Transient ischemia does not limit subsequent ischemic regional dysfunction in humans: a transesophageal echocardiographic study during minimally invasive coronary artery bypass surgery

Myocardial Preconditioning: Characteristics, Mechanisms, and Clinical Applications

Perioperative myocardial ischemia and dysfunction re main prevalent after cardiac surgery despite the use of conventional measures to provide myocardial protec tion. Myocardial preconditioning is a powerful, endog enously regulated means of myocardial protection that may also have some clinical usage for patients undergo ing cardiac surgical procedures. The paradoxical con cept of using ischemia as a stimulus for myocardial protection has been studied extensively in animals and humans. The specific characteristics and constituents of preconditioning have been well identified. The mecha nism remains to be completely elucidated due to differ ences among species and experimental models. Some pharmacologic agents are capable of mimicking the classic mechanism of ischemic preconditioning. Pharma cologic and ischemic preconditioning may have signifi cant clinical use and therapeutic efficacy as a means of providing myocardial protection during cardiac surgery, especially in procedures that do not use cardioplegia and cardiopulmonary bypass, such as minimally inva sive coronary artery bypass grafting. This article re views the characteristics, mechanisms, potential clini cal applications, and therapeutic efficacy of myocardial preconditioning.

Myocardial conditioning techniques in off-pump coronary artery bypass grafting

Off-pump coronary artery bypass surgery by avoiding cardioplegic arrest seems to reduce the risk of ischemic myocardial injury. However, even short-term regional ischemic periods, hemodynamic instability and arrhythmias associated with the procedure can be responsible for myocardial damage. Conditioning, a potential cardio-protective tool during on-pump cardiac surgery, has hardly been investigated in the context of off-pump surgery. There are virtually no large trials on remote ischemic preconditioning and the majority of reports have focused on central ischemic conditioning. Similarly, volatile anesthetic agents with conditioning effect like ischemic preconditioning have been shown to reduce cardiac injury during on-pump procedures but have not been validated in the off-pump scenario. Here, we review the available evidence on myocardial conditioning, either with ischemia/reperfusion or volatile anesthetic agents in patients undergoing off-pump coronary artery surgery.

Infarct-remodelled hearts with limited oxidative capacity boost fatty acid oxidation after conditioning against ischaemia/reperfusion injury

AIMS

Infarct-remodelled hearts are less amenable to protection against ischaemia/reperfusion. Understanding preservation of energy metabolism in diseased vs. healthy hearts may help to develop anti-ischaemic strategies effective also in jeopardized myocardium.

METHODS AND RESULTS

Isolated infarct-remodelled/sham Sprague-Dawley rat hearts were perfused in the working mode and subjected to 15 min of ischaemia and 30 min of reperfusion. Protection of post-ischaemic ventricular work was achieved by pharmacological conditioning with sevoflurane. Oxidative metabolism was measured by substrate flux in fatty acid and glucose oxidation using [(3)H]palmitate and [(14)C]glucose. Mitochondrial oxygen consumption was measured in saponin-permeabilized left ventricular muscle fibres. Activity assays of citric acid synthase, hydroxyacyl-CoA dehydrogenase, and pyruvate dehydrogenase and mass spectrometry for acylcarnitine profiling were also performed. Six weeks after coronary artery ligation, the hearts exhibited macroscopic and molecular signs of hypertrophy consistent with remodelling and limited respiratory chain and citric acid cycle capacity. Unprotected remodelled hearts showed a marked decline in palmitate oxidation and acetyl-CoA energy production after ischaemia/reperfusion, which normalized in sevoflurane-protected remodelled hearts. Protected remodelled hearts also showed higher β-oxidation flux as determined by increased oxygen consumption with palmitoylcarnitine/malate in isolated fibres and a lower ratio of C16:1+C16OH/C14 carnitine species, indicative of a higher long-chain hydroxyacyl-CoA dehydrogenase activity. Remodelled hearts exhibited higher PPARα-PGC-1α but defective HIF-1α signalling, and conditioning enabled them to mobilize fatty acids from endogenous triglyceride stores, which closely correlated with improved recovery.

CONCLUSIONS

Protected infarct-remodelled hearts secure post-ischaemic energy production by activation of β-oxidation and mobilization of fatty acids from endogenous triglyceride stores.

The role of myocardial ischaemic preconditioning during beating heart surgery: biological aspect and clinical outcome

Short periods of ischaemia consecutive to reperfusion periods before a sustained ischaemic condition, the so-called ischaemic preconditioning (IP), aim to protect myocardial cells against prolonged ischaemia. IP appears as a considerable endogenous cardioprotective mechanism decreasing the infarct size after total occlusion in either experimental models or humans. Angina periods before an acute coronary syndrome limit the myocardial infarction being protective for the myocardium. Our report aims to review the international bibliography of the IP during off-pump coronary artery bypass grafting.

Drugs mediating myocardial protection

The occurrence of myocardial ischaemia will result in either reversible or irreversible myocardial dysfunction. Even when revascularization is successful, some reperfusion injury may occur that transiently impairs myocardial function. Therefore, treatment should not only be directed towards prompt restoration of myocardial blood flow but measures should also be taken to prevent or alleviate the consequences of myocardial reperfusion injury. Over the years, various strategies have been developed. The present contribution reviews a number of these strategies focusing on pharmacological treatments that have been developed to address myocardial reperfusion injury.

Myocardial metabolism altered by ischemic preconditioning and enflurane in off-pump coronary artery surgery

OBJECTIVE

During off-pump coronary artery bypass (OPCAB) surgery, the heart is subjected to ischemia and reperfusion. The authors hypothesized that the volatile anesthetics are as effective as ischemic preconditioning (IPC) in preserving myocardial function during off-pump cardiac surgery, and this effect is because of multiple mechanisms of action. Therefore, the effects of enflurane with its calcium inhibition and antioxidative properties were compared with mechanical IPC in preserving myocardial cellular markers.

DESIGN

A prospective, randomized, controlled, and partly blinded study.

SETTING

A tertiary care university hospital.

PARTICIPANTS

Twenty-five patients undergoing elective single-graft OPCAB surgery.

INTERVENTIONS

Patients were randomized into 3 groups: (1) control (n = 8), (2) a single 5-minute ischemia/reperfusion interval of IPC before coronary occlusion (n = 9), and (3) 1.6% enflurane anesthesia 15 minutes before and during graft attachment (n = 8). Arterial and coronary sinus venous blood were analyzed for biochemical indices of ischemia and hydroxyl radical generation.

MEASUREMENTS AND MAIN RESULTS

Although the hemodynamic changes were small, myocardial lactate production in the control group increased by 120%, whereas in the enflurane group it decreased significantly (p < 0.01) compared with the control and IPC groups. Oxygen utilization in the control group was 44% higher (p < 0.03), and there was also a larger release of the hydroxyl radical-dependent adduct 2,3-dihydroxybenzoic acid (225% increase, p < 0.05) compared with both study groups. During reperfusion, initial anterior wall hypokinesis by TEE was observed, with slow recovery during reperfusion compared with early recovery in both study groups.

CONCLUSIONS

Coronary occlusion during OPCAB surgery results in increased production of ischemia-related metabolic products. The application of methods such as IPC or volatile anesthesia appears to reduce the metabolic deficit, free-radical production, and physiologic changes.

Cardioprotection afforded by ischemic preconditioning interferes with chronic beta-blocker treatment

OBJECTIVES

The efficacy of ischemic preconditioning of the heart has remained controversial. We investigated whether chronic treatment with beta-blockers affects the ischemic preconditioning in the isolated rat heart model.

DESIGN

Wistar rats were treated with propranolol (50 mg/kg/day, p.o.) (PRL), with nipradilol (10 mg/kg/day, p.o.) (NPL), or with vehicle, for 4 weeks. Isolated rat hearts were divided into global ischemia hearts (GI, PRL and NPL, each n=6) and ischemic preconditioned hearts (IP, PRL+IP and NPL+IP, each n=6).

RESULTS

Significant differences in left ventricular pressure were observed between the PRL and PRL+IP, and between the NPL and NPL+IP groups. In the NPL group, significant amelioration and preservation of left ventricular peak pressure, coronary flow, reduction of infarct size, and NOx preservation were observed. Lipid peroxidation in the NPL group was significantly reduced before and after global ischemia compared to the GI group.

CONCLUSIONS

The effect of ischemic preconditioning was abolished in the hearts of rats following oral treatment of propranolol or nipradilol. However, the administration of nipradilol protected the ischemic and reperfused myocardium, partly due to the prevention of lipid peroxide formation.

Que faut-il attendre de la chirurgie coronaire sans circulation extracorporelle ?

Coronary artery bypass surgery with beating heart (off-pump) has become more common in the last ten years allowing seven randomized studies with at least 60 patients, comparing off-pump and on-pump coronary bypass. Anaesthesia, monitoring and haemodynamic complications are described. Randomized studies concluded to less elevation of biochemical markers of myocardial and renal injury, less hydric inflation, less cerebral microemboli, reduction of homologous blood transfusions, of hospital stay and global costs. However in low risk patients no reduction in myocardial infarction, atrial fibrillation, stroke, acute renal failure, early reoperation, surgical site infection and mortality were observed. Non-randomized studies suggest a benefit in stroke and mortality in elderly patients but the possibility of incomplete revascularization remains.

Transesophageal Echocardiography for Monitoring Segmental Wall Motion During Off-Pump Coronary Artery Bypass Surgery

In this prospective, observational study, we evaluated whether transesophageal echocardiography allows for monitoring left ventricular segmental wall motion during cardiac displacement for off-pump coronary artery bypass (OPCAB) surgery. On the basis of a pilot study that showed frequent loss of transgastric views during OPCAB surgery, we analyzed only midesophageal views. The midesophageal 4-chamber view, 2-chamber view, and long-axis view were recorded in 60 patients after opening the chest and placing an epicardial stabilizer on the displaced heart. Using the 16-segment model, 2 echocardiographers independently performed offline analysis of segmental wall motion. The percentage of patients in whom >or=14 left ventricular segments were readable was calculated at baseline and after cardiac displacement and placement of an epicardial stabilizer. At baseline, >or=14 segments were readable in 59 (98%) of 60 patients. After cardiac displacement, >or=14 segments were readable during 58 (76%) of 76 revascularizations of the left anterior descending coronary artery (P < 0.01 versus baseline), during 33 (83%) of 40 revascularizations of the left circumflex coronary artery (P < 0.01 versus baseline), and during 29 (94%) of 31 revascularizations of the right coronary artery (not significant). We conclude that the number of readable segments decreased after cardiac displacement but that availability of >or=14 readable segments allowed for reliable monitoring of segmental wall motion in 4 of 5 patients during OPCAB surgery.

Intraoperative ischemia and long-term events after minimally invasive coronary surgery

BACKGROUND

Concern has been raised about the effects of prolonged left anterior descending (LAD) artery occlusion during minimally invasive direct coronary artery bypass graft surgery (MIDCABG). We sought to assess the impact of myocardial dysfunction during MIDCABG on long-term outcome and the protective role of collateral circulation on myocardial ischemia.

METHODS

Myocardial function was evaluated in 92 patients by intraoperative transesophageal echocardiography during MIDCABG.

RESULTS

Wall motion score index increased during LAD occlusion (p < 0.00l) and reverted after LAD reopening (p < 0.001 versus occlusion and p = not significant versus baseline). The change in wall motion score index (occlusion versus baseline) was higher in patients with multivessel disease (p < 0.05) and in patients with LAD Thrombolysis in Myocardial Infarction study classification flow grade 2 or less without collateral circulation (p < 0.05). Myocardial stunning was documented in 12 patients (13%). The 5-year adverse event rate (including death, myocardial infarction, and revascularization) was 12%. By multivariate Cox regression analysis, multivessel disease, but not perioperative ischemia or stunning, was the only predictor of event-free survival.

CONCLUSIONS

During MIDCABG anterior wall dysfunction is transient, with prompt recovery after completion of the anastamosis in most cases; myocardial stunning can be documented in a minority of patients. Flow either antegrade or retrograde in the LAD territory plays a protective role against the development of ischemia. Multivessel disease, but not perioperative ischemia or stunning, predicts long-term event-free survival.

Effects of intracoronary shunts on coronary endothelial coating in the human beating heart

BACKGROUND

Local occlusion of coronary arteries during beating heart revascularization leads to injury of the arterial wall especially disturbing the integrity of the endothelium. The aim of this study was to elucidate the effects of intracoronary shunts versus local occlusion with elastic silicone loops on the beating heart in human coronary arteries by scanning electron microscopy.

METHODS

Coronary arteries of patients with dilated cardiomyopathy (n = 4) or ischemic heart disease (n = 8) undergoing heart transplantation were locally occluded either with a silicone loop or with a shunt inserted after arteriotomy. Unmanipulated segments of the coronary arteries served as controls. Integrity of the endothelial lining was observed with scanning electron microscopy.

RESULTS

Scanning electron microscopy revealed a statistically significant higher injury after shunting compared with controls (p < 0.001) and vessel loop occlusion (p < 0.001). There was no difference between both patient groups according to control specimens or after manipulation.

CONCLUSIONS

From this investigation we conclude that insertion of intracoronary shunts during beating heart surgery leads to severe endothelial denudation in human coronary arteries. Therefore, at present we recommend using intracoronary shunts selectively in cases in which critical ischemia or technical difficulties as a result of anatomic conditions are expected during anastomosis and avoiding routine shunt insertion into coronary arteries during beating heart revascularization.

Anaesthetics and cardiac preconditioning. Part II. Clinical implications

There is compelling evidence that preconditioning occurs in humans. Experimental studies with potential clinical implications as well as clinical studies evaluating ischaemic, pharmacological and anaesthetic cardiac preconditioning in the perioperative setting are reviewed. These studies reveal promising results. However, there are conflicting reports on the efficacy of preconditioning in the diseased and aged myocardium. In addition, many anaesthetics and a significant number of perioperatively administered drugs affect the activity of cardiac sarcolemmal and mitochondrial K(ATP) channels, the end-effectors of cardiac preconditioning, and thereby markedly modulate preconditioning effects in myocardial tissue. Although these modulatory effects on K(ATP) channels have been investigated almost exclusively in laboratory investigations, they may have potential implications in clinical medicine. Important questions regarding the clinical utility and applicability of perioperative cardiac preconditioning remain unresolved and need more experimental work and randomized controlled clinical trials.

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

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

Remote preconditioning lessens the deterioration of pulmonary function after repeated coronary artery occlusion and reperfusion in sheep

PURPOSE

We investigated whether remote organ preconditioning (RPC) can preserve pulmonary function following repeated myocardial ischemia/reperfusion in a model mimicking multi-vessel off-pump coronary artery bypass (OPCAB) revascularization.

METHODS

Nine sheep (Group-RPC) underwent RPC by three episodes of five-minute occlusion and five-minute reperfusion of the iliac artery. Five sheep (Group-C) were time-matched controls. Afterwards, ten-minute occlusion and reperfusion of the left anterior descending, the first diagonal and the left circumflex coronary arteries were performed consecutively. Hemodynamic and respiratory parameters and arterial blood gases were measured until 120 min after the final coronary reperfusion. Anesthesia was maintained with halothane in oxygen and nitrous oxide. Animals were ventilated with a tidal volume of 15-20 mL.kg(-1) in a non-rebreathing system, and a respiratory rate 14-16 min, with 5-cm H(2)O positive end expiratory pressure after thoracotomy.

RESULTS

Repeated coronary occlusion and reperfusion was associated in this experimental model with an increase in pulmonary vascular resistance (PVR) and pulmonary arterial pressure (PAP) and a decrease in PaO(2) and PaO(2)/FIO(2) in Group-C. After 120 min reperfusion, PaO(2) and PaO(2)/FIO(2) in Group-RPC were higher (192 +/- 69 mmHg and 241 +/- 78 vs 115 +/- 54 mmHg and 129 +/- 64, P < 0.05), while PVR and PAP were lower than in Group-C. At 120 min of reperfusion, PaO(2) and PaO(2)/FIO(2) were inversely correlated with PVR (P < 0.01).

CONCLUSIONS

RPC by transient occlusion of the iliac artery improves lung gas exchange after repeated coronary artery occlusion and reperfusion mimicking OPCAB surgery, and preserves low PVR in sheep.

Ischemic preconditioning does not improve myocardial preservation during off-pump multivessel coronary operation

BACKGROUND

The value of ischemic preconditioning during coronary operations has remained controversial. The aim of this study was to evaluate the effects of ischemic preconditioning on myocardial energy metabolism and tissue injury during off-pump multivessel coronary surgery.

METHODS

Eleven patients with preceding preconditioning were compared with 11 patients without it. The preconditioning group underwent a 5-minute period of ischemia followed by a 5-minute reperfusion period before coronary occlusion for each of the first two anastomoses.

RESULTS

The transmyocardial differences (coronary sinus - arterial) in inosine and the sum of adenine degradation products increased in both groups, but the differences in xanthine and hypoxanthine increased only in the preconditioning group. Myocardial lactate production increased to a maximum of 0.09 mmol/L with preconditioning and to a maximum of 0.17 mmol/L without it. Transmyocardial pH differences increased to 0.03 U in both groups. The maximum postoperative concentration of creatine kinase-MB mass was 14.8 microg/L with preconditioning and 6.3 microg/L without preconditioning, and that of troponin I 7.4 microg/L and 5.2 microg/L, respectively. There were no statistically significant differences between the groups, however.

CONCLUSIONS

Ischemic preconditioning of 5 minutes followed by reperfusion of 5 minutes during off-pump multivessel coronary artery surgery did not prevent myocardial metabolic derangement and tissue injury and thus cannot be routinely recommended.

Myocardial ischemic preconditioning during minimally invasive direct coronary artery bypass grafting attenuates ischemia-induced electrophysiological changes in human ventricle

OBJECTIVE

Ischemic preconditioning (IPC) has been found to protect the myocardium in animal studies. However, clinical studies have been limited and the clinical effects of IPC are still uncertain. The purpose of this study was to assess whether IPC has any protective effect on the human myocardium during minimally invasive CABG (MIDCAB), by means of epicardial electrophysiological testing.

METHOD

Forty-five patients with left anterior descending artery disease who underwent a MIDCAB procedure were evaluated. In the present study, the electrical potentials which were not affected by cardio-pulmonary bypass or cardioplegia were measured. The ratio of longitudinal to transverse conduction velocity (phiL /phiT), and QT, JT dispersions were measured using plaque electrodes in the preischemic state, during a 5-minute coronary occlusion, during the subsequent 5-minute reperfusion, during 5- and 10-minute anastomosis periods, and after anastomosis.

RESULT

The phiL/phiT was 2.2 +/- 0.2 at baseline. Anisotropy was exaggerated during the 5-minute coronary occlusion (2.6 +/- 0.3). During anastomosis, conduction velocities were decreased, but showed no further deterioration (2.4 +/- 0.3, and 2.4 +/- 0.3, respectively). QT and JT dispersions were improved by reperfusion.

CONCLUSION

The effectiveness of IPC during the MIDCAB procedure was confirmed electrophysiologically. Anisotropy and dispersions were minimized after IPC, therefore IPC demonstrated antiarrhythmic protective effects on the human myocardium.

Evolution of OPCAB surgery in a single institution

Off-pump coronary artery bypass (OPCAB) grafting is becoming popular worldwide. The development of exposure and stabilization techniques have made this surgery a simple, safe, and routine procedure. The evolution of OPCAB surgery at our institution is presented and discussed.

Mechanisms of hemodynamic changes during off-pump coronary artery bypass surgery

PURPOSE

To describe the mechanisms of hemodynamic changes during off-pump coronary artery bypass graft surgery (OP-CABG).

SOURCE

Pertinent medical literature in the English and French languages was identified through a Medline computerized literature search and a manual search of selected articles, using off-pump coronary artery surgery, beating heart surgery, hemodynamic, and transesophageal echocardiography as key words. Human and animal studies were included.

PRINCIPAL FINDING

Hemodynamic variations in OP-CABG may be due to mobilization and stabilization of the heart, or myocardial ischemia occurring during coronary occlusion. Suction type and compression type stabilizers produce hemodynamic effects through different mechanisms. Heart dislocation (90 degrees anterior displacement) and compression of the right ventricle to a greater extent than the left ventricle are responsible for hemodynamic alterations when using suction type stabilizers. Compression of the left ventricular outflow tract and abnormal diastolic expansion secondary to direct deformation of the left ventricular geometry are proposed mechanisms for hemodynamic derangements with compression type stabilizer. Coronary occlusion during the anastomosis can have additional effects on left ventricular function, depending on the status of collateral flow. The value and limitations of electrocardiographic (ECG), hemodynamic and echocardiographic monitoring modalities during OP-CABG are reviewed.

CONCLUSIONS

In summary, hemodynamic changes which can either be secondary to the stabilization technique or to transient ischemia represent an important diagnostic challenge during off-bypass procedures. The mechanism can vary according to the stabilization system. Current monitoring such as ECG and hemodynamic monitoring are used but remain limited in establishing the cause of hemodynamic instability. Transesophageal echocardiography is used in selected patients to diagnose the etiology of hemodynamic instability and can direct therapy, particularly in those with severe myocardial systolic and diastolic dysfunction, mild to moderate mitral regurgitation, or for patients who are unstable during the procedure.

Intracoronary shunts reduce transient intraoperative myocardial dysfunction during off-pump coronary operations

BACKGROUND

This study investigated the hemodynamic changes in patients undergoing multiple vessel beating heart coronary revascularization in the presence or absence of an intracoronary shunt.

METHODS

Forty patients were randomized to off-pump with a shunt (n = 20) or with the proximal coronary artery occluded by a soft snare (n = 20). Hemodynamic measurements were recorded at base line, during construction, and after completion of each distal anastomosis.

RESULTS

Grafting of the left anterior descending coronary artery anastomosis was associated with a significant decrease in stroke volume, cardiac index, and mean arterial pressure, and an increase in pulmonary capillary wedge pressure and systemic vascular resistance in the snare but not in the shunt group. During grafting of the posterior descending coronary artery there was a marked decrease in stroke volume and cardiac index, and an increase in central venous pressure in both groups, and an increase in heart rate, mean pulmonary arterial pressure, pulmonary capillary wedge pressure, and systemic vascular resistance only in the snare group. The most extensive changes were observed during the circumflex coronary artery anastomosis with a reduction in stroke volume, cardiac index, and mean arterial pressure, and an increase in central venous pressure, pulmonary capillary wedge pressure, pulmonary arterial pressure, and systemic vascular resistance in both groups. In all settings, these changes were transient and recovered after the heart was returned to its anatomical position in the shunt group, whereas stroke volume and cardiac index remained reduced, and systemic vascular resistance was elevated in all settings in the snare group.

CONCLUSIONS

Stabilization of the left anterior descending coronary artery to perform the anastomosis resulted in temporary hemodynamic changes, which are prevented by the use of an intracoronary shunt. The hemodynamic deterioration during the construction of the posterior descending coronary artery and circumflex coronary artery anastomoses is transient in the shunt group, whereas the snaring technique is associated with an impairment of early functional recovery.

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.

Blockade of adenosine receptors with aminophylline limits ischemic preconditioning in human beings

BACKGROUND

Ischemic preconditioning is characterized by the limitation of infarct size or ischemic signs after one or more brief episodes of ischemia, a process that probably involves stimulation of adenosine receptors. One human model of ischemic preconditioning is repetitive occlusion of a coronary artery during angioplasty. By using this method of inducing ischemia, we tested the hypothesis that blockade of adenosine receptors with aminophylline would abolish ischemic preconditioning in human beings.

METHODS

Twenty-six patients undergoing angioplasty were randomly assigned to receive either aminophylline (6 mg/kg IV) or placebo before repetitive coronary occlusion (two 2-minute occlusions separated by 5 minutes). ST-segment changes on the surface electrocardiogram were used as a measure of myocardial ischemia. Serum theophylline levels and the conduction response to an intravenous bolus of adenosine were used to assess the efficacy of adenosine receptor blockade.

RESULTS

Repetitive coronary occlusion resulted in a reduction in ST-segment shift in 9 of 13 patients given placebo. In contrast, 9 of 13 patients receiving aminophylline had an increase in ST-segment shift on the second occlusion (P =.002). Patients receiving aminophylline (mean serum theophylline level of 8.38 +/- 0.45 mg/dL) did not have significant conduction block with intravenous adenosine.

CONCLUSIONS

Repetitive coronary occlusion reduces the signs of ischemia in human beings, a process limited by blockade of adenosine receptors.

L-Arginine given after ischaemic preconditioning can enhance cardioprotection in isolated rat hearts

OBJECTIVE

Ischaemic or pharmacological preconditioning with L-arginine has been reported to be insufficient for optimal cardioprotection. The ability of nitric oxide (NO) to enhance ischaemic preconditioning was assessed, and the role of L-arginine-induced ischaemic preconditioning in myocardial protection was determined.

METHODS

Isolated rat hearts were prepared and divided into six groups: control hearts (control, n=6) were perfused without global ischaemia at 37 degrees C for 160 min; global ischaemia hearts (GI, n=6) were subjected to ischaemia for 20 min and reperfusion for 120 min; ischaemic preconditioned hearts (IP, n=6) received 2 min of zero-flow global ischaemia followed by 5 min reperfusion, before 20 min of global ischaemia; L-arginine hearts (ARG, n=6) received 1 mmol/l L-arginine for 5 min, before 20 min of global ischaemia; ischaemic preconditioning plus nitro-L-arginine methyl ester hearts (IP+L-NAME, n=6) received 2 min of ischaemic preconditioning and 5 min reperfusion with 3 mmol/l L-NAME in Krebs-Henseleit buffer, before 20 min of global ischaemia; and ischaemic preconditioning plus L-arginine hearts (IP+ARG, n=6) received 2 min of ischaemic preconditioning and 5 min reperfusion with 1 mmol/l L-arginine in Krebs-Henseleit buffer. Haemodynamic parameters and coronary flow were recorded continuously. Nitrites and nitrates (NOx) were measured 5 and 60 min after reperfusion, and infarct size was also determined.

RESULTS

In the IP+ARG group, significant amelioration and preservation of left ventricular peak developed pressure and coronary flow was observed compared with the GI, IP, ARG and IP+L-NAME groups. Infarct size in the IP+ARG group was reduced significantly compared with that in the GI, IP, ARG and IP+L-NAME groups. Significant preservation of NOx was observed during reperfusion in the IP+ARG group compared with the GI group.

CONCLUSIONS

Inhibition of NO synthase with L-NAME had little impact on ischaemic preconditioning, suggesting that endogenous NO is not a major mediator of ischaemic preconditioning. Nevertheless, enhancement of the effects of ischaemic preconditioning can be achieved with L-arginine, a precursor of NO, improving post-ischaemic functional recovery and infarct size in the isolated rat heart.

Preconditioning protects the severely atherosclerotic mouse heart

BACKGROUND

Coronary atherosclerosis has profound effects on vascular and myocardial biology, and it has been speculated that the atherosclerotic heart does not benefit from ischemic preconditioning.

METHODS

To investigate if atherosclerosis would influence the preconditioning response, Apolipoprotein E/low density lipoprotein (LDL) receptor double knockout mice (ApoE/LDLr-/-) were fed an atherogenic diet (21% fat, 0.15% cholesterol) for 6 to 8 months. At that time, extensive atherosclerotic lesions throughout the coronary tree were seen in transverse sections stained with Oil Red-O. Hearts of ApoE/LDLr-/- mice were Langendorff-perfused with 40 minutes of global ischemia and 60 minutes reperfusion, and compared with C57BL/6 controls. Preconditioning with two episodes of 2 minutes of ischemia and 5 minutes reperfusion, or exposing the mice to a hyperoxic environment (O2 > 98%) for 60 minutes before heart perfusion, was performed.

RESULTS

Hearts of mice with coronary atherosclerosis had worse postischemic function, and increased infarct size and troponin T release compared to hearts of C57BL/6 mice. Ischemic preconditioning improved postischemic ventricular function, and reduced myocardial infarct size and troponin T release in both normal and ApoE/LDLr-/- mice. The effects were most pronounced in ApoE/LDLr-/- hearts. Exposure to hyperoxia exerted a similar protection of function and cell viability of ApoE/LDLr-/- mice hearts.

CONCLUSIONS

These findings suggest that the severely atherosclerotic heart may be protected by preconditioning induced by ischemia or hyperoxia.

Stunned myocardium after off-pump coronary artery bypass grafting

Off-pump coronary artery bypass grafting is increasingly performed. Because these procedures are associated with temporary myocardial ischemia, there is a risk of ischemia-related complications. We report two cases of myocardial stunning after off-pump coronary artery bypass grafting using the Octopus tissue stabilizer. On the basis of our experiences, means to prevent stunning are discussed.

Haemodynamic changes during beating heart coronary surgery with the 'Bristol Technique'

OBJECTIVES

Optimal exposure and stabilization of the target coronary vessel is essential to allow the construction of a precise coronary anastomosis during off pump coronary surgery. However, this might be achieved at the expense of significant haemodynamic deterioration, particularly while grafting the circumflex and the posterior descending coronary arteries. The present study was designed to assess the haemodynamic changes with the beating heart positioned for grafting the three main coronaries.

METHODS

Twenty-nine consecutive patients (21 male, mean age 62.6+/-7.1 years) undergoing off pump coronary surgery were enrolled in the study. Three different surgical settings of exposure and stabilization were used according to the site of anastomosis: left anterior descending (LAD - set-up 1; n=29), posterior descending (PDA - set-up 2; n=15), and circumflex (Cx - set-up 3; n=21) coronary arteries. Haemodynamic measurements were recorded before any cardiac manipulation (baseline) in set-ups 1, 2 and 3, and immediately after the completion of each distal anastomosis with the heart returned to its anatomical position.

RESULTS

There were no marked changes in heart rate (HR) and systemic mean arterial pressure during the construction of the anastomoses for any of the three surgical settings. Set-up 1 (LAD) showed a decrease of 15.5% in stroke volume (SV) and an increase of 9% in pulmonary capillary wedge pressure (PCWP) compared to baseline (both P<0.05), with all the other haemodynamic parameters remaining unchanged. Set-up 2 (PDA) showed a marked decrease in SV and cardiac index (CI), and an increase in central venous pressure (CVP) when compared to baseline (all P<0.05). The most extensive changes were observed in set-up 3 (Cx) with a considerable reduction in SV and CI, and an increase in CVP, PCWP, pulmonary arterial pressure, and systemic vascular resistance index (all P<0.05). These haemodynamic changes were transient and totally recovered after the heart was returned to its anatomical position.

CONCLUSIONS

Exposure and stabilization of the three main coronary arteries during beating heart surgery does not produce any appreciable change in systemic blood pressure and HR. The haemodynamic deterioration observed during the construction of the circumflex and posterior descending coronary arteries distal anastomoses is transient and well tolerated with no adverse clinical events.

Pharmacological modulation, preclinical studies, and new clinical features of myocardial ischemic preconditioning

The term "ischemic preconditioning (PC)" was first applied to canine myocardium subjected to brief episodes of ischemia and reperfusion that tolerated a more prolonged episode of ischemia better than myocardium not previously exposed to ischemia. Protective effect of myocardial ischemic PC was demonstrated in several animal species, resulting in the strongest endogenous form of protection against myocardial injury, jeopardized myocardium, infarct size, and arrhythmias other than early reperfusion. New onset angina before acute myocardial infarction, episodes of myocardial ischemia during coronary angioplasty or bypass surgery, and the "warm-up" phenomenon may represent clinical counterparts of the PC phenomenon in humans. Here, we have attempted to summarize pharmacological modulation, preclinical studies, and new clinical features of ischemic PC. To date, the pathophysiological basis of the "chemical PC" is still not well established, and "putting PC in a bottle" for clinical applications still remains a new pharmacological venture.

Complete myocardial revascularization on the beating heart with epicardial stabilization: anesthetic considerations

OBJECTIVE

To describe an anesthetic management protocol for patients undergoing cardiac surgery with multiple coronary artery bypass grafts without cardiopulmonary bypass (off-pump CABG surgery) by median sternotomy with mechanical stabilization.

DESIGN

Retrospective nonrandomized analysis.

SETTING

Tertiary care hospital.

PARTICIPANTS

Sixty-six consecutive patients on whom off-pump CABG surgery by median sternotomy was attempted.

INTERVENTIONS

Anesthesia was induced with a combination of etomidate and fentanyl; pancuronium bromide was given for muscle relaxation; and anesthesia was maintained with isoflurane, desflurane, or sevoflurane in 100% oxygen. Maintenance of normothermia was attempted by keeping the room temperature at 70 degrees F, warming all fluids to 41 degrees C, and using 2.5 L/min of fresh gas flows and a heat and humidity exchanger. When available, a convective forced-air blanket was used to cover patients' head and shoulders. Patients who were not slated for revascularization of the circumflex vessels and who had good ventricular function received central venous pressure monitoring (26%); all other patients received a pulmonary artery catheter.

MEASUREMENTS AND MAIN RESULTS

Of the 66 patients, 36% required an epinephrine infusion at a mean rate of 1.45+/-2.05 microg/min intraoperatively to maintain hemodynamic stability; 25% required inotropic support for < 12 hours in the intensive care unit.

CONCLUSION

Institution of systematic hemodynamic management was associated with the successful completion of the surgical procedure in 61 patients (92%). Only 5 patients required conversion to regular CABG surgery with cardiopulmonary bypass.

The LAST operation is safe and effective: MIDCABG clinical and angiographic evaluation

BACKGROUND

The aim of this study was to prospectively evaluate the angiographic results of a cohort of consecutive patients who underwent minimally invasive coronary artery revascularization.

METHODS

From May 1997 to December 1998, 150 consecutive patients underwent left internal mammary artery to left anterior descending artery anastomosis through a left minithoracotomy on a beating heart in the Cardiovascular Department of Cliniche Gavazzeni, Bergamo, Italy. The mean age was 61.6 years (range, 36 to 84 years); 121 patients (81%) were men. Isolated left anterior descending artery disease was present in 74 patients.

RESULTS

In-hospital patency was observed in 100% of the 149 angiographically controlled patients with no anomalies in 99.3% of the anastomoses. Anastomosis was performed on a diseased tract of the target vessel in 3 patients and a stenosis of the target vessel beyond the anastomosis was documented in 3 patients. In one case early angiographic control was not performed due to death of the patient on the 1st postoperative day. The morbidity included postoperative bleeding that required reopening (3.3%) and intraoperative myocardial infarction (2%).

CONCLUSIONS

A left internal mammary artery to left anterior descending artery anastomosis on a beating heart through a left minithoracotomy is an alternative approach to myocardial revascularization. Surgical invasiveness is limited, cardiopulmonary bypass risks are avoided, and the procedure is safe and effective. In our consecutive series, postoperative angiographic controls demonstrated graft patency in all patients and very high quality anastomoses. Midterm clinical follow-up (14 months) appears favorable.

Local cardiac wall stabilization influences the reproducibility of regional wall motion during off-pump coronary artery pass surgery

OBJECTIVE

Myocardial ischemia is a risk factor during off-pump coronary artery bypass procedures. The development of new regional wall motion abnormalities assessed by transesophageal echocardiography (TEE) is a very sensitive sign of myocardial ischemia. To facilitate anastomosis, the epicardial area of the anastomosis site is often immobilized by a "stabilizer." This study was designed to investigate whether cardiac wall stabilization with an epicardial stabilizer could affect the interpretation of wall motion during coronary anastomosis without cardiopulmonary bypass.

METHODS

The TEE videotapes of 15 adult patients were investigated. Left ventricular (LV) transgastric short and long axis views were divided according to a modified 16-segment method. LV wall motion was scored using a 5-grade scale by two independent blinded investigators during pre-occlusion, occlusion, and reperfusion of anastomosed coronary arteries. The wall motion scores of a stabilized segment combined with two adjacent segments were compared with those of non-stabilized segments. Interobserver agreement was assessed using the weighted kappa statistic.

RESULTS

A total of 216 segments were analyzed by two investigators. The interobserver kappa coefficient in pre-occlusion and reperfusion periods was 0.87, 0.87 and 0.86, 0.87, respectively, indicating high agreements without stabilizer. During the occlusion period in stabilized and non-stabilized segments, it was 0.59 and 0.76, respectively, showing significantly less reproducibility in the presence of stabilizer.

CONCLUSION

Cardiac wall stabilization affects the reproducibility in the interpretation of regional wall motion during off-pump coronary artery bypass surgery. Caution should be used when monitoring for myocardial ischemia using TEE during coronary artery bypass surgery with epicardial stabilizer.

Smaller infarct after preconditioning does not predict extent of early functional improvement of reperfused heart

We evaluated the ability of ischemic preconditioning to restore function to salvaged myocardium in rabbits. Although ischemic preconditioning reduces infarct size, few investigators studying recovery of function after coronary occlusions lasting >/=30 min have reported any mechanical benefit in preconditioned hearts. However, because myocardial function was seldom evaluated beyond 5 h after reperfusion stunning may have masked the benefit. Accordingly, rabbits were chronically instrumented with a pneumatic occluder around a branch of the left coronary artery, a pair of 1-mm ultrasonic crystals in the myocardial territory destined to become ischemic, and electrocardiogram (ECG) leads. One week after surgery the ECG and segment length tracing were recorded at rest, during 30-min occlusion and 1 h of reflow, and again at 24, 48, and 72 h. In ischemically preconditioned rabbits, 5-min coronary occlusion and 10-min reperfusion preceded the long occlusion. The beginning and end of systole were determined by recording the first and second heart sounds with a hand-held precordial microphone. Postmortem infarct size was measured with triphenyltetrazolium chloride. During the 30-min coronary occlusion all segments became nearly akinetic or bulged during systole. After 60 min of reflow there was little return of function in either group. Between 24 and 72 h there was minimal recovery in the control group (segment shortening equals 13.3 +/- 4.1% of baseline), whereas function was much better in preconditioned hearts (44.2 +/- 7.4% of baseline, P < 0.02). Infarct size as a percentage of risk zone was much smaller in preconditioned hearts (10.2 +/- 1.4 vs. 29.7 +/- 1.8%, P < 0.001). Thus there is a gradual recovery of systolic function of reperfused myocardium after a coronary occlusion. Although early mechanical recovery is significantly better after preconditioning, it is much less than would be predicted by the reduction of infarct size.

Ischemic preconditioning does not acutely improve load-insensitive parameters of contractility in in vivo stunned porcine myocardium

OBJECTIVE

Ischemic preconditioning has been shown to have no beneficial effect on segment shortening in in vivo regionally stunned myocardium. The purpose of this study was to determine whether ischemic preconditioning improves the recovery of postischemic ventricular function when contractility is assessed by load-insensitive measurements including end-systolic pressure length relations, preload recruitable stroke work, and preload recruitable stroke work area in in vivo regionally stunned porcine myocardium.

METHODS

Open chest, pentobarbital-anesthetized pigs were used. Regional ventricular function was monitored by measurements of segment shortening, stroke work, end systolic pressure length relations, preload recruitable stroke work, and preload recruitable stroke work area. The control group was submitted to 15 minutes of left anterior descending coronary artery occlusion and 3 hours of reperfusion. The preconditioned group underwent 2 cycles of 5-minute left anterior descending coronary artery occlusion and 10-minute reperfusion before 15 minutes of occlusion.

RESULTS

There was no infarct in either group. The preconditioning protocol significantly depressed preischemic segment shortening but not regional stroke work. Ischemic preconditioning had no significant beneficial effect on regional stroke work, end-systolic pressure length relations, preload recruitable stroke work, or preload recruitable stroke work area.

CONCLUSIONS

These results confirm that ischemic preconditioning does not ameliorate in vivo porcine myocardial stunning and indicate that ischemic preconditioning may have a limited cardioprotective role during cardiac operation.

Intracoronary shunt insertion prevents myocardial stunning in a juvenile porcine MIDCAB model absent of coronary artery disease

OBJECTIVE

The relevance of regional LV myocardial ischemia/reperfusion induced by temporary left anterior descending (LAD) coronary artery occlusion during minimally invasive direct coronary artery bypass (MIDCAB) grafting is controversial. The purpose of our study was (1) to determine the impact of conventional LAD occlusion during left internal thoracic artery (LITA)-LAD anastomosis on regional LV myocardial ischemia and function, and (2) to evaluate if intra-LAD shunt insertion during LITA-LAD anastomosis prevents potential regional LV ischemia and dysfunction in a pig model.

METHODS

In 20 anesthetized, mechanically ventilated pigs we performed LITA-LAD anastomosis on the beating heart without cardiopulmonary bypass during either 15 min LAD occlusion (occlusion-group; n = 10) or 15 min intra-LAD shunt insertion to maintain blood supply to the myocardium beyond the anastomosis (shunt-group; n = 10). Besides standard hemodynamics we determined the global and regional LV wall motion score index (WMSI) using epimyocardial echocardiography. To quantitate structural myocardial alteration we determined the inducible heat-shock protein-70 (HSP-70) in LV anterior wall myocardial biopsies. Data were recorded at baseline, at 15 min of LAD occlusion or shunt insertion, respectively, and at 30 min of reperfusion. At the end of the experiments we determined myocardial adenine nucleotide (ATP, ADP, AMP) and glycogen content.

RESULTS

In both groups WMSI was not significantly different at 15 min LAD occlusion or shunt insertion, respectively, as compared to baseline. However, at 30 min reperfusion both global and regional WMSI demonstrated significant LV dysfunction in the occlusion-group, whereas LV function in the shunt-group remained normal. This was associated with higher myocardial HSP-70 expression in the occlusion-group (P < 0.05). Myocardial adenine nucleotide and glycogen contents were significantly better preserved in the shunt-group.

CONCLUSIONS

Our data show that in a porcine MIDCAB model 15 min LAD occlusion and 30 min reperfusion result in significant myocardial stunning. In contrast, maintenance of LAD perfusion using intracoronary shunt insertion minimizes ischemia/reperfusion injury and prevents regional LV dysfunction. Although our experiments were conducted in healthy pig hearts absent from coronary artery disease, similar results may--at least partially--be expected in humans, and thus, intracoronary shunts could be a useful tool for myocardial protection during 'off-pump revascularization'.