Myocardial Hypoxia Research Articles

Hypoxia training attenuates left ventricular remodeling in rabbit with myocardial infarction.

ObjectivePrevious studies showed that hypoxia preconditioning could protect cardiac function against subsequent myocardial infarction injury. However, the effect of hypoxia on left ventricular after myocardial infarction is still unclear. This study therefore aims to investigate the effects of hypoxia training on left ventricular remodeling in rabbits post myocardial infarction.MethodsAdult male rabbits were randomly divided into three groups: group SO (sham operated), group MI (myocardial infarction only) and group MI-HT (myocardial infarction plus hypoxia training). Myocardial infarction was induced by left ventricular branch ligation. Hypoxia training was performed in a hypobaric chamber (having equivalent condition at an altitude of 4000 m, FiO214.9%) for 1 h/day, 5 days/week for four weeks. At the endpoints, vascular endothelial growth factor (VEGF) in the plasma was measured. Infarct size and capillary density were detected by histology. Left ventricular remodeling and function were assessed by echocardiography.ResultsAfter the 4-week experiment, compared with the group SO, plasma VEGF levels in groups MI (130.27 ± 18.58 pg/mL, P < 0.01) and MI-HT (181.93 ± 20.29 pg/mL, P < 0.01) were significantly increased. Infarct size in Group MI-HT (29.67% ± 7.73%) was deceased remarkably, while its capillary density (816.0 ± 122.2/mm2) was significantly increased. For both groups MI and MI-HT, left ventricular end-diastolic and end-systolic dimensions were increased whereas left ventricular ejection fraction was decreased. However, compared with group MI, group MI-HT diminished left ventricular end-diastolic (15.86 ± 1.09 mm, P < 0.05) and end-systolic dimensions (12.10 ± 1.20 mm, P < 0.01) significantly and improved left ventricular ejection fraction (54.39 ± 12.74 mm, P < 0.05).ConclusionHypoxia training may improve left ventricular function and reduce remodeling via angiogenesis in rabbits with MI.

Myocardial perfusion defects in scleroderma detected by contrast-enhanced cardiovascular magnetic resonance.

The authors investigated whether contrast-enhanced cardiovascular magnetic resonance (CMR) imaging may be used to detect early cardiac involvement in patients with systemic sclerosis (SSc). Twenty-six SSc patients (nine with diffuse cutaneous SSc and 17 with limited cutaneous SSc) and 13 sex- and age-matched healthy controls (HC) were studied. Contrast-enhanced CMR allowed the analysis of first-pass images (areas of hypo-enhancement indicating perfusion defects) and delayed images (persistent hyper-enhancement indicating fibrosis). Clinical variables including disease duration and presence of major visceral complications of SSc were investigated in each patient. Perfusion defects were detected in 53.8% of SSc patients but in none of the HC. Perfusion abnormalities were detected in 28.6% of SSc patients with disease duration less than 2years and in 29.2% of asymptomatic SSc patients. Delayed contrast enhancement was present in 25% of SSc patients but not in HC. All patients with delayed contrast enhancement showed first-pass hypoperfusion. Right ventricular wall thickness was significantly increased in all SSc patients when compared to HC (p<0.001); a similar trend was observed when SSc patients without pulmonary arterial hypertension were analysed (p<0.04). A trend to lower end-diastolic and end-systolic right ventricular volumes in SSc versus HC was observed (p<0.05 and p<0.04, respectively). Myocardial hypoperfusion is common in SSc and occurs early in the course of the disease. Co-localisation of perfusion defects and delayed contrast enhancement indicative of fibrosis suggests that myocardial hypoxia may play a role in the pathogenesis of myocardial fibrosis.

Genome-scale methods converge on key mitochondrial genes for the survival of human cardiomyocytes in hypoxia.

Any reduction in myocardial oxygen delivery relative to its demands can impair cardiac contractile performance. Understanding the mitochondrial metabolic response to hypoxia is key to understanding ischemia tolerance in the myocardium. We used a novel combination of 2 genome-scale methods to study key processes underlying human myocardial hypoxia tolerance. In particular, we hypothesized that computational modeling and evolution would identify similar genes as critical to human myocardial hypoxia tolerance. We analyzed a reconstruction of the cardiac mitochondrial metabolic network using constraint-based methods, under conditions of simulated hypoxia. We used flux balance analysis, random sampling, and principal component analysis to explore feasible steady-state solutions. Hypoxia blunted maximal ATP (-17%) and heme (-75%) synthesis and shrank the feasible solution space. Tricarboxylic acid and urea cycle fluxes were also reduced in hypoxia, but phospholipid synthesis was increased. Using mathematical optimization methods, we identified reactions that would be critical to hypoxia tolerance in the human heart. We used data regarding single-nucleotide polymorphism frequency and distribution in the genomes of Tibetans (whose ancestors have resided in persistent high-altitude hypoxia for several millennia). Six reactions were identified by both methods as being critical to mitochondrial ATP production in hypoxia: phosphofructokinase, phosphoglucokinase, complex II, complex IV, aconitase, and fumarase. Mathematical optimization and evolution converged on similar genes as critical to human myocardial hypoxia tolerance. Our approach is unique and completely novel and demonstrates that genome-scale modeling and genomics can be used in tandem to provide new insights into cardiovascular genetics.

Valsartan regulates myocardial autophagy and mitochondrial turnover in experimental hypertension.

Renovascular hypertension alters cardiac structure and function. Autophagy is activated during left ventricular hypertrophy and linked to adverse cardiac function. The angiotensin II receptor blocker, valsartan, lowers blood pressure and is cardioprotective, but whether it modulates autophagy in the myocardium is unclear. We hypothesized that valsartan would alleviate autophagy and improve left ventricular myocardial mitochondrial turnover in swine renovascular hypertension. Domestic pigs were randomized to control, unilateral renovascular hypertension, and renovascular hypertension treated with valsartan (320 mg/d) or conventional triple therapy (reserpine+hydralazine+hydrochlorothiazide) for 4 weeks after 6 weeks of renovascular hypertension (n=7 each group). Left ventricular remodeling, function, and myocardial oxygenation and microcirculation were assessed by multidetector computer tomography, blood oxygen level-dependent MRI, and microcomputer tomography. Myocardial autophagy, markers for mitochondrial degradation and biogenesis, and mitochondrial respiratory-chain proteins were examined ex vivo. Renovascular hypertension induced left ventricular hypertrophy and myocardial hypoxia, enhanced cellular autophagy and mitochondrial degradation, and suppressed mitochondrial biogenesis. Valsartan and triple therapy similarly decreased blood pressure, but valsartan solely alleviated left ventricular hypertrophy, ameliorated myocardial autophagy and mitophagy, and increased mitochondrial biogenesis. In contrast, triple therapy only slightly attenuated autophagy and preserved mitochondrial proteins, but elicited no improvement in mitophagy. These data suggest a novel potential role of valsartan in modulating myocardial autophagy and mitochondrial turnover in renovascular hypertension-induced hypertensive heart disease, which may possibly bolster cardiac repair via a blood pressure-independent manner.

Cardiac Hypoxia Imaging: Second-Generation Analogues of 64Cu-ATSM

Myocardial hypoxia is an attractive target for diagnostic and prognostic imaging, but current approaches are insufficiently sensitive for clinical use. The PET tracer copper(II)-diacetyl-bis(N4-methylthiosemicarbazone) ((64)Cu-ATSM) has promise, but its selectivity and sensitivity could be improved by structural modification. We have therefore evaluated a range of (64)Cu-ATSM analogs for imaging hypoxic myocardium. Isolated rat hearts (n = 5/group) were perfused with normoxic buffer for 30 min and then hypoxic buffer for 45 min within a custom-built triple-γ-detector system to quantify radiotracer infusion, hypoxia-dependent cardiac uptake, and washout. A 1-MBq bolus of each candidate tracer (and (18)F-fluoromisonidazole for comparative purposes) was injected into the arterial line during normoxia, and during early and late hypoxia, and their hypoxia selectivity and pharmacokinetics were evaluated. The in vivo pharmacokinetics of promising candidates in healthy rats were then assessed by PET imaging and biodistribution. All tested analogs exhibited hypoxia sensitivity within 5 min. Complexes less lipophilic than (64)Cu-ATSM provided significant gains in hypoxic-to-normoxic contrast (14:1 for (64)Cu-2,3-butanedione bis(thiosemicarbazone) (ATS), 17:1 for (64)Cu-2,3-pentanedione bis(thiosemicarbazone) (CTS), 8:1 for (64)Cu-ATSM, P < 0.05). Hypoxic first-pass uptake was 78.2% ± 7.2% for (64)Cu-ATS and 70.7% ± 14.5% for (64)Cu-CTS, compared with 63.9% ± 11.7% for (64)Cu-ATSM. Cardiac retention of (18)F-fluoromisonidazole increased from 0.44% ± 0.17% during normoxia to 2.24% ± 0.08% during hypoxia. In vivo, normoxic cardiac retention of (64)Cu-CTS was significantly lower than that of (64)Cu-ATSM and (64)Cu-ATS (0.13% ± 0.02% vs. 0.25% ± 0.04% and 0.24% ± 0.03% injected dose, P < 0.05), with retention of all 3 tracers falling to less than 0.7% injected dose within 6 min. (64)Cu-CTS also exhibited lower uptake in liver and lung. (64)Cu-ATS and (64)Cu-CTS exhibit better cardiac hypoxia selectivity and imaging characteristics than the current lead hypoxia tracers, (64)Cu-ATSM and (18)F-fluoromisonidazole.

Chronic Hypoxia Enhances Expression and Activity of Mitochondrial Creatine Kinase and Hexokinase in the Rat Ventricular Myocardium

Background: Creatine kinase (CK) and hexokinase (HK) play a key role in myocardial energy homeostasis. We aimed to determine CK and HK expression and enzyme activity in the left (LV) and right (RV) ventricles of rats adapted for 3 weeks to normobaric hypoxia (10 % O₂) either continuously (CNH) or intermittently with 1-h or 16-h normoxic episode per day. Methods: The Real-Time RT-PCR, Western blot, and enzyme-coupled assays were used. In addition, the effect of CNH on the HK co-localization with mitochondria, which can inhibit apoptosis, was assessed using immunofluorescence techniques. Results: CK and HK activities increased in the LV during all hypoxic adaptations, which was consistent with elevated protein levels of mitochondrial mtCKs, cytosolic CKB, HK1, and HK2 isoforms. Enzyme activities also increased in the hypoxic RV, but only CKB protein was elevated. No effect of CNH on HK1 or HK2 co-localization with mitochondria was observed. Conclusion: Up-regulation of mtCKs and HK isoforms may stimulate the respiratory chain and help to maintain energy homeostasis of chronically hypoxic myocardium and prevent oxidative stress. In this way, CK and HK enzymes can possibly participate in the establishment of ischemia-resistant phenotype of chronically hypoxic hearts.

Intraoperative interfascicular ventricular tachycardia: A rare occurrence

Intraoperative interfascicular ventricular tachycardia: A rare occurrence

Lights on for HIF-1α: Genetically Enhanced Mouse Cardiomyocytes for Heart Tissue Imaging

Background/Aims: The hypoxia inducible factor-1 (HIF-1) is a suitable marker for tissue oxygenation. We intended to develop cardiomyocytes (CMs) expressing the oxygen-dependent degradation domain of HIF-1α fused to the firefly luciferase (ODD-Luc) followed by proof-of-concept for its applicability in the assessment of heart muscle oxygenation. Methods and Results: We first generated embryonic stem cell (ESC) lines (ODD-Luc ESCs) from a Tg ROSA26 ODD-Luc/+ mouse. Subsequent CMs selection was facilitated by stable integration of an antibiotic resistance expressed under the control of the αMHC promoter. ODD-Luc ESCs showed a strong Luc-signal within 1 h of hypoxia (1% oxygen), which coincided with endogenous HIF-1α. Engineered heart muscle (EHM) constructed with ODD-Luc CMs confirmed the utility of the model to sense hypoxia, and monitor reoxygenation also in a multicellular heart muscle model. Pharmacologically induced inotropy/chronotropy under isoprenaline resulted in enhanced Luc-signal suggesting enhanced oxygen consumption, leading to notable myocardial hypoxia. Conclusions: ODD-Luc-CMs can be used to monitor dynamic changes of cardiomyocyte oxygenation in living heart muscle samples. We provide proof-of-concept for pharmacologically induced myocardial interventions and envision applications of the developed model in drug screens and fundamental studies of ischemia/reperfusion injury.

Hypoxia activates muscle-restricted coiled-coil protein (MURC) expression via transforming growth factor-β in cardiac myocytes

The expression of MURC (muscle-restricted coiled-coil protein), a hypertrophy-regulated gene, increases during pressure overload. Hypoxia can cause myocardial hypertrophy; however, how hypoxia affects the regulation of MURC in cardiomyocytes undergoing hypertrophy is still unknown. The aim of the present study was to test the hypothesis that hypoxia induces MURC expression in cardiomyocytes during hypertrophy. The expression of MURC was evaluated in cultured rat neonatal cardiomyocytes subjected to hypoxia and in an in vivo model of AMI (acute myocardial infarction) to induce myocardial hypoxia in adult rats. MURC protein and mRNA expression were significantly enhanced by hypoxia. MURC proteins induced by hypoxia were significantly blocked after the addition of PD98059 or ERK (extracellular-signal-regulated kinase) siRNA 30 min before hypoxia. Gel-shift assay showed increased DNA-binding activity of SRF (serum response factor) after hypoxia. PD98059, ERK siRNA and an anti-TGF-β (transforming growth factor-β) antibody abolished the SRF-binding activity enhanced by hypoxia or exogenous administration of TGF-β. A luciferase promoter assay demonstrated increased transcriptional activity of SRF in cardiomyocytes by hypoxia. Increased βMHC (β-myosin heavy chain) and BNP (B-type natriuretic peptide) protein expression and increased protein synthesis was identified after hypoxia with the presence of MURC in hypertrophic cardiomyocytes. MURC siRNA inhibited the hypertrophic marker protein expression and protein synthesis induced by hypoxia. AMI in adult rats also demonstrated increased MURC protein expression in the left ventricular myocardium. In conclusion, hypoxia in cultured rat neonatal cardiomyocytes increased MURC expression via the induction of TGF-β, SRF and the ERK pathway. These findings suggest that MURC plays a role in hypoxia-induced hypertrophy in cardiomyocytes.

Experimental study of the effect of Shenmai injection on post-cardiac arrest syndrome in rabbit

To observe the effects of Shenmai injection on post-cardiac arrest syndrome (PCAS) in rabbit and to discuss the underlying mechanism. Seventy-three rabbits were divided into sham operation group (n=10), model group (n=21), high and low dosage Shenmai group (each n=21) by random number table method. The animal model of cardiac arrest was reproduced by clamping the endotracheal tube. The rabbits in sham operation group were only given anesthesia and tracheostomy without producing asphyxia by clamping the trachea to produce asphyxia. Serum creatine kinase isoenzyme (CK-MB), alanine aminotransferase (ALT), creatinine (Cr), troponin I (cTnI), tumor necrosis factor-α (TNF-α), interleukin (IL-1β, IL-6) and nuclear transcription factors-ΚB (NF-ΚB) levels were determined before asphyxia and 3, 6, 12, 24, 48 hours after restoration of spontaneous circulation (ROSC), and dynamic changes in various parameters were determined in each group. All the indexes in model group and Shenmai groups were gradually increased after ROSC. IL-6 peaked at 6 hours, IL-1β peaked at 12 hours, CK-MB, cTnI, TNF-α and NF-ΚB peaked at 24 hours, ALT and Cr peaked at 48 hours. CK-MB, ALT, cTnI levels in high dosage Shenmai group were significantly lower than those in the model group 6 hours after ROSC [CK-MB (U/L): 571.69±24.39 vs. 587.98±22.38, ALT (U/L): 74.88±8.71 vs. 81.49±5.79, cTnI (μg/L): 7.82±1.52 vs. 8.97±1.87], serum levels of TNF-α and NF-ΚB 12 hours after ROSC [TNF-α(ng/L): 120.36±12.38 vs. 135.23±20.13, NF-ΚB (ng/L): 2.18±0.17 vs. 2.29±0.15], and the serum levels of IL-1β and IL-6 24 hours after ROSC in high dose Shenmai group were significantly lower than those in the model group [IL-1β (ng/L): 1.49±0.13 vs. 1.62±0.17, IL-6 (ng/L): 72.01±5.02 vs. 79.35±11.28], however, serum Cr in high dosage Shenmai group was significantly lower than in the model group at 24 hours after ROSC (μmol/L: 158.73±4.40 vs. 162.97±5.02, P<0.05 or P<0.01). In low dosage Shenmai group, the serum level of CK-MB, Cr, cTnI were significantly lower than those in the model group 24 hours after ROSC [CK-MB (U/L): 1 769.00±19.73 vs. 2 120.96±24.15, Cr (μmol/L): 159.32±3.02 vs. 162.97±5.02, cTnI (μg/L): 12.17±3.04 vs. 14.89±3.09,P<0.05 or P<0.01). But after ROSC, ALT, TNF-α, IL-1β, IL-6 and NF-ΚB showed no significant change as compared with model group. In high dosage Shenmai group, serum levels of CK-MB and cTnI at 6, 12 hours and TNF-α and IL-6 at 24 hours after ROSC were significantly lower than those in the low dosage Shenmai group(all P<0.05). Severity of injury of different organs in rabbit cardiac arrest model showed positive correlation with the alterations in serum TNF-α, IL-1β, IL-6, NF-ΚB after cardiopulmonary resuscitation. Early use of Shenmai injection after cardiopulmonary resuscitation can retard the development of PCAS, especially in the protection of ischemia and hypoxia of myocardium after cardiopulmonary resuscitation.

Muscarinic stimulation and pinacidil produce similar facilitation of tachyarrhythmia induction in rat isolated atria

Atrial tachyarrhythmias, the most common type of cardiac arrhythmias, are associated with greater stroke risk. Muscarinic cholinergic agonists have been shown to facilitate atrial tachyarrhythmia maintenance in the absence of cardiac disease. This has been attributed to action potential shortening, which enhances myocardial electrical anisotropy, and thus creates a substrate for reentrant excitation. In this study, we describe a similar effect of the ATP-sensitive K+ channel (KATP) opener pinacidil on tachyarrhythmia induction in isolated rat atria. Pinacidil, which activates a weakly inwardly-rectifying current in isolated atrial myocytes, enhanced arrhythmia induction in the right and left atria. This effect was abolished by the KATP blocker glibenclamide, but not by atropine, which rules out a possible indirect effect due to stimulation of acetylcholine release. However, pinacidil attenuated carbachol-induced tachyarrhythmia facilitation, which may indicate that the action of these agonists converges to a common cellular mechanism. Both agonists caused marked action potential shortening in isolated atrial myocytes. Moreover, during arrhythmia in the presence of pinacidil and carbachol, the atrial vectorelectrographic patterns were similar and consistent with reentrant propagation of the electrical activity. From these results, we conclude that the KATP channel opening is pro-arrhythmic in atrial tissue, which may pose as an additional risk in the scenario of myocardial hypoxia. Moreover, the similarity of the electrophysiological effects of pinacidil and carbachol is suggestive that the sole increase in background K+ conductance is sufficient for atrial tachyarrhythmia facilitation.

Preconditioning mesenchymal stem cells with caspase inhibition and hyperoxia prior to hypoxia exposure increases cell proliferation

Myocardial infarction is a leading cause of mortality and morbidity worldwide. Occlusion of a coronary artery produces ischemia and myocardial necrosis that leads to left ventricular (LV) remodeling, dysfunction, and heart failure. Stem cell therapy may decrease infarct size and improve LV function; the hypoxic environment, however, following a myocardial infarction may result in apoptosis, which in turn decreases survival of transplanted stem cells. Therefore, the effects of preconditioned mesenchymal stem cells (MSC) with hyperoxia (100% oxygen), Z-VAD-FMK pan-caspase inhibitor (CI), or both in a hypoxic environment in order to mimic conditions seen in cardiac tissue post-myocardial infarction were studied in vitro. MSCs preconditioned with hyperoxia or CI significantly decreased apoptosis as suggested by TUNEL assay and Annexin V analysis using fluorescence assisted cell sorting. These effects were more profound when both, hyperoxia and CI, were used. Additionally, gene and protein expression of caspases 1, 3, 6, 7, and 9 were down-regulated significantly in MSCs preconditioned with hyperoxia, CI, or both, while the survival markers Akt1, NF-κB, and Bcl-2 were significantly increased in preconditioned MSCs. These changes ultimately resulted in a significant increase in MSC proliferation in hypoxic environment as determined by BrdU assays compared to MSCs without preconditioning. These effects may prove to be of great clinical significance when transplanting stem cells into the hypoxic myocardium of post-myocardial infarction patients in order to attenuate LV remodeling and improve LV function.

KATP vs Purkinje fibers: Which should we shoot first, or should we?

backs. 4 ICDs, which are widely used to prevent arrhythmic SCDs, can also deliver inappropriate shocks that can not only damage the diseased heart but also provoke arrhythmias. In spite of these shortcomings, ICDs are the only available therapy that can effectively terminate VF soon after it initiates. Moreover, select antiarrhythmic medications such as beta-blockers and amiodarone are used to reduce the frequency of ICD shocks but are associated with undesirable side effects. 5 Additionally, ablation of proarrhythmic ventricular tissue can decrease the number of ICD shocks but does not significantly alter mortality rate and potentially can result in multiple complications 6 possibly due to electroporation damage. 7 Therefore, identifying novel mechanisms and therapeutic strategies to effectively treat malignant arrhythmias such as VF is an absolute necessity to improve prognosis for the growing population with cardiac disease. One important approach to achieve this goal is to determine the cellular basis of these fatal arrhythmias. Historically, ion channels that maintain normal electrical homeostasis across the cell membrane are the primary candidates to treat arrhythmias. The ATP-sensitive potassium current IK(ATP) is one such ion current that plays an important role in cardiac repolarization and contraction during both physiologic and especially pathologic conditions. 8 Specifically, KATP channels are known to play a cardioprotective role during myocardial ischemia and hypoxia, wherein the increased potassium efflux causes a reduction in action potential duration. Although beneficial, the anatomically heteterogeneous decrease in action potential duration and hence dispersed refractoriness also can increase the propensity for VF. 9–11 Experimental manipulation of the KATP channels using channel openers (e.g., pinacidil and diazoxide) and inhibitors (e.g., glibenclamide) has clearly established the channel’s role in the induction and maintenance of VF in different animal models, 8,12 explanted human hearts, 9 and in non–insulin-dependent diabetic patients during transient ischemia. 13 Clearly, activation of KATP channels could be one mechanism of ischemia-induced VF, especially in diseased, metabolically challenged hearts. Another important player implicated in VF development is the Purkinje fiber system (PS), where triggered activity has been proposed to initiate as well as maintain VF. 14,15 Premature beats originating in the PS may initiate VF, and ablation focused on these fibers can reduce the arrhythmic burden in patients with idiopathic VF. 14 In the canine heart,

Erythropoietin Combined with ACE Inhibitor Prevents Heart Remodeling in 5/6 Nephrectomized Rats Independently of Blood Pressure and Kidney Function

Background: Cardiovascular disease is the primary cause of mortality in patients with chronic kidney disease (CKD). Heart remodeling in CKD comprises mainly interstitial fibrosis and capillary loss. Beyond correcting renal anemia, erythropoietin (Epo) has potentially beneficial pleiotropic effects on heart remodeling. Methods: 12-week-old male Sprague-Dawley rats were randomized to 5/6 nephrectomy (NX) or sham operation (sham-op); subsequently, they received murine Epo (2.5 μg/kg/week), enalapril (12 mg/kg/day), Epo + enalapril, Epo + dihydralazine (25 mg/kg/day), or vehicle. Heart function and morphology was assessed after 16 weeks of treatment. Results: Compared with sham-op (81.2%), left ventricle fractional shortening was reduced in vehicle-treated NX (66.3%) and this was ameliorated by Epo (72.6%) and even prevented by enalapril (80.6%). Capillary length density was lower and the area of fibrosis more marked in vehicle-treated NX compared to sham-op. Capillary rarefaction and heart fibrosis were prevented in NX treated with Epo + enalapril and reduced in NX treated with enalapril and Epo + dihydralazine. Despite higher blood pressure, treatment with Epo reduced heart fibrosis but failed to prevent capillary loss. In parallel, expression of the p47phox NADPH oxidase was higher in untreated NX and was effectively reduced in NX treated with Epo + enalapril. Under basal conditions there was no difference between the groups regarding myocardial hypoxia as reflected by pimonidazole staining. Conclusion: Epo in combination with enalapril caused additive reduction of cardiac fibrosis and microvessel disease in 5/6 nephrectomized rats presumably by decreasing myocardial oxidative stress.

Letter to the Editor

I read with interest the article entitled: “Cardiac Troponin I in Calves with Congenital Heart Disease” (Suzuki, et al., JVIM, 2012 DOI: 10.1111/j.1939-1676.2012.00953.x).1 This study deals with an understudied area of internal medicine: cardiology in food animals. Adding evidence-based studies is of great importance but can be challenging especially for unfrequent diseases. The authors concluded that the blood levels of cardiac troponin I (cTnI) can be of interest in for diagnosing congenital heart disease (CHD) in calves. They also state that “using a cutoff value of ≥ 0.035 ng/mL, cTnI in plasma may distinguish calves with and without significant CHD with reasonnable sensitivity and specificity.” Designing of diagnostic accuracy studies is challenging not only in veterinary medicine but also in human medicine.2 The case selection of control group to assess the specificity of the cTnI levels needs to be discussed since it may certainly overestimate test accuracy. Using healthy control subjects in case-control studies commonly led to overestimation of diagnostic accuracy compared with cohort study.3 As discussed by the authors, the clinical diagnosis of CHD in calves is challenging without echocardiography since the clinical signs especially cardiac murmur can be found in calves without CHD (anemia, excitement or fever) as well as various signs of respiratory distress. It has been shown that cTnI can be increased in cattle due to various thoracic diseases4, 5 or endotoxemia.6 Such animals may represent a better group to establish the specificity of the diagnostic accuracy of cTnI in calves with heart murmur and CHD to calves with heart murmur due to various cardiorespiratory condition or endotoxemia/sepsis. Another concern that has not been addressed in that study is that the test accuracy has been determined in only 12 cases with various CHD and 19 healthy control animals. With this small sample although the receiver operating characteristic lead to interesting Se/Sp of this test in their sample of calves, the authors did not mention that before doing any inference of their best Se/Sp value of cTnI, they need to calculate the 95% confidence interval (CI) for their values. Such a small sample of animals would lead to a wider imprecision of their Se/Sp estimate to extrapolate to the general population that needs to be known by any clinician attempting to include cTnI determination in their diagnostic workup for suspected calves with CHD. Morerover, determining a threshold (here 0.035 ng/mL) although interesting, needs to be discussed in regard with the method of determination of cTnI. Previous studies in dogs7 have shown that normal ranges should be established for every technique/analyzer used for establishing cTnI levels since difference in the antibodies used in the assays could lead to differences in results obtained with different analyzers. Moving from this point, it is difficult to extrapolate the proposed threshold without comparisons of other point of care cTnI analyzers that could be used in the farm with portative analyzers that may be used for cTnI determination. Finally, despite having a threshold for diagnosing CHD in calves could be interesting, from a practical perspective, it would have been interesting to know if the cTnI values were quite different depending on the exact nature of CHD. The impact of the heart defect on cardiomyocytes oxygen delivery may (or may not) be different in a case of early VSD without any cardiac chamber modification whereas hypoxemia due to intracardiac shunt may lead to increased cTnI due to myocardial hypoxia in cyanotic heart disease (Tetralogy of Fallot or double outlet right ventricle which represent 6 of 12 cases investigated in the present study1). This study raises interesting points concerning potential interest of cTnI in the diagnosis of CHD in calves. However, the authors did not convince me that it could replace transthoracic echocardiography which is more specific in living animals and more sensitive (for experienced user) especially for commonly encountered CHD such as VSD. Having higher number of CHD calves and calves with various conditions that could clinically mimick CHD would be of great interest to investigate more accurately Se/Sp of this cardiac biomarker. Using the proposed threshold to diagnose CHD in calves without other confirmatory test would certainly lead to overdiagnosing CHD in calves with simple infectious respiratory conditions or endotoxemic condition.

Assessment of the electrocardiogram in dogs with visceral leishmaniasis

As myocarditis and arrhythmias have been shown to occur in both human beings and dogs with leishmaniasis, electrocardiograms of 105 dogs serologically positive for this disease were assessed for rhythm disturbances and changes in ECG waves. A few expressive alterations were seen, including sinus arrest, right bundle branch block, and atrial premature beats in 14.3%, 4.8%, and 4.8% of the studied subjects, respectively. Also, the analysis of ECG waves showed changes suggestive of left atrium and ventricle enlargements, and myocardial hypoxia in some animals. Although cardiac compromise has been previously reported in dogs with leishmaniasis, only a small subset of dogs showed any alteration in the electrocardiogram, which cannot support the occurrence of myocarditis in this investigation.

Flow Modulation Algorithms for Intra-Aortic Rotary Blood Pumps to Minimize Coronary Steal

Intra-aortic rotary blood pumps (IARBPs) have been used for partial cardiac support during cardiogenic shock, myocardial infarction, percutaneous coronary intervention, and potentially viable for long-term circulatory support. Intra-aortic rotary blood pump support continuously removes volume from the aortic root, which lowers left ventricular preload, external work (LVEW), and improves end-organ perfusion. However, IARBP support diminishes aortic root pressure and coronary artery. It may also create "coronary steal," which may produce a myocardial hypoxic state adversely affecting patient outcomes. Our objective was to develop IARBP flow modulation algorithms to eliminate coronary steal and improve the myocardial supply-demand ratio without compromising the clinical benefits of restored end-organ perfusion and reduced LVEW. The hemodynamic responses of the native ventricle, coronary, and systemic vasculature to timing and synchronization of IARBP flow modulation (cyclic variation of pump flow) were investigated using a clinical heart failure (HF) computer simulation model. A total of more than 150 combinations of varying pulse widths and time-shifts to modulate IARBP flow were tested at mean IARBP flow rates of 2, 3, and 4 L/min, and compared with HF baseline values (no IARBP support). Increasing IARBP support augmented cardiac output and diminished LVEW. Nonmodulated IARBP support significantly diminished mean diastolic coronary flow (-49%) and myocardial supply-demand ratio (-12%) compared with HF baseline. Intra-aortic rotary blood pump flow modulation increased mean diastolic coronary flow (+17%) and myocardial supply-demand ratio (+24%) compared with nonmodulated IARBP (constant flow). Modulation and synchronization of IARBP support augmented coronary artery perfusion and myocardial supply-demand ratio in simulated clinical HF while also restoring end-organ perfusion and reducing LVEW. Implementation of IARBP support with flow modulation may prevent myocardial hypoxia and improve patient outcomes. However, even with flow modulation, IARBP support provides a smaller improvement in myocardial supply demand ratio compared to ventricular assist devices and intra-aortic balloon pumps.

Erythropoietin as a new player in multiple neurohumoral dysregulations underlying chronic heart failure and therapeutic strategies against them

Patients with chronic overt heart failure (CHF) are frequently anemic despite elevated endogenous erythropoietin (EPO) levels due to blunting of EPO-induced JAK-STAT signaling in circulating erythroid progenitor cells [1]. EPO induces positive inotropic and lusitropic effects in the murine and human myocardium through PI3-K and PKCe isoform signaling to directly affect both calcium release dynamics and myofilament function [2], and an administration of EPO leads to significantly improved cardiac function without an increase in hematocrit following myocardial infarction in rabbits [3]. In contrast to CHF, atrial fibrillation (AF) and complete right bundle branch block (RBBB) in apparently healthy subjects are associated with increased hemoglobin levels [4] and the author speculated that increased blood levels of hemoglobin may reflect increased EPO secretion which results from subclinical tissue hypoperfusion caused by AF or RBBB in an apparently normal heart [4]. The increased blood levels of EPO and hemoglobin with an intact EPO signaling cascade may compensate for the subclinical adverse hemodynamic effects of AF or RBBB andprevent the development of CHF together with other compensatory mechanisms such as the renin–angiotensin– aldosterone system (RAAS) and sympathetic nervous system (SNS) in apparently normal heart. Acute activations of RAAS and SNS enhance cardiac performance and the activations lasting relatively short periods lead to ventricular hypertrophy. However, chronic hyperactivities of RAAS and SNS exacerbate CHF and strategies to reduce these hyperactivities using angiotensin converting enzyme inhibitors/angiotensin receptor blockers/aldosterone inhibitors and β-blockers have been established as the standard therapy for CHF. Hyperinsulinemia and insulin resistance may contribute to the progressive deterioration in myocardial function and associated clinical features of fatigue and reduced exercise tolerance in CHF [5]. Inhibition of hyperinsulinemia substantially improves pressure overload-induced cardiac dysfunction, improving myocardial hypoxia and decreasing cardiomyocyte death, and cardiomyocyte-specific reduction of insulin receptor expression prevents cardiac ischemia and hypertrophy and attenuated systolic dysfunction due to pressure overload in rodents [6]. Long-term treatment with metformin, but not with rosiglitazone, prevents the development of severe CHF in the spontaneously hypertensive insulin-resistant rats by a wide-spectrum interaction that involves molecular, structural, functional, and metabolic-energetic mechanisms [7]. Mechanical unloading after left ventricular assist device implantation corrects systemic and local metabolic derangements in advanced CHF, leading to reduced myocardial levels of toxic lipid intermediates and improved cardiac insulin resistance [8]. In moderate CHF, elevated leptin levels are associated with insulin resistance independently of body fat mass [9]. The compensatory activity of the cardiac natriuretic peptide system is attenuated as mortality increases in CHF patients with high plasma levels of natriuretic peptide [10], which suggests natriuretic peptide resistance. Beneficial effects of diuretics may include amelioration of natriuretic peptide resistance in addition to reduction of congestive symptoms and ventricular preload. These neurohumoral dysregulations and therapeutic strategies against them are summarized in Table 1. The history of CHF therapy suggests that suppression of natriuretic peptide system or EPO system may be a new potential therapeutic strategy for CHF.

Pigs in space

Despite the common knowledge that experimental data from animal models cannot readily be translated into human disease, clinical trials are often based on translational research performed on species evolutionarily distant from humans. The troublesome task of extrapolating the findings from one species to another has haunted physiological experimentation since its early dawn, and the issue is still relevant in cardiovascular science with the common use of genetically modified mice. For instance, diabetic and ischemic changes in the myocardium are often pursued using in-vivo and in-vitro models mainly based on rodent cardiovascular physiology and cellular biology 1. The concern does not stop with only speculative reservation. Modern pharmacological studies most often test new drugs on small animals, resulting in a series of disappointments in human phase-3 trials 2,3, which has certainly cost us astronomical sums and may have even led to disease and death. The cardiac response to myocardial hypoxia should ideally be pursued in models that mimic human anatomy, biochemistry, and function in both health and disease. In this context, we suggest the porcine heart as the best model of choice in experimental cardiovascular research because of the following hallmarks: first and foremost, the coronary blood supply to the myocardium equals that of the normal human anatomy 4. In contrast, the functional end arteries do not supply the heart muscle in other mammalian species. Second, the cardiac production of natriuretic peptides, the gold standard endocrine markers of heart failure, differs markedly among mammalian hearts, wherein normal hormonal expression resides in the human and porcine atria 5,6 but is most dominant in the ventricular chambers in, for instance, rodents 7. Such intrinsic differences are likely to affect the endocrine cardiac response during the disease. Finally, porcine and human cardiac functions are similar, which facilitates direct interpretation to human medicine 8. Elucidation of several cardiovascular disease entities can be achieved using porcine models. For instance, we compared the neonate cardiovascular response of pigs in terms of cardiac natriuretic peptide gene expression and found patterns similar to those of neonate children. This opens up for the possibility of studying, for instance, the effects of gestational diabetes on neonate physiology. Moreover, cardiac congenital anomalies present in humans can easily be induced in pigs, and the devices for treating these conditions can even be tested on pigs 9. Another major disease entity for cardiovascular endocrinology is heart failure, in which natriuretic peptides have a central role in both pathobiological and clinical diagnosis. Accurate biochemical tools have been developed for this peptide system in pigs 10, which is not the case for other species, including mice. With an increasing appreciation and understanding of the porcine transcriptome 11,12, as well as genetically modified pigs already over the doorstep 13,14, cardiovascular endocrinology should consider the best choice of animal models for the studies on human cardiovascular pathophysiology. In this respect, a completely new pig model for human atherosclerosis has just been developed at our university by inducing overexpression of the gene for liver-specific proprotein convertase subtilisin/kexin type 9 (PCSK9), which causes severe hypercholesterolemia and human-like atherosclerosis 15. This model may easily prove valuable for several types of translational research on atherosclerosis and also in diabetes complications. For now, we would like to advocate that the use of pigs should be pursued more eagerly in elucidating human cardiovascular endocrinology (as pigs are only found in space in the Muppet Show) 16,17. Acknowledgements Conflicts of interest There are no conflicts of interest.

Altering HIF-1α Through 2,3,7,8-Tetrachlorodibenzo-p-Dioxin (TCDD) Exposure Affects Coronary Vessel Development

Differential tissue hypoxia drives normal cardiogenic events including coronary vessel development. This requirement renders cardiogenic processes potentially susceptible to teratogens that activate a transcriptional pathway that intersects with the hypoxia-inducible factor (HIF-1) pathway. The potent toxin 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is known to cause cardiovascular defects by way of reduced myocardial hypoxia, inhibition of angiogenic stimuli, and alterations in responsiveness of endothelial cells to those stimuli. Our working hypothesis is that HIF-1 levels and thus HIF-1 signaling in the developing myocardium will be reduced by TCDD treatment in vivo during a critical stage and in particularly sensitive sites during heart morphogenesis. This inadequate HIF-1 signaling will subsequently result in outflow tract (OFT) and coronary vasculature defects. Our current data using the chicken embryo model showed a marked decrease in the intensity of immunostaining for HIF-1α nuclear expression in the OFT myocardium of TCDD-treated embryos. This area at the base of the OFT is particularly hypoxic during normal development; where endothelial cells initially form a concentrated anastomosing network known as the peritruncal ring; and where the left and right coronary arteries eventually connect to the aortic lumen. Consistent with this finding, anomalies of the proximal coronaries were detected after TCDD treatment and HIF-1α protein levels decreased in a TCDD dose-dependent manner.