Veronika Olejníčková

Isolated heart models: cardiovascular system studies and technological advances

Isolated heart model is a relevant tool for cardiovascular system studies. It represents a highly reproducible model for studying broad spectrum of biochemical, physiological, morphological, and pharmaceutical parameters, including analysis of intrinsic heart mechanics, metabolism, and coronary vascular response. Results obtained in this model are under no influence of other organ systems, plasma concentration of hormones or ions and influence of autonomic nervous system. The review describes various isolated heart models, the modes of heart perfusion, and advantages and limitations of various experimental setups. It reports the improvements of perfusion setup according to Langendorff introduced by the authors.

Moderate hypothermia during ex vivo machine perfusion promotes recovery of hearts donated after cardiocirculatory death

OBJECTIVES To establish the optimal machine perfusion temperature for recovery of hearts in a rodent model of donation after declaration of cardiocirculatory death (DCD). METHODS Hearts from male Lewis rats (n = 14/group) were subjected to 25 min of in situ warm (37°C) ischaemia to simulate DCD. They were then explanted and reperfused with diluted autologous blood for 60 min at 20, 25, 30, 33 or 37°C, after which they were stored at 0-4°C in Custodiol preservation solution for 240 min. Fresh-excised and cold-stored ischaemic hearts were used as controls. The viability of the different groups was assessed by comparing heart rate and left ventricular contractility in a Langendorff circuit, as well as perfusate levels of troponin-t and creatine kinase (CK), and myocardial levels of adenosine triphosphate (ATP) and reduced glutathione. RESULTS During ex vivo reperfusion, hearts in all groups resumed beating within minutes. The mean heart rate was highest in the 37°C group at 154.72 ± 33.01 beats × min(-1) (bpm), and declined in proportion to temperature to 39.72 ± 5.53 bpm at 20°C. Troponin-t levels were highest in the 37°C group (79.49 ± 20.79 µg/l), the values were significantly lower in all other reconditioned groups with a minimum of 12.472 ± 7.08 µg/l in the 20°C group (P < 0.0001). Tissue ATP levels ranged from 4.32 ± 1.71 µmol/g at 33°C to 4.59 ± 1.41 µmol/g at 30°C, all significantly higher than the mean ATP level of 1.41 ± 0.93 µmol/g in untreated ischaemic hearts (P < 0.0001). During Langendorff assessment, the mean heart rate and contractility of all groups were higher than those of cold-stored ischaemic hearts (P < 0.0001), yet not significantly different from those of fresh controls. The perfusate levels of troponin-t and CK, and myocardial levels of reduced-glutathione and ATP were not significantly different between groups. CONCLUSION Our results suggest that mild hypothermia during ex vivo reperfusion improves recovery of ischaemic hearts in a rodent DCD model.

Long-term haloperidol treatment prolongs QT interval and increases expression of sigma 1 and IP3 receptors in guinea pig hearts

Haloperidol is a neuroleptic drug used for a medication of various psychoses and deliria. Its administration is frequently accompanied by cardiovascular side effects, expressed as QT interval prolongation and occurrence of even lethal arrhythmias. Despite these side effects, haloperidol is still prescribed in Europe in clinical practice. Haloperidol binds to sigma receptors that are coupled with inositol 1,4,5-trisphosphate (IP3) receptors. Sigma receptors are expressed in various tissues, including heart muscle, and they modulate potassium channels. Together with IP3 receptors, sigma receptors are also involved in calcium handling in various tissues. Therefore, the present work aimed to study the effects of long-term haloperidol administration on the cardiac function. Haloperidol (2 mg/kg once a day) or vehiculum was administered by intraperitoneal injection to guinea pigs for 21 consecutive days. We measured the responsiveness of the hearts isolated from the haloperidol-treated animals to additional application of haloperidol. Expression of the sigma 1 receptor and IP3 receptors was studied by real time-PCR and immunohistochemical analyses. Haloperidol treatment caused the significant decrease in the relative heart rate and the prolongation of QT interval of the isolated hearts from the haloperidol-treated animals, compared to the hearts isolated from control animals. The expression of sigma 1 and IP3 type 1 and type 2 receptors was increased in both atria of the haloperidol-treated animals but not in ventricles. The modulation of sigma 1 and IP3 receptors may lead to altered calcium handling in cardiomyocytes and thus contribute to changed sensitivity of cardiac cells to arrhythmias.

Classification of ventricular premature and ischemic beats in animal electrograms

Many approaches have been proposed for automatic classification of different pathological events in ECG signals. Present study is focused on analysis and classification of non-ischemic, moderate and severe ischemic, and VPB segments in data obtained in rabbit isolated hearts. It is shown, that use of low number of morphological parameters calculated from electrograms combined with even simple classification method allows achieving of accurate results (with overall accuracy up to 0.99) for four types of the segments.

Effect of increased left ventricle mass on ischemia assessment in electrocardiographic signals: rabbit isolated heart study

BackgroundDetailed quantitative analysis of the effect of left ventricle (LV) hypertrophy on myocardial ischemia manifestation in ECG is still missing. The associations between both phenomena can be studied in animal models. In this study, rabbit isolated hearts with spontaneously increased LV mass were used to evaluate the effect of such LV alteration on ischemia detection criteria and performance.MethodsElectrophysiological effects of increased LV mass were evaluated on sixteen New Zealand rabbit isolated hearts under non-ischemic and ischemic conditions by analysis of various electrogram (EG) parameters. To reveal hearts with increased LV mass, LV weight/heart weight ratio was proposed. Standard paired and unpaired statistical tests and receiver operating characteristics analysis were used to compare data derived from different groups of animals, monitor EG parameters during global ischemia and evaluate their ability to discriminate between unchanged and increased LV as well as non-ischemic and ischemic state.ResultsSuccessful evaluation of both increased LV mass and ischemia is lead-dependent. Particularly, maximal deviation of QRS and area under QRS associated with anterolateral heart wall respond significantly to even early phase (the 1st-3rd min) of ischemia. Besides ischemia, these parameters reflect increased LV mass as well (with sensitivity reaching approx. 80%). However, the sensitivity of the parameters to both phenomena may lead to misinterpretations, when inappropriate criteria for ischemia detection are selected. Particularly, use of cut-off-based criteria defined from control group for ischemia detection in hearts with increased LV mass may result in dramatic reduction (approx. 15%) of detection specificity due to increased number of false positives. Nevertheless, criteria adjusted to particular experimental group allow achieving ischemia detection sensitivity of 89–100% and specificity of 94–100%, respectively.ConclusionsIt was shown that response of the heart to myocardial ischemia can be successfully evaluated only when taking into account heart-related factors (such as LV mass) and other methodological aspects (such as recording electrodes position, selected EG parameters, cut-off criteria, etc.). Results of this study might be helpful for developing new clinical diagnostic strategies in order to improve myocardial ischemia detection in patients with LV hypertrophy.

Calcium versus strontium handling by the heart muscle

Calcium plays a crucial role in numerous processes in living systems, from both intracellular and intercellular signalling to blood clotting. Calcium can be replaced by strontium in various intracellular processes due to high level of their similarity and strontium thus may serve as a valuable tool for different experimental studies. On the other hand, strontium is also used in clinical medicine and is commonly taken to the human body with food and water. The negative cardiac side effects of strontium therapy of osteoporosis and bone metastases are well known, but still not fully explained. This fact explains enhanced interest in this element and its impact on human body. This article reviews effects of calcium and strontium on several biochemical and physiological processes, with special emphasis on cardiac muscle.

Voltage sensitive dye di-4-ANNEPS prolongs impulse conduction through ventricles, but not through AV node in isolated rabbit heart

Voltage sensitive dyes are widely used for recording of action potential in various cardiac studies. The elementary condition for its application is the fact that measured electrophysiological parameters would not be affected by the measuring procedure itself. The RR interval prolongation in the presence of the most frequently used voltage sensitive dye di-4-ANEPPS has been reported, but its exact mechanism is not known. In this study, the impact of di-4-ANEPPS on impulse conduction through the atrioventricular (AV) node and through cardiac ventricles in isolated rabbit heart was examined. The impulse conduction through AV node in the presence of di-4-ANEPPS was prolonged only during dye loading in the 14th, 16th and 17th minute. Only sporadic AV blocks were observed. In comparison, the prolongation of impulse conduction through cardiac ventricles was observed from the 13th minute of loading and persisted to the end of this phase as well as over the whole wash out phase.

The effect of heart orientation on high frequency QRS components in multiple bandwidths

Reduced power of high frequency (HF) oscillations inside the QRS complex reflects ischemic pathology in the heart. In order to show spatial and frequency dependencies, we examined the effect of heart orientation on power of high frequency components under normal and ischemia condition within various frequency bands. Root mean square (RMS) of the signal in QRS region within frequency bands from 150 Hz to 550 Hz and heart rotation around longitudinal axes (360°) were computed from four rabbit isolated hearts. Experimental protocol included control, ischemic and reperfusion phases. This pilot study shows that RMS level of HF signal in non-ischemic heart differs within lead orientation and its maximum lies in a region around specific angle. Relative decrease in RMS value also depends on lead position. When depicted in spatial-frequency plane with polar coordinates, these relative changes contributes to specific patterns under both normal and ischemic conditions, which should be further examined.

The effect of voltage-sensitive dye di-4-ANEPPS on heart rate variability in Langendorff-perfused isolated rabbit heart

Optical mapping of heart electrical activity in Langendorff-perfused isolated hearts is based on voltage-sensitive dyes, of which the most commonly used one is di-4-ANEPPS. Prolongation of action potential duration by di-4-ANEPPS was reported in isolated cells; however, this phenomenon was not observed in the whole heart model. In order to search for other adverse phenomena of di-4-ANEPPS use, its effect on heart rate variability (HRV) was investigated during staining and washout periods in jive New Zealand White rabbit isolated hearts. Time domain, frequency domain and non-linear HRV parameters (21 in total) revealed that there are no significant changes between control, staining and washout periods. Voltage-sensitive dye di-4-ANEPPS does not affect HRV when applied into the isolated heart coronary system. It can be concluded that di-4-ANEPPS may be safely used in studies combining optical mapping and HRV analysis.