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.