Optimal myocardial preservation: cooling, cardioplegia, and conditioning

Hypothermia Prevents Cardiac Dysfunction during Acute Ischemia Reperfusion by Maintaining Mitochondrial Bioenergetics and by Promoting Hexokinase II Binding to Mitochondria

Background

Hypothermia (H), cardioplegia (CP), and both combined (HCP) are known to be protective against myocardial ischemia reperfusion (IR) injury. Mitochondria have molecular signaling mechanisms that are associated with both cell survival and cell death. In this study, we investigated the dynamic changes in proapoptotic and prosurvival signaling pathways mediating H, CP, or HCP-induced protection of mitochondrial function after acute myocardial IR injury.

Methods

Rats were divided into five groups. Each group consists of 3 subgroups based on a specific reperfusion time (5, 20, or 60 min) after a 25-min global ischemia. The time control (TC) groups were not subjected to IR but were perfused with 37 °C Krebs-Ringer's (KR) buffer, containing 4.5 mM K⁺, in a specific perfusion protocol that corresponded with the duration of each IR protocol. The IR group (control) was perfused for 20 min with KR, followed by 25-min global ischemia, and then KR reperfusion for 5, 20, or 60 min. The treatment groups were exposed to 17 °C H, 37 °C CP (16 mM K⁺), or HCP (17 °C + CP) for 5 min before ischemia and for 2 min on reperfusion before switching to 37 °C KR perfusion for the remainder of each of the reperfusion times. Cardiac function and mitochondrial redox state (NADH/FAD) were monitored online in the ex vivo hearts before, during, and after ischemia. Mitochondria were isolated at the end of each specified reperfusion time, and changes in O₂ consumption, membrane potential (ΔΨ_m), and Ca²⁺ retention capacity (CRC) were assessed using complex I and complex II substrates. In another set of hearts, mitochondrial and cytosolic fractions were isolated after a specified reperfusion time to conduct western blot assays to determine hexokinase II (HKII) and Bax binding/translocation to mitochondria, cytosolic pAkt levels, and cytochrome c (Cyto-c) release into the cytosol.

Results

H and HCP were more protective of mitochondrial integrity and, concomitantly, cardiac function than CP alone; H and HCP improved post-ischemic cardiac function by (1) maintaining mitochondrial bioenergetics, (2) maintaining HKII binding to mitochondria with an increase in pAkt levels, (3) increasing CRC, and (4) decreasing Cyto-c release during reperfusion. Bax translocation/binding to mitochondria was unaffected by any treatment, regardless of cardiac functional recovery.

Conclusions

Hypothermia preserved mitochondrial function and cardiac function, in part, by maintaining mitochondrial bioenergetics, by retaining HKII binding to mitochondria via upstream pAkt, and by reducing Cyto-c release independently of Bax binding to mitochondria.

Oxygenated machine perfusion at room temperature as an alternative for static cold storage in porcine donor hearts

Background

There is a continued interest in ex situ heart perfusion as an alternative strategy for donor heart preservation. We hypothesize that oxygenated machine perfusion of donor hearts at a temperature that avoids both normothermia and deep hypothermia offers adequate and safe preservation.

Methods

Cardioplegia‐arrested porcine donor hearts were randomly assigned to six hours of preservation using cold storage (CS, n = 5) or machine perfusion using an oxygenated acellular perfusate at 21°C (MP, n = 5). Subsequently, all grafts were evaluated using the Langendorff method for 120 min. Metabolic parameters and histology were analyzed. Systolic function was assessed by contractility and elastance. Diastolic function was assessed by lusitropy and stiffness.

Results

For both groups, in vivo baseline and post‐Langendorff biopsies were comparable, as were lactate difference and myocardial oxygen consumption. Injury markers gradually increased and were comparable. Significant weight gain was seen in MP (p = 0.008). Diastolic function was not impaired in MP, and lusitropy was superior from 30 min up to 90 min of reperfusion. Contractility was superior in MP during the first hour of evaluation.

Conclusion

We conclude that the initial functional outcome of MP‐preserved hearts was transiently superior compared to CS, with no histological injury post‐Langendorff. Our machine perfusion strategy could offer feasible and safe storage of hearts prior to transplantation. Future studies are warranted for further optimization.

Cardioprotective Solutions Exposure For 1 Hour in Hypoxia and Low Temperatures Affects Vascular Reactivity Differently

INTRODUCTION

Heart preservation benefits cardiac performance after operations decreasing morbidity but the contribution of the vascular reactivity has been neglected.

METHODS

We evaluated whether cardioprotective solutions, Krebs-Henseleit (KH), Bretschneider-HTK (BHTK), St. Thomas No. 1 (STH-1), and Celsior (CEL), affect vascular reactivity. Methods: Aortic rings from Wistar rats were used in two protocols. First, the rings were exposed to BHTK, STH-1 or CEL for 1 hour of hypoxia at 37 °C. Second, the rings were exposed to 10 °C or 20 °C for 1 hour under hypoxia. After treatment, the rings were immersed in KH at 37 °C, endothelial integrity was tested and concentration- response curves to phenylephrine were performed.

RESULTS

In the first protocol, the solutions did not damage the endothelium; CEL and BHTK reduced KCl-induced contractions but not STH- 1; only CEL and BHTK reduced vascular reactivity; there was a positive correlation between Rmax and KCl concentration. At 20 °C, 1 hour under hypoxia, the solutions produced similar KCl-induced contractions without endothelial damage. CEL, BHTK and STH-1 decreased vascular reactivity. At 10 °C, STH-1 increased reactivity but CEL and BHTK decreased. After 1 hour under hypoxia in CEL or BHTK solutions, reactivity was similar at different temperatures. At 20 °C, endothelial damage after exposure to STH-1 produced more vasoconstriction than CEL and BHTK. However, at 10 °C, endothelial damage after CEL and BHTK exposure elicited more vasoconstriction while STH-1 showed a small vasoconstrictor response, suggesting endothelial damage.

CONCLUSION

STH-1 decreased reactivity at 20 °C and increased at 10 °C. CEL promoted greater endothelial modulation at 10 °C than at 20 °C, while STH-1 promoted higher modulation at 20 °C than at 10 °C. Vascular tone was reduced by CEL and BHTK exposure, also depending on the KCl concentration.

Akt is a critical node of acute myocardial insulin resistance and cardiac dysfunction after cardiopulmonary bypass

AIMS

Acute myocardial insulin resistance is an independent risk factor for patients who undergo cardiac surgery with cardiopulmonary bypass (CPB). However, the underlying mechanism of insulin resistance during CPB has not been fully investigated.

MATERIALS AND METHODS

To explore the role of myocardial insulin resistance on the cardiac function and its underlying mechanism, CPB operation and pharmacological intervention were applied in mini pigs, and myocardial insulin signaling, glucose uptake, ATP production and cardiac function were examined.

KEY FINDINGS

Our data showed that CPB elicited not only hyperglycemia and hyperinsulinemia, but also inactivated Akt, and impaired the transposition of membrane glucose transporter-4 (GLUT-4), reduced glucose uptake and ATP production in the myocardium as well, which in turn was accompanied with cardiac dysfunction. Meanwhile, linear correlations were established among reduced myocardial glucose uptake, ATP production, and depressed cardiac systolic or diastolic function. Reactivation of Akt by SC79, an Akt agonist, partially alleviated myocardial insulin resistance and restored post CPB cardiac function via augmenting myocardial glucose uptake and ATP production.

SIGNIFICANCE

These findings revealed that acute myocardial insulin resistance due to inactivation of Akt played a key role in cardiac dysfunction post CPB via suppressing glucose metabolism related energy supply.

Deleterious effect of hypothermia in myocardial protection against cold ischemia: a comparative study in isolated rat hearts

BACKGROUND

There is a growing need to improve heart preservation benefit the performance of cardiac operations, decrease morbidity, and more important, increase the donor pool. Therefore, the objective of this study was to evaluate the cardioprotective effects of Krebs-Henseleit buffer (KHB), Bretschneider-HTK (HTK), St. Thomas No. 1 (STH-1), and Celsior (CEL) solutions infused at 10°C and 20°C.

METHODS

Hearts isolated from male albino Wistar rats and prepared according to Langendorff were randomly divided equally into 8 groups according to the temperature of infusion (10°C or 20°C) and cardioprotective solutions (KHB, HTK, STH-1, and CEL). After stabilization with KHB at 37°C, baseline values were collected (control) for heart rate (HR), left ventricle systolic pressure (LVSP), coronary flow (CF), maximum rate of rise of left ventricular pressure during ventricular contraction (+dP/dt) and maximum rate of fall of left ventricular pressure during left ventricular relaxation (-dP/dt). The hearts were then perfused with cardioprotective solutions for 5 minutes and kept for 2 hours in static ischemia at 20°C. Data evaluation used analysis of variance (ANOVA) in all together randomized 2-way ANOVA and Tukey's test for multiple comparisons. The level of significance chosen was P < .05.

RESULTS

We observed that all 4 solutions were able to recover HR, independent of temperature. Interestingly, STH-1 solution at 20°C showed HR above baseline throughout the experiment. An evaluation of the corresponding hemodynamic values (LVSP, +dP/dt, and -dP/dt) indicated that treatment with CEL solution was superior at both temperatures compared with the other solutions, and had better performance at 20°C. When analyzing performance on CF maintenance, we observed that it was temperature dependent. However, when applying both HTK and CEL, at 10°C and 20°C respectively, indicated better protection against development of tissue edema. Multiple comparisons between treatments and hemodynamic variable outcomes showed that using CEL solution resulted in significant improvement compared with the other solutions at both temperatures.

CONCLUSION

The solutions investigated were not able to fully suppress the deleterious effects of ischemia and reperfusion of the heart. However, these results allow us to conclude that temperature and the cardioprotective solution are interdependent as far as myocardial protection. Although CEL solution is the best for in myocardial protection, more studies are needed to understand the interaction between temperature and perfusion solution used. This will lead to development of better and more efficient cardioprotective methods.

Comparative analysis of the performance of various crystalloid cardioplegic solutions on myocardial protection after prolonged cold ischemia

INTRODUCTION

The quality and effectiveness of myocardial protection are fundamental problems to expand the use of and consequently good outcomes of donated hearts for transplantation.

OBJECTIVE

The purpose of this investigation was to compare the cardioprotective effects of Krebs-Henseleit, Bretschneider-HTK, St Thomas, and Celsior solutions using a modified nonrecirculating Langendorff column model of isolated perfused rat heart during prolonged cold storage.

MATERIALS AND METHODS

After removal 36 rat hearts underwent isolated perfusion into a Langendorff apparatus using Krebs-Henseleit solution for a 15-minute period of recovery; we excluded organs that did not maintain an aortic pressure above 100 m Hg. Subsequently, we equally distributed the hearts into four groups according to the cardioprotection solution; group 1, Krebs-Henseleit (control); group II, Bretschneider-HTK; group III, St Thomas; and group IV, Celsior. Each heart received the specific cardioplegic solution at 10°C for 2-hour storage at 20°C, before a 15 minutes perfusion with Krebs-Henseleit solution for recovery and stabilization. After 60 additional minutes of perfusion, every 5 minutes we determined heart rate (HR), coronary flow (CF), left ventricular systolic pressure (LVSP), and positive and negative peak of the first derivative of left ventricular pressure (+dP/dt and -dP/dt, respectively).

RESULTS

Comparative analysis by Turkey's test showed the following performances among the groups at 60 minutes of reperfusion: HR: II = IV > III > I; CF: II = IV > I = III; LVSP: IV > I = II = III; +dP/dt: IV > I = II = III; and -dP/dt: IV = II > I = II.

CONCLUSION

Cardioprotective solutions generally used in clinical practice are not able to avoid hemodynamic alterations in hearts exposed to prolonged ischemia. Celsior solution showed better performance than Bretschneider-HTK, St Thomas, and Krebs-Henseleit.

Modulation of mitochondrial bioenergetics in the isolated Guinea pig beating heart by potassium and lidocaine cardioplegia: implications for cardioprotection

Mitochondria are damaged by cardiac ischemia/reperfusion (I/R) injury but can contribute to cardioprotection. We tested if hyperkalemic cardioplegia (CP) and lidocaine (LID) differently modulate mitochondrial (m) bioenergetics and protect hearts against I/R injury. Guinea pig hearts (n = 71) were perfused with Krebs Ringer's solution before perfusion for 1 minute just before ischemia with either CP (16 mM K) or LID (1 mM) or Krebs Ringer's (control, 4 mM K). The 1-minute perfusion period assured treatment during ischemia but not on reperfusion. Cardiac function, NADH, FAD, m[Ca], and superoxide (reactive oxygen species) were assessed at baseline, during the 1-minute perfusion, and continuously during I/R. During the brief perfusion before ischemia, CP and LID decreased reactive oxygen species and increased NADH without changing m[Ca]. Additionally, CP decreased FAD. During ischemia, NADH was higher and reactive oxygen species was lower after CP and LID, whereas m[Ca] was lower only after LID. On reperfusion, NADH and FAD were more normalized, and m[Ca] and reactive oxygen species remained lower after CP and LID. Better functional recovery and smaller infarct size after CP and LID were accompanied by better mitochondrial function. These results suggest that mitochondria may be implicated, directly or indirectly, in protection by CP and LID against I/R injury.

Erythropoietin reduces necrosis in critically ischemic myocutaneous tissue by protecting nutritive perfusion in a dose-dependent manner

BACKGROUND

Erythropoietin (Epo), the primary regulator of erythropoiesis, has recently been shown to exert antiinflammatory and antiapoptotic properties in neuronal and myocardial tissue. We herein studied whether Epo pretreatment can reduce cell death and ischemic necrosis in a chronic in vivo model.

METHODS

C57BL/6 mice were treated daily for 3 consecutive days with either 500 IU EPO/kg body weight (bw) (group Epo 500, n = 8) or 5000 IU EPO/kg bw (group Epo 5000, n = 8) administered intraperitoneally 24 hours before surgery. Thereafter, a random pattern myocutaneous flap subjected to acute persistent ischemia was elevated and fixed into a dorsal skinfold chamber. Flap elevation in animals receiving the water-soluble vitamin E analog Trolox (6-hydroxy-2, 5, 7, 8-tetramethylchroman-2-carboxylic acid) served as a nonspecific antiinflammatory agent control group (Tro); untreated control animals (Con) received saline only. Capillary perfusion, leukocyte-endothelial cell interaction, apoptotic cell death, and tissue necrosis were determined over a 10-day observation period using intravital multifluorescence microscopy.

RESULTS

Epo 5000 (44 +/- 26 cm/cm(2)) but, more noticeably, Epo 500 (116 +/- 32 cm/cm(2)) improved capillary perfusion compared with the two control groups, particularly the Con group (9 +/- 7 cm/cm(2); P < .05). The ischemia-associated leukocytic inflammation was found drastically attenuated in both Epo-pretreatment groups. Epo 500 further decreased apoptotic cell death and was effective in significantly reducing tissue necrosis (16% +/- 4% vs Tro: 48% +/- 7% and Con: 52% +/- 4%; P < .001). No angiogenic blood vessel formation could be observed in either of the Epo groups. Of interest, Epo 5000-but not Epo 500-increased systemic hematocrit.

CONCLUSION

Despite the lack of neovascularization, Epo pretreatment was capable of reducing ischemic tissue necrosis by protecting capillary perfusion, ie, nutrition of the tissue. Low-dose pretreatment was more effective, a result that was most likely due to the better perfusion conditions without an increase of the hematocrit values. Thus, low-dose Epo pretreatment might represent a promising strategy to protect critically perfused ischemic tissue.

Purine metabolism and release during cardioprotection with hyperkalemia and hypothermia

This work investigates whether purine metabolism and release is related to cardioprotection with hyperkalemia and hypothermia. Langendorff guinea-pig hearts were used to either monitor metabolism during ischemia or to measure functional recovery, myocardial injury and release of purine during reperfusion. Hearts underwent 30 min ischemia using one of the following protocols: control (normothermic buffer), hyperkalaemia (high-potassium buffer), hypothermia (20 degrees C) and hyperkalemia + hypothermia. At the end of 30 min ischemia, hyperkalemia was associated with similar metabolic changes (rise in purine and lactate and fall in adenine nucleotides) to control group. Accumulation of purine was due to a rise in inosine, xanthine and hypoxanthine and was largely prevented by hypothermia and hyperkalemia + hypothermia. Upon reperfusion, there was a time-dependent release of all purine, lactate and AMP. A fast (peak in less than 20 sec) release of inosine, xanthine, hypoxanthine and lactate was highest in control followed by hyperkalemia then hypothermia and little release in hyperkalemia + hypothermia. Adenosine and AMP release was slow (peak at 3 min), only significant in control and was likely to be due to sarcolemmal disruption as the profile followed lactate dehydrogenase release. Recovery (left ventricular developed pressure) was 63% control, 82% hyperkalemia, 77% hypothermia and 98% for hyperkalemia + hypothermia. The loss of purine during reperfusion but not their production during ischemia is related to cardioprotection with hyperkalemia. The possibility that the consequences of hyperkalemia modulate a sodium-dependent purine efflux, is discussed. The reduced loss of purine in hypothermia or in hyperkalemia + hypothermia is likely to be due to a lower metabolic activity during ischemia.

Preservation of myocardial energy status by bovine hemoglobin solutions during ischemia

Compared to murine and human hemoglobin, bovine hemoglobin has a less exothermic oxygen binding and delivers oxygen even at low temperatures. This property could improve oxygen availability for myocytes during hypothermic arrest of hearts. The aim of this study was to evaluate the advantage of using cardioplegic solutions enriched with bovine hemoglobin when storing rat hearts. Hearts excised from rats after perfusion with different cardioplegic solutions (Celsior, Celsior plus 4% human hemoglobin, Celsior plus 4% and 8% bovine hemoglobin) were compared. Biopsies were obtained from the beating hearts before cardioplegic infusion and during a 48 h period of cold storage. Adenosine triphosphate, its catabolites and markers of oxidative stress were measured as indices of preservation. The results show that bovine hemoglobin-enriched solutions highly improve adenosine triphosphate content, decreasing its catabolites; no significant changes in antioxidant status were evident. The statistically significant difference was evident up to 6 h of storage. Doubling the concentration of bovine hemoglobin produces only slight improvement. Alternative hemoglobins with different properties may improve and prolong heart storage. As bovine hemoglobin delivers oxygen even at low temperatures, it improves energy content and anabolic reactions, without decreasing oxidative stress.

Role of apoptosis in myocardial stunning after open heart surgery

BACKGROUND

Myocardial preservation during open heart surgery is a subject of intense investigation. A prerequisite for further improvement is a better understanding of the underlying pathophysiologic mechanisms responsible for postoperative myocardial stunning. In this report, we analyzed the role of apoptosis in myocardial stunning.

METHODS

Myocardial samples were obtained from 11 patients undergoing elective coronary artery bypass grafting before (control) and after cardioplegic arrest and reperfusion. Specimens were examined for apoptosis by electron microscopy, in situ end-labeling of DNA fragments, and biochemically for mitochondrial cytochrome c release.

RESULTS

Electron microscopy revealed condensation and margination of nuclear chromatin after surgery, as well as swelling and membrane rupture in mitochondria of single myocytes surrounded by healthy cells. TUNEL-positive cells were also found. Cytochrome c release, an initial step in apoptosis, revealed a 3.4 +/- 0.4-fold increase during surgery (p < 0.0001). Furthermore, cytochrome c release from otherwise intact mitochondria showed a negative correlation with left ventricular function and a positive correlation with the duration of cardioplegic arrest and reperfusion (p < 0.05).

CONCLUSIONS

Our data demonstrate that programmed cell death is evident early after open heart surgery and correlates with declining cardiac contractility. We conclude that apoptosis may be an important mechanism in postoperative myocardial stunning.

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

BACKGROUND

Preservation of right ventricular myocardium is unsatisfactory in patients with critical stenosis or occlusion of the right coronary artery. The aim of this study was to investigate whether ischemic preconditioning (IP) improved the recovery of right ventricular function after coronary artery bypass grafting.

METHODS

Forty patients with three-vessel disease who had coronary artery bypass grafting were randomly assigned to the IP group (n = 20) or control group (n = 20). In the IP group, two cycles of two minutes of ischemia after three minutes of reperfusion were given before cross-clamping. Hemodynamic data were collected. Right ventricular ejection fraction was measured by thermodilution.

RESULTS

Right ventricular ejection fraction and right ventricular systolic volume index were decreased post-operatively (lowest value at 6 hours postoperatively). The changes in right ventricular ejection fraction were significantly milder in the IP group postoperatively (p = 0.012). The decrease in right ventricular systolic volume index postoperatively was also less in IP patients (p = 0.002). Fewer inotropic drugs were used in the IP group compared with controls.

CONCLUSIONS

Ischemic preconditioning had a myocardial protective effect on recovery of right ventricular contractility in patients who had coronary artery bypass grafting.

Bench to bedside: tumor necrosis factor-alpha: from inflammation to resuscitation

Proinflammatory mediators such as tumor necrosis factor-alpha (TNF) have been implicated in the pathophysiology in a number of acute disease states. Tumor necrosis factor-alpha can contribute to cell death, apoptosis, and organ dysfunction. Tumor necrosis factor-alpha can be generated with sepsis or ischemia-reperfusion by activation of cell mitogen-activated protein kinases and nuclear factor kappa B, leading to TNF production. A number of strategies to modulate TNF have been recently explored, including factors directed toward mitogen-activated protein kinases, TNF transcription, anti-inflammatory ligands, heat shock proteins, and TNF-binding proteins. However, TNF may also play an important role in the adaptive response to injury and inflammation. Control of the deleterious effects of TNF and other proinflammatory cytokines represents a realistic goal for clinical emergency medicine. The purpose of this article is to provide a background of relevance to emergency medicine academicians on the production and regulation of TNF, the acute effects of TNF on pathophysiology, and the rationale for therapeutic interventions directed toward TNF and the clinical experience with these strategies.

Multi-dose crystalloid cardioplegia preserves intracellular sodium homeostasis in myocardium

The goal of this study was to assess the effect of multi-dose St Thomas' cardioplegia on intracellular sodium homeostasis in a rat heart model. A new magnetic resonance method was applied which enable us to detect intracellular Na changes without chemical shift reagents. Three groups of isolated rat hearts were subjected to 51 min of ischemia and 51 min of reperfusion at 37 degrees C: Group 1-three infusions of St Thomas' cardioplegia every 17 min for 2 min (n=7); Group 2-single-dose infusion of cardioplegia at the beginning of stop-flow ischemia (n=8); and Group 3-clamp ischemia (n=3) without cardioplegia administration. Performance of the heart was assessed by rate-pressure product relative to the pre-ischemic level (RPP). An NMR method was applied which continuously detects the Na(i) concentration in the heart, using the ability of bound sodium to exhibit triple-quantum transitions and the growth of the corresponding signal when sodium ions pass from extracellular to intracellular space. Clamp ischemia without cardioplegia and 50 min of reperfusion left the heart dysfunctional, with Na(i) growth from the pre-ischemic level of 13.9+/-1.2 mM to 34.9+/-1.3 mM and 73. 9+/-1.9 mM at the end of ischemia and reperfusion, respectively. During single-dose cardioplegia the corresponding values for Na(i) were 30.2+/-1 mM and 48.5+/-1.7 mM (RPP=29%). Multiple infusions of cardioplegic solution resulted in a remarkable preservation of the heart's intracellular Na concentration with a non-significant increase in Na(i) during ischemia and only 16.7+/-1 mM, (P=0.01), after subsequent reperfusion (RPP=85%). The time course of Na(i) changes in the rat heart model demonstrates a prominent potential of multi-dose St Thomas' cardioplegia in preserving intracellular sodium homeostasis at 37 degrees C. The growth of Na(i) concentration during ischemia, as an indicator of the viability of the myocytes, can have a prognostic value for the heart's performance during reperfusion.

ATP-sensitive potassium channel activation mimics the protective effect of ischaemic preconditioning in the rat isolated working heart after prolonged hypothermic storage

1. Ischaemic preconditioning (IP) can significantly reduce the extent of infarct size, contractile dysfunction and necrosis in hearts from a number of animal species. Activation of ATP-sensitive potassium channels has been implicated in this process. The aims of the present study were to determine the extent to which IP preserves haemodynamic function in the rat isolated working heart model after prolonged hypothermic storage and to examine the involvement of activation of potassium channels in this process. 2. Hearts from Wistar rats were perfused on a Langendorff apparatus. After stabilization in working mode, baseline measurements of heart rate, aortic flow, coronary flow and cardiac output were performed. Hearts were randomized to one of six treatment groups: (i) untreated control; (ii) IP; (iii) 3 min perfusion with 200 mumol/L pinacidil; (iv) pinacidil vehicle; (v) 3 min perfusion with 10 mumol/L glibenclamide before IP; and (vi) 3 min perfusion with glibenclamide then pinacidil. Hearts were stored in an extracellular-based preservation solution for 6 or 12 h at 2-3 degrees C, remounted on the perfusion apparatus, stabilized as before and then haemodynamic measurements were repeated, after which time heart water contents were determined. 3. Recovery of haemodynamic function was markedly enhanced in the IP and pinacidil-treated groups compared with untreated and vehicle controls. These beneficial effects were completely blocked by glibenclamide. These results suggest that strategies for activating potassium channels in donor hearts may protect organs during hypothermic storage prior to transplantation.

Protective action of 17beta-estradiol in cardiac cells: implications for hyperkalemic cardioplegia

BACKGROUND

Hyperkalemic cardioplegic solutions effectively arrest the heart, but may also induce intracellular Ca2+ loading and cellular hypercontracture, which could contribute to ventricular dysfunction associated with global surgical ischemia. Recently, it has been proposed that 17beta-estradiol may possess protective properties in the ischemic myocardium. The purpose of the present study was to examine the action of 17beta-estradiol on cardiac cells exposed to hyperkalemic stress.

METHODS

Single ventricular cardiomyocytes, a preparation devoid of vascular and neuronal elements, were isolated from guinea pig hearts, loaded with a Ca2+-sensitive fluorescent probe, and imaged by digital epifluorescent microscopy. The emitted fluorescence of the probe, a measure of intracellular Ca2+ concentration, and cell length were simultaneously recorded during hyperkalemic challenge, in the absence or presence of 17beta-estradiol.

RESULTS

In control cardiomyocytes, the cytosolic concentration of Ca2+ was 138+/-11 nmol/L and cell length 93+/-11 microm. Exposure to high K+ (+16 mmol/L KCl) significantly increased cytosolic Ca2+ to 2,191+/-87 nmol/L (p < 0.001), and produced cell shortening (length at 39+/-5 microm; p < 0.001). 17beta-Estradiol (10 micromol/L) acutely prevented high K+ to induce either intracellular Ca2+ loading (144+/-13 nmol/L, p < 0.001) or hypercontracture (91+/-10 microm, p < 0.001). Tamoxifen (10 micromol/L), an antiestrogen, abolished the protective effect of 17beta-estradiol.

CONCLUSIONS

We conclude that 17beta-estradiol prevents hyperkalemia-induced Ca2+ loading and hypercontracture through a direct and tamoxifen-sensitive action in cardiomyocytes. This study raises the possibility that 17beta-estradiol should be considered as a cardioprotective adjunct toward a safer hyperkalemic cardioplegia.

Tumor necrosis factor in the heart

The heart is a tumor necrosis factor (TNF)-producing organ. Both myocardial macrophages and cardiac myocytes themselves synthesize TNF. Accumulating evidence indicates that myocardial TNF is an autocrine contributor to myocardial dysfunction and cardiomyocyte death in ischemia-reperfusion injury, sepsis, chronic heart failure, viral myocarditis, and cardiac allograft rejection. Indeed, locally (vs. systemically) produced TNF contributes to postischemic myocardial dysfunction via direct depression of contractility and induction of myocyte apoptosis. Lipopolysaccharide or ischemia-reperfusion activates myocardial P38 mitogen-activated protein (MAP) kinase and nuclear factor kappa B, which lead to TNF production. TNF depresses myocardial function by nitric oxide (NO)-dependent and NO-independent (sphingosine dependent) mechanisms. TNF activation of TNF receptor 1 or Fas may induce cardiac myocyte apoptosis. MAP kinases and TNF transcription factors are feasible targets for anti-TNF (i.e., cardioprotective) strategies. Endogenous anti-inflammatory ligands, which trigger the gp130 signaling cascade, heat shock proteins, and TNF-binding proteins, also control TNF production and activity. Thus modulation of TNF in cardiovascular disease represents a realistic goal for clinical medicine.

Antegrade cold blood cardioplegia is not demonstrably advantageous over cold crystalloid cardioplegia in surgery for congenital heart disease

OBJECTIVE

The superiority of blood cardioplegia in pediatric cardiac surgery has not previously been challenged in a controlled clinical trial. The purpose of this study was to compare antegrade cold blood versus cold crystalloid cardioplegia in pediatric cardiac surgery.

METHODS

One hundred thirty-eight pediatric patients (mean age 32 months; 95% CL 24.2 to 39.8 months; range 1 day to 15 years) were prospectively randomized to receive either cold blood (4:1 dilution, blood/Plegisol, potassium chloride 15 mEq/L; n = 62) or cold crystalloid (Plegisol; n = 76) cardioplegic solution during a variety of operations for congenital heart disease. Multiple doses of cold (4 degrees C) cardioplegic solution was administered antegradely in addition to topical cooling during ischemic arrest. Myocardial recovery and outcome measures were assessed by five clinical end points: (1) inotropic support, (2) echocardiographic assessment of ventricular function, (3) overall complication rate, (4) length of stay in the intensive care unit, and (5) 30-day survival. Multiple logistic regression and multivariate analysis of variance were used to investigate which of the following clinical determinants were contributory: (1) cardioplegia, (2) urgency of operation, (3) aortic crossclamp time, (4) age, and (5) cyanosis. Population data did not differ between the two cardioplegia groups (p > 0.05).

RESULTS

The most important clinical determinant of studied end points was the aortic crossclamp time (p < 0.05). The type of cardioplegic solution (blood vs crystalloid) was less important (p > 0.05). The only statistically significant difference between blood and crystalloid cardioplegia for the measured clinical end points was the level of intraoperative inotropic support (p < 0.05), although this did not correlate with any significant differences in measured ventricular function.

CONCLUSION

Our results suggest no clear clinical advantage of antegrade cold blood cardioplegia over crystalloid cardioplegia during hypothermic cardioplegic arrest in pediatric cardiac surgery. The aortic crossclamp time was the strongest predictor of measured outcomes.

Mechanism of constant contractile efficiency under cooling inotropy of myocardium: simulation

We have reported that, in canine hearts, cardiac cooling to 29 degrees C enhanced left ventricular contractility but changed neither the contractile efficiency of cross-bridge (CB) cycling nor the excitation-contraction coupling energy. The mechanism of this intriguing energetics remained unknown. To get insights into this mechanism, we simulated myocardial cooling mechanoenergetics using basic Ca2+ and CB kinetics. We assumed that both adenosinetriphosphatase (ATPase)-dependent sarcoplasmic reticulum (SR) Ca2+ uptake and CB detachment decelerated with cooling. We also assumed that all the ATPase-independent SR Ca2+ release, Ca2+ binding to and dissociation from troponin, and CB attachment remained unchanged. The simulated cooling shifted the CB force-free Ca2+ concentration curve to a lower Ca2+ concentration, increasing the Ca2+ responsiveness of CB force generation, and increased the maximum Ca(2+)-activated force. The simulation most importantly showed that these cooling effects combined led to a constant contractile efficiency when Ca2+ uptake and CB detachment rate constants changed appropriately. This result seems to account for our experimentally observed constant contractile efficiency under cooling inotropy.

Adaptive and maladaptive mechanisms of cellular priming

OBJECTIVE

The mechanisms of cellular priming resulting in both adaptive and maladaptive responses to subsequent injury and strategies for manipulating this priming to constructive therapeutic advantage are explored.

BACKGROUND DATA

A cell is prepared or educated by an initial insult (priming stimulus). Investigations in both laboratory animals and humans indicate that cells, organs, and perhaps even whole patients respond differently to a proximal second insult ("second hit") by virtue of this prior environmental history. The opportunity to achieve the primed state appears to be conserved across almost all cell types. The initial stimulus transmits a message to the cellular machinery that influences the cell's response to a subsequent challenge. This response may result in an exaggerated inflammatory response in the case of the neutrophil (an often maladaptive process) or an improved tolerance to injury by the myocyte (adaptive response). Our global hypothesis is that cellular priming is a conserved, receptor-dependent process that invokes common intracellular targets across multiple cell types. We further postulate that these targets create a language based on the transient phosphorylation and dephosphorylation of intracellular enzymes that is therapeutically accessible.

CONCLUSIONS

Priming is a conserved, receptor-dependent process transduced by means of intracellular targets across multiple cell types. The potential therapeutic strategies outlined involve the receptor-mediated manipulation of cellular events. These events are transmitted through an intracellular language that instructs the cell regarding its behavior in response to subsequent stimulation. Understanding these intracellular events represents a realistic goal of priming and preconditioning biology and will likely lead to clinical control of the primed state.

Mechanisms of cardiac preconditioning: ten years after the discovery of ischemic preconditioning

Cardiac preconditioning describes the phenomenon by which transient ischemia induces myocardial protection against subsequent ischemia and reperfusion injury. Ten years have passed since the original description of this potent cardiac protective strategy and within this period tremendous progress has been made elucidating the mechanisms of preconditioning. Mechanistic understanding may allow safe clinical application. This review (1) recalls the history of preconditioning and how it relates to the history of the investigation of endogenous adaptation; (2) summarizes the current mechanistic understanding of early preconditioning; (3) compares and contrasts the mechanisms of early versus delayed preconditioning; (4) suggests potential anti-inflammatory aspects of preconditioning; (5) examines limitations in laboratory models of preconditioning; and (6) explores the potential of using preconditioning clinically.

Left ventricular diastolic function after coronary artery bypass grafting: a correlative study with three different myocardial protection techniques

BACKGROUND

This study was designed to examine the effect of myocardial protection on diastolic function after cardiac operations.

METHODS

Subjects were patients with normal preoperative diastolic function who were scheduled for coronary artery bypass grafting. Group I received anterograde cardioplegia; group II received anterograde and retrograde cardioplegia; and group III was protected with ventricular fibrillation and intermittent aortic crossclamping. Operations were performed with mild hypothermia and ventricular venting through the left superior pulmonary vein in all cases. Left ventricular diastolic function was evaluated with pulsed-wave Doppler transesophageal echocardiography (samples at the mitral valve leaflet: four-chamber view) and left superior pulmonary vein flow velocity. The flow patterns were stored on videotape and sent to an independent investigator for analysis. Left ventricular ejection fraction was calculated with transesophageal echocardiography (short-axis view, two-dimensional and M-mode).

RESULTS

Left ventricular diastolic function, as measured by the ratio between the peak velocities during early filling and atrial contraction and by systolic diastolic superior pulmonary venous flow ratio, was significantly impaired in all three groups 5 minutes after discontinuation of cardiopulmonary bypass. At 1 hour after operation, these values had returned to control levels only in group III. There was an increased incidence of supraventricular arrhythmias in group III. There were no significant hemodynamic differences among the three groups.

CONCLUSIONS

Left ventricular diastolic function was severely impaired after cardiopulmonary bypass. The degree of impairment depended on the myocardial protection used. The impairment in diastolic function was less when ventricular fibrillation and intermittent aortic crossclamping were used, and greater when anterograde and retrograde cardioplegia were used.

Protein kinase C isoform diversity in preconditioning

Protein kinase C (PKC) appears to be a common intracellular effector and signal collector during cardiac preconditioning; however, it remains unknown whether agonists that activate different PKC isoforms are also linked to select aspects of myocardial protection. Using agonists that are known to activate unique combinations of PKC isoforms, we interrogated the relationship between isoform activation and the different aspects (pH, function, and viability) of endogenous myocardial protection. To study this, isolated rat hearts were subjected to ischemia-reperfusion (I/R) (20 min/40 min), without (control = Ctrl) or with receptor-dependent [phenylephrine (PE), 50 microM; adenosine (ADO), 125 microM] or -independent [phorbol myristate acetate (PMA), 100 nM] activation of PKC. Function, pH, and viability were assessed by rate pressure product (%RPP) and coronary flow (CF; ml/min), by 31P NMR, and by CF creatine kinase (CK; U/liter) leak, respectively. PMA, which activates PKC delta but not eta, resulted in intracellular pH (pHi) and viability protection, but did not protect against postischemic myocardial stunning. ADO, which activates PKC eta but not delta, protects against stunning, but not acidosis or necrosis. PE, which activates PKC delta and eta, provided global myocardial protection against necrosis, acidosis, and stunning. Different PKC isoforms may be linked to distinct aspects of myocardial protection. Targeted activation of PKC isoforms may allow precise mechanistic application of preconditioning-like myocardial protection.

Myocardial protection for cardiac surgery: the nursing perspective

The advancement of myocardial protection techniques is considered to be the most instrumental in achieving successful cardiac surgical outcomes. Although many issues complicate the efficacy of myocardial protection, warm cardioplegia is instituted more often as a better myocardial protection method for patients undergoing cardiac surgery. Understanding differences in patient response between warm and cold cardioplegia is essential for development of appropriate nursing intervention strategies and prevention of postoperative complications. Advanced practice nurses in cardiac surgical settings must continue to evaluate metabolic, functional, and hemodynamic variations of patients with different cardioplegia for positive patient outcomes.