The protective effects of preconditioning decline in aged patients undergoing coronary artery bypass grafting

Effects of ischaemic postconditioning in aortic valve replacement: a multicenter randomized controlled trial

OBJECTIVES

The effect of ischaemic postconditioning (IPost) on postcardioplegic cardiac function is not known. We hypothesized that IPost was cardioprotective in adult patients undergoing elective aortic valve replacement.

METHODS

In a multicentre, prospective, randomized trial, patients (n = 209) were randomized to either a standard operation (controls) or postconditioning. Immediately before the cross-clamp was released, patients in the postconditioning group underwent 3 cycles of flow/non-flow (2 min each) of normothermic blood via the antegrade cardioplegia line. The primary end point was cardiac index. Secondary end points included additional haemodynamic measurements, biomarkers of cardiomyocyte injury, renal function parameters, intra- and postoperative arrhythmias and use of inotropic agents.

RESULTS

There was no significant difference between the groups regarding cardiac index [mean between-group difference, 95% confidence interval (CI), 0.11 (-0.1 to 0.3), P = 0.27]. Postconditioning had no effect on other haemodynamic parametres. There was no between-group difference regarding troponin T or creatine kinase MB. Postconditioning reduced the relative risk for arrhythmias by 45% (P = 0.03) when postoperative atrial fibrillation and intraoperative ventricular fibrillation were combined. There were no differences in patients with/without diabetes, patients above/below 70 years of age or between the centres. However, after postconditioning, the cardiac index [95% CI, 0.46 (0.2-0.7), P = 0.001], cardiac output (P < 0.001), mean arterial pressure (P < 0.001) and left ventricular stroke work index (P < 0.001) were higher in males compared to females.

CONCLUSIONS

IPost had no overall cardioprotective effects in patients undergoing aortic valve replacement but improved postoperative cardiac performance in men compared to women.

[Perioperative cardioprotection - From bench to bedside : Current experimental evidence and possible reasons for the limited translation into the clinical setting]

Hintergrund

Ziel der perioperativen Kardioprotektion ist es, die Auswirkungen eines Ischämie- und Reperfusionsschadens zu minimieren. Aus anästhesiologischer Sicht spielt dieser Aspekt insbesondere in der Herzchirurgie bei Patienten mit Einsatz der Herz-Lungen-Maschine, aber auch allgemein bei längerfristigen hypotensiven Phasen oder perioperativen ischämischen Ereignissen im nichtkardiochirurgischen Setting eine wichtige Rolle. Im Laufe der letzten Jahre konnten diverse pharmakologische sowie nichtpharmakologische Strategien der Kardioprotektion identifiziert werden. Die Ergebnisse von Studien an isoliertem Gewebe sowie von tierexperimentellen In-vivo-Studien sind vielversprechend. Eine Translation dieser kardioprotektiven Strategien in die klinische Praxis ist bislang jedoch nicht gelungen. Große klinische Studien konnten keine signifikante Verbesserung des Outcome der Patienten zeigen.

Ziel der Arbeit

Dieser Übersichtsartikel gibt einen Überblick über die aktuelle experimentelle Evidenz pharmakologischer und nichtpharmakologischer Kardioprotektion. Außerdem sollen mögliche Gründe für die limitierte Translation diskutiert werden. Schließlich werden Möglichkeiten aufgezeigt, wie der Schritt „from bench to bedside“ in Zukunft doch noch gelingen könnte.

Material und Methoden

Narrative Übersichtsarbeit.

Ergebnisse und Diskussion

Trotz der vielversprechenden präklinischen experimentellen Ansätze zum Thema Kardioprotektion besteht nach wie vor eine große Diskrepanz zu den Ergebnissen aus großen klinischen Studien in der perioperativen Phase. Mögliche Gründe für die limitierte Translation könnten insbesondere Komorbiditäten und Komedikationen, die Wahl des Anästhesieverfahrens, aber auch die Wahl des Studiendesigns sein. Eine sorgfältige Studienplanung mit Berücksichtigung der genannten Probleme sowie ein simultaner Einsatz mehrerer kardioprotektiver Strategien mit dem Ziel eines additiven bzw. synergistischen Effekts stellen mögliche Ansätze für die Zukunft dar.

New advances in perioperative cardioprotection

With the increasing age of the general population, medical conditions necessitating a surgical intervention will increase. Concomitant with advanced age, the prevalence of type 2 diabetes mellitus will also increase. These patients have a two- to three-fold higher risk of occurrence of cardiovascular events and are at higher risk of perioperative myocardial ischemia. This review will discuss recent advances in the field of perioperative cardioprotection and focus specifically on strategies that have aimed to protect the diabetic and the aged myocardium. This review will not deal with potential putative cardioprotective effects of opioids and anesthetic agents, as this is a very broad area that would necessitate a dedicated overview.

Effects of Cardiovascular Risk Factors on Cardiac STAT3

Nuclear, mitochondrial and cytoplasmic signal transducer and activator of transcription 3 (STAT3) regulates many cellular processes, e.g., the transcription or opening of mitochondrial permeability transition pore, and its activity depends on the phosphorylation of Tyr705 and/or Ser727 sites. In the heterogeneous network of cardiac cells, STAT3 promotes cardiac muscle differentiation, vascular element formation and extracellular matrix homeostasis. Overwhelming evidence suggests that STAT3 is beneficial for the heart, plays a role in the prevention of age-related and postpartum heart failure, protects the heart against cardiotoxic doxorubicin or ischaemia/reperfusion injury, and is involved in many cardioprotective strategies (e.g., ischaemic preconditioning, perconditioning, postconditioning, remote or pharmacological conditioning). Ischaemic heart disease is still the leading cause of death worldwide, and many cardiovascular risk factors contribute to the development of the disease. This review focuses on the effects of various cardiovascular risk factors (diabetes, aging, obesity, smoking, alcohol, depression, gender, comedications) on cardiac STAT3 under non-ischaemic baseline conditions, and in settings of ischaemia/reperfusion injury with or without cardioprotective strategies.

Conditioning-induced cardioprotection: Aging as a confounding factor

The aging process induces a plethora of changes in the body including alterations in hormonal regulation and metabolism in various organs including the heart. Aging is associated with marked increase in the vulnerability of the heart to ischemia-reperfusion injury. Furthermore, it significantly hampers the development of adaptive response to various forms of conditioning stimuli (pre/post/remote conditioning). Aging significantly impairs the activation of signaling pathways that mediate preconditioning-induced cardioprotection. It possibly impairs the uptake and release of adenosine, decreases the number of adenosine transporter sites and down-regulates the transcription of adenosine receptors in the myocardium to attenuate adenosine-mediated cardioprotection. Furthermore, aging decreases the expression of peroxisome proliferator-activated receptor gamma co-activator 1-alpha (PGC-1α) and subsequent transcription of catalase enzyme which subsequently increases the oxidative stress and decreases the responsiveness to preconditioning stimuli in the senescent diabetic hearts. In addition, in the aged rat hearts, the conditioning stimulus fails to phosphorylate Akt kinase that is required for mediating cardioprotective signaling in the heart. Moreover, aging increases the concentration of Na⁺ and K⁺, connexin expression and caveolin abundance in the myocardium and increases the susceptibility to ischemia-reperfusion injury. In addition, aging also reduces the responsiveness to conditioning stimuli possibly due to reduced kinase signaling and reduced STAT-3 phosphorylation. However, aging is associated with an increase in MKP-1 phosphorylation, which dephosphorylates (deactivates) mitogen activated protein kinase that is involved in cardioprotective signaling. The present review describes aging as one of the major confounding factors in attenuating remote ischemic preconditioning-induced cardioprotection along with the possible mechanisms.

Nuclear Factor (Erythroid-Derived 2)-Like 2 and Thioredoxin-1 in Atherosclerosis and Ischemia/Reperfusion Injury in the Heart

SIGNIFICANCE

Redox signaling is one of the key elements involved in cardiovascular diseases. Two important molecules are the transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2) and the oxidoreductase thioredoxin-1 (Trx-1). Recent Advances: During the previous years, a lot of studies investigated Nrf2 and Trx-1 as protective proteins in cardiovascular disorders. Moreover, post-translational modifications of those molecules were identified that play an important role in the cardiovascular system. This review will summarize changes in the vasculature in atherosclerosis and ischemia reperfusion injury of the heart and the newest findings achieved with Nrf2 and Trx-1 therein. Interestingly, Nrf2 and Trx-1 can act together as well as independently of each other in protection against atherosclerosis and ischemia and reperfusion injury.

CRITICAL ISSUES

In principle, pharmacological activation of a transcription factor-like Nrf2 can be dangerous, since a transcription regulator has multiple targets and the pleiotropic effects of such activation should not be ignored. Moreover, overactivation of Nrf2 as well as long-term treatment with Trx-1 could be deleterious for the cardiovascular system.

FUTURE DIRECTIONS

Therefore, the length of treatment with Nrf2 activators and/or Trx-1 has first to be studied in more detail in cardiovascular disorders. Moreover, a combination of Nrf2 activators and Trx-1 should be investigated and taken into consideration. Antioxid. Redox Signal. 26, 630-644.

Time to Give Up on Cardioprotection?

The mortality from acute myocardial infarction (AMI) remains significant, and the prevalence of post-myocardial infarction heart failure is increasing. Therefore, cardioprotection beyond timely reperfusion is needed. Conditioning procedures are the most powerful cardioprotective interventions in animal experiments. However, ischemic preconditioning cannot be used to reduce infarct size in patients with AMI because its occurrence is not predictable; several studies in patients undergoing surgical coronary revascularization report reduced release of creatine kinase and troponin. Ischemic postconditioning reduces infarct size in most, but not all, studies in patients undergoing interventional reperfusion of AMI, but may require direct stenting and exclusion of patients with >6 hours of symptom onset to protect. Remote ischemic conditioning reduces infarct size in patients undergoing interventional reperfusion of AMI, elective percutaneous or surgical coronary revascularization, and other cardiovascular surgery in many, but not in all, studies. Adequate dose-finding phase II studies do not exist. There are only 2 phase III trials, both on remote ischemic conditioning in patients undergoing cardiovascular surgery, both with neutral results in terms of infarct size and clinical outcome, but also both with major problems in trial design. We discuss the difficulties in translation of cardioprotection from animal experiments and proof-of-concept trials to clinical practice. Given that most studies on ischemic postconditioning and all studies on remote ischemic preconditioning in patients with AMI reported reduced infarct size, it would be premature to give up on cardioprotection.

Ischaemic conditioning: pitfalls on the path to clinical translation

The development of novel adjuvant strategies capable of attenuating myocardial ischaemia-reperfusion injury and reducing infarct size remains a major, unmet clinical need. A wealth of preclinical evidence has established that ischaemic 'conditioning' is profoundly cardioprotective, and has positioned the phenomenon (in particular, the paradigms of postconditioning and remote conditioning) as the most promising and potent candidate for clinical translation identified to date. However, despite this preclinical consensus, current phase II trials have been plagued by heterogeneity, and the outcomes of recent meta-analyses have largely failed to confirm significant benefit. As a result, the path to clinical application has been perceived as 'disappointing' and 'frustrating'. The goal of the current review is to discuss the pitfalls that may be stalling the successful clinical translation of ischaemic conditioning, with an emphasis on concerns regarding: (i) appropriate clinical study design and (ii) the choice of the 'right' preclinical models to facilitate clinical translation.

Deletion of the aquaporin-4 gene alters expression and phosphorylation of protective kinases in the mouse heart

AIM

Aquaporins are channel-forming proteins highly permeable to water and some small molecular solutes. We have previously shown that aquaporin-4 knockout mice have increased tolerance to ischemia. However, the mechanism of cardioprotection was unclear. The aim of the current study was to investigate the effects of aquaporin-4 deletion on baseline expression and phosphorylation of some cardioprotective protein kinases.

METHODS

Proteins were extracted from hearts of aquaporin-4 knockout mice and littermate wild-type controls and analyzed with Western blot. Samples were taken from young (≤ 6 months of age), and old (≥ 1 year) mice.

RESULTS

Western blots showed three different isoforms of aquaporin-4 in wild types, likely representing M1, M23, and Mz. Total AMP-dependent kinase expression was decreased in aquaporin-4 knockout hearts by 18 ± 13% (p = 0.02), while the expression of Akt kinase, extracellular signal regulated kinase 1/2, protein kinase C-epsilon, mitogen-associated kinase P38 and C-Jun N-terminal kinase was unchanged. The phosphorylation of Akt kinase was reduced in hearts from knockout mice by 41 ± 16% (p = 0.01). No other alterations in phosphorylation were found. These effects were only detected in young mice.

CONCLUSION

Deletion of the aquaporin-4 gene decreased AMP-dependent kinase expression and Akt kinase phosphorylation in the heart. These changes may influence energy metabolism and endogenous cardioprotection.

Incremental value of the preoperative echocardiogram to predict mortality and major morbidity in coronary artery bypass surgery

BACKGROUND

Although echocardiography is commonly performed before coronary artery bypass surgery, there has yet to be a study examining the incremental prognostic value of a complete echocardiogram.

METHODS AND RESULTS

Patients undergoing isolated coronary artery bypass surgery at 2 hospitals were divided into derivation and validation cohorts. A panel of quantitative echocardiographic parameters was measured. Clinical variables were extracted from the Society of Thoracic Surgeons database. The primary outcome was in-hospital mortality or major morbidity, and the secondary outcome was long-term all-cause mortality. The derivation cohort consisted of 667 patients with a mean age of 67.2±11.1 years and 22.8% females. The following echocardiographic parameters were found to be optimal predictors of mortality or major morbidity: severe diastolic dysfunction, as evidenced by restrictive filling (odds ratio, 2.96; 95% confidence interval, 1.59-5.49), right ventricular dysfunction, as evidenced by fractional area change <35% (odds ratio, 3.03; 95% confidence interval, 1.28-7.20), or myocardial performance index >0.40 (odds ratio, 1.89; 95% confidence interval, 1.13-3.15). These results were confirmed in the validation cohort of 187 patients. When added to the Society of Thoracic Surgeons risk score, the echocardiographic parameters resulted in a net improvement in model discrimination and reclassification with a change in c-statistic from 0.68 to 0.73 and an integrated discrimination improvement of 5.9% (95% confidence interval, 2.8%-8.9%). In the Cox proportional hazards model, right ventricular dysfunction and pulmonary hypertension were independently predictive of mortality over 3.2 years of follow-up.

CONCLUSIONS

Preoperative echocardiography, in particular right ventricular dysfunction and restrictive left ventricular filling, provides incremental prognostic value in identifying patients at higher risk of mortality or major morbidity after coronary artery bypass surgery.

Efficacy of cardioprotective 'conditioning' strategies in aging and diabetic cohorts: the co-morbidity conundrum

Evidence obtained in multiple experimental models has revealed that cardiac 'conditioning' strategies--including ischaemic preconditioning, postconditioning, remote conditioning and administration of pharmacological conditioning mimetics--are profoundly protective and significantly attenuate myocardial ischaemia-reperfusion injury. As a result, there is considerable interest in translating these cardioprotective paradigms from the laboratory to patients. However, the majority of studies investigating conditioning-induced cardioprotection have utilized healthy adult animals devoid of the risk factors and co-morbidities associated with cardiovascular disease and acute myocardial infarction. The aim of this article is to summarize the growing consensus that two well established risk factors, aging and diabetes mellitus, may render the heart refractory to the favourable effects of myocardial conditioning, and discuss the clinical implications of a loss in efficacy of cardiac conditioning paradigms in these patient populations.

Ischemic preconditioning in the aging heart: from bench to bedside

Coronary artery disease is the leading cause of death in industrialized countries for people older than 65 years of age. The reasons are still unclear. A reduction of endogenous mechanisms against ischemic insults has been proposed to explain this phenomenon. Cardiac ischemic preconditioning represents the most powerful endogenous protective mechanism against ischemia. Brief episodes of ischemia are able to protect the heart against a following more prolonged ischemic period. This protective mechanism seems to be reduced with aging both in experimental and clinical studies. Alterations of mediators release and/or intracellular pathways may be responsible for age-related ischemic preconditioning reduction. Opposite studies are questionable for the experimental model used, the timing of ischemic preconditioning, and the selection of elderly patients. Several pharmacological stimuli failed to mimic ischemic preconditioning in the aging heart but exercise training and caloric restriction separately, and more powerfully taken together, are able to completely preserve and/or restore the age-related reduction of ischemic preconditioning.

Cardioprotection and ageing

With an increase in the elderly population and an increase in the prevalence of age-related cardiovascular disease, anesthesiologists are increasingly being faced with elderly patients with known or suspected ischemic heart disease in the perioperative period. Although early reperfusion remains the best strategy to reduce ischemic injury, reperfusion may damage the myocardium. Adjuvant therapy to revascularization is therefore necessary. To develop better strategies to prevent ischemia-reperfusion injury in older patients, we need to understand the aged myocardium, which has undergone structural and functional changes relative to the normal myocardium, resulting in reduced functional capacity and vulnerability to ischemia-reperfusion injury. In addition, innate or acquired cardioprotection deteriorates with aging. These changes in the aged myocardium might explain why there is poor translation of basic research findings from young animals to older patients. In this review, I discuss changes in intracellular signaling associated with myocardial ageing that have an effect on ischemia-reperfusion injury, and I discuss the efficacy of cardioprotection afforded by ischemic and pharmacologic pre-and post-conditioning in the aged myocardium. Finally, I outline strategies to restore protection in the aged myocardium.

Clinical application of ischemic preconditioning in the elderly

A mild stress such as brief ischemic episodes may protect the heart from a successive and more prolonged myocardial ischemia (ischemic preconditioning). This phenomenon is considered a typical "hormetic mechanism" by which the heart is immunized from pathological insults such as myocardial ischemia. This mechanism is reduced with aging and it may be restored and/or preserved by drugs such as adenosine or nicorandil, a mitochondrial K(ATP) channels, and lifestyle interventions such as physical activity and/or hypocaloric diet. Moreover, since the mechanisms involved in cardiac ischemic preconditioning have been established basic and clinical investigators are encouraged to test several drug in well-controlled animal and human studies in order to prevent and/or restore the age-related reduction of ischemic preconditioning.

[Cardiac biomarkers for diagnosis of myocardial infarction]

Diagnosis of postoperative myocardial infarction is often difficult, based on tools with a low sensitivity (clinical symptoms, EKG), or with a low specifity (old biomarkers, echocardiographic abnormalities) or inadequate for clinical practice (scintigraphy). Since 1995, clinicians may use more cardiospecific markers (troponin) allowing to modify strategy for postoperative myocardial infarction diagnosis. The aim of this review is to resume such an attitude.

Loss of cardioprotection with ageing

Not only the prevalence, but also the mortality due to ischaemic cardiovascular disease is higher in older than in young humans, and the demographic shift towards an ageing population will further increase the prevalence of age-related cardiovascular disease. In order to develop strategies aimed to limit reversible and irreversible myocardial damage in older patients, there is a need to better understand age-induced alterations in protein expression and cell signalling. Cardioprotective phenomena such as ischaemic and pharmacological pre and postconditioning attenuate ischaemia/reperfusion injury in young hearts. Whether or not pre and postconditioning are still effective in aged organs, animals, or patients, i.e. under conditions where such cardioprotection is most relevant, is still a matter of debate; most studies suggest a loss of protection in aged hearts. The present review discusses changes in protein expression and cell signalling important to ischaemia/reperfusion injury with myocardial ageing. The efficacy of cardioprotective manoeuvres, e.g. ischaemic pre and postconditioning in aged organs and animals will be discussed, and the development of strategies aimed to antagonize the age-induced loss of protection will be addressed.

Evaluation by Cardiac Troponin I: The Effect of Ischemic Preconditioning as an Adjunct to Intermittent Blood Cardioplegia on Coronary Artery Bypass Grafting

OBJECTIVE

Ischemic preconditioning (IPC) is commonly regarded as having a powerful internal protective effect on the organs. The mechanism of IPC is not clear yet, and the controversy over the benefits and protocol of IPC still continues. In this study, we used the sensitive and specific biochemical marker: cardiac troponin-I (CTnI) to evaluate whether IPC as an adjunct to intermittent cold blood cardioplegia (CBC) could reduce myocardial injury, as opposed to simple CBC during coronary artery bypass grafting (CABG).

METHODS

From May 2003 to December 2003, 40 patients with three vessel coronary artery disease (CAD) and stable angina, receiving first-time elective CABG, were randomly divided into two equal groups: IPC plus CBC (IPC + CBC group, n = 20); and CBC (CBC group, n = 20). The patients in IPC + CBC group received two cycles of ischemia (two min) and reperfusion (three min) before myocardial arrest induced by CBC. The patients in CBC group received 10-minute normothermic cardiopulmonary bypass (CPB) before CBC arrest. Clinical outcomes were observed during and after the operation. Serial venous blood samples were obtained before induction, after CPB, and postoperatively 6, 12, 24, and 72 hours. Hemodynamic indexes were obtained before and after the bypass by the radial catheter and Swan-Ganz catheter.

RESULTS

In both groups, there were no differences regarding operative parameters. Compared to the baseline, the level of CTnI increased after CPB, peaked 6-12 hours (p < 0.01). Compared to IPC + CBC group, plasma concentrations of CTnI in CBC group were significantly higher at 6 and 12 hours (p < 0.05). CI recovery in IPC + CBC group was more significant than CBC group at 12 and 24 hours (p < 0.05). IPC + CBC also shortened the time of postoperative mechanical ventilation (p < 0.05) after surgery.

CONCLUSION

Compared to the simple CBC in lower-risk CABG patients, IPC as an adjunct to CBC reduced CTnI release, improved heart function after surgery, and shortened the time of recovery in CAD patients.

Myocardial preconditioning and cardioprotection by volatile anaesthetics

The biological bases and the clinical applications of ischaemic and anaesthetic preconditioning are reviewed. Ischaemic preconditioning is an endogenous defensive phenomenon of the myocardium in which brief periods of ischaemia followed by reperfusion reduce the infarct size induced by longer ischaemic stimuli; both an early and a late phase may be distinguished. In the early phase, the mediators released activate ATP-dependent potassium channels and kinase cascade; these enzymes migrating at the level of various subcellular structures phosphorylate some end-effectors responsible for cardioprotection. Several molecules that are involved in the regulation of cell death during ischaemia-reperfusion injury have been proposed for such a role, including mitochondrial ATP-dependent potassium channels, connexins and cytoskeletal and mitochondrial proteins. In the late phase, the triggers and mediators themselves, plus nitric oxide, are responsible for the genetic reprogramming providing a protective effect via ex-novo synthesis of proteins. Volatile halogenated anaesthetics may induce a particular sort of pharmacological preconditioning, anaesthetic preconditioning, which presents some differences in the biochemical signalling mechanism but is able to give protection comparable to the ischaemic form. Anaesthetic preconditioning presents obvious advantages compared to ischaemic preconditioning, and researchers have tried to take advantage of this in the clinical setting, in cardiac surgical patients, in neuroprotection and to prolong the survival of organs destined for transplantation.

Ischemic Preconditioning by Unstable Angina Reduces the Release of CK-MB Following CABG and Stimulates Left Ventricular HSP-72 Protein Expression

BACKGROUND AND AIM

Whether the CK-MB reducing effect of ischemic preconditioning (IP) by unstable angina within 24 to 48 hours before CABG is achieved by early or by delayed preconditioning of left ventricular myocardium in humans is unknown. We investigated whether IP is associated with phosphorylation of p38 MAPK (characteristic for early preconditioning) or with increased protein expression of HSP-72 (characteristic for delayed preconditioning) at the time of CABG in patients.

METHODS

Nineteen patients were grouped according to the occurrence of ischemic episodes within 48 hours before CABG. The patients without angina were assigned to the control group (CON, n = 10) whereas patients who had experienced angina within 48 hours before CABG were assigned to the preconditioned group (IP, n = 9). The effect of IP on the CABG induced maximal release of creatine kinase (CK) and CK-MB was examined. Left ventricular biopsy specimens taken immediately before cross clamping from ischemic (ISCH) and from reference (REF) areas were processed to analyze p38 MAPK phosphorylation and HSP-72-protein expression.

RESULTS

While IP significantly reduced CK-MB (18.7 +/- 1.3 vs. 13.8 +/- 1.5 U/L, mean +/- SEM, p < 0.05), it only tended to reduce CK (292.7 +/- 32.8 vs. 274.1+/-31.1 U/L, p = NS, mean +/- SEM). CK-MB release for any given cross-clamp time was significantly reduced by IP (regression lines: CON, y= 0.4x+ 2, r= 0.8; IP, y= 0.1x+ 10, r= 0.2; p < 0.01, ANCOVA). There was no effect of IP on left ventricular p38 MAPK phosphorylation. IP increased left ventricular HSP-72-protein expression in ischemic areas when compared to reference areas (1.78 +/- 0.35 vs. 2.58 +/- 0.65, REF vs. ISCH, PhosphorImager units x10(6), mean +/- SEM, p < 0.05, ANCOVA).

CONCLUSIONS

Thus, in the human left ventricular myocardium there is a second window of protection lasting for at least 48 hours, while at that time the early phase of preconditioning has already gone.

Préconditionnement myocardique induit par les agents anesthésiques halogénés : bases fondamentales et implications cliniques

OBJECTIVE

Volatile halogenated anaesthetics offer a myocardial protection when they are administrated before a myocardial ischaemia. Cellular mechanisms involved in anaesthetic preconditioning are now better understood. The objectives of this review are to understand the anaesthetic-induced preconditioning underlying mechanisms and to know the clinical implications.

DATA SOURCES

References were obtained from PubMed data bank (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi) using the following keywords: volatile anaesthetic, isoflurane, halothane, sevoflurane, desflurane, preconditioning, protection, myocardium.

DATA SYNTHESIS

Ischaemic preconditioning (PC) is a myocardial endogenous protection against ischaemia. It has been described as one or several short ischaemia before a sustained ischemia. These short ischaemia trigger a protective signal against this longer ischaemia. An ischemic organ is able to precondition a remote organ. It is possible to replace the short ischaemia by a preadministration of halogenated volatile anaesthetic with the same protective effect, this is called anaesthetic PC (APC). APC and ischaemic PC share similar underlying biochemical mechanisms including protein kinase C, tyrosine kinase activation and mitochondrial and sarcolemnal K(ATP) channels opening. All halogenated anaesthetics can produce an anaesthetic PC effect. Myocardial protection during reperfusion, after the long ischaemia, has been shown by successive short ischaemia or volatile anaesthetic administration, this is called postconditioning. Ischaemic PC has been described in humans in 1993. Clinical studies in human cardiac surgery have shown the possibility of anaesthetic PC with volatile anaesthetics. These studies have shown a decrease of postoperative troponin in patient receiving halogenated anaesthetics.

Pre? and postconditioning during cardiac surgery

In spite of improved myocardial protection, postoperative arrhythmias and cardiac failure are still important problems causing morbidity and mortality in cardiac surgery. Ischemic preconditioning has been widely investigated experimentally with the purpose of identifying new therapeutic agents, but we have not unraveled the underlying mechanisms and we are not able yet to exploit them pharmacologically in clinical practice. Studies of preconditioning in cardiac surgery provide conflicting results, but the majority of studies show that ischemic preconditioning is an effective adjunct to myocardial protection in cardiac surgery. Interventions aimed at modifying reperfusion, or postconditioning, have the advantage that they also can be used after the ischemic insult has occurred, i.e. also in situations with "non-scheduled" ischemia. Postconditioning, as preconditioning, needs pharmacological mimics to be used routinely in settings of cardiac surgery or other human interventions. Possible common signaling pathways of the two phenomena are discussed, and suggested directions for clinical studies are outlined.

Preconditioning in intact and previously diseased myocardium: laboratory or clinical dilemma?

We studied the effects of various cycles of preconditioning (PC) (one cycle, 1 x PC; two cycles, 2 x PC; three cycles, 3 x PC; and four cycles, 4 x PC) on cardiac function, infarct size, and the incidence of reperfusion-induced arrhythmias in isolated hearts obtained from rabbits with hypercholesterolemia. After 8 weeks of hypercholesterolemia, hearts were subjected to 30 min of ischemia followed by 120 min of reperfusion. Various cycles of PC resulted in a "cycle-dependent" reduction in infarct size in the age-matched nonhypercholesterolemic group. In the 8-week hypercholesterolemic group, increasing cycles of PC resulted in a significant increase in infarct size from their nonpreconditioned ischemic/reperfused control value of 44 +/- 5% to 45 +/- 6%, 49 +/- 5%, 59 +/- 6% (p < 0.05), and 58 +/- 5% (p < 0.05), respectively. PC increased the vulnerability of the myocardium to reperfusion-induced arrhythmias in hypercholesterolemics indicating that PC may be an "intact heart" phenomenon. The effects of PC appear currently to be a dilemma in laboratories and clinics. The solution to the problem of PC in intact and diseased myocardium requires further data from two different sources: (a) previously "diseased" animals, and (b) diseased human myocardium from clinics. Once these data are available, then the effects under which PC will be beneficial rather than harmful could be established and the dilemma solved.

Fibrillation in patients subjected to coronary artery bypass grafting

OBJECTIVE

Atrial fibrillation is the most frequently encountered postoperative arrhythmic complication after coronary artery bypass grafting. Ischemic preconditioning has proved a potent endogenous factor in suppressing ischemia-reperfusion-induced arrhythmias. The protective effect of ischemic preconditioning on atrial fibrillation after coronary artery bypass grafting has not been studied. The purpose of the present study was to investigate whether ischemic preconditioning had an effect on postoperative atrial fibrillation in patients undergoing coronary artery bypass grafting.

METHODS

Eighty-five patients undergoing coronary artery bypass grafting were randomized into ischemic preconditioning and control groups. Holter data from 24-hour electrocardiography were collected 1 day before the operation to the second postoperative day. Atrial fibrillation was registered as positive if any atrial fibrillation event occurred.

RESULTS

The overall incidence of postoperative atrial fibrillation and sustained atrial fibrillation was 34.1% and 27.1%, respectively. The occurrence of atrial fibrillation was significantly lower in the ischemic preconditioning group (21.4% in patients undergoing ischemic preconditioning and 46.5% in control subjects, P =.015). Preoperative recent unstable angina did not influence the incidence of atrial fibrillation. Patients with atrial fibrillation had longer intensive care unit stays and compromised postoperative hemodynamic outcomes. Binary logistic regression analysis showed that ischemic preconditioning, preoperative mean heart rate, and postoperative pulmonary capillary wedge pressure were the independent predictors of atrial fibrillation.

CONCLUSIONS

Postcoronary artery bypass grafting atrial fibrillation is associated with more complicated postoperative outcome. Higher preoperative heart rate and postoperative pulmonary capillary wedge pressure were the independent predictors of atrial fibrillation. Recent unstable angina is not related to the occurrence of postcoronary artery bypass grafting atrial fibrillation. Ischemic preconditioning significantly suppresses postcoronary artery bypass grafting atrial fibrillation, suggesting that ischemic preconditioning can be used as an effective prophylactic method for postoperative atrial fibrillation.

Arrhythmias in off-pump coronary artery bypass grafting and the antiarrhythmic effect of regional ischemic preconditioning

OBJECTIVE

The authors sought to establish whether regional ischemic preconditioning (IP) reduces ischemic reperfusion arrhythmias in patients who undergo off-pump coronary artery bypass grafting (OPCAB).

DESIGN

A controlled, randomized, prospective study.

SETTING

A university hospital.

PARTICIPANTS

Thirty-two patients with left anterior descending coronary artery (LAD) or 2-vessel heart disease (including LAD) who were to undergo OPCAB were randomized into an IP and a control group.

INTERVENTIONS

IP was induced by occluding the LAD twice for a 2-minute period followed by 3-minute LAD reperfusion before bypass grafting of the first coronary vessel.

MEASUREMENTS AND MAIN RESULTS

Twenty-four-hour electrocardiography was recorded from the preoperative day to the second postoperative day. The heart rate (HR) was significantly elevated after surgery. Supraventricular extrasystole (SVES) events were similar before and after surgery. The incidence of patients with ventricular extrasystole (VES), supraventricular tachycardia (SVT), atrial fibrillation (AF), and ventricular tachycardia (VT) was significantly increased after the operation. Ventricular arrhythmias occurred mostly during anastomosis and the early reperfusion period and recovered 2 hours after reperfusion. Supraventricular tachyarrhythmias were mostly encountered 24 hours after reperfusion. IP significantly suppressed HR elevation, SVT, and VT after surgery. SVES, VES, and AF episodes were similar between the groups.

CONCLUSIONS

Arrhythmia was a common phenomenon during and after an OPCAB procedure. The present IP protocol significantly suppressed HR elevation, the episodes of SVT, and the incidence of VT after surgery.

Preconditioning and cardiac surgery

Preconditioning is in experimental studies the most powerful mode of cardioprotection known. The signal transduction pathways involve a variety of trigger substances, mediators, receptors, and effectors. The studies of preconditioning in cardiac surgery provide conflicting results but the majority of studies show that ischemic preconditiong is an effective adjunct to myocardial protection. However, ischemic preconditioning with repeated clamping of the aorta will never get widespread use. If the "preconditioning response" is to be exploited in cardiac surgery, targeting the underlying molecular mechanisms must provide easily applicable techniques or drugs, which are shown in large scale clinical studies to be beneficial.

Ischemic preconditioning suppresses ventricular tachyarrhythmias after myocardial revascularization

BACKGROUND

Ventricular fibrillation (VF) and tachycardia (VT) are the common and potential life-threatening complications after CABG. Ischemic preconditioning (IP) has been proved effective in reducing ischemia reperfusion arrhythmia in animals and humans. Whether IP is effective in suppressing postoperative VF/VT in patients with CABG has not been studied.

METHODS AND RESULTS

Eighty-six patients with CABG with stable and unstable 3-vessel disease were equally randomly assigned into an IP and a control group. The patients who received IP received 2 periods of 2-minute ischemia followed by 3-minute reperfusion. Twenty-four-hour electrocardiographic data were collected. IP resulted in fewer cases of VF after declamping (48.8% versus 79.1% in IP and control, P=0.004) and a shorter VF period (2.28+/-0.44 versus 4.41+/-0.51 minutes, P=0.002). The episodes of VT were significantly reduced in patients in the IP group during early reperfusion and 24 hours after reperfusion (0.65+/-0.16 versus 3.71+/-0.46, P=0.000 and 0.07+/-0.04 versus 2.12+/-1.41, P=0.002, respectively). De novo sustained VT occurred in 3 control patients as against none in the IP group after surgery. As a result, IP significantly curtailed the mechanical ventilation period and reduced the need for inotropes.

CONCLUSIONS

IP significantly reduced postoperative VF/VT in patients with CABG with 3-vessel disease. Suppression of VT during early reperfusion and 24 hours after reperfusion suggests early and delayed IP phenomena in patients undergoing CABG surgery.

Effect of age on alpha-calcitonin gene-related peptide-mediated delayed cardioprotection induced by intestinal preconditioning in rats

In the present study, we examined whether age-related reduction in cardioprotection of intestinal ischemic preconditioning is related to stimulation of the release and synthesis of calcitonin gene-related peptide (CGRP) in rats. Ischemia-reperfusion injury was induced by a 45-min coronary artery occlusion and 180-min reperfusion, and ischemic preconditioning was induced by six cycles of 4-min ischemia and 4-min reperfusion of the small intestine. The serum concentration of creatine kinase, infarct size, the expression of CGRP isoforms (alpha- and beta-CGRP) mRNA in lumbar dorsal root ganglia and CGRP concentration in plasma were measured. Pretreatment with intestinal ischemic preconditioning for 24 h significantly reduced infarct size and creatine kinase release concomitantly with a significant increase in the expression of alpha-CGRP mRNA, but not beta-CGRP mRNA, and plasma concentrations of CGRP at 6 months of age but not at 24 months of age. These results suggest that the delayed cardioprotective effect of intestinal ischemic preconditioning is decreased in senescent rats, and the age-related change is related to reduction of the synthesis and release of alpha-CGRP.