In addition to the definite therapeutic effect of implantable pacemakers on definite pathological sinus node syndrome (SSS) and atrioventricular block (AVB), some non-bradycardia conditions such as congestive heart failure, hypertrophic obstructive cardiomyopathy, and even paroxysmal atrial fibrillation (AF) are also starting to be included in the indications for clinical pacing therapy.
The indications for implantable pacemaker therapy are mainly “symptomatic bradycardia”, i.e. a series of symptoms such as syncope, near syncope, dizziness, blackness, etc., which are directly caused by an excessively slow heart rate, resulting in a decrease in cardiac output and insufficient blood supply to vital organs and tissues, especially the brain; long-term bradycardia can also cause systemic symptoms such as Prolonged bradycardia can also cause systemic symptoms such as fatigue, decreased exercise tolerance, and congestive heart failure. The indications for implantable pacemaker therapy are divided into the following three categories according to their degree of need.
Class I indications: Based on the condition, there is clear evidence or consensus among experts that pacing therapy is beneficial, useful or effective for the patient, which corresponds to the so-called absolute indications.
Class II indications: Depending on the condition, there is insufficient evidence or disagreement among experts regarding the benefits and effects of pacing therapy on patients. Class II indications are further divided into two subcategories, IIa (tending to support) and IIb (divergent opinions), according to the propensity of the evidence/opinion, corresponding to relative indications.
Class III indications: Pacemaker implantation is not needed/not advisable because experts agree that pacing therapy is ineffective or even harmful in some cases, depending on the condition of the patient, i.e. non-indications.
I. Which patients need a permanent cardiac pacemaker (question of indications)?
1. Sick sinus node syndrome (SSS)
SSS includes a series of arrhythmias, such as sinus bradycardia, sinus arrest, sinus block, and slow-fast syndrome, the latter of which can be characterized by alternating paroxysmal supraventricular tachycardia and bradycardia, so that pharmacological treatment of tachycardia can aggravate bradycardia and make treatment contradictory. Pacemaker implantation can certainly bring benefits to the quality of life of patients and can also lead to a longer survival time for some patients. The relationship between these arrhythmias and symptoms should be carefully evaluated when considering whether pacing should be performed, including the use of multiple tools such as ambulatory electrocardiography. For athletes and young people with a high level of long-term exercise, the heart rate is usually slow, often below 50 beats/min or even 40 beats/min, and even slower during rest and sleep, which can be below 40 beats/min, but the sinus node function is normal and asymptomatic, and the slow heart rate is due to enhanced vagal function, so pacing therapy is not considered.
Class I indications (absolute indications, i.e., indications that a pacemaker must be implanted)
(1) Pathological sinus node syndrome manifesting as symptomatic bradycardia or necessitating treatment with certain types and doses of drugs that can cause or aggravate bradycardia and produce symptoms.
(2) Those who have symptoms due to poor timing of the sinus node.
Class IIa indications (relative indications, implantation should benefit)
(1) Spontaneous or drug-induced sinus node malfunction with a heart rate <40 beats/min, with symptoms of bradycardia but not proven to be related to the bradycardia that occurred.
(2) Unexplained syncope, if combined with sinus node malfunction or found to have sinus node malfunction by electrophysiological examination.
Class IIb indications (relative indications, possible benefit of implantation)
Prolonged heart rate below 40 beats/min in the awake state, but with mild symptoms.
Class III indications (non-indications, should not be implanted)
(1) Asymptomatic patients, including sinus bradycardia (heart rate < 40 beats/min) due to long-term drug use.
(2) Patients with bradycardia-like symptoms that have been proven not to be due to sinus bradycardia.
(3) Symptomatic bradycardia caused by non-essential drugs.
2.Adult acquired atrioventricular block (AVB)
AVB is divided into degree I, degree II, and degree III (complete) block. High AVB is a severe degree II block in which more than 3 consecutive P waves are blocked. According to the anatomical classification, the location of the block can be on the Hirschsprung bundle, within the Hirschsprung bundle and under the Hirschsprung bundle. Depending on the severity of the block, patients can range from asymptomatic to syncope due to bradycardia or even ventricular tachycardia (ventricular tachycardia) secondary to bradycardia. the need for pacing in AVB depends on the location of the block and whether the patient is symptomatic.
Class I indications (absolute indications, i.e., indications that a pacemaker must be implanted for a definite benefit)
(1) Third-degree and high atrioventricular block at any block site with one of the following conditions
(1) Symptomatic bradycardia (including heart failure) due to atrioventricular block
② need medication to treat other arrhythmias or other diseases, and the drugs used can cause symptomatic bradycardia
③No clinical symptoms, but it has been confirmed that ventricular arrest ≥ 3 s or escape heart rate ≤ 40 beats/min in the awake state
④Atrial fibrillation with third-degree or high AVB at any anatomic level, asymptomatic in the awake state, with one or more long intervals of ≥5 s
⑤ irreversible AV block occurring after radiofrequency ablation of the atrioventricular junction zone or cardiac surgery
(6) Atrioventricular block associated with neuromuscular disorders (myasthenia gravis, Creutzfeldt-Jakob syndrome, etc.), whether symptomatic or not, is classified as a Class I indication because conduction block can worsen at any time.
(20 Symptomatic bradycardia from second-degree AV block of any site and type of block.
Class IIa indications (relative indications, which should benefit from pacemaker implantation)
(1) Asymptomatic third-degree AV block at any site with a mean ventricular rate of ≥40 beats/min at waking hours, especially in combination with cardiomyopathy and left ventricular dysfunction.
(2) Asymptomatic second-degree type II AV block with narrow QRS waves on ECG. If the QRS wave is wide, it should be classified as Class I indication.
(3) Asymptomatic second-degree type I AV block with an electrophysiological examination due to other conditions reveals that the block site is within or below the level of the Hitchcock bundle.
(4) First- or second-degree AV block with clinical manifestations similar to pacemaker syndrome.
Class IIb indications (relative indications, potential benefit of pacemaker implantation)
(1) Significant first-degree AV block (PR interval > 300 ms) in combination with symptoms of left ventricular malfunction or congestive heart failure, where shortening the AV interval may improve the symptoms of heart failure by reducing the left atrial filling pressure.
(2) Any degree of atrioventricular block associated with neuromyogenic disease (myasthenia gravis, Creutzfeldt-Jakob syndrome, etc.), whether symptomatic or not, because the block may worsen at any time.
Class III Class indications (non-indications, should not be implanted with a pacemaker)
(1) Asymptomatic atrioventricular block of the first degree.
(2) Second-degree type I AV block occurring above the Hirschsprung bundle and where the site of the block has not been determined to be within or below the Hirschsprung bundle.
(3) Atrioventricular block that is expected to recover and not recur.
3.Chronic bifurcation and trifurcation block
Double-branch and triple-branch block refers to two branches of the right bundle branch and the left bundle branch below the AV node on the ECG. Bifurcation block is defined as ECG evidence of conduction disturbance in one of the two branches of the right and left bundle branches below the AV node. Alternating bundle branch block (also known as bilateral bundle branch block) refers to the presence of evidence of block in all three branches on the ECG, such as right bundle branch and left bundle branch block on one consecutive ECG, or right bundle branch block combined with left anterior branch block on one ECG and right bundle branch block combined with left posterior branch block on the other ECG. Triple branch block is defined as ECG evidence of block in all three branches, such as alternating bundle branch block or two branches combined with first degree AVB. these patients have a higher chance of sudden death when they develop symptoms or progress to third degree AVB. Recurrent syncopal episodes are a common manifestation of two-branch and three-branch blocks. Prolonged HV interval on electrophysiological examination increases the chance of progression to AVB III and sudden death, and pacing therapy should be considered.
Class I indications (absolute indications, i.e., indications that a pacemaker must be implanted for a definite benefit)
(1) Double or triple branch block with intermittent third degree atrioventricular block.
(2) Bifurcation or trifurcation block with second-degree type II AV block.
(3) Alternating bilateral bundle branch block.
Class IIa indications (relative indications, should benefit from pacemaker implantation)
(1) Syncope due to atrioventricular block has not been confirmed, but syncope due to other causes (especially ventricular tachycardia) can be excluded.
(2) In the absence of clinical symptoms, HV intervals ≥100 ms are found on electrophysiological examination.
(3) Non-physiological block below the Hitchcock bundle induced by atrial pacing during electrophysiological examination.
Class IIb indications (relative indications, possible benefit from pacemaker implantation)
Any degree of branch block associated with neuromyogenic disease (myasthenia gravis, Creutzfeldt-Jakob syndrome, etc.), whether symptomatic or not, since the block can be exacerbated at any time.
Class III Class indications (non-indications, should not be implanted with a pacemaker)
(1) Branch block asymptomatic or not associated with atrioventricular block.
(2) Branch block with atrioventricular block of one degree, but without clinical symptoms.
4. Pacing therapy for AVB with acute myocardial infarction
In acute myocardial infarction with intraventricular block, except for simple left anterior branch block, the prognosis is mostly poor in the near and long term, and the incidence of sudden death increases. In patients with acute myocardial infarction with AVB, the main condition for pacing is not only the symptoms, but also the need for temporary pacing does not mean that permanent pacing is necessary in the future. When considering permanent pacing, attention must be paid to the type of conduction abnormality, the site of infarction, and the relationship between electrocardiographic disturbances and infarction. If the AVB associated with acute myocardial infarction is expected to recover or has no adverse effect on the long-term prognosis (in the case of lower wall acute myocardial infarction), then permanent pacemaker implantation is generally not required.
Class I indications (absolute indications for a definite benefit of pacemaker implantation, i.e., indications that a pacemaker must be implanted)
(1) Persistent second- or third-degree AV block below the Hitchcock bundle after acute myocardial infarction.
(2) Transient second- or third-degree AV block below the AV node with bundle branch block. Electrophysiological examination should be performed if the site of block is unclear.
(3) Persistent and symptomatic second- or third-degree atrioventricular block.
Class IIa indications (relative indications, should benefit from pacemaker implantation)
None
Class IIb indication (relative indication, potential benefit of pacemaker implantation)
Persistent second- or third-degree atrioventricular block at the level of the AV node.
Class III indications (non-indications, should not be implanted)
(1) Transient atrioventricular block without intraventricular block.
(2) Transient atrioventricular block with left anterior branch block.
(3) Pure left anterior branch block.
(4) Persistent one-degree AV block with chronic or unknown onset of bundle branch block.
5. Pacing therapy for children, adolescents and patients with congenital heart disease
The main indications for permanent pacing in children and adolescents are basically the same as those in adults. When considering arrhythmias in children and whether to perform permanent pacing therapy, the following situations should be carefully noted: (1) a significant proportion of children with congenital heart disease or after surgery for congenital heart disease have a circulatory status different from normal; (2) the definition of “bradycardia” in infants and children is not the same as that in adults. The frequency criteria for “bradycardia” in infants and children should take into account the age of the child; (3) congenital conduction system lesions may be asymptomatic even if there is significant bradycardia, especially in infants and children, but abnormal pathophysiological states do exist, such as mean heart rate, QT interval, cardiac output and exercise tolerance, which should be evaluated comprehensively; (4) many children have symptoms related to bradycardia Many children have symptoms related to bradycardia that are paroxysmal or transient, which are difficult to record and require repeated recording of the ECG.
Class I indications (absolute indications, i.e., indications that a pacemaker must be implanted)
(1) Second- to third-degree atrioventricular block combined with symptomatic bradycardia, poor cardiac function or low cardiac output.
(2) Symptoms of sinus node malfunction, which is manifested by age-inappropriate sinus bradycardia.
(3) Second- to third-degree atrioventricular block lasting > 7 to 14 d after surgery and not expected to recover.
(4) Congenital third-degree AV block combined with wide QRS escape rhythm, complex premature ventricular beats and poor cardiac function.
(5) Infants with congenital third-degree AV block with a ventricular rate < 50-55 beats/min or combined with congenital heart disease with a ventricular rate < 70 beats/min.
(6) Bradycardia-dependent sustained ventricular tachycardia (ventricular tachycardia) with or without a combined long QT interval for which pacing therapy has been shown to be effective.
Class IIa indications (relative indications, which should benefit from pacemaker implantation)
(1) Slow tachycardia syndrome requiring long-term pharmacological treatment (except digoxin).
(2) Congenital third-degree atrioventricular block, over 1 year of age, with a mean heart rate < 50 beats/min or with long intervals of 2 to 3 s, or in children with symptoms due to poor chronotropic function.
(3) Long QT syndrome combined with 2:1 second-degree AV block or third-degree AV block.
(4) Asymptomatic sinus bradycardia combined with complex organic heart disease with a heart rate < 40 beats/min at rest or > 3s long intervals.
(5) Patients with congenital heart disease with impaired hemodynamics due to bradycardia and atrioventricular dyssynchrony.
Class IIb indications (relative indications, possible benefit of pacemaker implantation)
(1) Temporary postoperative third-degree block with residual intraventricular double branch block after restoration of sinus rhythm.
(2) Infants and adolescents with congenital third-degree AV block who have an acceptable heart rate, narrow QRS waves, and normal cardiac function.
(3) Adolescents with combined congenital heart disease with a heart rate < 40 beats/min at rest or with > 3s long intervals but the patient is asymptomatic.
(4) Atrioventricular block of any degree (including first degree) associated with neuromyogenic disease, whether symptomatic or not, because the block may worsen at any time.
Class III Indications (non-indications, no pacemaker should be implanted)
(1) Temporary post-surgical AV block whose conduction has been restored.
(2) Asymptomatic post-surgical intraventricular double branch block with or without first degree AV block.
(3) Asymptomatic second-degree type I atrioventricular block.
(4) Asymptomatic sinus bradycardia in adolescents with heart rate > 40 beats/min, or maximum interval < 3s.
6.Pacing treatment of carotid sinus hypersensitivity and neurocardiogenic syncope
The cardiovascular response to stimulation of the carotid sinus leading to syncope or aura syncope is called carotid sinus hypersensitivity syndrome. It can be manifested as: (1) cardiac depressor reflex, which is sinus bradycardia or AVB, or both, due to increased vagal tone; (2) vascular depressor reflex, which is vasodilatation and decreased blood pressure secondary to decreased sympathetic tone, independent of heart rate changes; and (3) mixed type, which combines both cardiac and vascular depressor responses. Carotid sinus hypersensitivity syndrome can be diagnosed if the patient has symptoms of syncope or aura syncope and sinus arrest and/or AVB with a long interval >3s on carotid sinus compressions. In patients with carotid sinus hypersensitivity with a purely cardiac depressor reflex, permanent pacing can be effective in improving symptoms.
Class I indications (absolute indications for a definite benefit of pacemaker implantation, i.e. indications that a pacemaker must be implanted)
Syncope due to recurrent carotid sinus irritation, or ventricular arrest of more than 3 s due to slight pressure on the carotid sinus without any medication that may inhibit sinus node or atrioventricular conduction.
Class IIa indications (relative indications, which should benefit from pacemaker implantation)
(1) Recurrent episodes of syncope with a confirmed hypersensitive cardiac depressor reflex in the carotid sinus, although the cause is unknown.
(20 Clearly symptomatic neuro2cardiogenic syncope combined with spontaneous or tilt test-induced bradycardia.
Class IIb indication (relative indication, potential benefit of pacemaker implantation)
None.
Class III indications (non-indications, should not implant a pacemaker)
(1) Hypersensitive cardiac depressor reflex due to carotid sinus stimulation without significant symptoms or with only vagal stimulation symptoms.
(2) Recurrent episodes of syncope, dizziness, or vertigo in the absence of a cardiac depressor reflex induced by carotid sinus stimulation.
(3) Scene vasovagal syncope, avoidance of scene stimulation syncope no longer occurs.
II. Selection of the best pacing modality (the problem of model selection)
After determining the indications, it is crucial to select the best pacing mode in order to obtain good hemodynamic effects and efficacy. The following aspects should be considered when choosing the best pacing mode:
1. functional status of the atria
Patients undergoing permanent cardiac pacing may have persistent atrial fibrillation, highly enlarged atria or quiescent atria, and atrial-based pacing modalities (AAI, VDD, DDD, etc.) cannot be applied in this group. For atrial fibrillation and atrial flutter with fewer episodes, the use of atrial-based pacing modalities is not excluded based on the specific circumstances (e.g., length of history of atrial fibrillation episodes, frequency of episodes, duration of episodes, etc.) and consideration of the overall situation.
2. Atrioventricular node status
The function of the atrioventricular node is an important factor in the choice of pacing mode. For example, in patients with sinus node dysfunction, if there is no atrioventricular node lesion at the time of pacemaker implantation, an atrial pacing-based pacing mode can be used.
3. Heart rate response during exercise
The response of the sinus node to exercise is called the chronotropic response and is an important factor in the choice of pacing mode. For poor chronotropic response, rate-adaptive pacing, such as VVIR AAIR DDDR, can be used (the meaning of poor chronotropic response can also be extended to other rhythms in which the heart rate does not accelerate after exercise).
4.Left heart function status
Atrioventricular synchronization is essential for the systolic and diastolic functions of the left heart. When cardiac insufficiency, cardiomyopathy, and elderly patients should try to use physiological cardiac pacing modalities in order to maintain the role of atria and atrioventricular sequential functions and to prevent the occurrence of pacemaker syndrome, and if necessary, cardiac resynchronization therapy (CRT) should be considered.
The following pacing modalities are recommended for different types of symptomatic bradycardia according to the above principles.
① those with complete or high atrioventricular block with normal sinus function: VDD, DDD; those with poor variable time response: DDDR, VDDR.
(ii) Those with normal atrioventricular conduction function who exhibit simple sinus bradycardia: AAI; those with poor variable temporal response: AAIR.
③ those who exhibit frequent atrial fibrillation, atrial flutter, supraventricular tachycardia complicated by sinus arrest or significant sinus bradycardia (slow-fast syndrome): VVI, VVIR.
④In cases of double node lesions: DDD, DDDR.
⑤ Patients with pathological sinus node syndrome: DDD, DDDR; for patients with paroxysmal atrial fibrillation and atrial flutter, dual-chamber pacemaker therapy may also be used, while for patients with persistent or chronic atrial fibrillation, VVI and VVIR are used.