What Is a Dual-Chamber Pacemaker?

A pacemaker is an electronic therapeutic device implanted in the body. The pulse generator sends out electrical pulses powered by a battery. Through a lead electrode, it stimulates the myocardium that the electrode touches, stimulating and contracting the heart, thereby achieving treatment. Purpose of cardiac dysfunction due to certain arrhythmias. Since the first cardiac pacemaker was implanted into the human body in 1958, the pacemaker manufacturing technology and process have developed rapidly and the functions have become increasingly perfect. While the pacemaker was successfully used to treat bradyarrhythmias and saved thousands of patients' lives, pacemakers have also begun to be applied to tachyarrhythmias and non-ECG diseases, such as the prevention of paroxysmal atrial tachycardia. Arrhythmia, carotid sinus syncope, dual-chamber simultaneous medication refractory congestive heart failure, etc.

Basic Information

English name: cardiacpacemaker
Visiting department: Cardiology

Common locations: heart
Contagious: no

Pacemaker pacing principle

The pulse generator periodically issues a pulsed current of a certain frequency, which is transmitted to the myocardium (atrial or ventricle) contacted by the electrode through the lead and the electrode, so that local myocardial cells are stimulated by external electrical stimulation and are connected or gapped through the gap between the cells. The connection conducts to the surrounding myocardium, causing the entire atrium or ventricle to excite and in turn produce contractile activity. It needs to be emphasized that the myocardium must have the functions of excitation, conduction and contraction, and the cardiac pacing can play its role.

Components of a pacemaker pacing system

Artificial cardiac pacing system mainly includes two parts: pulse generator and electrode lead. Pulse generators are often referred to as pacemakers alone. In addition to the pacing function described above, the pacing system also has the sensing function of transmitting the heart's own ECG back to the pulse generator.

The pacemaker is mainly composed of a power source (that is, a battery, and now mainly uses a lithium-iodine battery) and an electronic circuit process, which can generate and output electrical pulses.

The electrode lead is a conductive metal wire wrapped with an insulating layer, and its function is to transmit the electrical pulses of the pacemaker to the heart and transmit the intracardiac electrocardiogram to the pacemaker's sensing circuit.

Pacemaker artificial heart pacing indication

Artificial heart pacing is divided into temporary and permanent, and they have different indications.

Indications for temporary cardiac pacing

Temporary cardiac pacing is a temporary or temporary artificial cardiac pacing that is not permanently implanted with a pacing electrode lead. The pacing electrode lead is generally placed for no more than 2 weeks. The pacemaker is placed outside the body. After the purpose of diagnosis, treatment and prevention is reached, the pacing electrode lead is removed. If you still need to continue pacing treatment, you should consider placing a permanent pacemaker. Any patient with bradycardia that is symptomatic or causes hemodynamic changes is the object of temporary cardiac pacing. The purpose of temporary cardiac pacing is usually divided into treatment, diagnosis, and prevention.

(1) Treatment

1) Onset of Alzheimer's syndrome: atrioventricular block and sinus node failure caused by various reasons (acute myocardial infarction, acute myocarditis, poisoning caused by digitalis or antiarrhythmic drugs, electrolyte disorders, etc.) The resulting cardiac arrest and the onset of Alzheimer's syndrome are absolute indications of emergency temporary cardiac pacing.

2) Transition of patients with unstable heart rhythms before placement of a permanent pacemaker.

3) Third-degree atrioventricular block caused by open heart surgery.

4) Bradycardia and / or persistent ventricular tachycardia induced by bradycardia ineffective with medication

(2) Diagnosis

As an auxiliary means for some clinical diagnosis and electrophysiological examination. For example, judge: sinus node function; atrioventricular node function; type of pre-excitation syndrome; reentrant arrhythmia; the effect of antiarrhythmic drugs.

(3) Prevention

1) Patients with high risk of apparent bradycardia are expected to have some chronic arrhythmias and cardiac conduction system insufficiency that are common in high-risk patients . Patients with tachyarrhythmia undergo cardioversion, and patients with preexisting left bundle branch block undergo right-heart catheterization.

2) Transition of pacemaker-dependent patients when replacing with a new pacemaker.

2. Indications for permanent cardiac pacing

With the improvement of pacing engineering, the indications for pacing therapy have gradually expanded. The main purpose of implanting a cardiac pacemaker in the early years was to save patients 'lives. Currently, it also includes restoring patients' working ability and quality of life. At present, the main indications can be simply summarized as severe heart diseases such as slow heartbeat, weak heart contraction, and cardiac arrest. In 2012, the American College of Cardiovascular Diseases / American Heart Association / American Heart Rhythm Association re-developed guidelines for implanting pacemakers.

(1) Type I indications mainly include

1) Patients with sinus node dysfunction Symptoms of sinus node dysfunction are recorded, including sinus arrest that often causes symptoms. Symptomatic poor-temporality. Because certain diseases must use certain drugs, and these drugs can cause sinus bradycardia and produce symptoms.

2) Adults with acquired atrioventricular block (AVB) Grade III AVB and high AVB at any block site with symptomatic bradycardia (including heart failure) or ventricular arrhythmia secondary to AVB . Long-term use of drugs for treating other arrhythmias or other diseases, which can cause degree AVB and high AVB (regardless of the block site) and symptomatic bradycardia. Asymptomatic patients with grade III AVB and high AVB at any block site in the awake state were recorded with a cardiac arrest of 3 seconds or longer, or an escape beat heart rate of less than 40 bpm, or an escape beat rhythm point Those below the sinoatrial node. The level III AVB and high AVB of any block site in the awake state. Asymptomatic atrial fibrillation and bradycardia have one or more long pauses of at least 5 seconds. AVB of any degree III and AVB at any block site after catheter ablation of the AV node. There is no degree III AVB and high AVB in any block site that may recover after cardiac surgery. Grade III AVB and high AVB at any block site due to sacral neuromuscular disease, such as tonic muscle dystrophy, Karns-Sayre syndrome, pseudohypertrophic muscular dystrophy, fibula Patients with muscular atrophy. AV AVB with bradycardia symptoms, regardless of type or block site. Asymptomatic grade III atrioventricular block at any block site with an average ventricular rate score or> 40 beats / min with enlarged heart or left ventricular dysfunction or block below the AV node. No degree II or III AVB during exercise without myocardial ischemia.

3) Patients with chronic bifurcation block accompanied by high AVB or transient III degree AVB. accompanied by type II AVB. Alternative bundle branch block.

4) Acute myocardial infarction with atrioventricular block After ST-segment elevation myocardial infarction, the persistent second-degree AVB of His-Purkinje system combined with alternating bundle branch block or -degree AVB; transient severe or Degree AVB under the atrioventricular node combined with bundle branch block;

persistent and symptomatic grade II or III AVB.

5) Those with carotid sinus hypersensitivity and cardiac neurogenic syncope Recurrent syncope caused by spontaneous carotid stimulation and carotid compression induced ventricular arrest time> 3s. Patients with persistent or symptomatic bradyarrhythmias who have not recovered hope for a heart transplant. long intermittent dependence of ventricular tachycardia, with or without QT interval prolongation.

Patients with NYHA IV heart failure who have a left ventricular ejection fraction 35%, complete left bundle branch block and QRS 150ms, sinus rhythm, heart function classification (NYHA) class II, III, or who can move after ideal drug treatment, CRT or CRT-ICD should be implanted.

The indications for ICD are as follows: Persistent ventricular tachycardia (VT) with ventricular fibrillation or hemodynamic instability, except for those who have other reversible causes of cardiac arrest; Organic heart disease and spontaneous persistence VT patients, regardless of whether the hemodynamic stability is stable; have a history of syncope, electrophysiological examination clearly induces continuous VT or ventricular fibrillation (VF) of hemodynamic instability; after 40 days of myocardial infarction, left ventricular ejection fraction 35%, NYHA or ; non-ischemic dilated cardiomyopathy, left ventricular ejection fraction 35%, NYHA or ; left ventricular dysfunction before myocardial infarction, left ventricular ejection 40 days after myocardial infarction Blood fraction 30%, NYHA grade ; after ventricular myocardial infarction, left ventricular ejection fraction 40%, non-persistent VT or electrophysiological examination induced VF or persistent VT.

(2) Type IIa indications mainly include

1) Sinus node dysfunction Sinus node dysfunction leads to a heart rate of <40 bpm, and there is clear evidence between symptoms and bradycardia, but whether bradycardia is recorded or not. Patients with unexplained syncope, clinical findings or electrophysiological examination-induced sinus node dysfunction.

2) Adults with acquired AVB Asymptomatic persistent third-degree AVB with a heart rate below 40 bpm without accompanying heart enlargement. Electrophysiological examination revealed asymptomatic second-degree AVB at or below the level of the His bundle. AVB of grade or is accompanied by hemodynamic performance similar to pacemaker syndrome. Asymptomatic type II AVB with narrow QRS wave. However, when the type II AVB is accompanied by a wide QRS wave, including the right bundle branch block, the indication is upgraded to class I.

3) Patients with chronic bifurcation block Although syncope is not confirmed to be caused by AVB, other causes (especially ventricular tachycardia) can be ruled out. Although there are no clinical symptoms, the electrophysiological examination revealed that the HV interval was 100ms. At the time of electrophysiological examination, the non-physiological block of His is induced by atrial pacing.

Repetitive syncope, no exact carotid stimulation event, and high-sensitivity cardiac suppression response with ventricular arrest time> 3 seconds should consider implanting a permanent pacemaker.

Tachycardia pacing is limited to patients with recurrent supraventricular tachycardia who fail catheter ablation and / or medication failure, or who cannot tolerate the side effects of the medication.

High-risk patients with long QT syndrome.

The following patients with heart failure can be implanted with CRT or CRTICD: Left ventricular ejection fraction 35%, complete left bundle branch block and QRS between 120ms and 149ms, sinus rhythm, cardiac function classification (NYHA) Patients with NYHA IV heart failure who can move after Grade or III or ideal drug treatment; Left ventricular ejection fraction 35%, non-left bundle branch block and QRS 150ms, sinus rhythm, heart function classification (NYHA) Patients with NYHA IV heart failure who can move after Grade or Grade III or ideal drug treatment; Heart failure patients with left ventricular ejection fraction 35% and AF with ideal drug treatment, if ventricular pacing is required or meets the CRT indication and Atrioventricular node ablation or drug treatment can guarantee 100% ventricular pacing; Left ventricular ejection fraction 35% after ideal drug treatment, and requires new equipment or replacement and relies on ventricular pacing (40%).

Sudden Cardiac Death (SCD) risk (main SCD risks: history of cardiac arrest, spontaneous persistent VT, spontaneous non-sustained VT, family history of SCD, syncope, left ventricular thickness 30mm, abnormal blood pressure response during exercise; possible SCD Risks: Patients with obstructive hypertrophic cardiomyopathy who have atrial fibrillation, myocardial ischemia, obstruction of the left ventricular outflow tract, high risk of mutation, and strong physical activity should be implanted with DDD-ICD.

The recommended indications of ICD are as follows: non-ischemic dilated cardiomyopathy, significant left ventricular dysfunction, and unexplained syncope; persistent ventricular tachycardia, even if the ventricular function is normal or near normal; one of patients with hypertrophic cardiomyopathy The above major SCD risk factors;

Arrhythmic right ventricular dysplasia / cardiomyopathy patients have a major risk factor for SCD (including electrophysiological examination-induced VT, non-persistent VT for ECG monitoring, male, severe right ventricular enlargement, extensive right ventricular involvement, < 5 years old, affected the left ventricle, had a history of cardiac arrest, and could not explain syncope); patients with long QT syndrome developed syncope and / or ventricular tachycardia when using beta blockers; waiting for a heart transplant outside the hospital Patients; Brugada syndrome with syncope; Brugada syndrome with ventricular tachycardia but no cardiac arrest; catecholamine-sensitive ventricular tachycardia, syncope and / or ventricular tachycardia after beta blockers; Patients with sarcoidosis, giant cell myocarditis, and trypanosomiasis.

Of course, the guidelines do not cover all clinical situations. For a specific patient, the indications for permanent cardiac pacing are not always clear. In general, irreversible, symptomatic bradycardia is the main indication for implanting a permanent pacemaker. The decision of whether a permanent pacemaker should be implanted should be made by the physician in charge, taking into account the patient's specific condition, the patient's wishes, and the financial situation.

Reasonable choice of pacemaker and pacemaker

Choosing a pacemaker for a particular patient is a problem that clinicians often face. The principles are as follows:

1. If there is chronic persistent atrial fibrillation or atrial quiescence

Select VVI (R).

2. Sinus node dysfunction

If there is no atrioventricular block or it is predicted that the recent probability of atrioventricular block is very low, choose AAI (R), otherwise choose DDD (R).

3. Atrioventricular block

If there is persistent atrial tachyarrhythmia, choose VVI (R); have diseased sinus syndrome, choose DDD (R); sinus node function is normal or the probability of sinus node dysfunction is expected to be low, choose VDD or DDD.

Single ventricular pacing is no longer recommended, and dual-chamber pacing increases survival-adjusted quality of life at generally accepted prices. As for the choice of implantation of AAI or DDD pacemaker, although DDD is more expensive, it should be considered that patients may develop AV block.

In addition, comprehensive consideration needs to be given to the patient's age, heart disease and associated diseases, economic status, and the general condition of the patient.

(1) Temporary cardiac pacing

There are five methods, including percutaneous pacing, transesophageal pacing, transthoracic puncture, open chest epicardial pacing, and transvenous pacing. At present, the latter is more selected.

Femoral veins, subclavian veins, or internal jugular veins are commonly used for temporary pacing electrode leads. Electrode lead displacement is more common than permanent cardiac pacing. Postoperative ECG monitoring should be strengthened, including early rise in pacing threshold, changes in sensory sensitivity, and electrode lead dislocation, especially for pacemaker-dependent persons. In addition, because the electrode leads communicate with the outside world through the puncture point, care should be taken to clean locally to avoid infection, especially for longer periods of time. In addition, the patient should remain supine after temporary pacing via the femoral vein, and the lower extremity is braked on the venipuncture side.

(2) Permanent cardiac pacing

The vast majority of endocardial electrode leads are currently used. Technical highlights include venous selection, lead electrode fixation, and implantation of pacemakers.

1) Vein selection The veins usually available for electrode lead insertion are: superficial veins include cephalic vein, external jugular vein, deep veins include subclavian vein, axillary vein internal jugular vein. Usually, the contralateral cephalic vein or subclavian vein is preferred. If it is unsuccessful, the internal or external jugular vein is selected.

2) Placement of the electrode wire According to the needs, the electrode wire is placed in the cardiac chamber that needs to be paced. Generally, passive fixing is used, and active electrode wire can also be used.

3) Implantation of pacemakers Generally, pacemakers are buried under the skin of the chest on the same side of the electrode lead. Connect the electrode lead to the pulse generator, and place the extra lead near the muscle surface and the pacemaker near the skin into the subcutaneous bag.

The method is to insert the electrode lead from the vein under the arm or clavicle, and insert it into a predetermined cardiac pacing position under X-ray fluoroscopy, fix and detect it. Then a pacemaker connected to the electrode lead is embedded in the chest, the skin is sutured, and the operation can be completed.

(3) Complications of permanent cardiac pacing

1) Complications related to implant surgery Most complications, such as careful operation during the operation, should be avoided, and some are difficult to completely avoid the rabbit. Incidence is closely related to the experience of the implant physician.

Arrhythmia usually does not require special treatment. Local bleeding can usually be absorbed by itself. When there is obvious hematoma formation, the blood can be squeezed out under pressure under strict aseptic conditions. Subclavian vein puncture complications and treatment of pneumothorax: A small amount of pneumothorax does not require intervention. Pneumothorax compresses the lung tissue> 30%, it is necessary to pump or place a drainage tube. Into the subclavian artery by mistake: The needle and / or guide wire should be removed and locally pressurized to stop bleeding (never insert an expansion tube), usually without special treatment. Heart perforation is rare. Handling: Carefully sprinkle the catheter back into the heart cavity, and closely observe the patient's blood pressure and heart condition. Once pericardial tamponade occurs, open the chest for pericardial drainage or cardiac repair. Avoid positioning on the perforation when continuing to place the electrode. Infection is rare. Treatment: Once the patients with local abscess formation have little chance of healing through conservative treatment, they should be cut open and drained as early as possible, debride, and remove the electrode lead in the wound. diaphragmatic stimulation is rare. Can cause stubborn hiccups. Left ventricular electrode leads are more common. Treatment: Reduce the pacemaker output or change to bipolar pacing. If symptoms persist, reposition the electrodes.

(4) Complications and treatment related to electrode lead

1) Threshold raising treatment: increase the energy output through program control, and need to replace the electrode position or lead wire if necessary.

2) X-ray examination can be found when the electrode dislocation and micro dislocation are obviously displaced, and the X-ray fluoroscopy of the micro dislocation reveals that the electrode tip is still in place, but the contact with the endocardium is actually poor. Treatment: Reoperation is usually required to adjust the electrode position.

3) The electrode wire is broken or the insulation layer is broken. If the impedance is very low, the insulation layer is considered to be broken; if the impedance is very high, the electrode wire is broken. Treatment: Need to re-implant a new electrode lead.

(5) Pacemaker-related complications and management

With the development of engineering, the failure of pacemakers such as pacemakers has become rare. Occasional pacemaker failure is pacemaker reset, the pacemaker battery is exhausted in advance, the former is due to external interference (such as strong Magnetic field), the pacemaker needs to be reprogrammed, and the latter needs to be replaced in time.

In addition, sensory dysfunction may still occur, and improper sensing parameters are often set for the pacemaker rather than the mechanical failure of the pacemaker itself, including poor perception and excessive perception.

(6) Complications and management related to the pacing system

1) Pacemaker Syndrome (PMS) Some patients who use a VVI pacemaker may experience signs of dizziness, fatigue, decreased mobility, hypotension, palpitations, and chest tightness. In severe cases, heart failure may occur. Pacemaker syndrome. Treatment: If PMS occurs and is not a pacing dependent person, slow down the pacing frequency to restore your heart rhythm as much as possible, and replace it with an atrioventricular sequential pacemaker if necessary.

2) Pacemaker-mediated tachycardia (PMT) is a tachycardia caused by the active and continuous participation of a dual-chamber pacemaker. For the atrial electrode to sense the back-propagating P wave, start the AVD and issue ventricular pulses at the end of the AVD. The latter excites the ventricle and then passes back to the ventricle, forming circular motor tachycardia. Preventricular contractions and poor atrial pacing are the most common causes of PMT. Prevention can be achieved through program control for longer PVARP, appropriate reduction of atrial sensory sensitivity, delayed sensory atrioventricular interval, or activation of pacemaker automatic prevention procedures for PMT. Termination methods include placing a magnet on the pacemaker, extending PVARP, program-controlled pacing methods for atrial nonsensing (DVI, VVI, DOO) or non-tracking mode (DDD), or enabling the automatic recognition and termination procedures of the PMT that the pacemaker has .

Pacemaker follow-up and troubleshooting

Unlike other interventional cardiac interventions, successful pacemaker implantation is only the relatively simple first step performed by a doctor. The tedious but important task is the long-term follow-up of patients after surgery. Follow-up work began on the day of implantation and continued throughout the patient's life.

1. Teach patients to self-test pulse after surgery

Because checking the pulse is a simple and effective way to monitor the pacemaker. When monitoring your pulse, make sure you are in the same physical state every day, such as when you wake up in the morning or after 15 minutes of meditation.

In the early stages of pacemaker placement, the pacing threshold is often unstable and needs to be adjusted in time. Therefore, it is necessary to visit the hospital regularly, usually once every two weeks within one month and once a month within three months (depending on the patient). There are many factors that cause the threshold to increase. In addition to the electrode location, factors such as insufficient sleep, full meals, antiarrhythmic drugs, and hypertension may have an effect. Therefore, postoperative patients should maintain a good mood, ensure a regular life and work and rest system, and avoid all possible adverse factors. The follow-up period and content follow-up should be loose on both ends.

2.Common faults and treatment

It is usually manifested as no stimulus, incapable of being captured, or imperceptible.

(1) No stimulation pulse

There may be one of the following common reasons:

1) If the problem can be solved after the magnet is placed, the reason is mostly over-perception or using some normal pacing functions such as lag. The former is mostly caused by electromagnetic interference, myoelectric potential, cross-sensing, or T-wave oversensing, etc., so the sensing sensitivity should be reduced, while the latter need not be processed.

2) Electrode lead or pacemaker failure: It may be due to loose or disconnected screws connected to the pacemaker, electrode lead conductor failure, or damage to the electrode lead insulation or battery exhaustion. Treatment: Re-tighten the screws or replace the pacing electrode lead or pacemaker.

(2) Failure to seize may have one of the following reasons

1) The pacing threshold is increased . The output of the electrode at the end of the electrode lead cannot effectively stimulate the myocardium connected to the electrode. Treatment: It can temporarily increase the output voltage and correct the possible causes, such as applying hormones, correcting electrolyte disorders, or changing the pacing position.

2) The electrode lead is faulty, the electrode is dislocated, or the battery is depleted. Replace or reposition the electrode lead or replace the pacemaker according to specific reasons.

(3) Can't perceive

It could be for one of the following reasons:

1) The endocardial signal is too small (temporary changes caused by electrolyte disturbances, acidosis, or permanent changes in local endocardium caused by myocardial infarction or cardiomyopathy): At this time, it is necessary to increase the sensitivity of the sensor or change the pacemaker position.

2) Electrode dislocation, malfunction or pacemaker failure. Relocate or replace the electrode lead or pacemaker according to specific reasons.

Pacemaker pacemaker safety

Many patients are concerned about the installation of pacemakers. In fact, it is safe to install pacemakers. Although many pacemaker complications and failures are listed above, the overall incidence is only about 1%. Among patients who meet the indications for pacemaker implantation, if the treatment can be standardized and followed up regularly, the benefits for these patients will far outweigh the disadvantages.