Stem cell-derived exosome patch with coronary artery bypass graft restores cardiac function in chronically ischemic porcine myocardium

OBJECTIVE

This study aimed to investigate whether or not the application of a stem cell-derived exosome-laden collagen patch (EXP) during coronary artery bypass grafting (CABG) can recover cardiac function by modulating mitochondrial bioenergetics and myocardial inflammation in hibernating myocardium (HIB), which is defined as myocardium with reduced blood flow and function that retains viability and variable contractile reserve.

METHODS

In vitro methods involved exposing H9C2 cardiomyocytes to hypoxia followed by normoxic coculture with porcine mesenchymal stem cells. Mitochondrial respiration was measured using Seahorse assay. GW4869, an exosomal release antagonist, was used to determine the effect of mesenchymal stem cells-derived exosomal signaling on cardiomyocyte recovery. Total exosomal RNA was isolated and differential micro RNA expression determined by sequencing. In vivo studies comprised 48 Yorkshire-Landrace juvenile swine (6 normal controls, 17 HIB, 19 CABG, and 6 CABG + EXP), which were compared for physiologic and metabolic changes. HIB was created by placing a constrictor on the proximal left anterior descending artery, causing significant stenosis but preserved viability by 12 weeks. CABG was performed with or without mesenchymal stem cells-derived EXP application and animals recovered for 4 weeks. Before terminal procedure, cardiac magnetic resonance imaging at rest, and with low-dose dobutamine, assessed diastolic relaxation, systolic function, graft patency, and myocardial viability. Tissue studies of inflammation, fibrosis, and mitochondrial morphology were performed posttermination.

RESULTS

In vitro data demonstrated improved cardiomyocyte mitochondrial respiration upon coculture with MSCs that was blunted when adding the exosomal antagonist GW4869. RNA sequencing identified 8 differentially expressed micro RNAs in normoxia vs hypoxia-induced exosomes that may modulate the expression of key mitochondrial (peroxisome proliferator-activator receptor gamma coactivator 1-alpha and adenosine triphosphate synthase) and inflammatory mediators (nuclear factor kappa-light-chain enhancer of activated B cells, interferon gamma, and interleukin 1β). In vivo animal magnetic resonance imaging studies demonstrated regional systolic function and diastolic relaxation to be improved with CABG + EXP compared with HIB (P = .02 and P = .02, respectively). Histologic analysis showed increased interstitial fibrosis and inflammation in HIB compared with CABG + EXP. Electron microscopy demonstrated increased mitochondrial area, perimeter, and aspect ratio in CABG + EXP compared with HIB or CABG alone (P < .0001).

CONCLUSIONS

Exosomes recovered cardiomyocyte mitochondrial respiration and reduced myocardial inflammation through paracrine signaling, resulting in improved cardiac function.

From Neurocardiology to Stroke-Heart Syndrome

The Stroke-Heart syndrome is a major chapter in neurocardiology. Both brain-heart and stroke-heart correlations are based on neurophysiological studies that define and describe the relation between the central autonomic system and cardiac function and it will be presented in this narrative review. The Stroke-Heart syndrome groups the entire spectrum of cardiac changes - clinical, ECG, echocardiographic, biological, morphological - that occur in the first 30 days from the onset of stroke, especially in the first days. Their presence significantly marks the evolution and prognosis of stroke. The damage resulted from hypothalamus-pituitary-adrenal axis activation and high catecholamine release (adrenergic storm) targets mainly the myocyte and the microcirculation.The Takotsubo syndrome and Stunned myocardium are distinct forms of neurogenic myocardial ischemia - with changes in ECG, parietal motility, and biological markers - usually reversible although evolution towards cardiac dysfunction is also possible. The concept of Stroke-Heart syndrome and the brain-heart correlation brought new scientific information regarding stress cardiomyopathy or neurogenic myocardial injury.

Cardioprotective Effect of Acute Intradialytic Exercise: A Comprehensive Speckle-Tracking Echocardiography Analysis

SIGNIFICANCE STATEMENT

Hemodialysis (HD) can lead to acute left ventricular (LV) myocardial wall motion abnormalities (myocardial stunning) due to segmental hypoperfusion. Exercise during dialysis is associated with favorable effects on central hemodynamics and BP stability, factors considered in the etiology of HD-induced myocardial stunning. In a speckle-tracking echocardiography analysis, the authors explored effects of acute intradialytic exercise (IDE) on LV regional myocardial function in 60 patients undergoing HD. They found beneficial effects of IDE on LV longitudinal and circumferential function and on torsional mechanics, not accounted for by cardiac loading conditions or central hemodynamics. These findings support the implementation of IDE in people with ESKD, given that LV transient dysfunction imposed by repetitive HD may contribute to heart failure and increased risk of cardiac events in such patients.

BACKGROUND

Hemodialysis (HD) induces left ventricular (LV) transient myocardial dysfunction. A complex interplay between linear deformations and torsional mechanics underlies LV myocardial performance. Although intradialytic exercise (IDE) induces favorable effects on central hemodynamics, its effect on myocardial mechanics has never been comprehensively documented.

METHODS

To evaluate the effects of IDE on LV myocardial mechanics, assessed by speckle-tracking echocardiography, we conducted a prospective, open-label, two-center randomized crossover trial. We enrolled 60 individuals with ESKD receiving HD, who were assigned to participate in two sessions performed in a randomized order: standard HD and HD incorporating 30 minutes of aerobic exercise (HDEX). We measured global longitudinal strain (GLS) at baseline (T0), 90 minutes after HD onset (T1), and 30 minutes before ending HD (T2). At T0 and T2, we also measured circumferential strain and twist, calculated as the net difference between apical and basal rotations. Central hemodynamic data (BP, cardiac output) also were collected.

RESULTS

The decline in GLS observed during the HD procedure was attenuated in the HDEX sessions (estimated difference, -1.16%; 95% confidence interval [95% CI], -0.31 to -2.02; P = 0.008). Compared with HD, HDEX also demonstrated greater improvements from T0 to T2 in twist, an important component of LV myocardial function (estimated difference, 2.48°; 95% CI, 0.30 to 4.65; P = 0.02). Differences in changes from T0 to T2 for cardiac loading and intradialytic hemodynamics did not account for the beneficial effects of IDE on LV myocardial mechanics kinetics.

CONCLUSIONS

IDE applied acutely during HD improves regional myocardial mechanics and might warrant consideration in the therapeutic approach for patients on HD.

An Adjuvant Stem Cell Patch with Coronary Artery Bypass Graft Surgery Improves Diastolic Recovery in Porcine Hibernating Myocardium

Diastolic dysfunction persists despite coronary artery bypass graft surgery (CABG) in patients with hibernating myocardium (HIB). We studied whether the adjunctive use of a mesenchymal stem cells (MSCs) patch during CABG improves diastolic function by reducing inflammation and fibrosis. HIB was induced in juvenile swine by placing a constrictor on the left anterior descending (LAD) artery, causing myocardial ischemia without infarction. At 12 weeks, CABG was performed using the left-internal-mammary-artery (LIMA)-to-LAD graft with or without placement of an epicardial vicryl patch embedded with MSCs, followed by four weeks of recovery. The animals underwent cardiac magnetic resonance imaging (MRI) prior to sacrifice, and tissue from septal and LAD regions were collected to assess for fibrosis and analyze mitochondrial and nuclear isolates. During low-dose dobutamine infusion, diastolic function was significantly reduced in HIB compared to the control, with significant improvement after CABG + MSC treatment. In HIB, we observed increased inflammation and fibrosis without transmural scarring, along with decreased peroxisome proliferator-activated receptor-gamma coactivator (PGC1α), which could be a possible mechanism underlying diastolic dysfunction. Improvement in PGC1α and diastolic function was noted with revascularization and MSCs, along with decreased inflammatory signaling and fibrosis. These findings suggest that adjuvant cell-based therapy during CABG may recover diastolic function by reducing oxidant stress–inflammatory signaling and myofibroblast presence in the myocardial tissue.

Left ventricular dyssynchrony and abnormalities in wall motion, assessed by gated-SPECT as ischemic auxiliary markers

INTRODUCTION

Left ventricular dyssynchrony (LVD) quantified by gated myocardial perfusion studies (MPS), through phase analysis (PA), has shown controversial results in myocardial stunning.

OBJECTIVES

Assessment of LVD and regional wall motion abnormalities (RWMA) in normal and ischemic patients.

METHODS

A cohort of 172 patients were studied. Summed Stress Score (SSS), Summed Resting Score (SRS), and Summed Difference Score (SDS) were evaluated. Group 1-patients with normal MPS (N = 133) and Group 2-patients with myocardial ischemia in the MPS (N = 39). LVD was evaluated through PA and RWM by visual analysis.

RESULTS

SSS 0 vs 9.8 ± 3.9 P = .0001; SDS 0 vs 9.8 ± 3.9 P = .0001; SRS 0 vs 0 P = NS, in G1 and G2. Significant differences were found in LVD between G1 and G2, bandwidth 36 ± 14 vs 63 ± 46 P = .0001; standard deviation 16 ± 10 vs 26 ± 15 P = .0001. In G1, 16% had LVD vs RWMA in 0%, P = .0001 and in G2, 59% with LVD vs 33% with RWMA, P = .03. Sensitivity for LVD 59% and for RWMA 33%, P = .03 and specificity for LVD 83% and for RWMA 100%, P = .0001.

CONCLUSION

Ischemic patients have LVD post-stress due to myocardial stunning. LVD measured by PA could be a useful tool to identify ischemia.

The utility of 82Rb PET for myocardial viability assessment: Comparison with perfusion-metabolism 82Rb-18F-FDG PET

BACKGROUND

82Rb kinetics may distinguish scar from viable but dysfunctional (hibernating) myocardium. We sought to define the relationship between 82Rb kinetics and myocardial viability compared with conventional 82Rb and 18F-fluorodeoxyglucose (FDG) perfusion-metabolism PET imaging.

METHODS

Consecutive patients (N = 120) referred for evaluation of myocardial viability prior to revascularization and normal volunteers (N = 37) were reviewed. Dynamic 82Rb 3D PET data were acquired at rest. 18F-FDG 3D PET data were acquired after metabolic preparation using a standardized hyperinsulinemic-euglycemic clamp. 82Rb kinetic parameters K1, k2, and partition coefficient (KP) were estimated by compartmental modeling RESULTS: Segmental 82Rb k2 and KP differed significantly between scarred and hibernating segments identified by Rb-FDG perfusion-metabolism (k2, 0.42 ± 0.25 vs. 0.22 ± 0.09 min-1; P < .0001; KP, 1.33 ± 0.62 vs. 2.25 ± 0.98 ml/g; P < .0001). As compared to Rb-FDG analysis, segmental Rb KP had a c-index, sensitivity and specificity of 0.809, 76% and 84%, respectively, for distinguishing hibernating and scarred segments. Segmental k2 performed similarly, but with lower specificity (75%, P < .001) CONCLUSIONS: In this pilot study, 82Rb kinetic parameters k2 and KP, which are readily estimated using a compartmental model commonly used for myocardial blood flow, reliably differentiated hibernating myocardium and scar. Further study is necessary to evaluate their clinical utility for predicting benefit after revascularization.

The functional significance of the last 5 residues of the C-terminus of cardiac troponin I

The C-terminal region of cardiac troponin I (cTnI) is known to be important in cardiac function, as removal of the last 17 C-terminal residues of human cTnI has been associated with myocardial stunning. To investigate the C-terminal region of cTnI, three C-terminal deletion mutations in human cTnI were generated: Δ1 (deletion of residue 210), Δ3 (deletion of residues 208-210), and Δ5 (deletion of residues 206-210). Mammalian two-hybrid studies showed that the interactions between cTnI mutants and cardiac troponin C (cTnC) or cardiac troponin T (cTnT) were impaired in Δ3 and Δ5 mutants when compared to wild-type cTnI. Troponin complexes containing 2-[4'-(iodoacetamido) anilino] naphthalene-6-sulfonic acid (IAANS) labeled cTnC showed that the troponin complex containing cTnI Δ5 had a small increase in Ca(2+) affinity (P < 0.05); while the cTnI Δ1- and Δ3 troponin complexes showed no difference in Ca(2+) affinity when compared to wild-type troponin. In vitro motility assays showed that all truncation mutants had increased Ca(2+) dependent motility relative to wild-type cTnI. These results suggest that the last 5 C-terminal residues of cTnI influence the binding of cTnI with cTnC and cTnT and affect the Ca(2+) dependence of filament sliding, and demonstrate the importance of this region of cTnI.

Investigation of myocardial stunning after cardiopulmonary resuscitation in pigs

OBJECTIVE

To investigate cardiac function and myocardial perfusion during 48 h after cardiopulmonary resuscitation (CPR), further to test myocardial stunning and seek indicators for long-term survival after CPR.

METHODS

After 4 min of untreated ventricular fibrillation, fifteen anesthetized pigs were studied at baseline and 2 h, 4 h, 24 h, and 48 h after restoration of spontaneous circulation (ROSC). Hemodynamic data, echocardiography and gated-single photon emission computed tomography myocardial perfusion images were carried out.

RESULTS

Mean arterial pressure (MAP), coronary perfusion pressure (CPP) and cardiac troponin I (CTNI) showed significant differences between eventual survival animals and non-survival animals at 4 h after ROSC (109.2 ± 10.7 mmHg vs. 94.8 ± 12.3 mmHg, P=0.048; 100.8 ± 6.9 mmHg vs. 84.4±12.6 mmHg, P=0.011; 1.60 ± 0.13 ug/L vs. 1.75 ± 0.10 ug/L, P=0.046). Mitral valve early-to-late diastolic peak velocity ratio, mitral valve deceleration time recovered 24 h; ejection faction and the summed rest score recovered 48 h after ROSC.

CONCLUSION

Cardiac systolic and early active relaxation dysfunctions were reversible within survival animals; cardiac stunning might be potentially adaptive and protective after CPR. The recovery of MAP, CPP, and CTNI could be the indicators for long-term survival after CPR.

Suppressed phospholamban levels differentiate irreversibly dysfunctional from hibernating myocardium in humans

OBJECTIVES

We studied whether dysfunction of human hibernating (HIB) and irreversibly dysfunctional myocardium (IRDM) are associated with altered levels of the sarcoplasmatic reticulum calcium handling proteins Ca2+-ATPase (SERCA2a) and its inhibitor phospholamban (PLB).

DESIGN

In 12 patients myocardial biopsies were taken during bypass surgery and analysed for contents of these proteins. We classified regions as control, HIB, or IRDM based on echocardiographic studies before and 6 months after surgery.

RESULTS

SERCA2a content (mean+/-SEM) was similar to control in HIB and IRDM (2.6 +/- 1.7, 3.8 +/- 2.0, and 3.4 +/- 1.9 units/g non-collagen protein (NCP), p = 0.40). PLB content was similar to control in HIB (2.6 +/- 0.4 and 3.5 +/- 0.5 units/microg NCP) but reduced in IRDM (0.9 +/- 0.2 units/microg NCP, p < 0.05). SERCA2a:PLB ratio, an indicator of SERCA2a activity, did not differ between control and HIB (1.2 +/- 0.3 and 1.4 +/- 0.4 units/microg NCP) but was increased in IRDM (5.1 +/- 1.7 units/microg NCP, p < 0.05).

CONCLUSIONS

Inappropriate SERCA2a activity due to suppressed PLB levels may represent a maladaptive mechanism in chronic ischemic myocardium being causally linked to irreversibility of left ventricular dysfunction.

Mechanical restitution curves reflect post-ischemic stunning in pigs

OBJECTIVES

The time constant of mechanical restitution (T(MRC)), proposed to reflect changes in calcium release and uptake, has been shown to increase in left ventricular (LV) failure. In this study, we tested the hypothesis that T(MRC) also can identify post-ischemic, reversible LV dysfunction (stunning).

DESIGN

Stunning was induced by a series of left main coronary artery occlusions in eight anesthetized open chest pigs. Left ventricular pressure-volume relations were assessed using a pressure-volume catheter during right atrial pacing. Mechanical restitution curves (MRCs) were constructed using two different measures of contractile response: maximal first derivative of pressure (CR(dP/dtmax)) and stroke work (CR(SW)).

RESULTS

Mean arterial pressure, stroke volume and dP/dtmax were decreased 30 min after stunning. Slopes of end-systolic pressure volume relation and preload recruitable stroke work, however, showed no significant changes after stunning. For MRCs based on CR(dP/dtmax), T(MRC) increased in all eight animals. Using CR(SW), T(MRC) increased in seven out of eight pigs.

CONCLUSIONS

Ischemia-reperfusion induce changes in MRCs based on CR(dP/dtmax), and CR(SW). The MRC concept may have potential as a clinical left ventricular performance index.

"Apical ballooning" - what is the cause?

The pathophysiology of takotsubo cardiomyopathy remains enigmatic. Here we attempted to define the link between the coronary arteries and the histopathological involvement of the left ventricle. We observed similarities and discrepancies between patients. All patients experienced stress prior to the event. We found a reduced coronary flow reserve in all patients and signs of hibernating myocardium on biopsy specimen. This raises a strong suspicion of stress-induced endothelial dysfunction with hibernating myocardium in the pathogenesis of this cardiomyopathy.

[Estimation of myocardial perfusion changes after surgical revasculization with single-photon emission computed tomography]

OBJECTIVE

to estimate myocardial perfusion performing single-photon emission computed tomography before and in early period after coronary artery bypass grafting; to predict results of complete myocardial revascularisation by preoperative perfusion data.

MATERIAL AND METHODS

Ten patients with stable coronary artery disease and resting left ventricular wall motion abnormalities (mean ejection fraction 37.7+/-6.5%, mean wall motion index 1.89+/-0.32) underwent 99mTc-MIBI myocardial perfusion single-photon emission computed tomography before and in early period (3 and 6 months) after coronary artery bypass grafting. We estimated myocardial perfusion, postoperative recovery and calculated scintigraphic indices.

RESULTS

The mean number of distal anastomoses was 3.5+/-0.9 and all of patients had complete myocardial revascularization. Postoperatively 39 (66.1%) after 3 months and 45 (76.3%) after 6 months of 59 revasculared segments with different degree of myocardial perfusion disorders improved. Postoperative (after 6 months) index of myocardial perfusion recovery was found more than 2 times better than predicted preoperatively, because there was no estimation of hibernating myocardium preoperatively.

CONCLUSIONS

Estimation of myocardial perfusion changes with single-photon emission computed tomography in early postoperative period, especially after 6 months, confirms the excellent and final results of complete surgical myocardial revascularization. Present protocol of myocardial perfusion investigation gives incomplete information in prediction of postoperative results of complete myocardial revascularization. Myocardial perfusion study performed after nitrate administration is the method of choice to predict correct results.

Cardioprotection in stunned and hibernating myocardium

Although myocardial ischemia was once thought to result in irreversible cellular damage, it is now demonstrated that in cardiac tissue, submitted to the stress of oxygen and substrate deprivation, endogenous mechanisms of cell survival may be activated. These molecular mechanisms result in physiological conditions of adaptation to ischemia, known as myocardial stunning and hibernation. These conditions result from a switch in gene and protein expression, which sustains cardiac cell survival in a context of oxygen deprivation and during the stress of reperfusion. The pattern of cell survival elicited by ischemia in myocardial stunning or hibernation results in the activation of cytoprotective mechanisms that will protect the heart against further ischemic damage, a condition referred to as ischemic preconditioning. The basic mechanisms underlying stunning and hibernation are still a matter of intense research, which includes the discovery and characterization of novel survival genes not described in the heart before, or the unraveling of new cellular processes, such as autophagy. Understanding how the molecular adaptation of the cardiac myocyte during stress sustains its survival in these conditions therefore might help defining novel mechanisms of endogenous myocardial salvage, in order to expand the conditions of maintained cellular viability and functional salvage of the ischemic myocardium.

Myocardial stunning following defibrillation threshold testing

Implantable cardioverter-defibrillators (ICDs) have a proven mortality benefit in appropriately selected people. Several retrospective studies, though, have postulated that appropriate ICD therapy may lead to fatal, pulseless electrical alternans (PEA). This case report describes an episode of transient PEA from myocardial stunning and standstill following defibrillation threshold testing. The risk of post-shock myocardial stunning and standstill should be kept in mind as a potential complication of testing. With rapid recognition and prompt intervention, this complication is potentially reversible.

Expression and activity patterns of nitric oxide synthases and antioxidant enzymes reveal a substantial heterogeneity between cardiac and vascular aging in the rat

We investigated the effects of aging and ischemia-reperfusion (I/R) injury on the expression and activity of nitric oxide (*NO) synthases and superoxide dismutase (SOD) isoforms. To this end we perfused excised hearts from young (6 months old) and old (31-34 months old) rats according to the Langendorff technique. The isolated hearts were, after baseline perfusion for 30 min, either subjected to 20 min of global no-flow ischemia followed by 40 min of reperfusion or were control-perfused (60 min normoxic perfusion). Both MnSOD and Cu,ZnSOD expression remained unchanged with increasing age and remained unaltered by I/R. However, SOD activity decreased from 7.55 +/- 0.1 U/mg protein in young hearts to 5.94 +/- 0.44 in old hearts (P<0.05). Furthermore, I/R led to a further decrease in enzyme activity (to 6.35 +/- 0.41 U/mg protein; P<0.05) in myocardium of young, but not in that of old animals. No changes in myocardial protein-bound 3-nitrotyrosine levels could be detected. Endothelial NOS (eNOS) expression and activity remained unchanged in aged left ventricles, irrespective of I/R injury. This was in steep contrast to peripheral (renal and femoral) arteries obtained from the same animals where a marked age-associated increase of eNOS protein expression could be demonstrated. Inducible NOS expression was undetectable either in the peripheral arteries or in the left ventricle, irrespective of age. In particular when associated with an acute pathology, which is furthermore limited to a certain time frame, changes in the aged myocardium with respect to enzymes crucially involved in maintaining the redox homeostasis, seem to be much less pronounced or even absent compared to the vascular aging process. This may point to heterogeneity in the molecular regulation of the cardiovascular aging process.

Myosin binding protein C is differentially phosphorylated upon myocardial stunning in canine and rat hearts — Evidence for novel phosphorylation sites

Myocardial stunning is the transient cardiac dysfunction that follows brief episodes of ischemia and reperfusion without associated myocardial necrosis. Currently, there is limited knowledge about its cellular and biochemical mechanisms. In order to better understand the underlying mechanisms of contractile dysfunction associated with the stunning, comprehensive proteomic studies using 2-D DIGE were performed using a regional stunning model in canine heart. Cardiac myosin binding protein C (cMyBP-C), a regulatory myofilament protein associated with the thick filament, and nebulette, a thin filament associated protein, were differentially expressed. Phosphoprotein specific staining indicated both protein changes were due to phosphorylation. Subsequent phosphorylation mapping of canine cMyBP-C using IMAC and MS/MS identified five phosphorylation sites, including three novel sites. In order to further evaluate this finding in a different model, cMyBP-C phosphorylation was examined in a rat model of global stunning. In the rat model, stunning was associated with increased phosphorylation of cMyBP-C at a critical calcium/calmodulin-dependent kinase II site, and the increased phosphorylation was largely inhibited when stunning was prevented by either ischemic preconditioning or reperfusion in the presence of low-calcium buffer. These data indicate cMyBP-C phosphorylation plays an important role in myocardial stunning.

Autophagy: a Novel Protective Mechanism in Chronic Ischemia

During the search for cardioprotective mechanisms in a porcine model of chronic myocardial ischemia and hibernating myocardium, we discovered evidence for autophagy, which could be involved in the protection against apoptosis. Autophagy is a cellular degradation process responsible for the turnover of unnecessary or dysfunctional organelles and cytoplasmic proteins, which become sequestered in a double-membrane-bound vesicle, termed autophagosome, and subsequently degrade upon fusion with lysosomes. The dauer phase in C. elegans shares similarities with the induction of autophagy in chronically ischemic (hibernating) myocardium. In this sense, autophagy is an essential mechanism for survival which is activated by environmental stresses and confers stress resistance to the organism. Our study provided insight into understanding of the protective mechanism of autophagy in chronic ischemia.

Pathomorphology of postinfarction myocardial ischemia during atherosclerotic obstruction of coronary arteries

Pathomorphological criteria of early postinfarction angina included segmentary atherosclerotic obstruction of the upper segments of the coronary artery supplying the infarction area, recurrent acute myocardial infarction, maximum decrease in vascularization of the left posterior ventricular wall; and individual changes in angioarchitectonics of the heart promoting hibernation of the myocardium. Pathognomonic morphological criteria of silent postinfarction myocardial ischemia included diffuse extensive atherosclerotic obstruction of lower segments in the coronary artery supplying the infarction area and total hypervascularization of the myocardium, first acute myocardial infarction of the left ventricular anterior wall, and maximum decrease in vascularization of the anterior and posterior wall in the left ventricle. These coronary-myocardial relationships contribute to stunning of the myocardium. Zones of hypokinesia and akinesia were revealed in the left ventricle, which reflects the phenomenon of resting myocardium associated with isolation of heart angioarchitectonics.

Assessment of myocardial viability by nuclear imaging techniques

The assessment of myocardial viability has become important in the diagnostic and prognostic work up of patients with ischemic cardiomyopathy. Patients with viable myocardium may benefit from revascularization in terms of improvement of function, symptoms, and prognosis. In contrast, patients without viable myocardium do not benefit and should be treated conservatively. Various nuclear imaging techniques are available.

[Myocardial viability, its importance for the therapeutic decision]

Myocardial viability detection is essential in patients with history of myocardial infarction whom develop ventricular dysfunction. Its detection influences the therapeutic decisions and the prognosis. Medical therapy in patients with ventricular dysfunction due to myocardial infarction and myocardial viability has been associated with higher morbidity and mortality rates than revascularization therapy, as well as improvements in the systolic function. Several imaging techniques used in the recognition of myocardial viability are available; these techniques are based on the assessment of the ventricular motion posterior to inotropic agents stimulation or on the demonstration of metabolic activity at the dysfunctional regions. In this study, some important aspects of each technique are reviewed, doing special emphasis in the utility of the Positron Emission Tomography (PET) which has been considered as the "gold standard" in the detection of myocardial viability.

Therapeutic angiogenesis in chronically ischemic porcine myocardium: comparative effects of bFGF and VEGF

BACKGROUND

Both vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) have been used in preclinical studies to induce new blood vessel growth in ischemic cardiac muscle with promising results. However, clinical trials have been much less convincing and further work is needed. This study expands on prior work by comparing the long-term proangiogenic effects of direct intramyocardial (IM) injection of bFGF, as well as IM and intravenous (IV) VEGF in a porcine model of chronic hibernating myocardium.

METHODS

Mini-swine with proximal 90% left circumflex (LCx) coronary stenosis subtending chronically ischemic, viable (hibernating) myocardium by positron emission tomography (PET) and dobutamine stress echocardiography (DSE) were randomized to IM bFGF (n = 5), IM VEGF(165) (n = 5), IV VEGF(165) (n = 5), IM vehicle (n = 5), or sham redo-thoracotomy (n = 4). The bFGF protein was administered in a total dose of 1.35 microg divided into 30 IM injections. IM VEGF(165) protein was administered in a total dose of 15 microg/kg divided into 30 injections; IV VEGF(165) was given at a dose of 50 ng. kg(-1). min(-1) for 200 minutes at three 72-hour intervals (30 microg/kg total dose). After 3 and 6 months the PET and DSE studies were repeated, and the animals were sacrificed for tissue vascular density and angiogenic protein analysis.

RESULTS

Myocardial blood flow (MBF) by PET was significantly improved 3 months posttreatment in the IM bFGF and IM VEGF(165) groups, differences that were sustained at 6 months. There was no significant increase in MBF 3-months posttreatment in the IV VEGF(165) group; however, at 6 months MBF was significantly improved. No change in MBF was seen in the IM vehicle or sham groups. Regional wall motion at rest and peak stress in the LCx region demonstrated small but statistically significant improvements by 6 months in the IM bFGF and IV VEGF(165) groups only; no improvement was seen in the IM VEGF(165), IM vehicle, or sham groups. Quantitative vascular density was significantly increased in the LCx regions of all treatment groups (IM bFGF, IM VEGF(165), IV VEGF(165)) 6-months postoperatively. No significant increase in LCx region myocardial bFGF or VEGF protein levels was seen in the treated animals at 6 months.

CONCLUSIONS

The IM bFGF, IM VEGF(165), and IV VEGF(165) all improve regional perfusion and vascular density 6-months posttherapy in the animal model utilized. Functional improvements were less consistent. Both bFGF and VEGF(165) may be useful therapies for improving regional perfusion in chronically ischemic myocardium, although combination therapy with additional growth factors or cellular therapies may be necessary if concomitant improvements in function are to be seen.

Intramyocardial and intracoronary basic fibroblast growth factor in porcine hibernating myocardium: a comparative study

OBJECTIVE

Therapeutic angiogenesis is an alternative method of revascularization for end-stage coronary artery disease. We determined the effects of intramyocardial and intracoronary basic fibroblast growth factor 2 on myocardial blood flow and function in a porcine model of hibernating myocardium.

METHODS

Twenty-four mini-swine with 90% left circumflex artery stenosis and documented hibernating myocardium by positron emission tomography and dobutamine stress echocardiography were randomized to intramyocardial basic fibroblast growth factor 2 at 0.6 microg/kg (mid-dose, n = 6, 30 injections/animal), 6 microg/kg (high-dose, n = 6, 30 injections/animal), or intramyocardial vehicle control (n = 6). The intracoronary group received 6 microg/kg basic fibroblast growth factor 2 (n = 6) into the right and left circumflex artery coronary arteries. Positron emission tomography and dobutamine stress echocardiography were repeated at 1 and 3 months.

RESULTS

In the vehicle group, normalized left circumflex artery myocardial blood flow was 0.74 +/- 0.04 at 1 month and 0.75 +/- 0.07 at 3 months compared with 0.68 +/- 0.03 at baseline. In the intracoronary group, myocardial blood flow was 0.71 +/- 0.03 at 1 month and 0.72 +/- 0.04 at 3 months compared with 0.67 +/- 0.04 at baseline. In the mid group, myocardial blood flow was 0.73 +/- 0.06 at 1 month and 0.85 +/- 0.05 at 3 months (P <.001) compared with 0.67 +/- 0.04 at baseline. In the high group, myocardial blood flow was 0.81 +/- 0.06 at 1 month and 0.83 +/-.04 at 3 months (P =.03) compared with 0.71 +/- 0.02 at baseline. No significant improvements in ischemia were demonstrated in any of the groups by dobutamine stress echocardiography at 1 or 3 months.

CONCLUSIONS

In porcine hibernating myocardium, intramyocardial basic fibroblast growth factor 2 significantly improved regional myocardial blood flow 3 months after treatment. There was no significant change in function in any of the 4 groups. These data suggest that intramyocardial dosing of basic fibroblast growth factor 2 (0.6 microg/kg) may be an optimal dose for improving perfusion in the treatment of end-stage coronary artery disease.

Rest perfusion defects in patients with no history of myocardial infarction predict the presence of a critical coronary artery stenosis

BACKGROUND

The rest/stress sequence in myocardial perfusion single photon emission computed tomography (SPECT) (MPS) permits evaluation of rest images before stress testing, allowing the identification of unexpected perfusion defects (PDs). We sought to study the angiographic correlates of these resting PDs.

METHODS AND RESULTS

This study comprised 139 consecutive patients with no history of myocardial infarction referred for MPS whose stress test was canceled because of the observation of unexpected resting PDs (rest group). Of these, 60 patients (43.2%) were referred for angiography after MPS (6.0 +/- 11.5 days). Angiographic referral rates and results were compared with those of a diagnostic population (n = 3565) who demonstrated stress-induced PDs (stress group) on rest/stress MPS. The mean age in the rest group was 73 +/- 12.5 years, and 73% were men. The frequency of referral for angiography was higher in the rest group (43.2% vs 19.8%, P <.0001). In addition, the rest group more frequently had significant coronary artery disease (CAD) (>/=70%) (95% vs 80%, P =.008) and critical CAD (>/=90%) (80% vs 66%, P =.038).

CONCLUSION

The rest/stress sequence for MPS enables the identification of patients with unexpected resting PD, usually resulting from critical CAD, in whom unnecessary stress testing can be avoided.

Relationship between the changes in myocardial perfusion and left ventricular ejection fraction after acute myocardial infarction. Study with myocardial contrast echocardiography

BACKGROUND AND OBJECTIVE

Myocardial contrast echocardiography has recently been proposed as a valid technique in the evaluation of myocardial perfusion after myocardial infarction. The objective of this study was to evaluate the relation between changes in myocardial perfusion assessed by myocardial contrast echocardiography and left ventricular ejection fraction after myocardial infarction.

PATIENTS AND METHODS

We prospectively studied 17 patients with acute myocardial infarction, on whom two echocardiographic studies were performed, at 48-72 hours and at 6 months. Left ventricular ejection fraction and myocardial perfusion were evaluated with myocardial contrast echocardiography (Multiple-Frame Triggering and Harmonic Angio). Basal, medial and distal segments of the interventricular septum (anterior location infarction) and inferior wall (inferior infarction) were assessed. Myocardial perfusion was classified semi-quantitatively as grade 0, 1 or 2 (absent, heterogeneous or homogeneous opacification, respectively), giving a perfusion score.

RESULTS

Left ventricular ejection fraction improved in 9 patients (53%), the proportion of grade 0 segments decreasing by 11 +/- 17%; by contrast, this proportion increased by 9 +/- 13% in patients with no improvement in ejection fraction (p = 0.028). Additionally, a significant correlation was observed between changes in ejection fraction and both perfusion score (r = 0.625; p = 0.007) and the proportion of grade 2 segments (r = 0.649; p = 0.005).

CONCLUSION

After myocardial infarction, there is a significant relation between changes in left ventricular ejection fraction and myocardial perfusion assessed by myocardial contrast echocardiography with i.v. agents.

[Evaluation of ultrastructural changes in the ischemic myocardium in surgically obtained biopsies of the left ventricle]

Electron microscopic evaluation of the degree of ischemic injury in diseased human hearts is a very useful tool in estimating the quality of any method of myocardial preservation. Ultrastructural alterations give accurate data in the clinical setting. Our semiquantitative scoring system was created considering existing evaluation systems and based on our own observations. Eight grades of ischemic injury were defined, ranging from 1 (normal ultrastructural appearance) to 8 (irreversible ischemic damage) with respect to integrity and swelling of mitochondria, nuclei, myofilaments, membranes, organelles and components, as well as extracellular structures.

Parathyroid hormone-related peptide improves contractile function of stunned myocardium in rats and pigs

The effect of synthetic parathyroid hormone (PTH)-related peptide [PTHrP(1-34)] on regional myocardial function was studied in 11 anesthetized pigs. Intracoronary infusion of PTHrP (cumulative dose: 14 +/- 1 microg) decreased coronary resistance to 33 +/- 2% of baseline (P < 0.05) and regional myocardial function to 90 +/- 3% of baseline (not significant). Ischemia-reperfusion alters the activity of several kinases and therefore possibly the myocardial effects of PTHrP. In stunned myocardium, induced by 20-min ischemia and 30-min reperfusion, the dose of PTHrP reducing coronary resistance to a minimum of 29 +/- 2% was decreased to 8 +/- 2 microg (P < 0.05). Regional myocardial function was no longer decreased but increased to 132 +/- 9% (P < 0.05). The increase in regional myocardial function during PTHrP was inversely related to baseline function at 30-min reperfusion in vivo (r = 0.9) as well as in myocytes isolated from stunned pig hearts (r = 0.7). In isolated rat hearts subjected to 30-min global ischemia followed by 30-min reperfusion, blockade of endogenous PTHrP by d-Trp(12)-Tyr(34)-PTH(7-34) attenuated the recovery of left ventricular developed pressure by 30 +/- 14% (P < 0.05). Thus endogenous and exogenous PTHrP impact on the function of stunned myocardium.

Role of adenosine in delayed preconditioning of myocardium

Myocardial protection conferred by ischemic preconditioning occurs in a bimodal time course. The early cardioprotection wanes rapidly and is succeeded by a delayed phase of protection reducing infarct development, myocardial stunning and arrhythmias. This 'second window' of preconditioning may be evident for up to 72 h. The current mechanistic paradigm for delayed preconditioning against infarction invokes roles for several freely-diffusible molecules, generated during the preconditioning period, that act in autocrine and/or paracrine fashion as triggers of cellular adaptation. These include adenosine, nitric oxide, reactive oxygen species and bradykinin. A role for adenosine receptor activation as a proximal molecular mechanism leading to delayed preconditioning against infarction was established in 1994. Pharmacological adenosine receptor blockade during preconditioning abolishes the acquisition of delayed protection, while transient adenosine A(1) or A(3) receptor activation fully recapitulates protection against infarction (but not against stunning or arrhythmias) 24 h later. Although nitric oxide is a co-trigger of delayed preconditioning, A(1) agonist-induced delayed protection is independent of nitric oxide production. Adenosine receptor activation causes the activation of a complex protein kinase signalling cascade and, putatively, the subsequent activation of gene transcription. The induction or post-translational regulation of several proteins is associated with A(1) agonist-induced delayed protection. These include the mitochondrial manganese-conjugated superoxide dismutase, and the 27-kDa heat shock protein. Opening of K(ATP) channels during the index ischaemic event is an obligatory downstream event mediating A(1) and A(3) agonist induced delayed protection. However, the mechanism of sub-acute regulation of K(ATP) channels following adenosine receptor activation is unknown. Evidence for induction of inducible nitric oxide synthase as a distal mechanism of A(1) agonist-induced delayed protection is equivocal.

Changes in excitation-contraction coupling in an isolated ventricular myocyte model of cardiac stunning

To investigate cardiac stunning, we recorded intracellular [Ca(2+)], contractions, and electrical activity in isolated guinea pig ventricular myocytes exposed to simulated ischemia and reperfusion. After equilibration, ischemia was simulated by exposing myocytes to hypoxia, acidosis, hyperkalemia, hypercapnia, lactate accumulation, and substrate deprivation for 30 min at 37 degrees C. Reperfusion was simulated by exposure to Tyrode solution. Field-stimulated myocytes exhibited stunning upon reperfusion. By 10 min of reperfusion, contraction amplitude decreased to 43.0 +/- 5.5% of preischemic values (n = 15, P < 0.05), although action potential configuration and sarcoplasmic reticulum Ca(2+) stores, assessed with caffeine, were normal. Diastolic [Ca(2+)] and Ca(2+) transients (fura 2) were also normal in stunned myocytes. In voltage-clamped cells, peak L-type Ca(2+) current was reduced to 47.4 +/- 4.5% of preischemic values at 10 min of reperfusion (n = 21, P < 0.05). Contractions elicited by Ca(2+)-induced Ca(2+) release and the voltage-sensitive release mechanism were both depressed in reperfusion. Our observations suggest that stunning is associated with reduced L-type Ca(2+) current but that alterations in Ca(2+) homeostasis and release are not directly responsible for stunning.

Ischemic shortening of action potential duration as a result of KATP channel opening attenuates myocardial stunning by reducing calcium influx

Action potential duration (APD) shortening due to opening of sarcolemmal ATP-dependent potassium (KATP) channels has been postulated to protect the myocardium against postischemic damage by reducing Ca2+ influx. This hypothesis was assessed, assuming that increased postischemic stunning due to KATP channel inhibition with glibenclamide could be reverted by the addition of the Ca2+ channel blocker diltiazem. Percent wall thickening fraction (%WTh, conscious sheep) and APD (open-chest sheep) were obtained from the following groups: control: 12 min ischemia by anterior descending coronary artery occlusion followed by 2 h reperfusion; glibenclamide: same as control, with glibenclamide (0.4 mg/kg) infused 30 min before ischemia; diltiazem: same as control, with diltiazem (100 microg/kg) administered prior to ischemia; glibenclamide+diltiazem: both drugs infused as in glibenclamide and diltiazem groups. APD was reduced in control ischemia. Conversely, KATP-channel blockade by glibenclamide lengthened APD and increased postischemic stunning (p < 0.01 vs. control); glibenclamide+diltiazem did not shorten APD but enhanced functional recovery (p < 0.01 vs. glibenclamide). Ca2+ channel blockade improvement of increased stunning provoked by KATP channel inhibition supports the hypothesis that APD shortening due to opening of KATP channels protects against postischemic stunning by limiting Ca2+ influx.

Physiological insulin concentrations protect against ischemia-induced loss of cardiac function in rats

This study determined whether insulin at pre- (fasting) and post-prandial concentrations increases coronary blood flow and improves cardiac function after acute ischemia during a situation of myocardial stunning. The experiments were performed using an isolated, erythrocyte perfused, working rat heart model. To the perfusate we added erythrocytes and 1.5% bovine serum albumin to improve clinical relevance. The following protocol was used: 8 min baseline performance assessment, 10 min pre-ischemic treatment, 12 min global ischemia, 20 min post-ischemic treatment and 8 min recovery assessment. Vehicle, 10 mIU l(-1) and 100 mIU l(-1) human insulin were tested (all n=6). No significant vasodilator response to insulin was observed either pre- or post-ischemically. After the 12-min ischemic insult, cardiac function returned dose-dependently to pre-ischemic values (function loss with 100 mIU l(-1) insulin: -0.2+/-0.4% vs. vehicle: 10.7+/-0.8%). This study clearly shows that in our clinically relevant model of moderate ischemia (stunning), insulin is highly cardioprotective at physiological concentrations. This may be explained primarily by higher glucose uptake, improving the myocardial energetic state during ischemia. Therefore, insulin should be considered for use when the myocardium is at acute risk for ischemic incidents.

Long-term results of coronary artery bypass grafting procedure in the presence of left ventricular dysfunction and hibernating myocardium

OBJECTIVE

Long-term left ventricular (LV) performance and patient outcome after coronary artery bypass grafting (CABG) procedure in the presence of depressed LV function and hibernating myocardium (HM) have been poorly determined. Therefore, we prospectively evaluated patients undergoing CABG with severe LV dysfunction and HM to elucidate postoperative prognosis.

METHODS

We enrolled 120 consecutive patients undergoing CABG with severe LV dysfunction and HM as assessed by dobutamine echocardiography and by rest-redistribution radionuclide (Thallium-201) study. Mean patient age was 60+/-9 years (range 31-77 years). Mean preoperative LVEF was 28%+/-9 (range 10-40%). All patients underwent echocardiographic study to assess LV recovery of function intraoperatively, prior to hospital discharge, at 3 months, at 1 year, and yearly during the follow-up. Univariate and multivariate analysis were performed to to evaluate predictors of postoperative survival.

RESULTS

There were 2 hospital (1.6%) and 15 late (12.5%) deaths, mainly for heart failure, leading to an actuarial survival of 80+/-6% and 60+/-9% at 5 and 8 years, respectively. LVEF significantly improved perioperatively (from 28+/-9% to 40+/-2%, P<0.01). Increase in LVEF, however, was gradually offset over the time (EF of 33+/-9%, 32+/-8%, and 30+/-9% at 3 months, and 12 months, and 8 years after surgery, respectively). Furthermore, patients who experienced limited LV functional recovery perioperatively had a more remarkable decline of LVEF thereafter, and suffered from recurrence of heart failure symptoms (freedom from heart failure 82+/-5% and 60+/-8% at 4 and 8 years respectively). Advanced preoperative NYHA Class, and age were independent risks factors for reduced postoperative survival. Preoperative angina and use of arterial conduits apparently did not influence patient morbidity and mortality at long term.

CONCLUSION

CABG procedure in the presence of HM enhances LV recovery of function and has a favourable prognosis. Functional benefit of the left ventricle, however, appears to be time-limited, despite remarkable improvement in patient functional capacity. Advanced preoperative heart failure, minimal perioperative improvement of LVEF, and age account for a poor long-term prognosis.

Myocyte apoptosis and reduced SR gene expression precede the transition from chronically stunned to hibernating myocardium

A systematic transition from chronic stunning to hibernation occurs as coronary flow reserve decreases to a critical level. Hibernating myocardium exhibits apoptosis-induced myocyte loss and a reduction in the expression of the sarcoplasmic reticulum (SR) Ca2+ ATPase but whether similar cellular changes occur in chronic stunning is unknown. Pigs with a chronic left anterior descending coronary artery (LAD) stenosis were studied one (n=9) or two (n=10) months after instrumentation. Anterior hypokinesis with normal levels of resting perfusion developed at each time-point, consistent with chronic stunning. After 1 month, sub-endocardial flow reserve was moderately reduced (adenosine/rest, LAD: 3.60+/-0.91 v Remote: 6.00+/-0.54, P<0.01) with no regional differences in SR protein expression, no increase in apoptosis (32+/-6 v 21+/-5 nuclei/10(6) myocyte nuclei, p-ns) and no regional myocyte loss (1976+/-44 v 1955+/-30 nuclei/mm2, p-ns). After 2 months, sub-endocardial flow reserve in chronically stunned myocardium was severely impaired (LAD: 1.41+/-0.21 v Remote: 5.59+/-0.96, P<0.01). There were small but significant reductions in LAD mRNA and protein levels for the SRCa2+ ATPase and phospholamban whereas calsequestrin was unchanged. In addition, regional myocyte apoptosis increased (127+/-24 v 55+/-9 nuclei/10(6) myocyte nuclei, P<0.01), resulting in the onset of myocyte loss (1293+/-50 v 1394+/-32 nuclei/mm2, P<0.01). Apoptosis-induced myocyte loss and reductions in SR protein expression are not invariably present in viable chronically dysfunctional myocardium. They are induced as the propensity of a region to develop reversible ischemia increases (as reflected by coronary flow reserve). The temporal progression indicates that alterations in SR protein expression and myocyte apoptosis precede the transition from chronically stunned to hibernating myocardium.

Effect of repeated regional myocardial ischemia in the rat heart on reperfusion arrhythmias and release of norepinephrine

We tested the hypothesis that repetitive regional myocardial ischemia in the rat could decrease reperfusion ventricular arrhythmias, possibly acting by diminished release of norepinephrine. Isolated perfused working rat hearts were pre-labeled with tritiated norepinephrine (NE3H). The efflux of 3H-labeled compounds was measured in the effluent coronary flow. Each heart was subjected to two consecutive periods of regional myocardial ischemia induced by ligature of the left coronary artery. The duration of the first ischemic period was 5 or 10 min and that of the second was 10 min. Serious rhythm disturbances did not occur during the first period of ischemia but did after reperfusion. The amount of NE3H liberated during the reperfusion period was more marked after an initial ischemic period of 10 min than after 5 min of ischemia. Reperfusion arrhythmias were of little importance after 5 min of ischemia but developed in a sustained pattern when reperfusion followed 10 min of ischemia. After 5 min of ischemia, the mean duration of reperfusion arrhythmias was 12.8 +/- 10.4 s during the first 3 min of reperfusion, but after 10 min of ischemia the mean duration of serious rhythm disturbances was 149.7 +/- 16.7 s. Reperfusion after the second 10-min occlusion increased the release of NE3H. In series 5-10, the percentage of NE3H compared with the total radioactivity was a mean of 71.4 +/- 3.3% during the 5 min of ligature, 79.0 +/- 5.3% during the first 3 min of reperfusion. During the 10-10 series in which the ligature was maintained for 10 min, the percentage of NE3H compared with the total radioactivity was 70.6 +/- 5.1%, 81.1 +/- 8.7% during the first 3 min of reperfusion. These results show no reduction of any catecholamine release or of reperfusion arrhythmias by repetitive regional ischemia and provide no evidence for any preconditioning effect after short periods of regional ischemia. The antiarrhythmic effects of repetitive myocardial ischemia such as preconditioning previously reported may depend on the exact protocols used.

Beta-adrenergic receptors and intracellular signalling pathway in stunned and non-ischemic regions of pig myocardium

The beta-adrenergic pathway may have a role in the pathophysiology of ischemic syndromes characterised by reversible left ventricular dysfunction, such as myocardial stunning and other clinical conditions of unstable angina or coronary spasms, or chronic reversible left ventricular dysfunction, which might be a consequence of repeated events of short-term ischemia ("repetitive stunning"). A partial-to-total occlusion of the left anterior descending coronary artery in pigs was used to induce short periods of ischemia (total ischemic time 12 +/- 2 min). Hypokinesis and dyskinesis of the myocardium were considered signs of myocardial dysfunction. We found a maintained function of the beta-adrenergic signalling system. Density and affinity of beta-adrenergic receptors were not different in stunned and non-ischemic regions, nor were cyclic AMP and cyclic GMP intracellular contents and ratio, nor well as the ratio of stimulatory/inhibitory G protein a subunits. Our findings are in agreement with a maintained beta-adrenergic signalling system in the pathophysiology of chronic reversible left ventricular dysfunction.

Actin is oxidized during myocardial ischemia

Exposure of isolated rat hearts to 30 min global ischemia followed by 60 min reperfusion resulted in a significant 80% increase (p <.05) in actin content of carbonyl groups, which was associated with significant depression (p <.05) of postischemic contractile function. This result supports the hypothesis that one mechanism of postischemic contractile dysfunction may be oxidation of contractile proteins.

[Preconditioning--endogenous defence mechanisms of the heart during ischemia]

BACKGROUND

The term "preconditioning" refers to the paradoxical phenomenon that pretreatment with a potential noxious stress-stimulus can increase cellular tolerance to subsequent noxious stress-stimuli. This was first described in an experimental model in dog hearts in which short-lasting periods of myocardial ischaemia resulted in reduced infarction during a subsequent long-lasting ischaemic period. Similar observations are made in other organs and species. Preconditioning is also used to describe pretreatment with other physical stress-stimuli or pharmacological agents that can increase resistance against cellular damage. This phenomenon probably represents a general adaptive response to cellular stress.

MATERIAL AND METHODS

This review focuses on preconditioning in the heart and the possible endogenous mechanisms involved. The potential clinical role of preconditioning is also discussed.

RESULTS

It is shown that preconditioning can reduce myocardial infarction in patients. However, protection against reduced contractility without infarction ("stunning") and arrhythmia is more uncertain. Several mechanisms might be involved; these are not fully clarified.

INTERPRETATION

Preconditioning is of great interest because its effect is vigorous and reproducible, with a potential for use in patients with coronary heart disease. Preconditioning also illustrates how activation of endogenous defence mechanisms can increase cellular tolerance to ischaemia or other stress stimuli.