Beta-blockade versus Buckberg blood-cardioplegia in coronary bypass operation

Activation of complement factor B contributes to murine and human myocardial ischemia/reperfusion injury

The pathophysiology of myocardial injury that results from cardiac ischemia and reperfusion (I/R) is incompletely understood. Experimental evidence from murine models indicates that innate immune mechanisms including complement activation via the classical and lectin pathways are crucial. Whether factor B (fB), a component of the alternative complement pathway required for amplification of complement cascade activation, participates in the pathophysiology of myocardial I/R injury has not been addressed. We induced regional myocardial I/R injury by transient coronary ligation in WT C57BL/6 mice, a manipulation that resulted in marked myocardial necrosis associated with activation of fB protein and myocardial deposition of C3 activation products. In contrast, in fB-/- mice, the same procedure resulted in significantly reduced myocardial necrosis (% ventricular tissue necrotic; fB-/- mice, 20 ± 4%; WT mice, 45 ± 3%; P < 0.05) and diminished deposition of C3 activation products in the myocardial tissue (fB-/- mice, 0 ± 0%; WT mice, 31 ± 6%; P<0.05). Reconstitution of fB-/- mice with WT serum followed by cardiac I/R restored the myocardial necrosis and activated C3 deposition in the myocardium. In translational human studies we measured levels of activated fB (Bb) in intracoronary blood samples obtained during cardio-pulmonary bypass surgery before and after aortic cross clamping (AXCL), during which global heart ischemia was induced. Intracoronary Bb increased immediately after AXCL, and the levels were directly correlated with peripheral blood levels of cardiac troponin I, an established biomarker of myocardial necrosis (Spearman coefficient = 0.465, P < 0.01). Taken together, our results support the conclusion that circulating fB is a crucial pathophysiological amplifier of I/R-induced, complement-dependent myocardial necrosis and identify fB as a potential therapeutic target for prevention of human myocardial I/R injury.

Esmolol before cardioplegia and as cardioplegia adjuvant reduces cardiac troponin release after cardiac surgery. A randomized trial

Background:

Cardioplegic solutions are the standard in myocardial protection during cardiac surgery, since they interrupt the electro-mechanical activity of the heart and protect it from ischemia during aortic cross-clamping. Nevertheless, myocardial damage has a strong clinical impact. We tested the hypothesis that the short-acting beta-blocker esmolol, given immediately before cardiopulmonary bypass and as a cardioplegia additive, would provide an extra protection to myocardial tissue during cardiopulmonary bypass by virtually reducing myocardial activity and, therefore, oxygen consumption to zero.

Materials and methods:

This was a single-centre, double-blind, placebo-controlled, parallel-group phase IV trial. Adult patients undergoing elective valvular and non-valvular cardiac surgery with end diastolic diameter >60 mm and ejection fraction <50% were enrolled. Patients were randomly assigned to receive either esmolol, 1 mg/kg before aortic cross-clamping and 2 mg/kg with Custodiol® crystalloid cardioplegia or equivolume placebo. The primary end-point was peak postoperative troponin T concentration. Troponin was measured at Intensive Care Unit arrival and at 4, 24 and 48 hours. Secondary endpoints included ventricular fibrillation after cardioplegic arrest, need for inotropic support and intensive care unit and hospital stay.

Results:

We found a reduction in peak postoperative troponin T, from 1195 ng/l (690–2730) in the placebo group to 640 ng/l (544–1174) in the esmolol group (p=0.029) with no differences in Intensive Care Unit stay [3 days (1-6) in the placebo group and 3 days (2-5) in the esmolol group] and hospital stay [7 days (6–10) in the placebo group and 7 days (6–12) in the esmolol group]. Troponin peak occurred at 24 hours for 12 patients (26%) and at 4 hours for the others (74%). There were no differences in other secondary end-points.

Conclusions:

Adding esmolol to the cardioplegia in high-risk patients undergoing elective cardiac surgery reduces peak postoperative troponin levels. Further investigation is necessary to assess esmolol effects on major clinical outcomes.

Strategies for Pharmacological Organoprotection during Extracorporeal Circulation Targeting Ischemia-Reperfusion Injury

Surgical correction of congenital cardiac malformations or aortocoronary bypass surgery in many cases implies the use of cardiopulmonary-bypass (CPB). However, a possible negative impact of CPB on internal organs such as brain, kidney, lung and liver cannot be neglected. In general, CPB initiates a systemic inflammatory response (SIRS) which is presumably caused by contact of blood components with the surface of CPB tubing. Moreover, during CPB the heart typically undergoes a period of cold ischemia, and the other peripheral organs a global low flow hypoperfusion. As a result, a plethora of pro-inflammatory mediators and cytokines is released activating different biochemical pathways, which finally may result in the occurrence of microthrombosis, microemboli, in depletion of coagulation factors and haemorrhagic diathesis besides typical ischemia-reperfusion injuries. In our review we will focus on possible pharmacological interventions in patients to decrease negative effects of CPB and to improve post-operative outcome with regard to heart and other organs like brain, kidney, or lung.

Myocardial protection in cardiac surgery: a historical review from the beginning to the current topics

Myocardial protection has become an essential adjunctive measure in cardiac surgery for a couple of decades, because since the 1950s, the methods of cardioprotection (cardioplegic solutions and related procedures) have been improved by the mechanism of myocardial ischemia/reperfusion-induced damage being unveiled through the untiring efforts of researchers and clinicians. The concept of myocardial protection in cardiac surgery was proposed along with introduction of hypothermic crystalloid potassium cardioplegia in the beginning and has been diversified by pharmacological additives, blood cardioplegia, temperature modulation (warm; tepid), retrograde cardioplegia, controlled reperfusion, integrated cardioplegia, and pre-and postconditioning. This historical review summarized experimental and clinical studies dealing with the methods and results of myocardial protection in cardiac surgery, introducing the newly developed concepts for the last decade and the current topics.

Protective effect of esmolol on myocardial ischemic injury during open heart surgery in children

OBJECTIVES

To investigate the efficacy of esmolol in protecting the myocardium from ischemia during pediatric cardiac surgery.

BACKGROUND

Esmolol, an ultra-short acting beta 1-adrenoceptor blocker, reduces myocardial injury in adult cardiac operations. However, this technique is rarely used in pediatric cardiac surgery.

METHODS

Thirty children with ventricular septal defect were randomly allocated to the esmolol group and the control group. Patients received intravenous esmolol (0.05 mg·kg(-1) ·min(-1) after tracheal intubation, 0.3 mg·kg(-1) ·min(-1) during cardiopulmonary bypass (CPB) and 0.03-0.05 mg·kg(-1) ·min(-1) until the end of surgery) or placebo, respectively.

RESULTS

Plasma levels of creatine kinase-MB, cardiac troponin I in the esmolol group 2 min after completion of CPB, at the end of surgery, 4 h after surgery, and the first postoperative day were significantly lower than those in the control group. Values of heart rate 10 min after induction, 2 min before institution of CPB, 2 min after completion of CPB, and at the end of surgery were significantly lower in the esmolol group; however, mean arterial pressure, CPB time, cross-clamp time, and the rate of heart spontaneous rebeating were not statistically different between two groups. Cumulative postoperative dosage of dopamine in the esmolol group (100.1 ± 53.1 mg) was significantly less than that in the control group (171.4 ± 92.1 mg).

CONCLUSIONS

Esmolol can protect the myocardium from ischemic injury during CPB in children and significantly reduce the use of inotropic drug.

Preliminary results of supra-hepatic intraaortic perfusion with nitroglycerin for patients with significant hepatic dysfunction

BACKGROUND

Preoperative hepatic dysfunction is a risk factor for postoperative fulminant hepatic failure and death. We noted persistent hepatic artery vasospasm in patients dying of postoperative hepatic failure. We hypothesized that an intra-aortic vasodilator such as nitroglycerin could attenuate vasospasm and prevent hepatic failure.

METHODS

Nineteen consecutive patients with significant preoperative hepatic dysfunction underwent cardiac surgery using cardiopulmonary bypass with continuous infusion of intra-aortic nitroglycerin via a catheter placed above the celiac axis. Serial hepatic artery Doppler studies were done perioperatively with and without the nitroglycerin infusion on. Hepatic artery Doppler, hepatic artery size, alterations in liver function and serum creatinine, and outcomes were noted. Survival was compared to the Euroscore and a hepatic risk score that was based on a historical cohort and reported literature.

RESULTS

One patient could not be weaned off cardiopulmonary bypass. In the remaining 18 patients, reversible hepatic arterial vasospasm was noted, and this persisted at 24 hours in 12 patients and 48 hours in 7 patients. All patients had resolution of vasospasm at 72 hours. Serial paired hepatic artery diameter measurements showed a significant difference (P < .001). There was a significant reduction in mortality (5.2 %) compared to historical control and predicted mortality (logistic Euroscore 37.4%, P = .023). None of the survivors had a significant alteration in hepato-renal function.

CONCLUSION

Intra-aortic nitroglycerin can attenuate hepatic arterial vasospasm induced by cardiopulmonary bypass and preserve hepatic function. This may reduce the risk associated with cardiopulmonary bypass and surgery in patients with liver dysfunction.

Therapeutic hypothermia and prevention of acute kidney injury: a meta-analysis of randomized controlled trials

BACKGROUND

Therapeutic hypothermia has been shown to reduce neurological morbidity and mortality in the setting of out-of-hospital cardiac arrest and may be beneficial following brain injury and cardiopulmonary bypass. We conducted a systematic review to ascertain the effect of therapeutic hypothermia on development of acute kidney injury (AKI) and mortality.

METHODS

We searched for randomized controlled trials in MEDLINE through February 2011. We included trials comparing hypothermia to normothermia that reported kidney-related outcomes including, development of AKI, dialysis requirement, changes in serum creatinine, and mortality. We performed Peto fixed-effect and random-effects model meta-analyses, and meta-regressions.

RESULTS

Nineteen trials reporting on 2218 patients were included; in the normothermia group, the weighted rate of AKI was 4.2%, dialysis requirement 3.7%, and mortality 10.8%. By meta-analysis, hypothermia was not associated with a lower odds of AKI (odds ratio [OR] 1.01, 95% confidence interval [CI] 0.68, 1.51; P=0.95) or dialysis requirement (OR 0.81; 95% CI 0.30, 2.19; P=0.68); however, by meta-regression, a lower target cooling temperature was associated with a lower odds of AKI (P=0.01). Hypothermia was associated with lower mortality (OR 0.69; 95% CI 0.51, 0.92; P=0.01).

CONCLUSIONS

In trials that ascertained kidney endpoints, therapeutic hypothermia prevented neither the development of AKI nor dialysis requirement, but was associated with lower mortality. Different definitions and rates of AKI, differences in mortality rates, and concerns about the optimal target cooling temperature preclude definitive conclusions.

Targeting for cardioplegia: arresting agents and their safety

Elective temporary cardiac arrest (cardioplegia) is often required during cardiac surgery. In the 1970 s, the development of hyperkalaemic cardioplegic solutions revolutionised cardiac surgery by offering effective chemically-induced cardiac arrest and myocardial protection during global ischaemia. Despite remaining the most widely-used cardioplegic technique, hyperkalaemia can have detrimental effects due to the Na and Ca loading of the cardiac cell induced by depolarisation of the cell membrane. Efforts over the last two decades to establish better cardioplegic agents have mainly remained limited to animal experiments. The failure of these approaches to progress to clinical trials may be due to a lack of clear criteria that a cardioplegic agent should meet at a cellular level and, more importantly, at a system level. In this review we attempt to define the criteria for the optimal cardioplegic agent. We also assess the suitability and clinical potential of previously-studied cardioplegic agents and suggest cellular targets, particularly those involved in cardiac excitation-contraction coupling, that may prove to be attractive options for the development of new cardioplegic drugs. Finally, we propose a multicellular target approach using a combination of pharmacological agents in order to offer better cardioplegic solutions.

Landiolol has a less potent negative inotropic effect than esmolol in isolated rabbit hearts

PURPOSE

We compared the negative chronotropic and inotropic effects of landiolol and esmolol, two clinically available short-acting beta1-blockers with high beta1-selectivity, using whole isolated rabbit heart preparations.

METHODS

Tachycardia was induced by continuous perfusion of 10(-7) M isoproterenol, and we used concentrations of landiolol or esmolol in ascending steps (1 . 10(-6), 3 . 10(-6), 1 . 10(-5), 3 . 10(-5), and 1 x 10(-4) M). Heart rate (HR), left ventricular developed pressure (LVDP), the maximal rates of left ventricular force development (LVdP/dt(max)), and myocardial oxygen consumption (MVO2) were measured and compared.

RESULTS

Both landiolol and esmolol produced dosedependent decreases in HR, LVDP, LVdP/dt(max), and MVO2. The HR lowering effects of the two agents were comparable. At concentrations of 3 . 10(-5) and 1 . 10(-4) M, esmolol produced more profound depression of LVDP (47 +/- 26 and 12 +/- 11 mmHg, respectively; mean +/- SD) and reduction of LVdP/dt(max) (650 +/- 287 and 120 +/- 103 mmHg x s(-1)) than landiolol (68 +/- 20 and 64 +/- 20 mmHg, and 897 +/- 236 and 852 +/- 240 mmHg.s(-1), respectively). At the same concentrations, esmolol caused more profound reduction in MVO(2) (40 +/- 11 and 35 +/- 10 microl x min(-1) x g(-1)) than landiolol (50 +/- 8 and 48 +/- 8 microl x min(-1) x g(-1)), respectively.

CONCLUSION

Our results indicate that in the isolated rabbit heart, landiolol and esmolol had equipotent negative chronotropic effects, however, landiolol had a less potent negative inotropic effect than esmolol.

Benefits and harms of perioperative beta-blockade

Cardiac events in patients undergoing surgery may have serious consequences for both short- and long-term postoperative prognosis. Recently conducted trials have not demonstrated beneficial effects of perioperative beta-blockade, although originally small trials with methodological flaws did suggest this. We evaluate the evidence for using perioperative beta-blockade in both cardiac and non-cardiac surgery, and conclude that there is no statistically significant effect on mortality and insufficient evidence for a reduction of the incidence of mycocardial infarction in meta-analyses of all randomized trials. However, confidence intervals of the intervention effects in the meta-analyses are wide, leaving room for both benefits and harms. The largest observational study performed suggests that perioperative beta-blockade is associated with higher mortality in patients with low cardiac risk or diabetes, and with lower mortality in patients with high cardiac risk undergoing non-cardiac surgery. Larger randomized trials are needed to determine dosage, optimal duration, and safety of therapy, and to identify populations in whom-and how-perioperative beta-blockade may be beneficial.

Efficacy of esmolol as a myocardial protective agent during continuous retrograde blood cardioplegia

OBJECTIVE

Esmolol, an ultra-short-acting beta-blocker, is known to attenuate myocardial ischemia-reperfusion injury. The aim of this study was to compare the effects of esmolol and potassium on myocardial metabolism during continuous normothermic retrograde blood cardioplegia.

METHODS

Forty-one patients operated on for isolated aortic valve stenosis were randomly assigned to continuous coronary infusion with either potassium or esmolol during cardiopulmonary bypass. Myocardial metabolism was assessed by measuring the transmyocardial gradient of oxygen content indexed to left ventricular mass of glucose, lactate, and nitric oxide. To do so, blood samples were simultaneously withdrawn upstream (in the cardioplegia line) and downstream of the myocardium (in the left coronary ostium) 10 and 30 minutes after aortic crossclamping.

RESULTS

Although the cardioplegia flow rate and pressure were similar, esmolol markedly reduced the transmyocardial gradient of oxygen content indexed to left ventricular mass compared with potassium: 13 +/- 6 vs 20 +/- 6 mL of oxygen per liter of blood per 100 g of myocardium, respectively, at 10 minutes and 16 +/- 8 vs 24 +/- 8 mL of oxygen per liter of blood per 100 g of myocardium, respectively, at 30 minutes (P =.009). Coronary glucose and lactate transmyocardial gradients were similar in both groups, indicating adequate myocardial perfusion in all patients at all times. In addition, during retrograde cardioplegia, esmolol showed a lower nitric oxide release compared with that caused by potassium (39 +/- 49 micro mol x L(-1) for potassium vs 14 +/- 8 micro mol x L(-1) for esmolol at 10 minutes and 39 +/- 47 micro mol x L(-1) for potassium vs 6 +/- 8 micro mol x L(-1) for esmolol at 30 minutes, P =.05). However, hemodynamic parameters and plasma troponin I levels remained unchanged postoperatively between the 2 types of cardioplegia.

CONCLUSION

Esmolol provides potent myocardial protection in hypertrophied hearts, at least in part, by reducing myocardial oxygen metabolism.

Mechanisms and alternative methods of achieving cardiac arrest

Elective cardiac arrest during surgery can be achieved by inducing depolarization, polarization, or influencing calcium mechanisms. Depolarized arrest, induced by elevating the extracellular potassium concentration, is currently the most commonly used technique. However, injury associated with ionic imbalance involving sodium and calcium overload, together with maintained metabolic processes aimed at correcting these imbalances, have lead to alternatives being sought. "Polarized" arrest, induced by sodium-channel blockers or by agents that activate potassium channels, has been shown to exert equal or superior protection. Similarly, agents that induce calcium desensitization may also prove to enhance protection. These alternative techniques, however, require extensive characterization before introduction into routine clinical use can be recommended.

Myocardial protection with oxygenated esmolol cardioplegia during prolonged normothermic ischemia in the rat

OBJECTIVE

We previously showed that arrest with multidose infusions of high-dose (1 mmol/L) esmolol (an ultra-short-acting beta-blocker) in oxygenated Krebs-Henseleit buffer (esmolol cardioplegia) provided complete myocardial protection after 40 minutes of normothermic (37 degrees C) global ischemia in isolated rat hearts. In this study we investigated the importance of oxygenation for protection with esmolol cardioplegia, compared it with that of St Thomas' Hospital cardioplegia, and determined the protective efficacy of multidose esmolol cardioplegia for extended ischemic durations.

METHODS

Isolated rat hearts (n = 6/group) were perfused in the Langendorff mode at constant pressure (75 mm Hg) with oxygenated Krebs-Henseleit bicarbonate buffer at 37 degrees C. The first part of the first study had four groups: (i) multidose (every 15 minutes) oxygenated (95% oxygen/5% carbon dioxide) Krebs-Henseleit buffer during 60 minutes of global ischemia, (ii) multidose deoxygenated (95% nitrogen/5% carbon dioxide) Krebs-Henseleit buffer during 60 minutes of global ischemia, (iii) multidose oxygenated esmolol cardioplegia during 60 minutes of global ischemia, and (iv) multidose deoxygenated esmolol cardioplegia during 60 minutes of global ischemia. The second part of the first study had three groups: (v) multidose St Thomas' Hospital solution during 60 minutes of global ischemia, (vi) multidose oxygenated St Thomas' Hospital solution during 60 minutes of global ischemia, and (vii) multidose oxygenated esmolol cardioplegia during 60 minutes of global ischemia. In the second study, hearts were randomly assigned to 60, 75, 90, or 120 minutes of global ischemia and at each ischemic duration were subjected to multidose oxygenated constant flow or constant pressure infusion of (i) Krebs-Henseleit buffer (constant flow), (ii) Krebs-Henseleit buffer (constant pressure), (iii) esmolol cardioplegia (constant flow), or (iv) esmolol cardioplegia (constant pressure). All hearts were reperfused for 60 minutes, and recovery of function was measured.

RESULTS

Multidose infusion of oxygenated esmolol cardioplegia completely protected the hearts (97% +/- 5%) after 60 minutes of 37 degrees C global ischemia. Deoxygenated esmolol cardioplegia was significantly less protective (45% +/- 8%). Oxygenation of St Thomas' Hospital solution did not alter its protective efficacy in this study (70% +/- 4% vs 69% +/- 7%). Infusion of esmolol cardioplegia at constant pressure provided complete protection for 60, 75, and 90 minutes (104% +/- 5%, 95% +/- 5%, and 95% +/- 3%, respectively), whereas protection with constant-flow esmolol cardioplegic infusion was significantly decreased at ischemic durations longer than 60 minutes. This decrease in efficacy of constant-flow esmolol cardioplegia was associated with increasing coronary perfusion pressure leading to myocardial injury.

CONCLUSIONS

Oxygenation of esmolol cardioplegia (Krebs-Henseleit buffer plus 1.0 mmol/L esmolol) was essential for optimal myocardial protection. Multidose infusion of oxygenated esmolol cardioplegia provided good myocardial protection during extended periods of normothermic ischemia. Esmolol cardioplegia may provide an efficacious alternative to hyperkalemia.

Esmolol protects the myocardium and facilitates direct version intracardiac operation with a beating heart

In recent years there has been renewed interest in beating heart surgery using the ultra-active and selective beta1-blocker, esmolol. However, there has not been a report of its use in direct version intracardiac surgery with beating heart. Twenty-four patients undergoing elective direct version intracardiac surgery (mitral valve replacement) were divided randomly into 2 groups: control group (normothermia cardiopulmonary bypass (CPB) direct version intracardiac beating heart surgery) and esmolol group (normothermia CPB direct version intracardiac beating heart surgery and intravenous esmolol drip during CPB to maintain heart rate at 30-50 beats/min). Steady hemodynamic parameters were maintained in both groups; however, the doses of dopamine used in control group were larger than those for the esmolol group (p<0.01). The myocardial ultrastructure was well maintained in both group, but the scores for myocardial mitochondria, glycogen grading and counting and the amount of adenosine triphosphate were higher in the esmolol group (p<0.05). There was no significant change in the malondialdehyde level in either group (p>0.05). Using esmolol in direct version intracardiac beating heart surgery protects the myocardium and facilitates the operation.

Myocardial fluid balance

Fluid accumulation in the cardiac interstitium or myocardial edema is a common manifestation of many clinical states. Specifically, cardiac surgery includes various interventions and pathophysiological conditions that cause or worsen myocardial edema including cardiopulmonary bypass and cardioplegic arrest. Myocardial edema should be a concern for clinicians as it has been demonstrated to produce cardiac dysfunction. This article will briefly discuss the factors governing myocardial fluid balance and review the evidence of myocardial edema in various pathological conditions. In particular, myocardial microvascular, interstitial, and lymphatic interactions relevant to the field of cardiac surgery will be emphasized.

Myocardial protection: the efficacy of an ultra-short-acting beta-blocker, esmolol, as a cardioplegic agent

OBJECTIVE

During myocardial revascularization, some surgeons (particularly in the United Kingdom) use intermittent crossclamping with fibrillation as an alternative to cardioplegia. We recently showed that intermittent crossclamping with fibrillation has an intrinsic protection equivalent to that of cardioplegia. In this study we hypothesized that arrest, rather than fibrillation, during intermittent crossclamping may be beneficial. Because esmolol, an ultra-short-acting beta-blocker, is known to attenuate myocardial ischemia-reperfusion injury, we compared the protective effect of esmolol arrest with that of intermittent crossclamping with fibrillation and conventional cardioplegia (St Thomas' Hospital solution).

METHODS

Isolated rat hearts were Langendorff perfused at either constant flow (14 mL/min) or constant pressure (75 mm Hg) with oxygenated Krebs-Henseleit bicarbonate buffer (37 degrees C), and left ventricular developed pressure was assessed. In study 1 (constant flow perfusion) 8 groups (n = 6 hearts per group) were studied: (1) 40 minutes of global ischemia; (2) 2 minutes of St Thomas' Hospital infusion and 40 minutes of ischemia; (3) multidose (every 10 minutes) infusions of St Thomas' Hospital solution during 40 minutes of ischemia; (4) 2 minutes of esmolol infusion and 40 minutes of ischemia; (5) multidose (every 10 minutes) esmolol infusions during 40 minutes of ischemia; (6) continuous infusion of esmolol for 40 minutes during coronary perfusion; (7) intermittent (4 x 10 minutes) ischemia with ventricular fibrillation; and (8) intermittent (4 x 10 minutes) ischemia preceded by intermittent esmolol administration. All protocols were followed by 60 minutes of reperfusion. Further experiments (study 2) examined the esmolol administration method in hearts perfused by constant pressure.

RESULTS

An optimal arresting dose of 1.0 mmol/L esmolol was established. In study 1 recovery of left ventricular developed pressure (expressed as percentage of preischemic value) was 7% +/- 4%, 28% +/- 8%, 70% +/- 5%, 8% +/- 1%, 90% +/- 4%, 65% +/- 3%, 71% +/- 5%, and 76% +/- 5% in groups 1 to 8, respectively. Intermittent esmolol arrest with global ischemia provided equivalent myocardial protection to intermittent crossclamping with fibrillation, continuous esmolol perfusion, and multidose St Thomas' Hospital solution. Surprisingly, multidose esmolol infusion was more protective than all other treatments. In further experiments (study 2) optimal recovery was obtained with multiple esmolol infusions (by constant flow or constant pressure), but continuous esmolol infusion (at constant flow) was less effective than constant pressure infusion.

CONCLUSIONS

Intermittent arrest with esmolol did not enhance protection of intermittent crossclamping with fibrillation; however, multiple esmolol infusions during global ischemia provided improved protection. Administration (constant flow or constant pressure) of arresting solutions influenced outcome only during continuous infusion. Multidose esmolol arrest may be a beneficial alternative to intermittent crossclamping with fibrillation or conventional cardioplegia.

Ischemia increases detectable endothelial nitric oxide synthase in rat and human myocardium

The aims of the present study were to establish if myocardial ischemia/reperfusion is associated with altered eNOS activity and if myocardial eNOS detection depends on its activity. We determined detectable eNOS in (1) myocardium of isolated perfused rat hearts subjected to either global or regional ischemia and (2) in left ventricular biopsies from patients undergoing two different methods of myocardial protection (i.e., intermittent cold blood cardioplegia and continuous coronary perfusion with warm, beta-blocker-enriched blood) during coronary artery surgery. NOS detection was performed by NADPH-d staining and three eNOS-antibodies against different eNOS epitopes. In addition, activity dependent alteration of detectable eNOS was proofed by bradykinin treatment for 2 to 10 min. Ischemic and receptor mediated eNOS activation increased NADPH-d reactivity and eNOS immunoreaction as measured by antibodies against either amino acids of a central bovine eNOS domain or the human eNOS N-terminal end. In contrast, the antibody against the human eNOS C-terminal end exhibited no alteration of eNOS immunoreaction. The transient eNOS activation was associated with increased cGMP content. In human myocardium subjected to ischemia during cardiac surgery we found that early reperfusion increases eNOS activity. These data demonstrate a strong association between myocardial ischemia/reperfusion and increased eNOS activity as measured by immunocytochemical staining against specific eNOS epitopes. It appears that eNOS activation and subsequent NO release may act as a regulatory system to counter balance the potentially deleterious effects of myocardial ischemia/reperfusion.

Activation of myocardial constitutive nitric oxide synthase during coronary artery surgery

OBJECTIVE

The role of nitric oxide (NO) in myocardial ischemia/reperfusion is controversial. While some studies have shown cardioprotective effects of NO, others suggested that increased myocardial NO release secondary to ischemia may contribute to reperfusion injury. However, the impact of cardioplegia-induced myocardial ischemia/reperfusion on the activity of the NO-producing enzyme constitutive NO-synthase (cNOS or NOS-III) has not been investigated.

METHODS

Twenty elective CABG patients were randomized to receive myocardial protection using either intermittent cold blood cardioplegia with 'hot-shot' (CBC; n=10) or continuous warm blood enriched with the ultra-fast-acting beta-blocker esmolol (WBE; n=10). We collected transmural LV biopsies prior to cardiopulmonary bypass (CPB), at the end of the cross-clamp period, and at the end of CPB. Specimen were subjected to immunocytochemical staining against myocardial NOS-III and cGMP using polyclonal antibodies. NOS-III activity was determined using TV-densitometry (gray units) and cGMP content using a semiquantitative score. Global myocardial metabolism was assessed by arterio-coronary sinus lactate concentration difference (a-csD(LAC)). For LV function determination we measured the fractional area of contraction (FAC) using TEE.

RESULTS

In CBC hearts a-csD(LAC) was significantly decreased following cross-clamp removal as compared to pre-CPB indicating global ischemia during cross-clamp. In contrast, a-csD(LAC) was unchanged in WBE hearts indicating absence of relevant ischemia in this group. In CBC hearts NOS-III activity did not change from pre-CPB (35.6+/-11.1 U) to the end of the cross-clamp period (38. 0+/-8.1 U; P=0.2), but increased significantly to 48.5+/-12.1 U at the end of CPB following initial warm blood reperfusion (P=0.026). In WBE hearts NOS-III activity remained unchanged throughout (29. 2+/-10.8, 35.1+/-11.8, and 32.2+/-14.7 U, respectively; 0.3). At the end of CPB, nine CBC hearts, but only one WBE heart showed increased cGMP content (P=0.002). Compared to pre-CPB, FAC in the CBC group was 109+/-25% following weaning off CPB (P=0.26), but was slightly decreased to 87+/-22% at 4 h post-CPB (P=0.03). In the WBE group FAC remained unchanged compared to pre-CPB throughout (103+/-21 and 96+/-37%, respectively; 0.5).

CONCLUSIONS

Our data show that global myocardial ischemia and reperfusion induced by CBC is associated with myocardial NOS-III activation and increased cGMP content suggesting increased NO release. In contrast, avoidance of ischemia by use of WBE prevented NOS-III and c-GMP increase. As LV function was decreased at 4 h post-CPB in the CBC group, these data suggest that increased NO release secondary to NOS-III activation may have contributed to ischemia-reperfusion injury as has been shown experimentally.

Myocardial protection with high-dose beta-blockade in acute myocardial ischemia

OBJECTIVE

The risk of postoperative cardiac dysfunction is markedly increased by emergency coronary artery bypass grafting in the presence of acute myocardial ischemia. High dose beta-blockade during continuous coronary perfusion has been suggested as an alternative to conventional cardioplegia and this technique has been applied successfully in high risk patients for coronary artery bypass grafting (CABG) surgery. This study compared high dose beta-blockade with esmolol to continuous warm blood cardioplegia in a clinically oriented model of acute left ventricular (LV) ischemia and reperfusion.

METHODS

Twelve dogs were subjected to 60 min of regional LV ischemia by left anterior descending branch (LAD) ligation. Cardiopulmonary bypass (CPB) and aortic crossclamp were applied after 45 min of ischemia. Thereafter, high dose beta-blockade during continuous coronary perfusion (ESMO, n = 6) or antegrade continuous warm blood cardioplegia (WBC, n = 6) were maintained for 60 min. Myocardial water content (measured from endomyocardial biopsies using a microgravimetric technique), global LV function (preload recruitable stroke work: PRSW), and regional LV function (echocardiographic wall motion score) were determined at baseline and after weaning from CPB.

RESULTS

During aortic crossclamp interstitial edema formation was significantly higher in the WBC group with an average water gain of 2.2 +/- 0.49 vs. 0.76 +/- 0.12% in the ESMO group. Thereafter, edema resolved in both groups, but myocardial water gain remained significantly higher in the WBC group at 60 and 120 min post CPB (0.98 +/- 0.19 and 1.13 +/- 0.32% vs. 0.07 +/- 0.25 and 0.04 +/- 0.08%). Global LV function was significantly higher in the ESMO group at 60 and 120 min post CPB (PRSW 103 +/- 6 and 94.7 +/- 4.6% of baseline vs. 85.3 +/- 4.9 and 74.7 +/- 7.6% of baseline). However, regional LV function showed no significant difference between groups.

CONCLUSIONS

High-dose beta-blockade during continuous coronary perfusion may allow the surgeon to utilize the advantages of warm heart surgery, while avoiding the interstitial edema formation and temporary cardiac dysfunction associated with continuous warm blood cardioplegia. In high risk patients such as patients with unstable angina or after failed PTCA, high-dose beta-blockade may be an applicable alternative to cardioplegic arrest.