Age Factors ; Animals ; Atrial Fibrillation ; etiology ; Atrial Function ; physiology ; Dogs ; Female ; Male ; Refractory Period, Electrophysiological ; physiology

The effect of acute ischemia on the electrophysiological characteristics of the three layers myocardium of canine in vivo was investigated. Twelve canines were divided into two groups randomly: acute ischemia (AI) group and sham operation (SO) group. By using the monophasic action potential (MAP) technique, MAP and effective refractory period (ERP) of the three layers myocardium were measured by specially designed plunge needle electrodes and the transmural dispersion of repolarization (TDR) and transmural dispersion of ERP (TDE) were analyzed. The results showed that in the AI group, MAP duration (MAPD) was shortened from 201.67 +/- 21.42 ms to 169.50 +/- 13.81 ms (P < 0.05), but ERP prolonged to varying degrees and TDE increased during ischemia. In the SO group, MAPD and ERP did not change almost. Among of the three layers myocardium of canine, MAPD was coincident in two groups. It was concluded that during acute ischemia, MAPD was shortened sharply, but there was no significant difference among of the three layers myocardium. The prolonged ERP was concomitant with increased TDE during acute ischemia, which may play an important role in the occurrence of arrhythmias induced by acute ischemia. These findings may have important implications in arrhythmogenesis.
Action Potentials/*physiology ; Electrodes ; Heart/physiopathology ; Myocardial Ischemia/*physiopathology ; Myocardium/*metabolism ; Random Allocation ; Refractory Period, Electrophysiological/*physiology

OBJECTIVETo observe effects of acupuncture at Neiguan (PC 6) on function of sinoatrial node, so as to provide experimental basis for clinical application of Neiguan (PC 6) to treatment of heart diseases.

METHODSFifty cases of heart diseases were randomly divided into 2 groups, a no-blocking group (n = 35) and a blocking group (n = 15). In the no-blocking group, sinoatrial node recovery time (SNRT), sinoatrial conduction time (SACT), sinoatrial node effective refractory period (SNERP) and heart rate (HR) were determined by using esophagus-left cardiac atrium regulating pulsation technique before and after acupuncture at Neiguan (PC 6); and in the blocking group, the vegetative nerve was blocked by intravenous injection of Propanolol and Atropine, and then SNRT, SACT, SNERP and intrinsic heart rate (IHR) were detected before and after acupuncture.

RESULTSIn the no-blocking group there were significant differences in SACT, SNERP and HR (all P < 0.05) and no significant difference in SNRT (P > 0.05) before and after treatment. In the blocking group, there were no significant differences in SNRT, SACT and SNERP and a significant difference in IHR before and after acupuncture (P < 0.05).

CONCLUSIONAcupuncture at Neiguan (PC 6) has a significant effect on function of sinoatrial node, and the mechanism is possibly related with the bidirectional regulative action of acupuncture at Neiguan (PC 6) on the autonomic nerve in the sinoatrial node.

Acupuncture Points ; Acupuncture Therapy ; Adult ; Female ; Heart Rate ; Humans ; Male ; Middle Aged ; Refractory Period, Electrophysiological ; Sinoatrial Node ; physiology

The effects of sound duration and sound pattern on the recovery cycles of inferior collicular (IC) neurons in constant frequency-frequency modulation (CF-FM) bats were explored in this study. Five leaf-nosed bats, Hipposideros armiger (4 males, 1 female, 43-50 g body weight), were used as subjects. The extracellular responses of IC neurons to paired sound stimuli with different duration and patterns were recorded, and the recovery was counted as the ratio of the second response to the first response. Totally, 169 sound-sensitive IC neurons were recorded in the experiment. According to the interpulse interval (IPI) of paired sounds when neurons reached 50% recovery (50% IPI), the recovery cycles of these IC neurons were classified into 3 types: fast recovery (F, the 50% IPI was less than 15 ms), short recovery (S, the 50% IPI was between 15.1 and 30 ms) and long recovery (L, the 50% IPI was more than 30 ms). When paired CF stimuli with 2 ms duration was used, the ratio of F neurons was 32.3%, and it decreased to 18.1% and 18.2% respectively when 5 and 7 ms CF stimuli were used. The ratios of S and L neurons were 41.5%, 33.7%, 29.1% and 26.2%, 48.2%, 52.7% respectively when 2, 5 and 7 ms CF stimuli were used. The average 50% IPI determined after stimulation with paired 2 ms, 5 ms and 7 ms CF sounds were (30.2 ± 27.6), (39.9 ± 29.1) and (49.4 ± 34.7) ms, respectively, and the difference among them was significant (P< 0.01). When the stimuli of paired 2 ms CF sounds were shifted to paired 2 ms FM sounds, the proportion of F, S and L neurons changed from 32.3%, 41.5%, 26.2% to 47.7%, 24.6%, 27.7%, respectively, and the average 50% IPI decreased from (30.2 ± 27.6) to (23.9 ± 19.0) ms (P< 0.05, n = 65). When paired 5+2 ms CF-FM pulses were used instead of 7 ms CF sounds, the proportion of F, S and L neurons changed from 18.2%, 29.1%, 52.7% to 29.1%, 27.3%, 43.6%, respectively, and the average 50% IPI decreased from (49.4 ± 34.7) to (36.3 ± 29.4) ms (P< 0.05, n = 55). All these results suggest that the CF and FM components in echolocation signal of CF-FM bats play different roles during bats' hunting and preying on. The FM component of CF-FM signal presenting in the terminal phase can increase the number of F type neurons and decrease the recovery cycles of IC neurons for processing high repetition echo information, which ensures the bat to analyze the target range and surface texture more accurately.
Acoustic Stimulation ; methods ; Action Potentials ; physiology ; Animals ; Chiroptera ; physiology ; Echolocation ; physiology ; Female ; Inferior Colliculi ; cytology ; physiology ; Male ; Neurons ; classification ; physiology ; Refractory Period, Electrophysiological ; physiology

The aim of this article was to investigate the dependence of ventricular wallstress-induced refractoriness changes on pacing cycle lengths and its mechanism in anaesthetized rabbits. The rabbit heart preparation was used. The left ventricular afterload was increased by partially clipping the root of the ascending aorta. The changes in effective refractory periods (ERP) induced by the left ventricular afterload rising were examined at different pacing cycle lengths (1000, 500, 300 and 200 ms). In addition, the effect of streptomycin on these changes was also observed. The results are as follows: (1) The rising of left ventricular afterload led to marked changes in ERP at rapidly pacing cycle lengths (300 ms, 21+/-5 ms, 17.0%; 200 ms, 19+/-3 ms, 18.8%. P<0.01) than at slow ones (1000 ms, 3+/-2 ms, 1.5%; 500 ms, 7+/-3 ms, 4.0%. P>0.05); (2) Streptomycin inhibited the changes caused by the left ventricular afterload rising at pacing cycle lengths 300 ms and 200 ms (P>0.05). It is suggested that ventricular wallstress-induced refractoriness changes are pacing cycle length-dependent, and the effect of streptomycin appears to be consistent with the inhibition of stretch-activated ion channels.
Animals ; Aorta ; Cardiac Pacing, Artificial ; Constriction ; Mechanoreceptors ; drug effects ; physiology ; Rabbits ; Refractory Period, Electrophysiological ; drug effects ; Streptomycin ; pharmacology ; Ventricular Function ; drug effects ; physiology

BACKGROUNDBased on the hypothesis that pulmonary vein isolation could result in the damage of the epicardial fat pads, this study aimed to investigated the impact of right upper pulmonary vein (RUPV) isolation on vagal innervation to atria.

METHODSBilateral cervical sympathovagal trunks were decentralized in 6 dogs. Metoprolol was given to block sympathetic effects. Multipolar catheters were placed into the right atrium (RA) and coronary sinus (CS). RUPV isolation was performed via transseptal procedure. Atrial effective refractory period (ERP), vulnerability window (VW) of atrial fibrillation (AF), and sinus rhythm cycle length (SCL) were measured at RA and distal coronary sinus (CSd) at baseline and vagal stimulation before and after RUPV isolation. Serial sections of underlying tissues before and after ablation were stained with haematoxylin and eosin.

RESULTSSCL decreased significantly during vagal stimulation before RUPV isolation (197 +/- 21 vs 13 +/- 32 beats per minute, P < 0.001), but remained unchanged after RUPV isolation (162 +/- 29 vs 140 +/- 39 beats per minute, P > 0.05). ERP increased significantly before RUPV isolation compared with that during vagal stimulation [(85.00 +/- 24.29) ms vs (21.67 +/- 9.83) ms at RA, P < 0.001; (90.00 +/- 15.49) ms vs (33.33 +/- 25.03) ms at CSd P < 0.005], but ERP at baseline hardly changed after RUPV isolation compared with that during vagal stimulation [(103.33 +/- 22.50) vs (95.00 +/- 16.43) ms at RA, P = 0.09; (98.33 +/- 24.83) vs (75.00 +/- 29.50) ms at CSd, P = 0.009]. The ERP shortening during vagal stimulation after RUPV isolation decreased significantly [(63.33 +/- 22.51) ms vs (8.33 +/- 9.83) ms at RA, P < 0.005; (56.67 +/- 20.66) ms vs (23.33 +/- 13.66) ms at CSd, P < 0.05]. AF was rarely induced at baseline before and after RUPV isolation (VW close to 0), while VW of AF to vagal stimulation significantly decreased after RUPV isolation [(40.00 +/- 10.95) vs 0 ms at RA, P < 0.001; (45.00 +/- 32.09) vs (15.00 +/- 23.45) ms at CS, P < 0.05]. The architecture of individual ganglia was significantly altered after ablation.

CONCLUSIONSThe less ERP shortening to vagal stimulation and altered architecture of individual ganglia after right upper pulmonary vein isolation indicate that isolation may result in damage of the epicardial fat pads, thereby attenuating the vagal innervation to atria. The decreased vulnerability window of atrial fibrillation indicates that vagal denervation may contribute to its suppression.

Animals ; Atrial Fibrillation ; etiology ; physiopathology ; surgery ; Dogs ; Female ; Ganglia ; pathology ; Heart Atria ; innervation ; Male ; Pulmonary Veins ; surgery ; Refractory Period, Electrophysiological ; Vagus Nerve ; physiology

OBJECTIVETo investigate the effects of short-term rapid atrial pacing on the electrophysiological characteristics of atrium in hyperthyroidism.

METHODSForty-six adult rabbits were randomly divided into 4 groups: normal control group (n=10), pacing group (n=10), hyperthyroidism group (n=14), hyperthyroidism/pacing group (n=12). Baseline AERP and AERPs after pacing 2, 4, 6 h were determined in all groups at driver cycle length (DCL) of 200 ms, 150 ms and 130 ms.

RESULTIn pacing group, AERPs at different DCL (200 ms, 150 ms and 130 ms) were shortened after rapid pacing 2, 4, 6 h when compared with before pacing and control group (P<0.01). AERPs (at DCL of 200 ms, 150 ms and 130 ms) in hyperthyroidism group were shorter than those in control group at all time points (P<0.01). AERPs (at DCL of 200 ms, 150 ms and 130 ms) in hyperthyroidism/pacing group after rapid pacing 2, 4, 6 h were shorter than those in pacing 0 h (P<0.01) and hyperthyroidism group (P<0.05). AERP200-150 and AERP200-130 in pacing group after rapid pacing 2, 4, 6 h were significantly different from at pacing 0 h and control group (P<0.01). AERP200-150 and AERP200-130 in hyperthyroidism and hyperthyroidism/pacing group were significantly different from control group at all time points (P<0.01). No differences were observed in AERP200-150 and AERP200-130 between hyperthyroidism group and hyperthyroidism/pacing group.

CONCLUSIONHyperthyroidism and short-term atrial pacing in the presence of hyperthyroidism can lead to remodeling of atrial electrophysiology.

Animals ; Atrial Fibrillation ; etiology ; physiopathology ; Cardiac Pacing, Artificial ; Electrophysiology ; Female ; Heart Atria ; physiopathology ; Hyperthyroidism ; physiopathology ; Male ; Rabbits ; Random Allocation ; Refractory Period, Electrophysiological ; physiology

AIMTo investigate the intrinsic mechanisms underlying spike programming at pyramidal neurons and interneurons in layer II/III of sensorimotor cortex.

METHODSElectrical signals at the cortical neurons were recorded in current clamp model with multi-clamp700B Amplifiers. Signals were inputted into pClamp and Origin for data acquisition and analyses.

RESULTSCompared to pyramidal neurons, interneurons express the higher capacity of spikes and the more stability of spike programming, which are mechanistically caused by lower threshold potentials and shorter refractory periods.

CONCLUSIONThe refractory periods and threshold potentials directly influence the programming of sequential spikes.

Action Potentials ; physiology ; Animals ; Animals, Newborn ; Cerebral Cortex ; cytology ; physiology ; Differential Threshold ; physiology ; Interneurons ; physiology ; Neurons ; physiology ; Patch-Clamp Techniques ; Pyramidal Cells ; physiology ; Rats ; Rats, Sprague-Dawley ; Refractory Period, Electrophysiological ; physiology ; Synaptic Transmission ; physiology

Electrical instability easily induces a unidirectional conduction block, resulting in ventricular tachycardia (VT) or even fibrillation (VF). Cardiac memory affects dynamic electrical characteristics through previous pacing so that it makes the memory important in arrhythmia study. This paper investigates the impact of the rapid pacing duration on cellular excitability and its mechanism. Based on the canine endocardial single cell, a one-dimensional tissue model was developed. Simulations were realized with OpenMP parallel programming method. The results showed that with repetitive pacing, the cellular excitability became low while the conduction velocity decreased. Accumulation of intracellular [Ca2+]i and [Na+]i and depletion of [K+]i led to the shift of membrane current-voltage curves, changing the membrane resistance. Excitability determined by the resistance at the large width of stimulus pulse, therefore, it suggested that [Ca2+]i and [K+]i-induced memory formed the ionic substrates for the alteration of excitability.
Action Potentials ; Animals ; Computer Simulation ; Dogs ; Electric Stimulation ; Electrocardiography ; Heart Conduction System ; physiopathology ; Myocardial Contraction ; physiology ; Myocytes, Cardiac ; physiology ; Refractory Period, Electrophysiological ; physiology ; Tachycardia, Ventricular ; etiology ; physiopathology ; Ventricular Fibrillation ; etiology ; physiopathology

OBJECTIVETo investigate the changes of guinea pig heart electrophysiological properties caused by increasing left ventricular preload, and to assess the effects of tetradrine on these changes.

METHODWorking model preparation of guinea pig hearts in vitro was used, and the preload of left ventricle was increased by adjusting the prefusion pressure of left atria. The changes of heart electrophysiologic parameters including monophasic action potential duration (MAPD90), monophasic action potential amplitude (MAPA), effective refractory period (ERP) and ventricular fibrillation threshold (VFT) were observed before and after altering the preload of left ventricle, and compared in the absence and presence of tetradrine, streptomycin or verapamil.

RESULTThe rising of left ventricular preload led to shortening of MAPD90, ERP, and to descent of MAPA, VFT (all P<0.01). Both Tetradrine and streptomycin inhibited these changes of heart electrophysiologic parameters caused by elevation of left ventricular afterload (all P<0.01). In contrast, verapamil had no effects on the preload-related electrophysiological changes (all P>0.05).

CONCLUSIONElectrophysiologic changes caused by increasing left ventricular preload may be inhibited by tetrandrine, through inhibition of stretch-activated ion channels.

Action Potentials ; drug effects ; Alkaloids ; isolation & purification ; pharmacology ; Animals ; Anti-Arrhythmia Agents ; isolation & purification ; pharmacology ; Benzylisoquinolines ; isolation & purification ; pharmacology ; Calcium Channel Blockers ; pharmacology ; Drugs, Chinese Herbal ; isolation & purification ; pharmacology ; Female ; Guinea Pigs ; Heart ; physiology ; In Vitro Techniques ; Male ; Plants, Medicinal ; chemistry ; Refractory Period, Electrophysiological ; drug effects ; Stephania tetrandra ; chemistry ; Streptomycin ; pharmacology ; Ventricular Function, Left ; drug effects ; Verapamil ; pharmacology