动物实验,心肌细胞 z-bo 2020-08-26 449

　　Introduction: The aging of the rat heart is characterized by mild to moderate left ventricular hypertrophy by increasing the volume of myocardial cells. In addition, the decrease in the number of cardiomyocytes is a consequence of necrosis and/or apoptosis. This is accompanied by uncontrolled expression and production of fibronectin and collagen, which contributes to the expansion of the extracellular matrix and collagen compartment. With age, the natural growth of cardiomyocytes is accompanied by structural and functional remodeling, which involves the redistribution of spatial and electrical gap connections. The gap junction was found almost entirely in the intercalary disk. Locate the terminal-to-terminal spatial coupling of cardiomyocytes. A structure

　　Gap junction mismatch usually occurs in the sinoatrial node (SA) node and the atrium and Purkinje cell myocardial node. In normal ventricle growth, aging and cardiovascular disease gap junction cell distribution changes. The decrease in intercellular coupling, due to age-related collagen deposition and decreased expression of connexin (CX), especially CX40, may be responsible for delayed activation and conduction failure at the branch sites of the conductive system. The source library may not match, because the three-dimensional structure changes will affect the pulse propagation. In terms of cardiac cell electrophysiology, the action potential is prolonged, the intracellular calcium ions increase, and the contraction period is prolonged. It is especially worth noting that compared with young rats, the AP repolarization time of left ventricular cardiomyocytes of old rats is longer. The natural aging process is accompanied by a series of changes in the autonomous control of the cardiovascular system.

　　Materials and methods: Telemetry system, ECG recording and analysis: 21 18-month-old animals were implanted with telemetry transmitters and monitored continuously for the next six months. Only seven animals survived until the age of 24 months and were also used in subsequent experiments. Seven 12-month-old animals served as the control group in this study. The telemetry transmitter implantation was performed according to the procedure described by Sgoifo and colleagues, which allowed bipolar lead ECG recording of Y-lead vector ECG. The emitter is placed in the abdominal cavity, the electrode (non-inverted) is fixed to the dorsal surface of the xiphoid process, and the other electrode (inverted) is placed in the anterior mediastinum close to the right atrium. This electrode position can ensure high-quality ECG recording even with strenuous physical activity. After the operation, the animals were bred separately and injected with gentamicin sulfate (0.2ml/kg) for two days, and there was a 30-day recovery period before ECG recording. Receive the ECG signal through a radio telemetry receiver placed in the cage. A 15-minute continuous ECG recording was performed on the elderly animals once a week, between 8 and 10 am on the same day of the week. Control animals: 12-month-old animals undergo a 15-minute continuous ECG recording. Use customized software for offline analysis of ECG signals: 1. RR interval, time interval between the two, continuous R wave peak; 2. PQ interval, P wave time interval (atrial depolarization) and QRS wave Initial (ventricular depolarization); 3. QRS wave time; 4. QT interval, QRS onset time interval and T wave end point (ventricular repolarization); 5. QTc interval, QT interval heart rate correction formula (Bazett Formula); 6. Obtain the frequency domain index of heart rate variability (HRV) to increase the sympathetic and parasympathetic nerves of heart rate.

　　Epicardial potential mapping: The epicardial potential was implemented on seven aged rats (24 months old) who had completed 6-month telemetry ECG recording and seven control animals. Animals were anesthetized with Domitor (0.015 ml/100 g) and Imalgene (0.04 ml/100 g). During anesthesia, additional anesthesia is provided, and the heart under artificial respiration is exposed through a medial incision. Body temperature was kept constant under the irradiation of infrared lamp 37uc. In the experiment, the exposed heart and chest were covered with a plastic film that kept it moist and at a constant temperature. This study used a high-density epicardial electrode array. A regular array of 868 rows and columns of electrodes are assembled on a surgical gauze with a 1 mm square grid corresponding to the distance between the electrodes.

　　Myocardial histopathology: After the heart mapping, the animals were sacrificed, and the epicardial position of the electrode array was determined by the fiducial markers. The heart was quickly removed from the chest, weighed, and fixed in a 10% formaldehyde solution for 24-48 hours. Take out the atria and ventricles of the heart and embed them in paraffin wax. Each wax block is completely sectioned to a thickness of 4 mm. These parts are then dyed for fiber orientation and fibrosis analysis. The atrium and ventricular myocardium are evaluated for fibrosis.

　　Result: Telemetry ECG signal: QRS waveform: During the six-month aging process, the telemetry ECG signal showed that the waveform shape of the QRS wave gradually changed and the waveform was complex. Six of the seven animals are initially positive (R-type) and gradually become negative (rS-type). The QRS wave of only one animal is always positive although its shape gradually changes. Figure 1 shows the typical electrocardiogram of the control group animals and the aging animals gradually showed QRS wave polarity reversal within six months. Specifically, within three months, the QRS wave in the ECG display interval is positive, and R-type and RS-type appear alternately. The QRS wave in the fourth month changed to R type again and became RS type in the last two months.

　　Waveform and interval time: ECG duration, waveform and time interval measured during the six-month aging process compared with the control group (Figure 2). The PQ interval showed an initial extension and was statistically significant after the fourth month. The total increase was 18% (control group: 48.563.4 ms vs sixth month: 57.164.1 ms). After the third month, QRS showed a significant linear increase. The QRS complex increase time in the sixth month was 53%. After the first month, the QT interval showed a gradual increase in duration. The QT interval growth rate for the sixth month was 52%. There is no significant change in the center rate during the aging process.

　　Heart rate variability: Heart rate variability analysis shows that the total power value gradually decreases significantly from the third month. The decline rate in the sixth month was 65%. The high-frequency spectral power values in the first five months are similar, and compared with the control value, the value in the sixth month is lower. In the sixth month, it decreased by 47%. , There is no significant change in the low frequency/high frequency ratio, and there is no significant difference according to the RR interval.

　　Incidence of arrhythmia: the control group rats had no spontaneous arrhythmia. The incidence of arrhythmia in six-month old mice increases. Different types of arrhythmia are classified according to their origin, such as impulse formation or conduction abnormalities.

　　1. Pulse forming arrhythmia: In this category, it describes the representatives of sinus arrhythmia, atrial premature beats and ventricular premature beats.

　　A. Sinus intermittent: Figure 3A 6 sinus beats and 190ms RR interval followed by a 300ms RR interval. This increase in cycle length represents a sinus pause due to the recovery of SR.

　　B. Atrial premature contraction: Figure 3b shows three sinus beats with an RR interval of 150 milliseconds, followed by a premature sinus beat with a coupling interval of 100 milliseconds and a compensation interval of 170 milliseconds. The RR interval resumed continuous sinus beat, 150ms. Another premature sinus beat originated from a 100 millisecond coupling interval and a compensatory interval of 170 milliseconds. After a 150ms RR interval, continuous sinus beats resumed.

　　2 Impulse conduction arrhythmia: In this category, it is described as second-degree atrioventricular arrhythmia (AV) and abnormal ventricular block.

　　A. Second-degree atrioventricular block: Figure 3D The first 3 beats are composed of the PP interval, 250 ms and 55 ms between PQ. The P wave has a 300msPP interval, which may be characteristic of second-degree atrioventricular block because it does not follow the QRS wave. The borderline escape beat represented by the QRS complex has a P wave and a very short PQ interval before it, and shows the same QRS shape and duration. The characteristic is the PP interval of 300ms, the PQ interval of 55ms and the same QRS duration.

　　B. Abnormal ventricular conduction: Figure 3e PP interval 180ms. QRS complex is characterized by two different forms. Although there are similar QRS durations, 3 QRSs are R type and the others are rS type. Isolated, bizarre QRS complexes are not always ectopic ventricular discharges, but may be due to temporary indoor conduction abnormalities. In order to more accurately define these conditions, the term "phase" abnormal ventricular conduction was introduced to distinguish temporary forms from "non-phase" or "permanent" forms of abnormal ventricular conduction.

　　The number and complexity of arrhythmic events in the aging process increase, especially in the last three months of age. Figure 4A shows that all arrhythmia events are abnormal pulse formation and abnormal pulse conduction. The number of arrhythmia events increases with age. Abnormal pulse formation occurred in the fourth month, and a peak of abnormal pulse conduction appeared in the sixth month. In the six-month record, to a large extent, the total number of pulse-forming arrhythmias exceeds the number of pulse-conducting arrhythmias. All pulse forming and pulse conduction arrhythmias are grouped according to their origin as supraventricular and ventricular arrhythmias. And ventricular arrhythmia increased from the first month, supraventricular arrhythmia peaked in the fifth month, and ventricular arrhythmia peaked in the sixth month. In general, the total number of supraventricular arrhythmias greatly exceeds the total number of ventricular arrhythmias.

　　Myocardial histopathology: Microscopic analysis of cardiac atrial muscle shows the orientation of various myocardial cell bundles. The space between the myocardium is occupied by connective tissue and microcirculatory blood vessels, usually parallel to the long axis of the muscle fiber. The atrial myocardium of the elderly heart is characterized by significant collagen deposition and myocardial cell myolysis phenomenon, that is, the striated muscle nuclear damage causes blank areas.

　　Conclusion: We prove that longitudinal electrocardiogram is essential for the study of the progression of cardiac aging. Although the eye uses a limited animal model, it still has an impact on treatment. This result provides insights for human aging, early detection of the possibility of age-mediated cardiac electrophysiological deterioration and the potential of early treatment to delay this process.