Beneficial effects of ischemic preconditioning on right ventricular function after coronary artery bypass grafting

Repeated ischaemic preconditioning: a novel therapeutic intervention and potential underlying mechanisms

What is the topic of this review? This review discusses the effects of repeated exposure of tissue to ischaemic preconditioning on cardiovascular function, the attendant adaptations and their potential clinical relevance. What advances does it highlight? We discuss the effects of episodic exposure to ischaemic preconditioning to prevent and/or attenuate ischaemic injury and summarize evidence pertaining to improvements in cardiovascular function and structure. Discussion is provided regarding the potential mechanisms that contribute to both local and systemic adaptation. Findings suggest that clinical benefits result from both the prevention of ischaemic events and the attenuation of their consequences. Ischaemic preconditioning (IPC) refers to the phenomenon whereby short periods of cyclical tissue ischaemia confer subsequent protection against ischaemia-induced injury. As a consequence, IPC can ameliorate the myocardial damage following infarction and can reduce infarct size. The ability of IPC to confer remote protection makes IPC a potentially feasible cardioprotective strategy. In this review, we discuss the concept that repeated exposure of tissue to IPC may increase the 'dose' of protection and subsequently lead to enhanced protection against ischaemia-induced myocardial injury. This may be relevant for clinical populations, who demonstrate attenuated efficacy of IPC to prevent or attenuate ischaemic injury (and therefore myocardial infarct size). Furthermore, episodic IPC facilitates repeated exposure to local (e.g. shear stress) and systemic stimuli (e.g. hormones, cytokines, blood-borne substances), which may induce improvement in vascular function and health. Such adaptation may contribute to prevention of cardio- and cerebrovascular events. The clinical benefits of repeated IPC may, therefore, result from both the prevention of ischaemic events and the attenuation of their consequences. We provide an overview of the literature pertaining to the impact of repeated IPC on cardiovascular function, related to both local and remote adaptation, as well as potential clinical implications.

New technique of local ischemic preconditioning induction without repetitive aortic cross-clamping in cardiac surgery

Background

Several studies have demonstrated that local ischemic preconditioning can reduce myocardial ischemia–reperfusion injury in cardiac surgery patients; however, preconditioning has not become a standard cardioprotective intervention, primarily because of the increased risk of atheroembolism during repetitive aortic cross-clamping. In the present study, we aimed to describe and validate a novel technique of preconditioning induction.

Methods

Patients undergoing coronary artery bypass grafting (12 women and 78 men; mean age, 56 ± 11 years) were randomized into 3 groups: (1) Controls (n = 30), (2) Perfusion (n = 30), and (3) Preconditioning (n = 30). All patients were operated under cardiopulmonary bypass using normothermic blood cardioplegia. Preconditioning was induced by subjecting the hemodynamically unloaded heart to 2 cycles of 3 min of ischemia and 3 min of reperfusion with normokalemic blood prior to cardioplegia. In the Perfusion group, the heart perfusion remained unaffected for 12 min. Troponin I (TnI) levels were analyzed before surgery, and 12, 24, 48 h, and 7 days after surgery. The secondary endpoints included the cardiac index, plasma natriuretic peptide level, and postoperative use of inotropes.

Results

Preconditioning resulted in a significant reduction in the TnI level on the 7th postoperative day only (0.10 ± 0.05 and 0.33 ± 0.88 ng/ml in Preconditioning and Perfusion groups, respectively, P < 0.05). In addition, cardiac index was significantly higher in the Preconditioning group than in the Control and Perfusion groups just after weaning from cardiopulmonary bypass. The number of patients requiring inotropic support with ≥ 2 agents after surgery was significantly lower in the Preconditioning and Perfusion group than in the Control group (P < 0.05). No complications of the procedure were recorded in the Preconditioning group.

Conclusions

The preconditioning procedure described can be performed safely in cardiac surgery patients. The application of this technique of preconditioning was associated with certain benefits, including improved left ventricular function after weaning from cardiopulmonary bypass and a reduced need for inotropic support. However, the infarct-limiting effect of preconditioning in the early postoperative period was not evident. The procedure does not involve repetitive aortic cross-clamping, thus avoiding possible embolic complications.

Xenon is not superior to isoflurane on cardiovascular function during experimental acute pulmonary hypertension

BACKGROUND

Acute right ventricular afterload increase is a known perioperative challenge for the anaesthetic regime especially for patients with a compromised right ventricle. The accused negative inotropic action of volatile anaesthetics, with the exception of xenon, might be crucial for the adaptation of the right ventricle.

METHODS

Reversible pulmonary hypertension (mean pressure 40 mmHg) was induced by an infusion of the stable thromboxane A(2) analog U46619 in a porcine model (n = 35). The effects of 70 vol% xenon and 0.9 vol% isoflurane on biventricular function were studied by conductance catheter technique. Inflammation and myocardial injury was quantified using serum probes [tumour necrosis factor α (TNFα), interleukin 6 (IL-6), troponin] and myocardial tissue [B natriuretic peptide (BNP), TNFα, activated caspase 3] by enzyme-linked immunosorbance assays and reverse-transcription polymerase chain reaction.

RESULTS

After wash in of xenon global haemodynamic parameters remained stable whereas isoflurane caused a systemic vasodilation. This led to a significant decrease in mean arterial pressure in the isoflurane group whereas cardiac output remained stable. Both substances did not alter the biventricular contractility nor did they induce changes in preload for both ventricles. Xenon led to an additional increase in right ventricular afterload, whereas isoflurane reduced pulmonary vascular resistance. No effects on systemic inflammatory response and myocardial injury were found, whereas higher apoptosis rate and expression of BNP and IL-6 was determined in the right ventricle.

CONCLUSIONS

These results do not support the idea that xenon is more beneficial than isoflurane in right ventricular failure during pulmonary hypertension. Isoflurane did not compromise systolic ventricular function during acute PHT it only led to vasodilation in contrast to xenon.

Anti-ischemic effects of inotropic agents in experimental right ventricular infarction

BACKGROUND

Right ventricular (RV) function is an important determinant of survival after myocardial infarction. The efficacy of reperfusion therapy might be increased by the cardioprotective action of inotropic agents, which are used for symptomatic therapy in situations with compromised hemodynamics. Therefore, we used a porcine model of RV ischemia and reperfusion (IR) injury to study the influence of milrinone, levosimendan and dobutamine on the extent and degree of myocardial injury.

METHODS

IR injury was induced by temporary ligation of the distal right coronary artery for 90 min, followed by 120 min of reperfusion. Treatment was initiated 30 min after coronary artery occlusion. A bolus of milrinone (n=12; 50 microg/kg) and levosimendan (n=10; 24 microg/kg) was applied in different groups, followed by continuous infusion of the drugs at 0.5 and 0.2 microg/kg/min, respectively. The effects on myocardial injury and inflammation were compared with a control (n=12) and a dobutamine group (n=10), where treatment was started with an infusion of 5 microg/kg/min.

RESULTS

Milrinone and levosimendan reduced the resulting infarct size with respect to the area at risk (41.7+/-10.2%, 45.7+/-8.1%) when compared with the control group (58.3+/-6.1%). In contrast, dobutamine had no effect (55.8+/-7.7%). All drugs reduced the number of neutrophils infiltrating into the different myocardial regions and the circulating levels of interleukin-6. Increased levels of tumor necrosis factor alpha during reperfusion were only abated by milrinone and levosimendan.

CONCLUSIONS

Cardioprotective properties of milrinone and levosimendan were demonstrated for the first time in a clinically relevant model of RV infarction.

Establishment of a porcine right ventricular infarction model for cardioprotective actions of xenon and isoflurane

BACKGROUND

Right ventricular (RV) function is an important determinant of post-operative outcome. Consequences of RV infarction might be limited by pre-conditioning with volatile anesthetic drugs. Therefore, we used a porcine model of RV ischemia and reperfusion (IR) injury to study the influence of isoflurane and xenon on the extent and degree of myocardial injury.

METHODS

IR injury was induced by a 90-min ligation of the distal right coronary artery and 120-min reperfusion in thiopental anesthetized pigs. A control group (n=12) was compared with two groups, which received either 0.55 minimum alveolar concentration (MAC) isoflurane (n=10) or xenon (n=12) starting 60 min before ischemia. Myocardial injury was described by three criteria: the infarct size related to area at risk (IS/AAR), the infiltration of neutrophils as determined by myeloperoxidase (MPO) activity, and the plasma levels of tumor necrosis factor alpha (TNFalpha), interleukin 6 (IL-6), myoglobin and troponin-T (TnT).

RESULTS

IS/AAR was reduced from 58.3+/-6.2% in the control group to 41.8+/-7.8% after isoflurane and 42.7+/-8.5% after xenon pre-treatment, which equals an absolute reduction of 16.5% [95% confidence interval (CI): 10.9-22.1] and 15.5% (95% CI: 10.1-20.9). The maximum increase of TnT could be observed within the xenon group. Both treatment groups were characterized by lower MPO activity, in the infarct and periinfarct region and lower plasma concentrations of TNFalpha and IL-6.

CONCLUSIONS

It could be demonstrated for the first time in a model of RV infarction that the continuous application of isoflurane or xenon before, during and after ischemia reduced the extent (size) and severity (inflammation) of myocardial injury.

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.

Brief pressure overload of the left ventricle preconditions rabbit myocardium against infarction

BACKGROUND

Several nonischemic stimuli have been shown to precondition myocardium. We investigated cardioprotective effects and underlying mechanisms of brief pressure overload of the left ventricle in this study.

METHODS

Brief pressure overload of the left ventricle was achieved by two 10-minute partial snaring of the ascending aorta so that systolic left ventricular pressure was raised 50% above the baseline value. Ischemic preconditioning was elicited by two 10-minute coronary artery occlusions. Ten minutes after different pretreatments, myocardial infarction was induced by a 60-minute coronary artery occlusion followed by 3-hour reperfusion. Area at risk and myocardial infarct was determined by blue dye injection and triphenyl tetrazolium chloride staining.

RESULTS

The myocardial infarct size, expressed as percentage of area at risk, was significantly reduced in the pressure overload group (15.9% +/- 2.9%, p < 0.001, n = 9) as well as in the ischemic preconditioning group (14.9% +/- 1.9%, p < 0.001, n = 9) versus the control group (30.0% +/- 6.9%, n = 10). Pretreatment with a blocker of stretch-activated ion channels (gadolinium, 40 micromol/kg, intravenous) abolished the protection induced by pressure overload and ischemic preconditioning. Gadolinium itself did not alter the extent of infarct. There was no significant difference in hemodynamics, area at risk, and mortality among all groups of animals.

CONCLUSIONS

Brief pressure overload of the left ventricle by partial snaring of the ascending aorta preconditioned rabbit myocardium against infarction. The underlying mechanism might be related to activation of stretch-activated ion channels.

Decreased right ventricular function after coronary artery bypass grafting and its relation to exercise capacity: A tricuspid annular motion–based study

BACKGROUND

Decreased right ventricular (RV) function is a known echocardiographic finding after coronary artery bypass grafting (CABG). For patients with heart failure, RV dysfunction is a predictor of poor exercise capacity. The significance and time course of RV dysfunction and its relation to exercise capacity after CABG have not been elucidated, however.

OBJECTIVES

In this prospective study, we assessed RV function measured from echocardiographic tricuspid annular motion (TAM) before and after CABG and its relation to exercise capacity.

METHODS

In 99 patients accepted for CABG, we did a baseline echocardiographic investigation before operation, followed by repeated echocardiograms 3 months and 1 year after CABG. RV function was assessed using the magnitude of TAM measured at the RV free wall. An exercise stress test and coronary angiography were performed before and 3 months after CABG.

RESULTS

RV function assessed by TAM was significantly reduced 3 months after CABG (22.4 vs 14.5 mm, P <.001) compared with preoperative measurements and remained so after 1 year (14.7 mm, P <.001). Left ventricular systolic function was unchanged 3 months after CABG. The 1-year echocardiographic follow-up showed paradoxical septal movement in 96% of the patients. Exercise capacity improved significantly 3 months after CABG compared with before (1.6 vs 1.83 W/kg, P <.001). These finding are independent of the state of the right coronary artery.

CONCLUSIONS

One year after CABG, RV function remained depressed and septal motion remained paradoxical compared with the preoperative investigation, suggesting that these postoperative findings might be permanent in the majority of patients. Despite the reduced RV function, exercise performance 3 months after CABG was improved. The depressed RV function, measured from TAM after CABG, probably lacks clinical significance.

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.

Perioperative myocardial ischemia reperfusion injury

Myocardial I-R injury contributes to adverse cardiovascular outcomes after cardiac surgery. The pathogenesis of I-R injury is complex and involves the activation, coordination, and amplification of several systemic and local proinflammatory pathways (Fig. 4). Treatment and prevention of perioperative morbidity associated with myocardial I-R will ultimately require a multifocal approach. Combining preoperative risk stratification (co-morbidity and surgical complexity), minimizing initiating factors predisposing to SIRS, limiting ischemia duration, and administering appropriate immunotherapy directed toward systemic and local proinflammatory mediators of I-R injury, should all be considered. In addition, the role of the genetic-environmental interactions in the pathogenesis of cardiovascular disease is also being examined. Thus, in the near future, preoperative screening for polymorphisms of certain inflammatory and coagulation genes should inevitably help reduce morbidity by permitting the identification of high-risk cardiac surgical patients and introducing the opportunity for gene therapy or pharmacogenetic intervention [42,64].

Cardiomyocyte apoptosis and ischemic preconditioning in open heart operations

BACKGROUND

The aim of the present study was to ascertain the percentage of left apical myocardial apoptosis in three-vessel coronary artery bypass grafting patients quantitatively and the impact of ischemic preconditioning.

METHODS

Twenty-one patients with three-vessel disease who had elective coronary artery bypass grafting were randomized in a ratio of 2:1 to ischemic preconditioning (n = 14) or a control group (n = 7). The ischemic preconditioning protocol was established by two cycles of ascending aorta occlusion for 2 minutes followed by 3 minutes of reperfusion. Myocardial samples from the apex of the left ventricle were taken using a Tru-Cut needle before aortic cross-clamping and immediately after declamping. The percentage of apoptosis was analyzed by TUNEL methods. Data on hemodynamics and biochemical markers were collected.

RESULTS

Low levels of myocardial apoptosis were found before the operation (0.01% +/- 0.00%). During the early reperfusion period, the percentage of myocardial apoptotic cells significantly increased (0.15% +/- 0.05%, p = 0.008). Ischemic preconditioning significantly improved cardiac index and right ventricular ejection fraction recovery after the operation (p = 0.036 and 0.001 respectively, repeated measure) but had no effect on myocardial apoptosis before and after the operation (0.01 +/- 0.00 versus 0.01 +/- 0.00, p = 0.658 and 0.12% +/- 0.04% versus 0.23% +/- 0.14%, p = 0.302).

CONCLUSIONS

Cardioplegic myocardial ischemia during open heart operation was associated with induction of cardiomyocyte apoptosis in humans. Attenuation of postoperative cardiac dysfunction by ischemic preconditioning appeared to be independent of apoptosis.

Ischemic preconditioning is not cardioprotective in senescent human myocardium

BACKGROUND

Cellular and functional changes secondary to aging could impair myocardial tolerance to ischemia and affect the heart's response to ischemic preconditioning.

METHODS

We investigated the impact of cardiac aging on preconditioning in right atrial trabeculae of adult patients (< or = 55 years) and senescent patients (> or = 70 years) with coronary artery disease. Specimens were subjected to 30 minutes of simulated ischemia (hypoxic substrate-free superfusion) with and without 5 minutes of ischemic pretreatment. Postischemic contractile recovery was measured and expressed as percentage of base line force values.

RESULTS

During the reoxygenation period, trabeculae of adult patients but not those of senescent patients improved after ischemic preconditioning. After 40 minutes of reoxygenation, preconditioned adult trabeculae developed 57% +/- 5% of their preischemic force (nonpreconditioned control 44% +/- 5%, p < 0.01), senescent trabeculae recovered to 44% +/- 4% (control 45% +/- 3%). Especially myocardium from adult patients with Canadian Cardiovascular Society (CCS) stage III angina pectoris treated with ACE inhibitors recovered well (70% +/- 7%; control 50% +/- 8%, p < 0.01), contrasting with trabeculae from patients with CCS stage II angina (44% +/- 5%; control 40% +/- 10%). Ischemia-inducible Hsp70 (human heat shock protein) was additionally measured after reoxygenation. Total Hsp70 mRNA was elevated in preconditioned myocardium along with its contractile recovery (r = 0.33, p = 0.07). Because the control transcription, analyzing 18S rRNA and beta-actin, was reduced by ischemia but recovered in preconditioned trabeculae, relative Hsp70 mRNA was not altered.

CONCLUSIONS

Our data indicate that ischemic preconditioning has no beneficial effect on the postischemic functional recovery of senescent human myocardium.

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.

Regional ischemic preconditioning enhances myocardial performance in off-pump coronary artery bypass grafting

OBJECTIVES

We intended to investigate whether ischemic preconditioning (IP) enhances myocardial performance in patients who undergo off-pump coronary artery bypass grafting (CABG).

DESIGN

A controlled, randomized, prospective study.

SETTING

A university hospital.

PATIENTS

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

INTERVENTIONS

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

MEASUREMENTS AND RESULTS

Registration included hemodynamic data from the peripheral artery and the pulmonary artery, and the measurement of cardiac troponin I (CTnI) and creatine kinase isoenzyme MB (CK-MB) values. IP resulted in a complete recovery of the mean stroke volume index (SVI) after the operation. In the control subjects, the mean SVI showed a significant reduction postoperatively (p = 0.039). On the first postoperative day, the increase in the mean heart rate (HR) was also significantly lower in the IP patients. The CTnI level was statistically significantly lower in the IP group (p = 0.043), and IP patients tended to have a smaller CK-MB release after surgery (not significant). The duration of mechanical ventilation, the length of stay in the ICU, and the use of inotropic medication did not increase after the IP protocol.

CONCLUSIONS

Two cycles of regional 2-min IP in the LAD, followed by 3 min of reperfusion, proved to be applicable and safe in patients undergoing off-pump myocardial revascularization, it tended to decrease the immediate myocardial enzyme release, it prohibited the postoperative increase in HR, and it enhanced the recovery of SVI.

Myocardial lactate production is not involved in the ischemic preconditioning mechanism in coronary artery bypass graft surgery patients

OBJECTIVE

To study the relationship between ischemic preconditioning (IP) and lactate production and their impact on coronary artery bypass graft surgery patients.

DESIGN

Prospective, randomized, controlled study.

SETTING

University hospital.

PARTICIPANTS

Eighty 3-vessel disease coronary artery bypass graft surgery patients with stable and unstable angina pectoris.

INTERVENTIONS

The IP patients were preconditioned with 2 periods of 2-minute ischemia followed by 3-minute reperfusion before aortic cross-clamping.

MEASUREMENTS AND MAIN RESULTS

The cardiac index (CI) after surgery was significantly higher in the IP group than in controls among stable patients (p = 0.013). IP was not effective in CI recovery in unstable patients. The baseline values of lactate production were 11.6%, 20.3%, -7.0%, and -2.9% in stable IP, stable control, unstable IP, and unstable control patients. Compared with baseline, lactate production increased significantly after the IP protocol (39.0% and 47.5% in the stable and unstable patients), and operation (47.5%, 31.7%, 35.4%, and 35.6% in stable IP, stable control, unstable IP, and unstable control patients) but not after 10 minutes of cardiopulmonary bypass (29.7% and 19.0% in the stable and unstable patients). There were no differences among the groups in lactate production after the operation. Lactate production after the IP protocol was negatively associated with CI recovery after surgery in the IP patients (p = 0.026).

CONCLUSION

The IP effects do not include modulation of lactate production. IP induces lactate production, but it seems not to be involved in the triggering process.

Ischemic preconditioning and nicorandil pretreatment improve donor heart preservation

The present study investigated the effects of ischemic preconditioning (IPC) and nicorandil pretreatment on myocardial storage in a donor heart preservation model. Isolated rat hearts were separated into groups: group 1, non-preconditioned control group; group 2, 2.5 min of normothermic ischemia followed by 15 min of normothermic Langendorff perfusion (one IPC cycle); and group 3, 2 cycles of IPC. All hearts were subsequently stored in University of Wisconsin solution at 4 degrees C for 2, 4 and 6h, and the concentrations of high-energy phosphate metabolites were measured for each time point. Heart function parameters (aortic flow, coronary flow and cardiac output) were measured when the heart was reperfused following the 2, 4 or 6 h of preservation. The effects of nicorandil, an ATP-sensitive potassium channel opener, on heart function following preservation were also evaluated. Nicorandil was injected intravenously before heart harvesting. The results showed that the energy status was well preserved in the IPC groups. The 2-cycle IPC group showed better recovery of heart function following preservation. Pretreatment with nicorandil also improved functional recovery of the heart following preservation. The present study showed that IPC of the rat heart resulted in improved myocardial energy metabolism and functional recovery after hypothermic preservation, and that nicorandil has potential for pharmacological preconditioning in heart preservation for transplantation.