Ionic mechanisms of the depression of automaticity and conduction in the rabbit atrioventricular node caused by hypoxia or metabolic inhibition and protective action of glucose and valine

Differences in the serum metabolic profile to identify potential biomarkers for cyanotic versus acyanotic heart disease

BACKGROUND

Growth retardation, malnutrition, and failure to thrive are some of the consequences associated with congenital heart diseases. Several metabolic factors such as hypoxia, anoxia, and several genetic factors are believed to alter the energetics of the heart. Timely diagnosis and patient management is one of the major challenges faced by the clinicians in understanding the disease and provide better treatment options. Metabolic profiling has shown to be potential diagnostic tool to understand the disease.

OBJECTIVE

The present experiment was designed as a single center observational pilot study to classify and create diagnostic metabolic signatures associated with the energetics of congenital heart disease in cyanotic and acyanotic groups.

METHODS

Metabolic sera profiles were obtained from 35 patients with cyanotic congenital heart disease (TOF) and 23 patients with acyanotic congenital heart disease (ASD and VSD) using high resolution 1D ¹H NMR spectra. Univariate and multivariate statistical analysis were performed to classify particular metabolic disorders associated with cyanotic and acyanotic heart disease.

RESULTS

The results show dysregulations in several metabolites in cyanotic CHD patients versus acyanotic CHD patients. The discriminatory metabolites were further analyzed with area under receiver operating characteristic (AUROC) curve and identified four metabolic entities (i.e. mannose, hydroxyacetone, myoinositol, and creatinine) which could differentiate cyanotic CHDs from acyanotic CHDs with higher specificity.

CONCLUSION

An untargeted metabolic approach proved to be helpful for the detection and distinction of disease-causing metabolites in cyanotic patients from acyanotic ones and can be useful for designing better and personalized treatment protocol.

Serum Metabolomics Profiling to Identify Biomarkers for Unstable Angina

Although statistical evidence is clear regarding the dangerousness of unstable angina (UA), a form of coronary heart disease (CHD) characterised by high mortality and morbidity globally, it is important to recognise that diagnostic precision for the condition is unfavourable. In the present research, to gain insight into candidate biomarkers, the author draws on ¹H NMR-based serum metabolic profiling to analyze the unstable angina pectoris (UAP) metabolic signatures; this constitutes an effective way to produce medical diagnosis. 101 unstable angina pectoris patients and 132 healthy controls were enrolled and 22 serum samples from each group were analyzed. Effective separation was noted regarding the UAP and control groups, and, for the former group considered in relation to their counterpart, the serum concentrations of Lac, m-I, lipid, VLDL, 3-HB, and LDL were higher whereas the concentrations of Thr, Cr, Cho, PC/GPC, Glu, Gln, Lys, HDL, Ile, Leu, and Val were lower. The conclusion drawn in view of the results is that the plasma metabolomics examined by ¹H NMR displayed promise for biomarker identification for UA. In addition to this, the analysis illuminated the metabolic processes of UA.

Amino acids as metabolic substrates during cardiac ischemia

The heart is well known as a metabolic omnivore in that it is capable of consuming fatty acids, glucose, ketone bodies, pyruvate, lactate, amino acids and even its own constituent proteins, in order of decreasing preference. The energy from these substrates supports not only mechanical contraction, but also the various transmembrane pumps and transporters required for ionic homeostasis, electrical activity, metabolism and catabolism. Cardiac ischemia - for example, due to compromise of the coronary vasculature or end-stage heart failure - will alter both electrical and metabolic activity. While the effects of myocardial ischemia on electrical propagation and stability have been studied in depth, the effects of ischemia on metabolic substrate preference has not been fully appreciated: oxygen deprivation during ischemia will significantly alter the relative ability of the heart to utilize each of these substrates. Although changes in cardiac metabolism are understood to be an underlying component in almost all cardiac myopathies, the potential contribution of amino acids in maintaining cardiac electrical conductance and stability during ischemia is underappreciated. Despite clear evidence that amino acids exert cardioprotective effects in ischemia and other cardiac disorders, their role in the metabolism of the ischemic heart has yet to be fully elucidated. This review synthesizes the current literature of the metabolic contribution of amino acids during ischemia by analyzing relevant historical and recent research.

Light-dark dependence of electrocardiographic changes during asphyxia and reoxygenation in a rat model

The aim of this study was to evaluate the effect of ventilation on electrocardiographic time intervals as a function of the light-dark (LD) cycle in an in vivo rat model. RR, PQ, QT and QTc intervals were measured in female Wistar rats anaesthetized with both ketamine and xylazine (100 mg/15 mg/kg, i.m., open chest experiments) after adaptation to the LD cycle (12:12h) for 4 weeks. Electrocardiograms (ECG) were recorded before surgical interventions; after tracheotomy, and thoracotomy, and 5 minutes of stabilization with artificial ventilation; 30, 60, 90 and 120 seconds after the onset of apnoea; and after 5, 10, 15, and 20 minutes of artificial reoxygenation. Time intervals in intact animals showed significant LD differences, except in the QT interval. The initial significant (p<0,001) LD differences in PQ interval and loss of dependence on LD cycle in the QT interval were preserved during short-term apnoea-induced asphyxia (30–60 sec) In contrast, long-term asphyxia (90–120 sec) eliminated LD dependence in the PQ interval, but significant LD differences were shown in the QT interval. Apnoea completely abolished LD differences in the RR interval. Reoxygenation restored the PQ and QT intervals to the pre-asphyxic LD differences, but with the RR intervals, the LD differences were eliminated. We have concluded that myocardial vulnerability is dependent on the LD cycle and on changes of pulmonary ventilation.

24 h rhythm of the ventricular fibrillation threshold during normal and hypoventilation in female Wistar rats

A 24 h rhythm of the ventricular fibrillation threshold (VFT) was investigated in female Wistar rats under conditions of normal ventilation (NV) (17 animals) and hypoventilation (HV) (10 animals). The animals were adapted to a daily 12:12 h light-dark cycle with the dark period from 18:00 to 06:00 under constant temperature conditions. The experiments were performed in pentobarbital anesthesia (40 mg/kg ip, open chest experiments) during the whole year, and the obtained results were averaged independently of the seasons. During NV, the VFT in female rats showed a significant 24 h rhythm (p < 0.01) with the mesor 2.59 +/- 0.53 mA, amplitude 0.33 +/- 0.11 mA, and acrophase -338 degrees (at 22:53 h) and the confidence intervals from -288 degrees to -7 degrees (from 19:12 to 00:28 h) using the population mean cosinor test. The maximal values of the VFT were measured in the active phase between 24:00 and 03:00 h. During HV, the rhythmicity of the VFT showed a more pronounced biphasic character with a smaller peak between 15:00 h and 18:00 h hours and a higher peak between 24:00 h and 03:00 h of the daily regime. Hypoventilation significantly decreased the VFT (p < 0.001) at each interval of the measurement. It is concluded that the electrical stability of the heart measured by the VFT shows a significant 24 h rhythm in female Wistar rats and that HV decreased the VFT during the whole 24 h period.

Prolonged repolarization during hypoxemia in epicardial electrogram: difference from ischemia and a competitive action of cyclic AMP

The effects of regional hypoxemia and ischemia on epicardial electrogram were studied in anesthetized, open-chest dogs. The left circumflex artery (LCx) was cannulated and perfused with either arterial blood or hypoxic solution. A contact electrode for recording monophasic action potential (MAP) was applied to the epicardial site of the LCx area. Epicardial electrograms and MAP in the LCx perfusion territory were recorded 1) just before and at the end of a 2-min coronary occlusion (ischemia) and 2) just before and at the end of a 2-min perfusion of hypoxic solution (hypoxemia). The activation-recovery interval (ARI), defined as an interval from the minimum derivative of the QRS complex to the maximum derivative of the T-wave in the unipolar electrogram, changed linearly with MAP duration during above interventions. The ARI decreased by 29% from 189 +/- 14 to 134 +/- 30 ms during ischemia (p < .001), and it increased by 39% from 183 +/- 11 to 254 +/- 31 ms during hypoxemia (p < .001). Hypoxemia produced a giant negative T-wave whose pattern was not modified by pretreatments with autonomic nerve blockers (propranolol and atropine), a Ca2+ channel blocker (verapamil), an ATP-sensitive K+ channel (KATP blocker (5-hydroxydecanoate or transient outward K+ current (I(to) blocker (4-aminopyridine). Isoproterenol, forskolin or aminophylline inhibited both the appearances of giant negative T and the ARI prolongation. Accordingly, unlike ischemia, hypoxemia prolongs repolarization process and this prolongation is inhibited by the augmentation of intracellular cyclic AMP.

Impulse formation and conduction of excitation in the atrioventricular node

Meijler et al. have recently challenged the classical concept of AV nodal conduction (the conduction hypothesis) and suggest that the AV node might be controlling ventricular rhythmicity through its automaticity electrotonically modulated by atrial excitation (the modulated pacemaker hypothesis). This article critically evaluates the three major arguments of Meijler: (1) the absence of convincing evidence for conduction of excitation in the AV node; (2) the prevalence of disproportionately short AV intervals in larger animals; and (3) elimination of RR intervals shorter than the cycle length of ventricular pacing during atrial fibrillation, to judge which of these two hypotheses would more satisfactorily explain various experimental and clinical findings accumulated in the past. Previous observations including microelectrode mapping of the rabbit AV junction during regular sinus rhythm as well as second-degree AV block, clinical and experimental studies on concealed conduction, and studies on the ventricular response to atrial fibrillation appear to be compatible with the conduction hypothesis, whereas clearcut evidence for automatic impulse formation in the AV node has not been presented, except in a small number of hearts showing spontaneous AV junctional rhythms. In view of these observations and theoretical considerations based on comparative anatomy of the AV node-His-Purkinje system and on the latest experimental study on the equine AV node, the authors conclude that the conduction hypothesis appears to better explain all the available data, except perhaps in a few cases with second-degree intra-AV nodal block.