What is atrial fibrillation? There is a conduction system of special myocardial fibers within the walls of the heart, whose function is to generate impulses and conduct them to all parts of the heart, causing the atrial and ventricular muscles to contract in a certain rhythm. This system consists of the sinoatrial node, atrioventricular node, atrioventricular bundle, left and right atrioventricular bundle branches on either side of the ventricular septum, and many fine branches to the ventricular papillary muscle and ventricular wall. The sinoatrial node is located deep in the epicardium of the right atrium, and the rest of the system is distributed in the subendocardial layer, separated from the myocardial membrane by connective tissue. The myocardial fibers that make up this system are clustered into knots and bundles, innervated by sympathetic, parasympathetic, and peptidergic fibers, and richly populated by capillaries. According to this year’s study, the cardiac myocytes that make up the cardiac conduction system are divided into the following three types. Pacemaker cells, or P cells for short. These cells make up the sinus and atrioventricular nodes and are small, shuttle-shaped or polygonal, embedded in a mass of denser connective tissue, with fewer organelles in the cytoplasm, a few myogenic fibers and small swallowing vesicles, but containing more glycogen. Physiological studies have demonstrated that these cells are the pacing points for myocardial excitation. Migrating cells. These cells are found mainly in the periphery of the sinus and atrioventricular nodes and in the atrioventricular bundle and act as impulse conductors. Some of the migrating cells located in the sinus node are connected to the myocardial fibers of the atria, which transmit impulses to the atria. However, it is not clear how impulses from the sinus node are transmitted to the atrioventricular node. The structure of the migrating cells is intermediate between the pacemaker cells and the myocardial fibers. The cells are elongated, thinner and shorter than the myocardial fibers, and contain slightly more myogenic fibers in the cytoplasm than the P cells. Purkinje fibers or bundle cells. They form the atrioventricular bundle and its branches. These cells are shorter and wider than the myocardial fibers, with 1-2 nuclei in the center of the cell, abundant mitochondria and glycogen in the cytoplasm, and fewer myogenic fibers, located at the periphery of the cell. The cells are connected to each other by a well-developed intercalated disc. Physiological studies have shown that these cells are capable of rapid impulse transmission, and cells at the end of the branches of the atrioventricular bundle are connected to the ventricular myofibers, which transmit impulses to all parts of the ventricles. The normal human heart beat is coordinated by a special electrical conduction system capable of transmitting “instructions”. The conduction system is like a telephone line, where the central command can be transmitted down one level. In normal sinus rhythm, the excitation of the heart begins in the sinus node, located in the upper right part of the right atrium, which is the equivalent of the “dispatch center” of the electrical grid, and is transmitted through the three inter-nodal bundles to the “minor node” between the atria and the ventricles –The atrium and ventricle can beat one after the other, which is controlled by the atrioventricular node. The atria and ventricles can beat one after another, which is controlled by the AV node. Then, through the AV node, the left and right conduction bundles are transmitted to the left and right bundles, and the left and right bundle branches descend along the deep surface of the endocardium on both sides of the ventricular septum and send out branches, which get finer and finer and finally divide into Purkinje fibers, which are distributed in the myocardium of the left and right ventricles to control the contraction and diastole of the myocardium, thus ensuring the pumping function of the heart to meet the needs of the body. Atrial fibrillation, referred to as atrial fibrillation, is one of the most common clinical symptoms of cardiac arrhythmia. In atrial fibrillation, the direction of excitation conduction within the atria is inconsistent and the frequency is fast and irregular, causing the atria to lose effective contraction. Although the protective effect of the atrioventricular node prevents all of these excitations from reaching the ventricles, the ventricular rate (heart rate) can still reach 100-160 beats/min, which is faster than the normal sinus heart rate, and the rhythm is definitely not uniform. Patients often present with a fast and irregular self-perceived heartbeat and an irregular pulse.