.17 +/- 0.02 to 0.09 +/- 0.02 (p < 0.05). In contrast, pyruvate enhanced myocardial energy status, because the myocardial phosphorylation potential index ratio increased from 0.20 +/- 0.03 to 0.55 +/- 0.08 (p < 0.01). These experimental findings suggest that under certain circumstances the use of beta-receptor agonists to treat myocardial stunning may be suboptimal, if not undesirable. Further investigation is warranted to determine the optimum therapy for the stunned heart.

Incomplete, delayed functional recovery late after reperfusion following acute myocardial infarction: "maimed myocardium"

The objective of the current editorial is to introduce a new concept ("maimed myocardium") that we believe describes more accurately the incomplete, delayed recovery of LV function that may occur late after reperfusion after AMI. It has been demonstrated previously that myocardium remains viable for a prolonged period in many patients with nonsustained coronary occlusion, despite the occurrence of myocardial necrosis; late reperfusion may result in myocardial salvage in reversibly ischemic (stunned) segments (complete recovery) and in intensely injured (maimed) segments that display partial return of LV function over time (incomplete recovery). Clinically, the basis for maimed myocardium is the observation that delayed, LV functional recovery may occur in partially infarcted segments where there has been an antecedent ischemic insult of sufficient duration to result in some degree of myocardial necrosis. Certain acute coronary syndromes characterized by nonsustained coronary occlusion followed by spontaneous reperfusion (e.g., non-Q-wave AMI) or drug-induced reperfusion induced by the exogenous administration of thrombolytic therapy are associated with incomplete, delayed recovery of LV function as detected clinically by partial improvement in serial radionuclide-ejection measurement, enhanced metabolic integrity of cardiac tissue by F-18 deoxyglucose myocardial imaging, and scintigraphic findings of reverse thallium redistribution--findings that support the presence of partially viable myocardium that has been incompletely salvaged during reperfusion late after AMI. Experimentally, delayed LV functional recovery has been reported in animal models in which prolonged coronary occlusion (hours to days) followed by reperfusion is associated with late recovery of regional LV function in myocardial segments subtending border (stunned) zones and central infarct (maimed) zones. In studies in animals and human beings, postextrasystolic potentiation and pharmacologic inotropic interventions may augment maimed and stunned segments, although the magnitude of regional contractile reserve that can be unmasked with these interventions is quantitatively less in the maimed than in stunned segments. In summary, the propensity of intensely injured or partially infarcted LV segments to display intermediate functional recovery followed by reperfusion late after coronary occlusion suggests that even severely depressed but residually viable cardiac muscle can be salvaged incompletely over time.(ABSTRACT TRUNCATED AT 400 WORDS)

Free radicals, calcium homeostasis, heat shock proteins, and myocardial stunning

Repeated brief ischemic episodes result in prolonged depression of contractile function despite the absence of irreversible damage, a phenomenon called myocardial stunning. Considerable evidence exists to suggest that oxygen radicals, particularly the hydroxyl radical formed as a result of Fenton reaction or nitric oxide-peroxynitrite pathway, may contribute to the pathogenesis of myocardial stunning. The generation of free radicals may cause sarcoplasmic reticulum dysfunction, and both of these mechanisms may lead to calcium overload, which in turn could exacerbate the damage initiated by oxygen radicals. Antioxidant therapy has been shown to effectively attenuate or even prevent the development of prolonged depression of contractility in many studies. In addition, preconditioning with brief ischemic insults is able to trigger protection, which appears to attenuate stunning 24 to 48 hours later. The mechanism of this protection is not known, although one or more members of the heat shock protein family may have a role in protection against stunning.