The slowing down mechanism of heart rate during growth of the body after birth was studied in isolated rabbit heart and sinus node (SN) preparation with Langendorff perfusion method, conventional microelectrode recording and perforated patch for recording pacemaker current I(f). The radioimmunoassay was also used to measure the concentration of cAMP within SN cells. The results indicate that without the influence of nervous and humoral factors, the spontaneous heart rate would also become slower as the rabbit grew older, which is due to the decrease of spontaneous depolarized rate of phase 4 in SN cells. The negative directed shift of the threshold potential of I(f) and the decrease in cAMP concentration within SN cells may be responsible for the phenomenon. The results obtained suggest that besides the nervous and humoral factors which influence the heart rate, the changes in automaticity of SN cell itself may take part in the slowing down process as the body grows up.
Animals ; Cyclic AMP ; physiology ; Heart Rate ; In Vitro Techniques ; Microelectrodes ; Perfusion ; Rabbits ; Sinoatrial Node ; physiology

In this paper are proposed four heartbeat models which correspond to two different positions of the ectopic pacemaker and two coupling styles of the sinus and ectopic pacemakers. The models computed are based on the modified Ikeda phase resetting model. Most of the heartbeat modes are periodic; they exhibit "Arnold's tongue" structure in parameter plane of perturbing frequency and strength. When the ectopic pacemaker is located in the ventricle, there are bistable dynamic modes. The abnormal hearbeat rhythms of bigeminy and trigeminy in clinical medicine have been observed when coupling strength is weaker in odd resetting or refractory time is longer in even resetting.
Cardiac Pacing, Artificial ; methods ; Computer Simulation ; Electrocardiography ; Heart Rate ; physiology ; Humans ; Models, Cardiovascular ; Sinoatrial Node ; physiology

Instantaneous chaometry was defined on uniformity theory constructed by the present authors. The sample data, sinus heart rate data and arrhythmia heart rate data from MIT-BIH were analyzed with instantaneous chaometry (ICM); the situation not being distinguished with HRV can be differentiated with ICM. The normal sinus rhythm was found to be of three evident characteristics: (1) instant returning to zero, (2) stability-stable characteristic of ICM on the initial position, (3) interval of mean: 2-7, variance: 1.5-5. The third characteristic shows that the variability of ICM is necessary. The studies on arrhythmia database showed that arrhythmia cases exhibited no returning to zero, nonstability of ICM on the initial position, too small mean or standard deviation, respectively. Evidently, the arithmetic of ICM is simple; ICM can be easily applied in clinical and pathologic analyses.
Arrhythmias, Cardiac ; physiopathology ; Electrocardiography ; methods ; Heart Rate ; physiology ; Humans ; Male ; Middle Aged ; Signal Processing, Computer-Assisted ; Sinoatrial Node ; physiology

OBJECTIVETo precisely visualize cardiac anatomic structures and simultaneously depict electro-mechanical events for the purpose of precise underblood intervention.

METHODSIntracardiac high-resolution tissue Doppler imaging was used to map real time myocardial contractions in response to electrical activation within the anatomic structure of the cardiac conductive system using a canine open-chest model.

RESULTSThe detailed inner anatomic structure of the cardiac conductive system at different sites (i.e., sino-atrial, atrial wall, atrial-ventricular node and ventricular wall) with the inside onset and propagation of myocardial velocity and acceleration induced by electrical activation was clearly visualized and quantitatively evaluated.

CONCLUSIONThe simultaneous single modality visualization of the anatomy, function and electrical events of the cardiac conductive system will foster target pacing and precision ablation.

Animals ; Dogs ; Echocardiography, Doppler ; Electrocardiography ; Heart Conduction System ; diagnostic imaging ; physiology ; Myocardial Contraction ; Sinoatrial Node ; diagnostic imaging ; physiology

To evaluate the possibility and accuracy of Doppler tissue image (DTI) on assessment of normal and abnormal ventricular activation and contraction sequence, 9 open chest canine hearts were analyzed by acceleration mode, M-mode, and spectrum mode DTI. Our results showed that: (1) Acceleration mode DTI could show the origin of activation and conduction sequence on line; (2) M-mode DTI revealed that the activation in mid-interventricular septum was earlier than that in mid-left ventricular posterior wall at sinus activation; (3) Spectrum DTI showed the ventricular endocardium was activated earlier than the ventricular epicardium in all segments at sinus rhythm. The earliest site of activation of the normal ventricular wall was at middle interventricular septum; the latest site was at basal-posterior wall; the contraction sequence was different at the different walls; (4) During abnormal ventricular activation, mid-left ventricular posterior wall was activated earliest in accordance with the pacing sites. Abnormal ventricular activation was slower than sinus activation, and the contraction sequence varied at different sites of ventricular wall. It is concluded that DTI can be used to localize the origin of normal or abnormal myocardial activation and to assess the contraction sequence conveniently, accurately and non-invasively.
Echocardiography, Doppler/instrumentation ; Echocardiography, Doppler/*methods ; Heart Ventricles/*ultrasonography ; Myocardial Contraction/*physiology ; Sinoatrial Node/physiology ; Tachycardia/physiopathology ; Tachycardia/ultrasonography

To evaluate the possibility and accuracy of Doppler tissue image (DTI) on assessment of normal and abnormal ventricular activation and contraction sequence, 9 open chest canine hearts were analyzed by acceleration mode, M-mode, and spectrum mode DTI. Our results showed that: (1) Acceleration mode DTI could show the origin of activation and conduction sequence on line; (2) M-mode DTI revealed that the activation in mid-interventricular septum was earlier than that in mid-left ventricular posterior wall at sinus activation; (3) Spectrum DTI showed the ventricular endocardium was activated earlier than the ventricular epicardium in all segments at sinus rhythm. The earliest site of activation of the normal ventricular wall was at middle interventricular septum; the latest site was at basal-posterior wall; the contraction sequence was different at the different walls; (4) During abnormal ventricular activation, mid-left ventricular posterior wall was activated earliest in accordance with the pacing sites. Abnormal ventricular activation was slower than sinus activation, and the contraction sequence varied at different sites of ventricular wall. It is concluded that DTI can be used to localize the origin of normal or abnormal myocardial activation and to assess the contraction sequence conveniently, accurately and non-invasively.
Animals ; Dogs ; Echocardiography, Doppler ; instrumentation ; methods ; Heart Ventricles ; diagnostic imaging ; Myocardial Contraction ; physiology ; Sinoatrial Node ; physiology ; Tachycardia ; diagnostic imaging ; physiopathology

Normal rhythm in a healthy human heart originates from the natural biological pacemaker, the sinoatrial (SA) node which locates in the right atrium. SA node dysfunction or atrial-ventricular (AV) conduction block causes improper heart rate (bradycardia). Such dysfunction, if severe enough, is currently treated by implanting an electronic pacemaker which has been well established technically, but there are some limitations and inadequacies. Recently, progress in developing engineered cardiac biopacemakers with use of genes or cells has been made in experimental animal models. The hyperpolarization-activated cyclic-nucleotide-modulated (HCN) channel (pacemaker channel) modulates cardiac automaticity via the hyperpolarization-activated cation current (I(f)). HCN genes have been delivered to animal myocardium via viral vectors or HCN-transferred cells for recreating biological pacemakers. Approaches with non-HCN genes or transplantation of beating cells are also novel and have been investigated for generating cardiac biopacers. This article summarizes the progresses in research on recreation of cardiac biopacemakers. Genetically engineered biological pacemaker holds great promise to potentially cure severe bradycardia if critical issues, such as their stability and longevity, are properly solved.
Biological Clocks ; physiology ; Bradycardia ; therapy ; Genetic Engineering ; Heart ; Heart Rate ; Heart Ventricles ; Humans ; Ion Channels ; Myocardium ; Pacemaker, Artificial ; Sinoatrial Node

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

OBJECTIVETo establish a reliable approach to primary culture and identification of sinoatrial node (SAN) cells.

METHODSThe SAN cells were cultured from SAN tissue removed from neonatal Wistar rats and purified with differential attachment and 5'-bromodeoxyuridine (BrdU) treatment. The obtained cells were morphologically observed with inverted microscopy and transmission electron microscopy. Its action potential was recorded using electrophysiological methods.

RESULTSThree distinctly different cells were observed in the cultured SAN cells: spindle, triangle and irregular. Of these, the spindle cells comprised the greatest proportion, with their shape, structure and electrophysiological characteristics consistent with those of the pacemaker cells of SAN. The triangle cells were similar in features to the similarly shaped myocytes located in the atrial myocardium.

CONCLUSIONSThe culture method of differential attachment combined with BrdU treatment is a reliable approach to growing SAN cells. Of the cells cultured from SAN, the spindle cells appear to function as pacemaker cells.

Animals ; Animals, Newborn ; Cells, Cultured ; Female ; Male ; Microscopy, Electron ; Rats ; Rats, Wistar ; Sinoatrial Node ; cytology ; physiology ; ultrastructure

AIMTo investigate the effects of exogenous NO donors sodium nitroprusside (SNP) and 3-morpholinosydnonimine (SIN-1) on automaticity of the rabbit sino-atrial node in vitro and the action mechanism.

METHODSThe intracellular microelectrode technique is used to record the action potentials of rabbit sino-atrial node and APA (amplitude of AP), V(max) (maximal rate of depolarization), VDD (velocity of diastolic depolarization), RPF (rate of pacemaker firing) are analyzed.

RESULTSSNP(10(-5) - 10(-2) mol/L) increased its RPF and VDD dose-dependently. 10(-3) mol/L SNP increased RPF (beats/min) from 163 +/- 10.8 to 195.0 +/- 13.1 increased VDD (mV/s) from 50.3 +/- 9.6 to 70.2 +/- 12.1 (P < 0.01). SIN-1(10(-3) - 10(-2) mol/L) also increased RPF and VDD (P < 0.01).10(-4) mo/L Methylene blue (MB), a blocker of GMP cyclase, prevented the positive chronotropic effect and increasement of VDD induced by 10(-3) mol/L SNP totally (P < 0.01). 2. CsCl (2 mmol/L), a blocker of I(f) prevented the increasement of RPF and VDD in part (P < 0.05). 3. NIF (0.46 micromol/L), a blocker of I(Ca-L, had no significant effects on chronotropic effect and increasement of VDD (P < 0.01).

CONCLUSIONExogenous NO can increase the automaticity of rabbit sino-atrial node in vitro. The chronotropic effect is involved in NO-cGMP pathway and results from increasement of I(f) in the sino-atrial node at least in part; I(ca-L) is unlikely to play a major role in this effect.

Action Potentials ; Animals ; Heart Rate ; Molsidomine ; analogs & derivatives ; pharmacology ; Nitric Oxide ; metabolism ; Nitroprusside ; pharmacology ; Rabbits ; Sinoatrial Node ; drug effects ; physiology