Mitochondrial and Contractile Function of Human Right Atrial Tissue in Response to Remote Ischemic Conditioning.

Background Remote ischemic preconditioning ( RIPC ) by repeated brief cycles of limb ischemia/reperfusion attenuates myocardial ischemia/reperfusion injury. We aimed to identify a functional parameter reflecting the RIPC -induced protection in human. Therefore, we measured mitochondrial function in right atrial tissue and contractile function of isolated right atrial trabeculae before and during hypoxia/reoxygenation from patients undergoing coronary artery bypass grafting with RIPC or placebo, respectively. Methods and Results One hundred thirty-seven patients under isoflurane anesthesia underwent RIPC (3×5 minutes blood pressure cuff inflation on the left upper arm/5 minutes deflation, n=67) or placebo (cuff uninflated, n=70), and right atrial appendages were harvested before ischemic cardioplegic arrest. Myocardial protection by RIPC was assessed from serum troponin I/T concentrations over 72 hours after surgery. Atrial tissue was obtained for isolation of mitochondria ( RIPC /placebo: n=10/10). Trabeculae were dissected for contractile function measurements at baseline and after hypoxia/reoxygenation (60 min/30 min) and for western blot analysis after hypoxia/reoxygenation ( RIPC /placebo, n=57/60). Associated with cardioprotection by RIPC (26% decrease in the area under the curve of troponin I/T), mitochondrial adenosine diphosphate-stimulated complex I respiration (+10%), adenosine triphosphate production (+46%), and calcium retention capacity (+37%) were greater, whereas reactive oxygen species production (-24%) was less with RIPC than placebo. Contractile function was improved by RIPC (baseline, +7%; reoxygenation, +24%). Expression and phosphorylation of proteins, which have previously been associated with cardioprotection, were not different between RIPC and placebo. Conclusions Cardioprotection by RIPC goes along with improved mitochondrial and contractile function of human right atrial tissue. Clinical Trial Registration URL: https://www.clinicaltrials.gov . Unique identifier: NCT 01406678.

The Left Atrial Appendage Revised.

Nonvalvular atrial fibrillation is associated with a 4- to 5-fold strokes increase and may be responsible for 15% to 20% of all strokes in the elderly. In this scenario, the left atrial appendage thrombus would be the associated with 90% of cases. The use of anticoagulants, percutaneous devices, and the left atrial appendage surgical exclusion is still an open discussion. For left atrial appendage procedures, relevant anatomic spatial relationships have to be emphasized, besides the chance of the normal physiological functioning would be eliminated with the proceedings. There are evidences that the left atrial appendage closure during routine cardiac surgery is significantly associated with an increased risk of early postoperative atrial fibrillation. Therefore, the purpose of this review is to focus basic aspects for continuous medical education. In summary, the rationale of this text is to emphasize anatomical and pharmacological aspects involved in the simple surgical exclusion of left atrial appendage under cardiopulmonary bypass. There are several operative techniques, but to conclude this revision it will present one of them based on the discussed basic sciences.

The left atrial appendage revised

Abstract Nonvalvular atrial fibrillation is associated with a 4- to 5-fold strokes increase and may be responsible for 15% to 20% of all strokes in the elderly. In this scenario, the left atrial appendage thrombus would be the associated with 90% of cases. The use of anticoagulants, percutaneous devices, and the left atrial appendage surgical exclusion is still an open discussion. For left atrial appendage procedures, relevant anatomic spatial relationships have to be emphasized, besides the chance of the normal physiological functioning would be eliminated with the proceedings. There are evidences that the left atrial appendage closure during routine cardiac surgery is significantly associated with an increased risk of early postoperative atrial fibrillation. Therefore, the purpose of this review is to focus basic aspects for continuous medical education. In summary, the rationale of this text is to emphasize anatomical and pharmacological aspects involved in the simple surgical exclusion of left atrial appendage under cardiopulmonary bypass. There are several operative techniques, but to conclude this revision it will present one of them based on the discussed basic sciences.

Macrophage precursor cells from the left atrial appendage of the heart spontaneously reprogram into a C-kit+/CD45- stem cell-like phenotype.

BACKGROUND: The developmental origin of the c-kit expressing progenitor cell pool in the adult heart has remained elusive. Recently, it has been discovered that the injured heart is enriched with c-kit(+) cells, which also express the hematopoietic marker CD45. METHODS AND RESULTS: In this study, we characterize the phenotype and transcriptome of the c-kit+/CD45+/CD11b+/Flk-1+/Sca-1±(B-type) cell population, originating from the left atrial appendage. These cells are defined as cardiac macrophage progenitors. We also demonstrate that the CD45+ progenitor cell population activates heart development, neural crest and pluripotency-associated pathways in vitro, in conjunction with CD45 down-regulation, and acquire a c-kit+/CD45-/CD11b-/Flk-1-/Sca-1+ (A-type) phenotype through cell fusion and asymmetric division. This putative spontaneous reprogramming evolves into a highly proliferative, partially myogenic phenotype (C-type). CONCLUSIONS: Our data suggests that A-type cells and cardiac macrophage precursor cells (B-type) have a common lineage origin, possibly resolving some current conundrums in the field of cardiac regeneration.

Cardiac atrial appendage stem cells engraft and differentiate into cardiomyocytes in vivo: A new tool for cardiac repair after MI.

BACKGROUND: This study assessed whether autologous transplantation of cardiac atrial appendage stem cells (CASCs) preserves cardiac function after myocardial infarction (MI) in a minipig model. METHODS AND RESULTS: CASCs were isolated from right atrial appendages of Göttingen minipigs based on high aldehyde dehydrogenase activity and expanded. MI was induced by a 2h snare ligation of the left anterior descending coronary artery. Upon reperfusion, CASCs were intramyocardially injected under NOGA guidance (MI-CASC, n=10). Non-transplanted pigs (MI, n=8) received sham treatment. 3D electromechanical mapping (EMM) and cardiac MRI were performed to assess left ventricular (LV) function. MI pigs developed LV dilatation at 2 months (2M), while in the MI-CASC group volumes remained stable. Global LV ejection fraction decreased by 16 ± 8% in MI animals vs 3 ± 10% in MI-CASC animals and regional wall thickening in border areas was better preserved in the MI-CASC group. EMM showed decreased viability and wall motion in the LV for both groups POST-MI, whereas at 2M these parameters only improved in the MI-CASC. Substantial cell retention was accompanied by cardiomyogenic differentiation in 98±1% of the transplanted CASCs, which functionally integrated. Second harmonic generation microscopy confirmed the formation of mature sarcomeres in transplanted CASCs. Absence of cardiac arrhythmias indicated the safety of CASC transplantation. CONCLUSION: CASCs preserve cardiac function by extensive engraftment and cardiomyogenic differentiation. Our data indicate the enormous potential of CASCs in myocardial repair.

Altered apoptosis-related signaling after cardioplegic arrest in patients with uncontrolled type 2 diabetes mellitus.

BACKGROUND: We investigated the effects of cardioplegic arrest and reperfusion (CP/Rep) on myocardial apoptosis and key apoptotic mediators, such as apoptosis-inducing factor, caspase 3, caspase 8, caspase 9, poly(adenosine diphosphate-ribose) polymerase, B-cell lymphoma 2 (Bcl-2) family proteins, and protein kinase C (PKC), in uncontrolled type 2 diabetic, controlled type 2 diabetic, and nondiabetic patients. METHODS AND RESULTS: Right atrial tissue was harvested pre- and post-CP/Rep from uncontrolled type 2 diabetic patients (hemoglobin A1c=9.6 ± 0.25), controlled type 2 diabetic patients (hemoglobin A1c=6.5 ± 0.15), and nondiabetic patients (hemoglobin A1c=5.4 ± 0.12) undergoing coronary artery bypass grafting (n=8/group). Terminal deoxynucleotidyl transferase dUTP nick-end labeling staining was used for the identification of apoptotic cells. Total and modified apoptosis-inducing factor, Bcl-2 family proteins, phospho-PKC-α, phospho-PKC-ß1, and poly(adenosine diphosphate-ribose) polymerase were quantified by immunoblotting or immunohistochemistry. At baseline, the number of apoptotic cells and expression of total apoptosis-inducing factor, Bcl-2, Bak, and Bax in the pre-CP/Rep atrial tissue from uncontrolled type 2 diabetic patients were significantly increased compared with those of nondiabetic or controlled type 2 diabetic patients (P<0.05). After CP/Rep, the amount of apoptotic cells, apoptosis-inducing factor, phospho-Bad, phospho-PKC-α, phospho-PKC-ß1, and cleaved poly(adenosine diphosphate-ribose) polymerase in post-CP/Rep atrial tissue were increased in all 3 groups compared with pre-CP/Rep. These increases after CP/Rep were more pronounced in the uncontrolled type 2 diabetic group. In addition, there were significant increases in the expression of cleaved caspase 8 and caspase 9 in the basal and post-CP/Rep atrium of uncontrolled type 2 diabetic group compared with nondiabetic or controlled type 2 diabetic group. CONCLUSIONS: Uncontrolled diabetes mellitus is associated with increases in myocardial apoptosis and expression of key apoptosis mediators at baseline and in the setting of CP/Rep.

Novel treatments for cardiovascular disease prevention.

The purpose of this review is to describe novel pharmacologic and nonpharmacologic preventive therapies, as well as new strategies to improve delivery of available therapies. Cardiovascular disease (CVD) is the leading cause of death worldwide, and prevention plays a critical role in curbing the global epidemic. Despite available treatment for tobacco addiction, platelet inhibition, blood pressure, and lipid lowering for reduction of atherosclerotic disease, significant gaps in treatment of total CVD remain. We review a range of new preventive treatment options, including drugs for tobacco cessation, platelet/thrombotic inhibition, lipid- and blood pressure-lowering; nonpharmacologic options such as left atrial appendage closure devices and caloric restriction; and strategies such as fixed-dose combination drugs, laboratory screening for drug tailoring, and community-based prevention programs. CVD preventive research continues to evolve and provide clinicians and patients with novel pharmacologic and nonpharmacologic therapies, including new preventive strategies.

Left atrial appendage occlusion: lessons learned from surgical and transcatheter experiences.

Since the 1950s, the pathophysiologic role of the left atrial appendage (LAA) has been known in thromboembolic disease. A variety of surgical techniques have been described to close the LAA, with various degrees of efficacy. Today, transcatheter devices for LAA occlusion may offer a less invasive solution. This review looks at the surgical experience with LAA occlusion, with a focus on the techniques of closure, the prospects for stroke reduction, and the percutaneous trials completed so far, to formulate some meaningful conclusions about the status of LAA closure today.

The effects of both noradrenaline and CGP12177, mediated through human beta1 -adrenoceptors, are reduced by PDE3 in human atrium but PDE4 in CHO cells.

(-)-Noradrenaline and (-)-CGP12177 activate beta(1)-adrenoceptors through a high (H)- and low-affinity (L) site, respectively. The positive inotropic effects of (-)-noradrenaline are blunted by phosphodiesterase4 (PDE4) but not PDE3, while both PDE isoenzymes, acting in concert, prevent the effects of (-)-CGP12177 through beta(1)-adrenoceptors in rat ventricle. We sought to unravel the role of PDE3 and PDE4 on signals through the H and L sites in human myocardium. The kinetics of matching positive inotropic effects of (-)-noradrenaline (20 nM) and (-)-CGP12177 (100 nM) were investigated on human atrial trabeculae in the absence and presence of the PDE3 inhibitor cilostamide (300 nM), PDE4 inhibitor rolipram (1 microM) or both. The influence of cilostamide and rolipram on agonist-evoked cyclic adenosine monophosphate (cAMP) increases were also compared in Chinese hamster ovary (CHO) cells expressing recombinant human beta1 -adrenoceptors. (-)-Noradrenaline and (-)-CGP12177 caused matching inotropic responses that faded during a 60-min time course. Cilostamide, but not rolipram, increased the positive inotropic effects and abolished the time dependent fade of both agonists. In CHO cells, rolipram, but not cilostamide, enhanced the cAMP signals caused by both (-)-noradrenaline and (-)-CGP12177. PDE3, but not PDE4, blunts the positive inotropic effects of both (-)-noradrenaline and (-)-CGP12177 through H and L sites, respectively, of human atrial beta1 -adrenoceptors. However, in CHO cells, PDE4 blunts the cAMP signals of both (-)-noradrenaline and (-)-CGP12177. Neither CHO cells nor the rat ventricle are appropriate models for the beta1 -adrenoceptor-evoked signalling to PDE3 observed in human atrium.

(-)-Adrenaline elicits positive inotropic, lusitropic, and biochemical effects through beta2 -adrenoceptors in human atrial myocardium from nonfailing and failing hearts, consistent with Gs coupling but not with Gi coupling.

Activation of either coexisting beta1- or beta2 -adrenoceptors with noradrenaline or adrenaline, respectively, causes maximum increases of contractility of human atrial myocardium. Previous biochemical work with the beta2 -selective agonist zinterol is consistent with activation of the cascade beta2 -adrenoceptors-->Gsalpha-protein-->adenylyl cyclase-->cAMP-->protein kinase (PKA)-->phosphorylation of phospholamban, troponin I, and C-protein-->hastened relaxation of human atria from nonfailing hearts. However, in feline and rodent myocardium, catecholamines and zinterol usually do not hasten relaxation through activation of beta2 -adrenoceptors, presumably because of coupling of the receptors to Gi protein. It is unknown whether the endogenously occurring beta2 -adrenoceptor agonist adrenaline acts through the above cascade in human atrium and whether its mode of action could be changed in heart failure. We assessed the effects of (-)-adrenaline, mediated through beta2 -adrenoceptors (in the presence of CGP 20712A 300 nM to block beta1 -adrenoceptors), on contractility and relaxation of right atrial trabecula obtained from nonfailing and failing human hearts. Cyclic AMP levels were measured as well as phosphorylation of phospholamban, troponin I, and protein C with Western blots and the back-phosphorylation procedure. For comparison, beta1 -adrenoceptor-mediated effects of (-)-noradrenaline were investigated in the presence of ICI 118,551 (50 nM to block beta2 -adrenoceptors). The positive inotropic effects of both (-)-noradrenaline and (-)-adrenaline were accompanied by reductions in time to peak force and time to reach 50% relaxation. (-)-Adrenaline caused similar positive inotropic and lusitropic effects in atrial trabeculae from failing hearts. However, the inotropic potency, but not the lusitropic potency, of (-)-noradrenaline was reduced fourfold in atrial trabeculae from heart failure patients. Both (-)-adrenaline and (-)-noradrenaline enhanced cyclic AMP levels and produced phosphorylation of phospholamban, troponin I, and C-protein to a similar extent in atrial trabeculae from nonfailing hearts. The hastening of relaxation caused by (-)-adrenaline together with the PKA-catalyzed phosphorylation of the three proteins involved in relaxation, indicate coupling of beta2 -adrenoceptors to Gs protein. The phosphorylation of phospholamban at serine16 and threonine17 evoked by (-)-adrenaline through beta2 -adrenoceptors and by (-)-noradrenaline through beta1 -adrenoceptors was not different in atria from nonfailing and failing hearts. Activation of beta2 -adrenoceptors caused an increase in phosphorylase a activity in atrium from failing hearts further emphasizing the presence of the beta2 -adrenoceptor-Gsalpha-protein pathway in human heart. The positive inotropic and lusitropic potencies of (-)-adrenaline were conserved across Arg16Gly- and Gln27Glu-beta2 -adrenoceptor polymorphisms in the right atrium from patients undergoing coronary artery bypass surgery, chronically treated with beta1 -selective blockers. The persistent relaxant and biochemical effects of (-)-adrenaline through beta2 -adrenoceptors and of (-)-noradrenaline through beta1 -adrenoceptors in heart failure are inconsistent with an important role of coupling of beta2 -adrenoceptors with Gialpha-protein in human atrial myocardium.

Impact of left atrial appendage exclusion on left atrial function.

OBJECTIVES: We sought to investigate the short-term and midterm effects of left atrial appendage exclusion on left atrial function. Left atrial appendage exclusion is considered a possible therapeutic option for stroke prevention in patients with atrial fibrillation. Favorable outcomes have encouraged widespread use of left atrial appendage exclusion for cardiac surgical patients-even for patients in sinus rhythm who have stroke risk factors; however, the chronic effects on left atrial function of left atrial appendage exclusion are unclear. METHODS: Nineteen mongrel dogs (29.7 +/- 5.2 kg) in sinus rhythm were studied. The Doppler signals from the pulmonary venous flow, transmitral flow, and tissue Doppler imaging of mitral annular motion were obtained before and after left atrial appendage exclusion. Dogs were evaluated in the same manner at 7 days (n = 2), 30 days (n = 7), or 90 days (n = 10) after left atrial appendage exclusion. RESULTS: Except for a significant increase in early diastolic transmitral flow velocity after left atrial appendage exclusion (P = .01), no significant differences were found in any parameters related to the transmitral flow and tissue Doppler imaging measurements throughout follow-up. The systolic components of pulmonary venous flow at follow-up revealed a significant reduction relative to baseline (peak systolic velocity P < .0001, systolic velocity-time integral P < .0001), despite the lack of significant changes in left atrial pressure, left ventricular volume, and stroke volume. CONCLUSION: Left atrial appendage exclusion may affect left atrial reservoir function in the short-term and midterm periods. Further long-term studies with more clinically relevant models are needed.

Role of IKur in controlling action potential shape and contractility in the human atrium: influence of chronic atrial fibrillation.

BACKGROUND: The ultrarapid outward current I(Kur) is a major repolarizing current in human atrium and a potential target for treating atrial arrhythmias. The effects of selective block of I(Kur) by low concentrations of 4-aminopyridine or the biphenyl derivative AVE 0118 were investigated on right atrial action potentials (APs) in trabeculae from patients in sinus rhythm (SR) or chronic atrial fibrillation (AF). METHODS AND RESULTS: AP duration at 90% repolarization (APD90) was shorter in AF than in SR (300+/-16 ms, n=6, versus 414+/-10 ms, n=15), whereas APD20 was longer (35+/-9 ms in AF versus 5+/-2 ms in SR, P<0.05). 4-Aminopyridine (5 micromol/L) elevated the plateau to more positive potentials from -21+/-3 to -6+/-3 mV in SR and 0+/-3 to +12+/-3 mV in AF. 4-Aminopyridine reversibly shortened APD90 from 414+/-10 to 350+/-10 ms in SR but prolonged APD90 from 300+/-16 to 320+/-13 ms in AF. Similar results were obtained with AVE 0118 (6 micromol/L). Computer simulations of I(Kur) block in human atrial APs predicted secondary increases in I(Ca,L) and in the outward rectifiers I(Kr) and I(Ks), with smaller changes in AF than SR. The indirect increase in I(Ca,L) was supported by a positive inotropic effect of 4-aminopyridine without direct effects on I(Ca,L) in atrial but not ventricular preparations. In accordance with the model predictions, block of I(Kr) with E-4031 converted APD shortening effects of I(Kur) block in SR into AP prolongation. CONCLUSIONS: Whether inhibition of I(Kur) prolongs or shortens APD depends on the disease status of the atria and is determined by the level of electrical remodeling.

Electrophysiological effects of agmatine on human atrial fibers.

The objective of the present study was to study the electrophysiological effects of agmatine on human atrial fibers obtained at cardiac surgery using standard microelectrode techniques. Agmatine (1 to approximately 10 mM) decreased the action potential amplitude (APA), maximum upstroke velocity of phase 0 depolarization (Vmax), velocity of diastolic (phase 4) depolarization (VDD), rate of pacemaker firing (RPF), and action potential duration at 50 and 90% of repolarization (APD(50-90)) in a concentration-dependent manner. Pretreatment with N(G)-nitro-L-arginine methyl ester (L-NAME, 0.5 mM), a NOS inhibitor, did not affect the electrophysiological effects of agmatine (5 mM) on human atrial fibers. The effects of agmatine (5 mM) could be blocked completely by pretreatment with idazoxan (0.1 mM), an alpha-2 adrenergic receptor (alpha2-AR) and imidazoline receptor (IR) antagonist. All these results indicate that the effects of agmatine on human atrial fibers are likely due to a decrease of intracellular calcium mediated by IR and/or alpha2-AR.