Richard M. Engelman

The Society of Thoracic Surgeons Practice Guideline Series: Blood Glucose Management During Adult Cardiac Surgery

The Society of Thoracic Surgeons Practice Guideline Series : Blood Glucose Management During Adult Cardiac Surgery

Effects of Red-Cell Storage Duration on Patients Undergoing Cardiac Surgery

BACKGROUND Some observational studies have reported that transfusion of red-cell units that have been stored for more than 2 to 3 weeks is associated with serious, even fatal, adverse events. Patients undergoing cardiac surgery may be especially vulnerable to the adverse effects of transfusion. METHODS We conducted a randomized trial at multiple sites from 2010 to 2014. Participants 12 years of age or older who were undergoing complex cardiac surgery and were likely to undergo transfusion of red cells were randomly assigned to receive leukocyte-reduced red cells stored for 10 days or less (shorter-term storage group) or for 21 days or more (longer-term storage group) for all intraoperative and postoperative transfusions. The primary outcome was the change in Multiple Organ Dysfunction Score (MODS; range, 0 to 24, with higher scores indicating more severe organ dysfunction) from the preoperative score to the highest composite score through day 7 or the time of death or discharge. RESULTS The median storage time of red-cell units provided to the 1098 participants who received red-cell transfusion was 7 days in the shorter-term storage group and 28 days in the longer-term storage group. The mean change in MODS was an increase of 8.5 and 8.7 points, respectively (95% confidence interval for the difference, -0.6 to 0.3; P=0.44). The 7-day mortality was 2.8% in the shorter-term storage group and 2.0% in the longer-term storage group (P=0.43); 28-day mortality was 4.4% and 5.3%, respectively (P=0.57). Adverse events did not differ significantly between groups except that hyperbilirubinemia was more common in the longer-term storage group. CONCLUSIONS The duration of red-cell storage was not associated with significant differences in the change in MODS. We did not find that the transfusion of red cells stored for 10 days or less was superior to the transfusion of red cells stored for 21 days or more among patients 12 years of age or older who were undergoing complex cardiac surgery. (Funded by the National Heart, Lung, and Blood Institute; RECESS ClinicalTrials.gov number, NCT00991341.).

Role of Akt Signaling in Mitochondrial Survival Pathway Triggered by Hypoxic Preconditioning

Background—The signaling pathways that control ischemia/reperfusion-induced cardiomyocyte apoptosis in heart have not been fully defined. In this study, we investigated whether Akt signaling has a role in the antiapoptotic pathways of preconditioning against hypoxia/reoxygenation (H/R). Methods and Results—Primary cultures of adult rat ventricular myocytes (ARVMs) were subjected to preconditioning (PC) by exposing the cells to 10 minutes of hypoxia followed by 30 minutes of reoxygenation. Non-PC and PC myocytes were subjected to 90 minutes of hypoxia followed by 120 minutes of reoxygenation. Hypoxic-PC protected the myocytes from subsequent H/R injury, as evidenced by decreased apoptosis and LDH release and increased cell viability. H/R-induced cytochrome c release and activation of caspase-3 and -9 were blocked by PC. This protective effect was inhibited by treating the cells with LY294002 (50 μmol/L), a PI3 kinase inhibitor, for 10 minutes before and during PC. PC also induced phosphorylation of Akt and BAD. Protein levels of Bcl-2 in mitochondria were maintained in PC. ARVMs were infected with either a control adenovirus (Adeno lac-Z), an adenovirus expressing dominant-negative Akt, or an adenovirus expressing constitutively active Akt. Ectopic overexpression of constitutively active Akt protected ARVMs from apoptosis induced by hypoxia/reoxygenation compared with Adeno lac-Z. In contrast, dominant negative Akt overexpression abolished the antiapoptotic effect of PC. Conclusions—Our data demonstrated that in adult cardiomyocytes, the antiapoptotic effect of PC against H/R requires Akt signaling leading to phosphorylation of BAD, inhibition of cytochrome c release, and prevention of caspase activation.

Role of xanthine oxidase inhibitor as free radical scavenger: A novel mechanism of action of allopurinol and oxypurinol in myocardial salvage

Xanthine oxidase (XO) has been hypothesized to be a potential source of oxygen-derived free radicals during reperfusion of ischemic myocardium based on the fact that allopurinol, a XO-inhibitor, can reduce reperfusion injury. In this communication we report that both allopurinol and oxypurinol, the principle metabolite of allopurinol, prevent the reperfusion injury in isolated pig heart. However, we found that neither pig heart nor pig blood contain any XO activity. Our study showed a direct free radical scavenging action of these XO-inhibitors during ischemia and reperfusion, as judged by the reduction of free radical signals when compared using an Electron Paramagnetic Resonance Spectrometer. Using a Luminometer, we also confirmed that both allopurinol and oxypurinol can scavenge ClO2, HOCl, and significantly inhibit free radical signals generated by activated neutrophils. These XO-inhibitors, however, failed to scavenge O2. and OH. radicals. Our results suggest that these XO-inhibitors salvaged the ischemic-reperfused myocardium by scavenging free radicals, and not by inhibiting XO in the pig heart.

Thioredoxin redox signaling in the ischemic heart: an insight with transgenic mice overexpressing Trx1

This study examined if thioredoxin, the major redox-regulator in the mammalian system, plays any role in the redox signaling of ischemic myocardium. Isolated working rat hearts were made globally ischemic for 30 min followed by 2 h of reperfusion. Another group of hearts was rendered tolerant to ischemia by four cyclic episodes of 5 min ischemia each followed by another 10 min of reperfusion. Reperfusion of ischemic myocardium resulted in the downregulation of thioredoxin 1 (Trx1) expression, which was upregulated in the adapted myocardium. The increased expression of Trx1 was completely blocked with cis-diammine-dichloroplatinum (CDDP), an inhibitor of Trx1. CDDP also abolished cardioprotection afforded by ischemic adaptation as evidenced by a reduction of post-ischemic ventricular recovery, increase in myocardial infarct size and cardiomyocyte apoptosis. The decreased amount of reactive oxygen species in the adapted heart was increased significantly, when Trx1 was blocked with CDDP. The cardioprotective role of Trx1 was further confirmed with transgenic mouse hearts overexpressing Trx1. The Trx1 mouse hearts displayed significantly improved post-ischemic ventricular recovery and reduced myocardial infarct size as compared to the corresponding wild-type mouse hearts. Taken together, the results of this study implicate a crucial role of Trx1 in redox signaling of the ischemic myocardium.

Influence of steroids on complement and cytokine generation after cardiopulmonary bypass

BACKGROUND It is recognized that the inflammatory mediators complement and cytokines are generated during cardiopulmonary bypass as an endogenous response to extracorporeal circulation. METHODS Nineteen randomized patients (10 steroid/9 nonsteroid) entered an institutional review board-approved protocol to measure complement and interleukin level generation before and after elective coronary revascularization. The steroid regimen involved 1 g of methylprednisolone sodium succinate intravenously before bypass and 4 mg of dexamethasone every 6 hours for four doses during the first 24 hours of recovery. Complement and interleukin levels were measured before bypass, immediately after bypass, and at 24, 48 and 72 hours of recovery. RESULTS In the nonsteroid group, there was a significant elevation in all inflammatory mediators relative to the steroid group. The predominant changes occurred at 24 hours after operation. CONCLUSIONS Steroids produced a dramatic reduction in complement and interleukin levels. The number of patients was clearly too small to document a clinical consequence of steroid administration.

Epicardial activation of the intact human heart without conduction defect.

To describe the epicardial ventricular activation sequence in the intact human heart, we obtained epicardial maps from 11 patients with normal QRS undergoing open heart surgery. Epicardial breakthrough (EBT), defined as the emergence of a radially propagating epicardial wavefront, occurred in three to five sites in each patient, and was earliest in the anterior right ventricle, 7-25 msec (mean 17 msec) after the onset of the QRS in all patients. Subsequent EBT occurred in the inferior right ventricle (10 sites in 10 patients), in the anterolateral left ventricle (13 sites in 10 patients), and the inferior left ventricle (eight sites in seven patients). Latest epicardial activation (LEA), defined as the latest site of recordable epicardial activity, occurred in the basal segments in all patients, anteriorly in the right ventricle in five patients, and inferiorly in six patients, four on the right and two on the left. LEA occurred 63-96 msec (mean 77 msec) after the onset of the QRS, and was recorded within 20 msec of the end of the QRS in all patients. Sequence of epicardial activation reflected a fusion process among the wavefronts. This descriptive and quantitative data should provide a suitable basis for comparison of abnormal ventricular activation sequences in patients undergoing surgery for preexcitation or ventricular tachycardia.

Hypoxic preconditioning preserves antioxidant reserve in the working rat heart

OBJECTIVE The aim was to examine whether intracellular antioxidants play a role in myocardial preservation following hypoxic preconditioning. METHODS Isolated working rat hearts were subjected to 30 min ischaemia and 30 min reperfusion. Control hearts were compared to hearts preconditioned with 10 min hypoxia. Left ventricular function and lactate dehydrogenase (LDH) release were measured in each group. Ascorbate dependent (ADAR) and thiol dependent (TDAR) components of the endogenous myocardial antioxidant reserve were assessed using electron spin resonance spectroscopy. RESULTS a Hypoxic preconditioning had no effect on left ventricular function after 10 min reoxygenation. During reperfusion, the hypoxically preconditioned hearts had a significantly increased survival rate, aortic flow, developed pressure, and dP/dtmax, and a reduced lactate dehydrogenase release, compared to non-preconditioned controls (P < 0.05). Preconditioned hearts also had significantly higher preservation of baseline ADAR (79%) and TDAR (96%) compared with control hearts, (70%) and (77%), respectively (P < 0.05). CONCLUSIONS Hypoxic preconditioning enhances functional recovery and reduces cell necrosis following global ischaemia in the working rat heart. This phenomenon may, in part, be mediated through enhanced ascorbate and thiol components of the antioxidant reserve.

Targeted Disruption of the Mouse Sod I Gene Makes the Hearts Vulnerable to Ischemic Reperfusion Injury

The role of Cu/Zn-superoxide dismutase (SOD) in myocardial ischemic reperfusion injury was studied by using a mouse model with targeted disruption of the mouse Sod I gene. Inactivation of the functional mouse Sod I gene in hearts by gene targeting (Sod I(+/-)) resulted in a 50% reduction of Cu/Zn-SOD mRNA and significant reduction of Cu/Zn-SOD enzyme activity compared with that of wild-type Sod I(+/+) mice. Cu/Zn-SOD mRNA could not be detected in Sod I(-/-) heart. The isolated buffer-perfused hearts from the knockout mice devoid of any functional copy of the Sod I (Sod I(-/-)) and matched nontransgenic control mice were subjected to 30 minutes of global ischemia followed by 2 hours of reperfusion. For both groups of mice, the postischemic functional recovery for the hearts was lower than the baseline, but the recovery for the Sod I(-/-) was less compared with the wild-type mice. Thus, the postischemic recovery of the developed force and the maximum first derivative of the developed force were consistently lower for the Sod I(-/-) mouse hearts compared with wild-type control hearts. The coronary flow was lower compared with the baseline levels for both groups of hearts, but there was no significant difference between the groups. The myocardial infarction determined from the ratio of infarct size/area of risk was higher for the Sod I(-/-) mice compared with the control mice. The amount of creatine kinase release from the wild-type mouse hearts was less compared with the Sod I(-/-) mouse hearts. In concert, a reduced amount of oxidative stress was found in the hearts of wild-type mice compared with Sod I(-/-) mouse hearts. These results documented that Sod I(-/-) mouse hearts were more susceptible to ischemic reperfusion injury compared with corresponding wild-type mouse hearts, suggesting that the Sod I gene constitutes an important defense element for the hearts.

Nitric oxide signaling in ischemic heart

OBJECTIVE Several recent studies have implicated a role of endogenous nitric oxide (NO) in the pathophysiology of myocardial ischemic/reperfusion injury. However, the mechanism by which NO exerts its beneficial/detrimental effects remains unknown. This study examined the intracellular signaling of NO by studying the role of the NO-cGMP signaling pathway on the phospho-diesteratic breakdown and turnover of phosphoinositides during myocardial ischemia and reperfusion. METHODS Isolated working rat hearts were made ischemic for 30 min followed by 30 min of reperfusion. A separate group of hearts were pre-perfused with 3 mM L-arginine for 10 min prior to ischemia. The release of NO was monitored using an on-line amperometric sensor. The aortic flow and developed pressure were examined to determine the effects of L-arginine on ischemic/reperfusion injury. For signal transduction experiments, sarcolemmal membranes were radiolabeled by perfusing the isolated hearts with [3H]myoinositol and [14C]arachidonic acid. Hearts were then perfused for 10 min in the presence or absence of L-arginine via the Langendorff mode. Ischemia was induced for 30 min followed by 30 min of reperfusion. Experiments were terminated before L-arginine and after L-arginine treatment, after ischemia, and during reperfusion. Biopsies were processed to determine the isotopic incorporation into various phosphoinositols as well as phosphatidic acid and diacylglycerol. cGMP was assayed by radioimmunoassay and SOD content was determined by enzymatic analysis. RESULTS The release of NO was diminished following ischemia and reperfusion and was augmented by L-arginine. L-Arginine reduced ischemic/reperfusion injury as evidenced by the enhanced myocardial functional recovery. cGMP, which remained unaffected by ischemia and reperfusion, was stimulated significantly after L-arginine treatment. The cGMP level persisted up to 10 min of reperfusion and then dropped slightly. Reperfusion of ischemic myocardium resulted in significant accumulation of radiolabeled inositol phosphate, inositol bisphosphate, and inositol triphosphate. Isotopic incorporation of [3H]inositol into phosphatidylinositol, phosphatidylinositol-4-phosphate, and phosphatidylinositol-4,5-bisphosphate was increased significantly during reperfusion. Reperfusion of the ischemic heart prelabeled with [14C]-arachidonic acid resulted in modest increases in [14C]diacylglycerol and [14C]phosphatidic acid. Pretreatment of the heart with L-arginine significantly reversed this enhanced phosphodiesteratic breakdown during ischemia and early reperfusion. However, at the end of the reperfusion the inhibitory effect of L-arginine on the phosphodiesterases seems to be reduced. In L-arginine-treated hearts, SOD activity was progressively decreased with the duration of reperfusion time. CONCLUSIONS The results suggest for the first time that NO plays a significant role in transmembrane signaling in the ischemic myocardium. The signaling seems to be transmitted via cGMP and opposes the effects of phosphodiesterases by inhibiting the ischemia/reperfusion-induced phosphodiesteratic breakdown. This signaling effect appears to be reduced as reperfusion progresses. These results, when viewed in the light of free radical chemistry of NO, suggest that such on- and off-signaling of NO may be linked to its interaction with the superoxide radical generated during the reperfusion of ischemic myocardium.