Tolerance of isolated rabbit hearts to short ischemic periods is affected by increased LV mass fraction.

Hypertrophied hearts are known for increased risk of arrhythmias and are linked with reduced ischemic tolerance. However, still little is known about state characterized only by increased left ventricle (LV) mass fraction. Seventeen isolated rabbit hearts with various LV mass were divided into two groups according to LV weight/heart weight ratio (LVW/HW ratio), namely group H and L (with higher and lower LVW/HW ratio, respectively) and underwent three short cycles of global ischemia and reperfusion. The differences in electrogram (heart rate, QRS(max), mean number, onset and dominant form of ventricular premature beats) and in biochemical markers of myocardial injury (creatine kinase, lactate dehydrogenase - LDH) and lipid peroxidation (4-hydroxy-2-nonenal - 4-HNE) were studied. As compared to group L, hearts in group H exhibited lower tolerance to ischemia expressed as higher incidence and severity of arrhythmias in the first ischemic period as well as increase of LDH and 4-HNE after the first reperfusion. In the third cycle of ischemia-reperfusion, the preconditioning effect was observed in both electrophysiological parameters and LDH release in group H. Our results showed consistent trends when comparing changes in electrograms and biochemical markers. Moreover, 4-HNE seems to be good potential parameter of moderate membrane alteration following ischemia-reperfusion injury.

Motion artefact in voltage-sensitive fluorescent dye emission during repeated ischemia of isolated heart.

Motion artefact (MA) in voltage-sensitive fluorescent signals causes significant debasement of action potential. During ischemia and reperfusion in isolated rabbit heart, this artefact develops in a manner which may be described by the time of its onset, level, and shape. The MA during ischemia: (a) may become substantial with approximately two minutes delay after establishing global ischemia; (b) may be almost twice as high as the physiological action potential and decreases both with time and repetition of ischemia; (c) the MA shape is unpredictable and depends on individual rabbit.

Application of the optical method in experimental cardiology: action potential and intracellular calcium concentration measurement.

It has been shown that, in addition to conventional contact electrode techniques, optical methods using fluorescent dyes can be successfully used for cardiac signal measurement. In this review, the physical and technical fundamentals of the method are described, as well as the properties of the most common systems for measuring action potentials and intracellular calcium concentration. Special attention is paid to summarizing limitations and trends in developing this method.

Three-dimensional electrogram in spherical coordinates: application to ischemia analysis.

Three-dimensional electrogram was used for analysis of ischemia manifestation in isolated hearts. Three parameters based on spherical coordination system were used in this study - amplitude of electrical heart vector, its azimuth and elevation. The parameters were presented as a trend. This approach reflected ischemic changes in a manner which can be easily observed and evaluated. Ischemia was analysed in seven isolated hearts of New Zealand white rabbits. It was found that (a) ischemia changes heart electric vector, (b) ischemic preconditioning has a protective effect, and (c) both of these findings can be clearly observed by the proposed method.

Experimental methods for simultaneous measurement of action potentials and electrograms in isolated heart.

Monophasic action potential (MAP) can be recorded from the heart surface by optical method based on fluorescence measurement. The motion of isolated heart during experiment caused additional noise in recorded signal. The motion artifact can be eliminated by ratiometric fluorescence emission measurements. This study is based on experiments in which optical MAP measurement is done by single-wavelength and dual-wavelength measurement of fluorescence emission. Both recording setups are presented and their advantages and disadvantages are discussed. MAPs recorded by both methods from isolated rabbit hearts perfused according to Langendorff are presented. Simultaneous electrograms (EG) and MAPs recording are analyzed and measurement of velocity of impulse conduction through heart tissue is presented.

Effects of voltage sensitive dye di-4-ANEPPS on guinea pig and rabbit myocardium.

Voltage-sensitive dyes (VSDs) are used to record transient potential changes in various cardiac preparations. In our laboratory, action potentials have been recorded by optical probe using di-4-ANEPPS. In this study, the effects of two different ways of staining were compared in guinea pig and rabbit isolated hearts perfused according to Langendorff: staining either by coronary perfusion with low dye concentration or with concentrated dye as a bolus into the aorta. Staining with low dye concentration lead to its better persistence in the tissue. Electrogram and coronary flow were monitored continuously. During the staining and washout of the dye, prominent electrophysiological changes occurred such as a decrease in spontaneous heart rate, partial atrioventricular block and changes of ST-T segment, accompanied by a decrease in mean coronary flow. No production of hydroxyl radicals was found by HPLC which excluded significant ischemic damage of the myocardium. Good viability of the stained preparation was supported by unchanged electron microscopy. Since in rabbit hearts the VSD-induced arrhythmogenesis was less pronounced, we conclude that the rabbit myocardium is more resistant to the changes triggered by VSD application. It may be due to different properties of the membrane potassium channels in the cardiomyocytes of these two species.

Comparison of Point Similarity Measures for Atlas-based Registration of MRI Brain Images.

High-dimensional deformable registration of MRI brain images is presented here. The deformation is driven by local forces estimated from point similarities based on joint histogram and with the use of prior information obtained from tissue probability maps available in selected commonly used brain atlases. Three point similarity measures are tested in an experiment with data obtained from standard Simulated Brain Database.

Analysis of optical recording stability using wavelet entropy of action potentials.

A method based on wavelet entropy is presented for analysis of optically recorded action potentials to assess stability of the experiment. The action potentials are recorded using fluorescent voltage-sensitive dye di-4-ANEPPS by optical means. The acquired signals are preprocessed using averaging with filtered residue method and decomposed by continuous wavelet transform. Entropy is then computed using the wavelet coefficients. Wavelet entropy helps to detect possible amplitude and frequency changes in the signals caused by photo-bleaching.

Wavelet transform in electrocardiography--data compression.

An application of the wavelet transform to electrocardiography is described in the paper. The transform is used as a first stage of a lossy compression algorithm for efficient coding of rest ECG signals. The proposed technique is based on the decomposition of the ECG signal into a set of basic functions covering the time-frequency domain. Thus, non-stationary character of ECG data is considered. Some of the time-frequency signal components are removed because of their low influence to signal characteristics. Resulting components are efficiently coded by quantization, composition into a sequence of coefficients and compression by a run-length coder and a entropic Huffman coder. The proposed wavelet-based compression algorithm can compress data to average code length about 1 bit/sample. The algorithm can be also implemented to a real-time processing system when wavelet transform is computed by fast linear filters described in the paper.