[Electrophysiological mechanisms of heart rate stability of the hibernating mammals during hypothermia].

Despite more than 100 years of study, the mechanisms of natural resistance of the hibernator heart to cardiac arrhythmias during hypothermia has remained unknown. Renewed optimism in this area of research comes with recent methodological advances which enable to shed light on the hidden secrets of the hibernator's heart. This review discusses basic mechanisms of hypothermic ventricular arrhythmias and highlights some recent findings from the hibernator's heart electrophysiology, which may have an antiarrhythmic potential for the human heart as well.

[Hypothermia induced alteration of refractoriness in the ventricular myocardium of ground souirrel Citellus undulatus].

Bioelectrical activity and refractoriness in ventricular myocardium of the hibernator--ground squirrel Citellus undulatus were investigated during hypothermia. Experiments were performed with use of isolated, perfused preparations of papillary muscle from right ventricular. Preparations were obtained from hibernating (HS), summer active (SAS) squirrels and from rats. Bioelectrical activity was registered using the standard microelectrode technique at 37-17 degrees C. Action potentials duration (APD), refractoriness duration (RD) and the velocity of the action potential wave front (dV/dt) were estimated. Hypothermia induced APD and RD prolongation were demonstrated in all groups of experimental animals. However, normalized RD was significantly longer in the HS group during hypothermia than in SAS and rats. Ratio of RD to APD in HS group exceeds unity at 17 degrees C, which allows to suggest so called "postrepolarization refractoriness" during hypothermia. Also, HS reveal more prominent preservation of dV/dt during hypothermia than SAS and rat. Significant prolongation of RD and maintenance of normal excitation conduction during hypothermia probably plays essential role in hibernators resistivity to cold induced arrhythmias.

[Influence of new III class antiarrhythmic drug Niferidil (RG-2) on bioelectrical activity of rat pulmonary veins myocardium].

Myocardial cells in pulmonary veins are thought to play a major role in the initiation and maintenance of atrial arrhythmias, including atrial fibrillation. In experiments on rat pulmonary veins, antiarrhythmic drug niferidil (RG-2) produced increase of APD90% and functional refractory period and decrease of action potential amplitude and slope of APD restitution curve. Thus niferidil (RG-2) exerts stronger action on pulmonary veins than left atrium. This can take important part in Niferidil (RG-2) antiarrhythmic activity.

[Comparative study of cardiac alternans of action potential duration in hypothermia in rabbits and ground squirrels].

Cardiac alternans is a promising predictor of sudden death, yet its role in the mechanism of hypothermic arrhythmia induction is unclear. We aimed to investigate the effect of hypothermia on spatial-temporal characteristics of repolarization pattern in the Langendorff-perfused hearts of summer active (SA, n = 6) and winter hibernating (WH, n = 7) ground squirrels Spermophilus undulatus and rabbits (n = 5), who were immobilized with the excitation-contraction uncoupler BDM (10 mM) and optically mapped using the voltage sensitive dye di-4-ANNEPS and CCD camera (128 x 128 pixels; 500 frames/sec). Action potential duration (APD) restitution was quantified over the posterior epicardial heart surface and estimated using Nolasco-Dahlen criterion. In rabbit hearts, hypothermia resulted in arrhythmogenic overshoots of APD alternans as well as increase of APD restitution curve steepness. In contrast, significant APD alternans were observed in SA hearts at 27 degrees C, and at 17 degrees C in WH hearts. Moreover, slope of APD restitution curve in ground squirrels hearts did not reached arrhythmogenic threshold (43 +/- 9 degrees and 39 +/- 5 degrees for SA and WH respectively). Our results demonstrate different resistance of hibernating and non-hibernating mammals against induction of arrhythmogenic cardiac alternans which is closely associated with adaptive changes in intracellular Ca2+ cycling during hibernation.

[Spatiotemporal characteristics of activation of the heart of hibernating and non-hibernating mammals during hypothermia].

The heart of hibernating mammals is known to demonstrate the nature\'s model of resistance to rhythm disturbances, including ventricular arrhythmias, during hypothermia. However, electrophysiological mechanism of this phenomenon is not completely understood. Using optical mapping technique with voltage-sensitive dye di-4-ANEPPS, we investigated the spatiotemporal characteristics of ventricular activation in Langendorff-perfused hearts of winter hibernating ground squirrels Spermophyllus undulatus and rabbits at temperatures from +37 degrees C to +3 degrees C. In rabbit hearts, reduction of temperature from 37 to 17 degrees C resulted in significant decrease of conduction velocity and increase of conduction anisotropy. Excitation failure was observed in the rabbit heart at 12+/-1 degree C. In contrast, ground squirrels exhibited significantly faster conduction velocity compared with rabbits at all temperatures and insensibility of conduction anisotropy to cooling down to 3C which can protect the hibernator heart against arrhythmias during hypothermia.

[Effect of nibentan on dispersion of repolarization of ventricular myocardium in the rabbit].

Among factors determining development of polymorphic ventricular tachycardia torsades de pointes under influence of class III antiarrhythmic drugs great value is attributed to enhanced heterogeneity of repolarization of ventricular myocardium which can cause functional conduction blocks and development of re-entry of excitation. In this work with the help of optical mapping of electrical activity of the heart we investigated effect of nibentan (0.3 and 1 mM) on chronotopography of repolarization of epicardial surface of ventricles of isolated after Langendorf rabbit heart (n=5). For assessment of heterogeneity of repolarization we measured the following parameters: standard deviation of mean action potential duration (APDm) along mapped region (SD-APD), dispersion index (DI=1000 SD-APDm), maximal dispersion (Dmax=APDmax-APDmin). Nibentan in concentrations 0.3 and 1 mM increased APD at the level of 90% repolarization (APD90%) from 231 +/- 12 to 277 +/- 7 ms (p < 0.05) 318 +/- 7 ms (p < 0.001), respectively, but in concentration 1 mM it practically did not affect parameters of heterogeneity of repolarization (SD-APD: from 4.4 +/- 0.9 to 5.7 +/- 1.1 ms, p=0.4; DI: from 19.1 +/- 4.2 to 18.0+3.5, p=0.8; Dmax: from 16.6 +/- 2.5 to 24.8 +/- 4.3 ms, < 0.05). These results show that nibentan in the range of clinically used doses does not effect heterogeneity of ventricular myocardium. This can explain low proarrhythmic effect of nibentan.

[The effect of hypothermia on the wavelength and vulnarability to ventricular arrhythmias in mammals].

Arrhythmias developing in isolated Langendorff-perfused heart following the cooling of the perfusion solution from +37 to +3 degrees C were studied in rats and winter hibernating ground squirrels Citellus undulatus with application of no drugs. In rats, hypothermia significantly increased the probability of ventricular arrhythmias (from 22 +/- 6 % at 37 degrees C to 56 +/- 14 % at 17 degrees C). Excitation failure was observed in the rat hearts below 10 +/- 1 degrees C. The appearance of arrhythmias was closely correlated with a decrease in the wavelength which strongly suggests a reentrant mechanism of the hypothermic arrhythmias. In contrast, ground squirrels showed insensibility of the wavelength to cooling and were resistant to arrhythmias during hypothermia.

[Gas-chromatographic laparocentesis in the diagnosis of closed injuries of hollow abdominal organs]. / Gazokhromatograficheskii laparotsentez v diagnostike zakrytykh povrezhdenii polykh organov zhivota.

A principally new method of diagnostics of closed injuries of hollow organs of the abdomen was used in clinical practice in 36 patients. It consists in performing laparocentesis in combination with gas chromatography. The technique, indications and contraindications to gas chromatographic laparocentesis as a method of diagnostics of such injuries are described.