Heterogeneity of propagation of excitation in epicardium of pulmonary veins ostia in rabbit during cooling.

OBJECTIVE: The purpose of this research was to study the propagation of the excitation wave along epicardium in the area of the pulmonary veins ostia in rabbit in normal conditions and while cooling. METHODS: The excitation wave spreading along epicardium in the area of pulmonary veins ostia in the left atrium at 36-37 degrees C and when cooling to 32 degrees C was studied by the method of electrocardiochronotopography in rabbit of Chinchilla species, five months age. The size of the registering surface of the electrode was 1.08 x 1.08 cm. RESULTS: The time of depolarization when cooling from 36 degrees C to 32 degrees C changes unevenly in various zones of pulmonary veins. On the epicardium of pulmonary veins area at temperature reduction from 36 degrees C to 33 degrees C, change in the direction of excitation and essential reduction of depolarization time, and its significant increase under further cooling to 32 degrees C were observed. In the middle part of the left atrium at temperature reduction, change in the main direction of the excitation wave propagation, shift of the location of the areas of the latest depolarization were revealed and the front become more homogeneous. CONCLUSION: In the area of the left atrium base the heterogeneity of the front of depolarization at temperature reduction was revealed.

Changes in ionic currents and reduced conduction velocity in hypertrophied ventricular myocardium of Xin alpha-deficient mice.

OBJECTIVE: mXin alpha, a downstream target gene of Nkx2.5 transcription factor, was shown to encode a proline-rich and Xin repeats-containing protein which localizes to the intercalated disc of adult hearts. Our previous voltage-clamp studies have shown that the ventricular myocytes of mXin alpha -deficient mice exhibited a significant reduction in K+ currents (Ito and IK1), L-type Ca2+ currents, and maximum diastolic potential, leading to the development of early afterdepolarization (EAD) and arrhythmias. However, changes in cationic inward currents could also contribute to the genesis of EAD and arrhythmias in mXin alpha -deficient mice. METHODS: The present study aims to characterize changes in Na+ currents on depolarization and transient inward currents (Iti) on repolarization. Conduction velocity (CV) on the frontal surface of ventricles were also measured and compared. RESULTS: Results of optical mapping on the Langendorff-perfused hearts at 37oC revealed a 36% reduction of CV in mXin alpha -/- ventricle. Pacing (3 Hz)-induced tachyarrhythmias were more frequently found and ventricular fibrillation (VF, 21 Hz for 5 min) occurred in one out of 8 mXin alpha-/- heart. When perfused at 30 degrees C, no VF was observed in both types of preparations. Voltage-clamp study on isolated ventricular myocytes at 37 degrees C shows increase in INa and Iti in mXin alpha -/- cardiomyocytes thus could explain the occurrence of re-entrant triggered arrhythmias. CONCLUSION: The present results revealed that the CV was slower, but INa and Iti were increased in mXin alpha -/-cardiomyocytes thus were prone to reentrant triggered arrhythmias. Hypothermia could reduce the occurrence of arrhythmias.

Activation and repolarization patterns in the ventricular epicardium under sinus rhythm in frog and rabbit hearts.

Our study compared the contributions of activation sequence and local repolarization durations distribution in the organization of epicardial repolarization in animals with fast (rabbit) and slow (frog) myocardial activation under sinus rhythm. Activation times, repolarization times and activation-recovery intervals (ARI) were obtained from ventricular epicardial unipolar electrograms recorded in 13 Chinchilla rabbits (Oryctolagus cuniculus) and 10 frogs (Rana temporaria). In frogs, depolarization travels from the atrioventricular ring radially. ARIs increased progressively from the apex to the middle portion and finally to the base (502+/-75, 557+/-73, 606+/-79 ms, respectively; P<0.01). In rabbits, depolarization spread from two epicardial breakthroughs with the duration of epicardial activation being lower than that in frogs (17+/-3 vs. 44+/-18 ms; P<0.001). ARI durations were 120+/-37, 143+/-45, and 163+/-40 ms in the left ventricular apex, left, and right ventricular bases, respectively (P<0.05). In both species, repolarization sequence was directed from apex to base according to the ARI distribution with dispersion of repolarization being higher than that of activation (P<0.001). Thus, excitation spread sequence and velocity per se do not play a crucial role in the formation of ventricular epicardial repolarization pattern, but the chief factor governing repolarization sequences is the distribution of local repolarization durations.