A flexibly mounted microdialysis probe was used to measure the concentration of interstitial adenosine in in vivo rat hearts. The level of adenosine during perfusion of adenosine 5'-monophosphate (AMP) was given as an index of the activity of ecto-5'-nucleotidase in the tissue. The adenosine dialysate measured the concentration using reversed-phase high performance liquid chromatography (HPLC) and the absorbance of the column eluate was monitored at 260 nm using an ultraviolet detector. The baseline level of adenosine concentration measured in the absence of exogenous AMP was -0.5 μM, which was lower than the level of adenosine concentration seen in the presence of 100 μM AMP (-9 μM). In the presence of the selective inhibitor of ecto-5'-nucleotidase, α, β-methyleneadenosine-5'-diphosphate (AOPCP) at a concentration of 100μM in the perfusate, AMP (100 μM) -induced increases of adenosine in the dialysate were completely inhibited and remained at -0.5 μM, a level close to the baseline. When various concentrations of AMP (ranging from 10 to 1000μM) were applied through the probe, the steady state levels of dialysate adenosine rose with increases in the concentration of AMP. The EC₅₀ values was 107.2 μM. This value is much closer to the Km for 'ecto-'than that for 'cytosolic'5'-nucleotidase. Ecto-5'-nucleotidase has a lower Km for AMP (-20 μM) than does cytosolic 5'-nucleotidase (-3 mM). Under a constant supply of substrate (AMP) a limiting factor for the production of adenosine would be the activity of the catalytic enzyme for this reaction, namely ecto-5'-nucleotidase.

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Background : It is well known that many patients with heart failure have sleep apnea syndrome (SAS). It is also reported that cycles of apnea and heart rate are similar in SAS. In this study, we examined whether it would be possible to confirm the existence of SAS by fractal analysis as one of the procedures of heart rate variability (HRV) analysis. Methods : Before and after SAS treatment, fifteen patients performed 24-hour ambulatory electrographic recordings and sleep apnea examinations. Thirteen patients were male. The mean age was 72 years old. The basic heart rhythm was sinus rhythm in all cases. HRV analysis was performed by fast Fourier transform analysis and displayed results by the method to calculate a fractal dimension to detect SAS components. Results : Before SAS treatment, the apnea hypopnea index (AHI) was more than 20 in all patients. They also showed the abnormal power increase from 0.01 to 0.04Hz, that is SAS components, in HRV analysis at baseline. After SAS treatment, their AHI decreased and SAS components also became smaller or disappeared, but SAS components still presented when SAS treatment was insufficient. Conclusion : The abnormal power increase shown by fractal analysis of HRV reflected the existence of SAS, and this power disappeared after SAS treatment. Detecting this power is useful for predicting SAS and confirming efficacy of treatment.

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The relationship between electrocardiographic RR and QT interval variabilities were evaluated, based on the QT variability ratio (VR) in prepubescent children, to investigate the influence of aging. One hundred and seventy-six subjects with no heart disease, ranging from infants to school children, were categorized into 6 groups for a comparative study ; Group I(17 infants aged 0 to 6 months), Group II(21 infants aged 7 to 11 months), Group III(28 infants aged 1 year), Group IV(37 children aged 2 to 3 years), Group V(36 children aged 4 to 5 years), Group VI(37 children aged 6 to 7 years). Regarding the methods, the RR-interval and QT-interval of 120 heart beats were measured at rest to calculate the VR based on the standard deviation of the RR-interval (SDRR) and the standard deviation of the QT-interval (SDQT) in order to investigate the relationship with the age of subjects (months). As a result, there were no gender differences between groups for VR, SDRR and SDQT, and VR decreased in accordance with aging, but became stable when the children reached school age. This study supports the potential application of the standard value of VR by age to evaluate imbalances in the cardiac cycle and myocardial repolarization.

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We present a 22-year-old male without previous cardiac disease, who suddenly collapsed due to ventricular fibrillation during American football practice He had no family history of unexplained sudden death or syncope. Bystander-initiated cardiopulmonary resuscitation (CPR) was not provided there, and shocks using automated external defibrillator (AED) were delivered by rescue crews. Fortunately, the patient recovered without after-effects. Investigations such as electrocardiograms (ECGs), echocardiography, coronary computed-tomography angiography and cardiac magnetic resonance imaging (MRI) did not reveal any significant cardiac abnormalities. A 3-dimentional electroanatomical voltage mapping of the right ventricle (RV) revealed the presence of low-voltage areas around the RV outflow tract, although no sustained ventricular arrhythmia (VA) was induced by ventricular programmed stimuli. Signal-averaged ECG revealed a positive result for ventricular late potentials. It was quite difficult to distinguish cardiac diseases predisposed to VAs from commotio cordis, therefore an implantable cardioverter-defibrillator (ICD) implantation was performed and appropriate shocks were later delivered. This patient case may be helpful to learn how to deal with cardiopulmonary arrest during exercise and also demonstrate the necessity for placement of AEDs in public facilities including recreation grounds and CPR training of lay persons.

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