In 1973, Schnitzler first reported the application of floating electrode catheters for temporary cardiac pacing at the bedside, and this technology has rapidly gained popularity abroad and has now become one of the essential medical techniques for hospital resuscitation. The purpose of cardiac pacing is not only to provide heart rate support, but more importantly, to provide normal or near-normal hemodynamic effects, to restore the patient’s work capacity and improve quality of life, and to have some diagnostic and cardiac information storage functions. Temporary cardiac pacing is an emergency and effective measure for the treatment of severe arrhythmias and an emergency means of cardiopulmonary resuscitation, providing an important safety measure for patients with cardiac disorders undergoing non-cardiac surgery to safely, smoothly and successfully pass through the surgical anesthesia period, and its application in the perioperative period is gradually increasing. The history of artificial cardiac pacemakers dates back to the early 19th century, when Aldini used direct current stimulation to resuscitate the heart of a severed corpse in 1804. It was not until 1932 that Hyman succeeded in stimulating rabbits in cardiac arrest with an electrical stimulator, named the pacemaker, and in 1952 Zoll first used extracorporeal transthoracic pacing. Larsson was implanted with the world’s first implantable pacemaker. In the same year, Furman and Robinson pioneered the transvenous implantation of endocardial pacing electrodes by placing the first intravenous catheter electrode into the right ventricular outflow tract under X-ray. 1963 saw the application of ventricular on-demand pacing (VVI) by Lemberg and Castellenos, which is considered the standard pacing modality. 1973 saw Schnitzler first report the application of floating electrode catheters for temporary cardiac pacing at the bedside. The indications for pacemakers have been continuously broadened from slow arrhythmias to ventricular tachycardia, hypertrophic obstructive cardiomyopathy, dilated cardiomyopathy, drug-refractory congestive heart failure, and the treatment of atrial fibrillation. The normal and abnormal electrophysiological properties of the heart are based on the physiological properties of the myocardium, which is rhythmically contracting and diastolic. The myocardium has four physiological properties: excitability, autoregulation, conduction and contractility. The first three are based on the bioelectrical activity of the myocyte membrane, collectively referred to as electrophysiological properties, which express the excitatory function of the heart, form the onset and propagation of excitation within the heart, and trigger contraction. Artificial cardiac pacing is also based on the electrophysiological properties of the heart and aims to cause mechanical contraction of the myocardium, with which artificial cardiac pacing is closely related. 1. Autoregulation and cardiac pacing: The ability of the myocardium to automatically generate rhythmic excitation without external stimulation. The degree of autoregulation is measured by the frequency of automatic excitation (beats/min). The highest autoregulation is found in the sinus node, which emits impulses that directly control the electrical activity of the entire heart and is the origin of normal cardiac excitation, called the normal pacing point. If impulses are issued from a pacing point other than the sinus node, which temporarily or permanently controls the heart, it is called an ectopic rhythm. 2. Conductivity and conduction disorders: Cardiac muscle cells have the ability to conduct excitation. The degree of conductivity is measured by the speed of excitation conduction. The intracardiac conduction time is about 0.22s, including 0.06s for intraatrial and intraventricular conduction and 0.1s for atrioventricular junction. slow conduction in the atrioventricular junction allows atrial excitation and contraction to precede the ventricle, which is conducive to full ventricular filling; at the same time, slow conduction there also makes it easy for conduction block to occur. 3. Excitability and undershoot: In artificial pacing, the minimum stimulus value that can cause cardiac excitation is the pacing threshold of the heart. During the overdue period, asynchronous pacing pulses may fall in the ventricular fibrillation phase and cause fatal arrhythmias. Types of cardiac pacing systems Pacemakers consist of a generator, wires and electrodes. The power supply generates electrical energy, and the generator issues pacing pulses, which are transmitted to the electrodes through the wires, and the pacing pulses stimulate the heart muscle due to the contact between the electrodes and the heart, causing excitation and contraction of the heart. (i) Types of electrodes 1. Bipolar and unipolar: Pacemaker circuits require two electrodes, and those in which both electrodes contact the heart are called bipolar pacing; those in which one electrode contacts the heart and the other contacts tissues other than the heart are called unipolar pacing. Endocardial, epicardial, and myocardial electrodes: pacing electrodes sent into the heart cavity through a vein to contact the endocardium are called endocardial electrodes; pacing electrodes implanted through the chest cavity to contact the epicardium are called epicardial electrodes; pacing electrodes piercing the myocardium of the heart wall are called myocardial electrodes. (ii) Types of pacemakers In 1987, NASPE/BPEG (North American Society of Pacing and Electrophysiology/British Cardiac Pacing and Electrophysiology Organization) introduced a pacemaker coding system, in which the five letters of the code represent the functions of different types of pacemakers. For example, VVI indicates ventricular pacing-ventricular sensing-R-wave suppression type pacemaker, and DDD indicates dual-chamber pacing-double-chamber sensing-R-wave suppression type or P-wave triggered pacemaker. 2. Synchronous pacemakers are the second generation products. It can sense the electrical signal of its own heartbeat and adjust the timing of its pacing pulse delivery according to the patient’s heart rate, thus avoiding the competition between the pacing pulse and itself. Synchronization refers to the sensing function, which includes P-wave synchronization (sensing of atrial beats) and R-wave synchronization (sensing of ventricular beats). After sensing its own pacing signal, the pacemaker responds in two ways: triggered and inhibited. Triggered means that the pacemaker senses its own pacing signal and immediately delivers a pacing pulse to stimulate the heart to pace. The inhibitory type is when the pacemaker senses its own heartbeat and then cancels the next scheduled pulse to sense its own heartbeat to start the pacing cycle, also known as the on-demand type. Synchronous pacemakers are widely used clinically and are safer, and include: (1) P-wave triggered pacemakers (AAT); (2) R-wave triggered pacemakers (VVT); (3) P-wave inhibited pacemakers (AAI); and (4) R-wave inhibited pacemakers (VVI) (Figure 2A). However, the atrium cannot contract sequentially and even produces ventricular-atrial retrograde transmission, which reduces cardiac output by 10%-35% and can easily lead to pacemaker syndrome. 3. Sequential pacemakers are implanted with two electrode leads, which are often placed in the right atrium (atrium) and the right ventricle apical part (ventricle) for sequential atrioventricular pacing. It is characterized by atrial contraction followed by ventricular contraction, in line with physiological pacing. Because it maintains the sequence of atrial and ventricular contractions, its hemodynamic effect is superior to that of simple ventricular pacing. (1) Atrial synchronous ventricular pacemaker (VAT); (2) Atrial synchronous R-wave suppressed ventricular pacemaker (VDD); (3) R-wave suppressed atrial sequential pacemaker (DVI); and (4) Atrial all-purpose pacemaker (DDD), which includes both VDD and DVI, are ideal for the treatment of SSS combined with AVB. 4. Program-controlled pacemaker is a new type of physiological pacemaker, which can automatically change the pacing frequency according to the physiological needs of the body (body movement, respiratory rate, ventilation, body temperature, blood pH, etc.). Such as frequency-responsive pacemakers. 5. Anti-tachyarrhythmic pacemakers have the function of sensing and timely termination of tachycardia, with on-demand pacing function in case of concomitant bradycardia and sinus quiescence, and are suitable for refractory tachycardia. At present, the application of such pacemakers is limited due to the ideal effect of radiofrequency ablation in the treatment of tachyarrhythmias. 6. Buried automatic pacing and cardioversion defibrillator (AIPCD) can pace slow rhythms and anti-tachyarrhythmias, and it can also repace and defibrillate, and it has therapeutic effects on various arrhythmias, and it also has the functions of non-invasive program control and data recording. Indications for pacemakers The indications for permanent pacing are single electrode contacting the endocardium and pacemakers with unrelated electrodes buried in the subcutaneous tissue of the anterior pectoralis major muscle. Powered by lithium batteries, it can be used for 6-8 years and up to 14-15 years. In 1998, the American College of Cardiology (ACC) and the American Heart Association (AHA) jointly developed the ACC/AHA Guidelines for the Implantation of Pacemakers and Arrhythmia Devices, which describe the indications for permanent pacing of sinus node dysfunction and acquired atrioventricular indications for permanent pacing therapy for sinus node dysfunction and acquired atrioventricular block.