What is a pacemaker? A pacemaker is an electronic therapeutic device implanted in the body, which stimulates the heart muscle contacted by the electrodes through the electrical impulses issued by the pulse generator and conducted by the electrode wires, simulating the generation and conduction of heart impulses and causing the heart to excite and contract, thus achieving the purpose of treating the heart dysfunction caused by certain arrhythmias (mainly slow arrhythmias). Since the first pacemaker was implanted in the human body in 1958, pacemaker manufacturing techniques and technologies have developed rapidly and their functions have become increasingly sophisticated. While the application of pacemakers has successfully treated slow arrhythmias and saved the lives of thousands of patients, pacemakers have also begun to be applied to tachyarrhythmias and non-cardiac diseases, such as the prevention of paroxysmal atrial tachyarrhythmias, carotid sinus syncope, and biventricular synchronization for drug-refractory congestive heart failure. Components of an artificial pacemaker An artificial cardiac pacing system consists of two main parts: the pulse generator and the electrode leads. The pulse generator is often referred to as the pacemaker alone. In addition to the pacing function, the pacing system also has the function of sensing the heart’s own ECG activity back to the pulse generator. The pulse generator consists of a power supply (i.e., a battery, nowadays lithium-iodine batteries are used) and an electronic circuit that generates and outputs electrical pulses. The electrode lead is a conductive metal wire wrapped with an outer insulating layer, whose function is to transmit the electrical impulses from the pacemaker to the heart and to transmit the intracavitary ECG of the heart to the pacemaker’s sensing line. Indications for Artificial Pacemaker Implantation As the understanding of arrhythmia mechanisms improved and pacing engineering was refined, the indications for pacing therapy gradually expanded. In the early years, the main purpose of pacemaker implantation was to save the patient’s life, but nowadays it is also necessary to include restoration of the patient’s work capacity and quality of life. In 2012, the American College of Cardiology/American Heart Association/American Heart Rhythm Association reformulated the guidelines for pacemaker implantation, which include the following three categories. The main indications for Class I include: (1) Sinus node insufficiency: (1) Documented symptomatic sinus node dysfunction, including frequent sinus arrests that cause symptoms. (2) Adults with acquired atrioventricular block (AVB): ① Grade III AVB and high AVB at any block site, complicated by symptomatic bradycardia (including heart failure) or with ventricular arrhythmias secondary to AVB. ②Taking long-term medication for other arrhythmias or other diseases that can lead to Grade III AVB and high AVB (regardless of the block site), complicated by symptomatic bradycardia. ③Patients with third degree AVB and high AVB at any block site in the awake state who are asymptomatic and have been recorded as having a cardiac arrest of 3 seconds or longer, or a fugitive heart rate of less than 40 bpm, or a fugitive rhythm pacing point below the sinoatrial node ④Third degree AVB and high AVB at any block site in the awake state, asymptomatic atrial fibrillation and bradycardia who have one or more long intervals of at least 5 seconds. ⑤ III degree AVB and high AVB at any block site following catheter ablation of the AV node. ⑥ III degree AVB and high AVB at any block site without possible recovery after cardiac surgery. ⑦ III degree AVB and high AVB at any block site due to neuromuscular disease, such as ankylosing myotonic dystrophy, Kearn-Sayre syndrome (Kearn-Sayre syndrome) , pseudohypertrophic muscular dystrophy, and patients with peroneal muscular atrophy. (8) AVB of degree II with bradycardia symptoms, regardless of fractionation or block site. (⑨) Patients with asymptomatic grade III AVB at any block site with mean ventricular rate fraction or >40 beats/min with cardiomegaly or abnormal left ventricular function or block below the atrioventricular node. (1) II degree III AVB during exercise without myocardial ischemia. Patients with chronic double branch block: ① with high AVB or first-pass III degree AVB. ② with II degree II AVB. ③ with alternating bundle branch block. (3) Acute myocardial infarction with AV block: ① persistent degree II AVB of the His-Purkinje system combined with alternating bundle branch block or degree III AVB after ST-segment elevation myocardial infarction; ② transient severe degree II or III AVB under the AV node combined with bundle branch block; ③ persistent and symptomatic degree II or III AVB. (4) Carotid sinus hypersensitivity and Cardiac neurological syncope in: ① Recurrent syncope due to spontaneous carotid stimulation and carotid compression-induced ventricular arrest time > 3s. ②Patients after cardiac transplantation with persistent or symptomatic slow arrhythmias with no hope of recovery. (3) Long interval-dependent ventricular tachycardia with or without prolonged QT interval. (5) Patients with left ventricular ejection fraction ≤ 35%, complete left bundle branch block with QRS ≥ 150ms, sinus rhythm, cardiac function class (NYHA) II or III or NYHA class IV heart failure who are active after ideal drug therapy should be implanted with CRT or CRT-D. Class IIa indications mainly include: (1) Sinus node insufficiency resulting in a heart rate <40 bpm, with clear evidence of a link between symptoms and bradycardia, whether or not bradycardia is recorded. (2) Those with unexplained syncope, where sinus node dysfunction is found clinically or induced by electrophysiological examination. (2) In adults with acquired AVB: ① asymptomatic persistent grade III AVB with escape heart rate below 40 bpm without cardiomegaly. (2) Asymptomatic degree II AVB found at or below the level of the His bundle on electrophysiological examination. (3) Degree I or II AVB with hemodynamic manifestations similar to pacemaker syndrome. (iv) Asymptomatic degree II type II AVB with narrow QRS waves. However, when degree II type II AVB with wide QRS waves, including right bundle branch block, the indications are upgraded to category I. (3) Patients with chronic double branch block: ① Although it is not confirmed that syncope is caused by AVB, other causes (especially ventricular tachycardia) can be excluded. (2) Although there are no clinical symptoms, electrophysiological examination reveals HV interval ≥100ms. (3) Non-physiological block below the His bundle induced by atrial pacing during electrophysiological examination. (4) Recurrent syncope without a definite carotid stimulation event and highly sensitive cardiac depression in response to ventricular arrest time > 3 s. Consider implantation of a permanent pacemaker. (5) Pacing for tachycardia is limited to patients with supraventricular tachycardia who have failed catheter ablation and/or pharmacologic therapy, or who cannot tolerate pharmacologic side effects and have recurrent episodes of tachycardia. (6) Patients at high risk of long QT syndrome. (7) The following patients with heart failure can be implanted with CRT or CRTCICD: ① Patients with left ventricular ejection fraction ≤ 35%, complete left bundle branch block with QRS between 120ms and 149ms, sinus rhythm, NYHA class II or III heart failure or NYHA class IV heart failure who are active after ideal drug therapy; ② Patients with left ventricular ejection fraction ≤ 35%, non-left bundle branch (ii) Patients with heart failure of NYHA class IV who have left ventricular ejection fraction ≤35%, non-left bundle branch conduction block and QRS ≥150ms, sinus rhythm, NYHA class II, III or active after ideal drug therapy; (iii) Patients with heart failure who have left ventricular ejection fraction ≤35% combined with atrial fibrillation after ideal drug therapy, if ventricular pacing is required or if CRT is indicated and 100% ventricular pacing can be guaranteed after atrioventricular node ablation or drug therapy (4) Patients with left ventricular ejection fraction ≤35% after ideal drug therapy who require new or replacement devices and are dependent on ventricular pacing (40%). (8) Patients with obstructive hypertrophic cardiomyopathy at risk of sudden cardiac death (SCD) (major SCD risks: history of cardiac arrest, spontaneous sustained VT, spontaneous nonsustained VT, family history of SCD, syncope, left ventricular thickness ≥30 mm, abnormal blood pressure response during exercise; possible SCD risks: atrial fibrillation, myocardial ischemia, left ventricular outflow tract obstruction, high risk of sudden changes, during strong competitive physical activity) DDD-ICD should be implanted. Indications for ICD implantation are as follows: ① non-ischemic dilated cardiomyopathy with significant left ventricular function abnormalities and unexplained syncope; ② persistent ventricular tachycardia, even if ventricular function is normal or near normal; ③ patients with hypertrophic cardiomyopathy with more than one major SCD risk factor; ④ patients with arrhythmogenic right ventricular dysplasia/cardiomyopathy with one major SCD risk factor ( including electrophysiologically induced VT, nonsustained VT on ECG monitoring, male, severe right ventricular enlargement, extensive right ventricular involvement, < 5 years of age, involvement of the left ventricle, history of cardiac arrest, unexplained syncope); ⑤ Patients with long QT syndrome presenting with syncope and/or ventricular tachycardia on beta-blocker application; ⑥ Patients awaiting out-of-hospital cardiac transplantation; ⑦ Patients with syncope in Brugada syndrome; ⑧ Brugada syndrome with ventricular tachycardia without cardiac arrest; ⑨ patients with catecholamine-sensitive ventricular tachycardia who develop syncope and/or ventricular tachycardia despite beta-blockers; ⑩ patients with cardiac nodal disease, giant cell myocarditis, and South American trypanosomiasis. Of course the guidelines do not cover all clinical situations. The indications for permanent cardiac pacing implantation are not always clear for a specific patient. Usually, irreversible, symptomatic bradycardia is the main indication for implantation of a permanent pacemaker. The decision to implant a permanent pacemaker should be made by the responsible physician, taking into account the patient's specific condition, the patient's wishes, and financial situation.