sinus bradycardia



OVERVIEW

Definition of Sinus Bradycardia

Sinus bradycardia is sinus rhythm in adults, but at a rate of less than 60 beats per minute. It is referred to as sinus bradycardia.

Sinus Rhythm: refers to the rhythm in which agitation originates in the sinus node and is the dominant rhythm controlling the electrical activity of the entire heart. It is a normal heart rhythm.

In adolescents and adults, the normal sinus frequency is 60 to 100 beats/minute; in infants and children, the frequency is faster than in adults.

Staging

As an arrhythmia due to decreased autoregulation of the sinus node, sinus bradycardia can be categorized as physiologic sinus bradycardia or pathologic sinus bradycardia.

The frequency of physiologic sinus bradycardia is usually 50 beats/minute.

Morbidity

Sinus bradycardia can occur at any age.

According to the literature, the incidence of sinus bradycardia in people over 65 years of age is 11.61%.

Etiology

Causes

Physiologic sinus bradycardia

It is common in healthy young people, athletes, the elderly, or heavy laborers, and usually occurs during quiet or sleep.

Pathologic sinus bradycardia

Increased vagal excitability: mostly caused by vagal excitability, humoral mechanism via extracardiac nerve conduction, or direct action on the sinus node.

Cardiac diseases

Impaired sinus node function: Inflammation, ischemia, toxicity or degenerative changes lead to impaired sinus node function, which can progress to pathological sinus node syndrome in severe cases.

Damaged myocardium: myocarditis, pericarditis, myocardiosclerosis, etc.

Acute myocardial infarction: sinus bradycardia occurs in 10% to 15% of patients, commonly in the early stages of acute inferior wall myocardial infarction, usually transient.

Extracardiac disease: usually accompanied by increased vagal excitability.

Intracranial diseases: such as cerebrovascular disease, brain tumor and other diseases that cause increased intracranial pressure.

Metabolic diseases: e.g. hypothyroidism, hypopituitarism.

Recovery from certain infectious diseases: e.g. influenza, typhoid, measles, diphtheria, etc.

Electrolyte disorders: e.g. hyperkalemia, uremia.

Obstructive jaundice.

Severe hypoxia, hypothermia.

Drugs: drugs that directly inhibit sinus node function or cause increased vagal excitability, e.g., cholinomimetics (e.g., scopolamine), neostigmine, amiodarone, β-blockers (e.g., propranolol, metoprolol, atenolol), nondihydropyridine calcium channel blockers (e.g., verapamil, diltiazem), digitalis, tranquilizers, or anesthetics.

Pathogenesis

Due to decreased autoregulation of the sinus node.

Symptoms

The severity of clinical symptoms depends on the hemodynamic impact of bradycardia.

Sinus bradycardia but heart rate > 40 times / min, hemodynamic changes are not big, such as no serious organic heart disease, generally no clinical symptoms, or only chest tightness, palpitations and other minor discomforts; if the combination of serious organic heart disease, can cause the heart, brain, kidneys and other important organs of the reduced blood flow, dizziness, shortness of breath, chest pain, and so on, the serious cases of syncopal precursor or syncope.

If the heart rate is less than 40 beats/minute, the blood volume of cardiac excretion is obviously reduced, which can cause insufficient perfusion of the heart, brain and kidneys, and there will be chest tightness, chest pain, dizziness, fatigue, blackout, memory loss and so on, and fainting occurs in serious cases.

Consultation

Department of Medicine

Cardiovascular Medicine

Routine physical examination reveals abnormal electrocardiogram results, or symptoms such as fatigue, panic, blackouts, dizziness, etc. It is recommended to consult the Department of Cardiovascular Medicine in a timely manner.

Emergency Department

Sudden and severe palpitations and dyspnea, etc., it is recommended to go to the Emergency Department immediately.

In case of loss of consciousness, respiratory and cardiac arrest, immediately call 120 emergency and perform CPR on the patient at the same time.

Preparation

Preparing for your visit: registration, information preparation, common problems

Tips for seeking medical treatment

Physiological bradycardia may occur in special groups such as long-term physical laborers, athletes, etc. It is necessary to go to the hospital to rule out other organic diseases.

Checklist for medical preparation

What are the main symptoms?

What are the triggering and relieving factors for the symptoms?

How many times a day do these symptoms occur? How long do they last?

Is there a family history of the condition?

Are there any drug or food allergies?

Are there any other medical conditions?

What medications have you been taking recently?

Specialized tests: electrocardiogram (including routine electrocardiogram, 24-hour ambulatory electrocardiogram, electrocardiogram exercise test, etc.), echocardiogram, coronary arteriogram, cardiac magnetic resonance test

Routine tests: blood test

Other tests: thyroid function test, polysomnography

Calcium channel blockers: verapamil, diltiazem

β-blockers: propranolol, nadolol

Diagnosis

Diagnostic basis

ECG is the primary diagnostic basis; try to record the ECG when symptomatic and present it to the physician at the visit.

Medical history

Physiologic sinus bradycardia: mostly healthy young people, athletes, manual laborers, occurs at night during sleep.

Pathologic sinus bradycardia: most often combined with heart disease (e.g., impaired sinus node function, myocarditis, cardiomyopathy, etc.), taking medications that affect the function of the sinus node or increase the excitability of the vagus nerve.

Clinical manifestations

Mild cases may be asymptomatic, or have mild chest tightness and palpitations; severe cases may have blackouts and syncope.

Routine electrocardiogram

The diagnostic criteria of ECG are as follows.

P wave: sinus P wave.

Adults: frequency <60 beats/min, usually 40-59 beats/min, usually not less than 40 beats/min. Less than 45 beats/min is considered severe sinus bradycardia.

Children: Heart rate diagnostic criteria for sinus bradycardia in infants and children are <100 beats/min under 1 year of age, <80 beats/min between 1 and 6 years of age, and the same as for adults over 6 years of age.

PR interval: 0.12 to 0.25 seconds.

QRS waves: each P wave is immediately followed by a normal QRS wave with normal morphology and time frame.

T-wave and U-wave: may be normal, or may show low amplitude of T-wave, U-wave is often more obvious.

Ambulatory electrocardiogram

By recording the 24-hour ECG, we can understand when sinus bradycardia occurs, and how sinus bradycardia relates to symptoms and daily life, and clarify the cause of the disease and the severity of the disease.

The 24-hour sinus beats are less than 80,000 beats.

Differential Diagnosis

Second degree sinus block

Similarity: palpitations, chest tightness, blackout, fatigue, chest pain and even fainting in severe cases.

Differences: can be identified by electrocardiogram. Second-degree sinus atrial block can be divided into second-degree type I and second-degree type II.

Second-degree type I sinus block: PP interval shortens progressively until there is a long PP interval, which is shorter than twice of the basic PP interval.

Second degree type II sinus block: the long PP interval is an integral multiple of the basic PP interval.

2:1 sinus atrioventricular block

Similarity: palpitations, chest tightness, blackouts, weakness, chest pain, and even syncope in severe cases.

Difference: can be identified by electrocardiogram.

2:1 sinus block: refers to 2 times sinus excitation, 1 time down to the atrium, 1 time blocked in the sinus-atrial junction area, the long interval is exactly 2 times the sinus cycle. after the disappearance of 2:1 sinus block, sinus heart rate increases exponentially; activities can make the 2:1 sinus block temporarily disappeared or transformed into a high degree of sinus block.

Sinus bradycardia: a gradual change in frequency, often accompanied by sinus arrhythmia (i.e., irregular excitation from the sinus node, markedly uneven speed of the cardiac cycle, and a difference of greater than 0.12 seconds between different PP intervals on the electrocardiogram).

Treatment

Principles of treatment

A heart rate ≥50 beats/minute and asymptomatic usually requires no treatment.

If there are symptoms related to insufficient perfusion of vital organs due to insufficient cardiac output because of a slow heart rate, medications such as isoproterenol can be applied temporarily; pacemaker implantation is recommended for those without reversible factors.

General treatment

The majority of sinus bradycardias are asymptomatic and of no clinical significance, and therefore do not require treatment.

For sinus bradycardia secondary to other diseases, the primary disease should be actively treated, and symptomatic supportive therapy should be taken at the same time.

Drug treatment

For patients with heart rate <40 beats/min, or patients with organic heart disease (especially acute myocardial infarction), whose blood supply of heart, brain, kidney and other important organs is affected by the decrease of cardiac output in sinus bradycardia and who are symptomatic, the drugs to increase the heart rate can be temporarily applied through intravenous route, such as anti-M cholinergic receptor drugs. Isoprenaline may also be used in patients with non-coronary artery disease.

Anti-M cholinergic receptor drugs

They can increase heart rate and relieve symptoms associated with bradycardia.

Contraindicated in patients with enlarged prostate.

Isoprenaline

Increases myocardial contractility and heart rate.

Used when anti-M cholinergic receptor therapy is ineffective or contraindicated.

Contraindicated in patients with coronary artery disease.

All drugs should be used in accordance with medical advice and should not be adjusted or discontinued on their own.

Implantation of cardiac pacemakers

Cardiac pacemakers are electronic therapeutic devices that are implanted in the body to control the heart rate.

An electrical pulse is delivered by a pulse generator to stimulate the heart to excite and contract, temporarily or permanently increasing the heart rate in patients with bradycardia, thereby reducing the risk of serious conditions.

Temporary Pacemaker

A temporary pacemaker can be implanted intravenously to maintain a normal heart rate and rhythm in patients with severe organic heart disease.

After removal of the cause, the temporary pacemaker can be removed if the voluntary heart rate returns to normal; if it does not (e.g., in the case of sinus bradycardia with symptoms due to sick sinus node syndrome), it will need to be replaced with a permanent pacemaker.

Permanent pacemaker

Indicated for the following conditions.

Sinus node dysfunction resulting in severe bradycardia, combined with significant symptoms, even syncope, and ineffective drug therapy.

Organic heart disease with sinus bradycardia, combined with sinus arrest or persistent recurrent sinus block without escape rhythm, or syncope or A.S. syndrome, or ineffective drug therapy.

Epilepsy-induced episodic bradycardia that is not effectively treated with antiepileptic therapy.

Precautions for the use of pacemakers

Keep away from equipment with high voltage electricity or items with magnetic properties such as magnets and induction cookers.

Pacemakers with MRI-compatible functions can undergo magnetic resonance imaging under the guidance of a doctor.

Seek medical attention when abnormal function occurs.

Prognosis

Cure

Physiologic sinus bradycardia usually requires no treatment.

Pathologic sinus bradycardia can be cured with aggressive treatment after removal of the causative agent.

Hazard

Symptomatic patients who are not treated in time may experience worsening symptoms and hemodynamic disorders, which may affect life safety.

The installation of a pacemaker will limit the places where you can move and the things you can use in your life.

Daily

Daily Management

Promote a healthy lifestyle.

Dietary management

Ensure adequate intake of protein, unsaturated fat, vitamins, minerals, dietary fiber and water. Choose soybean products, dairy products, lean meat, fish (may be consumed 1~2 times a week), fresh fruits, fresh vegetables and nuts.

Control sugar intake appropriately, and choose cereals and potatoes instead of refined rice and noodles.

Avoid diets high in salt and fat. Control salt intake to less than 5 grams per day, and avoid deep-fried, pickled and barbecued foods.

Avoid raw, cold, hard or too hot food, chew slowly and avoid overeating.

Eat less irritating food such as chili, coffee, strong tea and mustard.

Exercise management

Exercise appropriately, choose sports such as brisk walking, jogging, playing tai chi, swimming, square dancing, cycling, etc., or choose sports according to the doctor’s instruction.

Exercise in moderation and avoid overwork.

If you feel uncomfortable during exercise, you should stop and rest immediately.

Work and rest management

Regular work and rest, avoid staying up late.

Others

Safety: If dizziness, blackouts or syncope occur, sit down or lie down immediately to avoid falling.

Stop smoking and avoid second-hand smoke.

Stop drinking alcohol.

Disease monitoring

If symptoms do not improve or new symptoms appear, consult a doctor.

Prevention

Active treatment of primary diseases

Actively preventing and treating various cardiac and extracardiac diseases that can cause sinus bradycardia, and eliminating the causative factors in time is the key to preventing the occurrence of this disease.

Reasonable use of drugs

Strictly grasp the indications and dosage of drugs, use drugs that slow down the heart rate and affect cardiac conduction cautiously, and avoid overdose and misuse.

It is forbidden to use digitalis preparations, β-blocking drugs and other anti-arrhythmic drugs that obviously slow down the heart rate.

Reasonable diet to prevent heart disease

Improve dietary structure to ensure adequate nutrition; avoid overeating and maintain appropriate body weight.

Avoid high salt, high sugar, high fat, salted and fried foods.

Eat less stimulating foods such as chili peppers, coffee, strong tea and mustard.

Eat more foods rich in dietary fiber, such as whole grains, fresh vegetables and fruits, etc. Food types should be diversified and alternated.

Improve life habits

Maintain a good mood and mindset.

Combine work and rest, and avoid excessive exercise.