sick sinus node syndrome (SNS)



Overview.

Definition

Sick sinus node syndrome is a syndrome of arrhythmias and clinical symptoms caused by dysfunction of the sinus node pacing and/or conduction due to lesions of the sinus node and its adjacent tissues, referred to as sick sinus syndrome.

Most of the disease has a slow onset, and a few have an acute onset (see acute myocardial infarction and acute myocarditis).

Hereditary Sick Sinus Node Syndrome

It can be seen in fetuses, infants, or children with or without structural cardiac abnormalities, and there is a clear familial tendency for its onset.

It is inherited in autosomal dominant and autosomal recessive forms. More than 10 causative genes have been reported to be associated with hereditary sick sinus node syndrome, such as SCN5A, HCN4, MYH6 and LMNA.

Epidemiology

It is mostly seen in the elderly. It has a prevalence of 1/600 in cardiac patients over 65 years of age; in the normal population, the prevalence is about 0.08%.

Some studies have shown that for every 5 increase in body mass index (BMI), the incidence of the disease increases by 0.23 times; for every 5-year increase in age, the incidence of the disease increases by 0.73 times.

It is rare in children without congenital heart disease.

Causes

Causes

Nonspecific, degenerative fibrous degeneration of the sinus node: age-related degeneration is the most common etiology. With age, there is progressive fibrosis within the sinus node and the pacemaker cells (P cells) are gradually replaced by fibrous tissue.

Decreased arterial blood supply to the sinus node

In coronary artery disease, chronic insufficiency of coronary artery blood supply causes long-term ischemia of the sinus node, which affects the function of the sinus node.

In myocardial infarction, obstruction of the right coronary artery or the left rotary branch leads to interruption of the blood supply to the sinus node, affecting the function of the sinus node. Common in acute inferior wall infarction.

Myocarditis and cardiomyopathy: cardiomyopathies including myocardial amyloidosis, cardiac tuberculosis and various immune myocarditis are also common causes of this disease.

Neuropathy: autonomic dysfunction, increased vagal tone, can significantly inhibit sinus node function.

Drug factors: certain antiarrhythmic drugs, such as digitalis drugs, acetylcholine, etc., inhibit sinus node function, resulting in sinus node dysfunction.

Frequent and prolonged tachyarrhythmias, such as atrial tachycardia, atrial flutter and atrial fibrillation, can inhibit sinus node function and lead to sinus node dysfunction. Sinus node function may gradually recover after tachyarrhythmias are effectively controlled.

Others: such as carotid sinus hypersensitivity, cerebrovascular accident, hyperkalemia and severe sleep apnea syndrome, in addition to genetic factors.

Symptoms

Main Symptoms

The disease usually starts insidiously and progresses slowly, with slow-type arrhythmia as the main symptom, and there are mostly no obvious symptoms in the early stage. When the disease develops to a certain degree, it mainly manifests as symptoms of insufficient blood supply to the brain, heart, kidneys and other organs due to bradycardia or cardiac arrest, which reduces the volume of cardiac excretion.

Insufficient blood supply to the brain: dizziness, drowsiness, insomnia, irritability, and in severe cases, impaired consciousness, vertigo, blackout or fainting.

Insufficient blood supply to the heart: palpitations, fatigue, angina pectoris (manifested as squeezing pain in the anterior region of the heart), heart failure (manifested as dyspnea, pallor, cyanosis, etc.).

Renal blood supply insufficiency manifestation: there may be lumbago, oliguria, and azotemia in severe cases.

Complications

Heart failure

When the disease is severe, it can lead to serious insufficiency of blood supply to the heart, resulting in heart failure. It manifests as weakness, dyspnea, pallor and cyanosis.

Thromboembolism

In slow-fast syndrome, especially in atrial fibrillation, thromboembolism can occur in high-risk patients due to loss of contractility of the atria and stagnation of blood flow. The embolus often comes from the left atrium and can lead to pulmonary embolism and cerebral embolism.

It can manifest as sudden dyspnea, severe chest pain, hemiparesis, aphasia, and impaired consciousness.

Consultation

Department of Medicine

Cardiovascular Medicine

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

Emergency Medicine

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

Consultation Tips

Sick sinus syndrome can occur in patients with heart disease, metabolic disease, etc. It is recommended to consult a doctor when symptoms occur.

Preparation Checklist

What are the main symptoms?

What are the triggers and relievers of 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, X-ray examination

Sodium channel blockers: propafenone, quinidine, lidocaine

Potassium channel blockers: amiodarone, dronedarone

Diagnosis

Disease diagnosis

The diagnosis is confirmed on the basis of typical ECG findings and the presence of a clear correlation between clinical symptoms and ECG changes.

To determine the relationship between symptoms and ECG changes, a single or multiple ambulatory electrocardiogram or electrocardiograph may be used, which may be supported by the recording of significant bradycardia or cardiac arrest in conjunction with the onset of symptoms such as syncope.

Sinus node dysfunction in early or atypical cases may be intermittent or may be characterized by sinus bradycardia as the primary or only manifestation, which is often difficult to diagnose.

Medical history

A history of coronary artery disease, myocarditis, or cardiomyopathy is often present.

Clinical manifestations

In mild cases, there may be no symptoms, or there may be dizziness, drowsiness, insomnia, irritability or palpitations, chest tightness, etc. In severe cases, there may be dizziness, sleepiness, insomnia, irritability or palpitations.

In severe cases, there may be dizziness, blackout, syncope or angina pectoris (squeezing pain in the precordial region), heart failure (dyspnea, pallor, cyanosis, etc.).

Electrocardiogram

Conventional electrocardiogram

Sinus bradycardia: non-drug-induced persistent and significant sinus bradycardia, typically with a heart rate <50 beats/minute, and not correctable with anti-M cholinergic receptor drugs.

Sinus arrest or sinus block.

Sinus block coexists with atrioventricular block.

Bradycardia-tachycardia syndrome: referred to as slow-fast syndrome, this refers to alternating episodes of bradycardia with atrial tachyarrhythmias (atrial flutter, atrial fibrillation, or atrial tachycardia).

Other ECG changes

Slow ventricular rate in atrial fibrillation in the absence of antiarrhythmic drugs, or its episodes are preceded or followed by sinus bradycardia and/or one degree of atrioventricular block.

The increase in heart rate after exercise is not significant.

Atrioventricular junction zone escape rhythms.

Some have atrial tachyarrhythmias as the first manifestation, with sinus arrest on reversal (i.e., fast-slow syndrome), and bradycardia or both occurring after several years or more.

Ambulatory electrocardiogram

An ambulatory electrocardiogram (ECG) is a continuous recording of changes in the electrocardiogram, which makes it easier to detect abnormalities than a conventional electrocardiogram.

The disease is highly suspected if the ambulatory ECG analysis shows an average heart rate of <50 beats/min, or a prolonged slow heart rate (<40 beats/min) with sinus atrial block, and sinus arrest.

ECG recorder

Patients can carry this device with them, and when suspicious symptoms such as palpitations and chest tightness occur, they can collect ECG information on their own anytime, anywhere, and then the doctor can judge the relationship between the symptoms and the arrhythmia.

Sinus Node Electrophysiology

This can be done by artificial intra-atrial pacing or by transesophageal manipulation.

Measures sinus node recovery time, sinus conduction time, and corrected sinus node recovery time.

Transesophageal method: A catheter electrode is inserted nasally to the lower and middle esophagus adjacent to the left atrial site, and an esophageal electrocardiogram can be recorded. Transcatheter electrode stimulation of the left atrium allows evaluation of sinus node pacing function and sinus conduction function.

Other

Vagal tone can be measured if it is suspected to be due to vagal hypertonia.

Differential Diagnosis

It is necessary to differentiate from various other types of arrhythmia, mainly by electrocardiography.

Pathologic sinus bradycardia

Similarities

When the disease is mild, both may have no performance, or only mild palpitations and chest tightness; when the disease is severe, both may have dizziness, precordial pain, and even fainting.

Early or atypical pathological sinus node syndrome may have sinus bradycardia as the main or only ECG manifestation.

Differences

Sick sinus node syndrome exhibits sinus bradycardia that cannot be corrected with medications such as anti-M cholinergic receptor agents and does not result in a significant increase in heart rate after exercise.

In addition to sinus bradycardia, sick sinus node syndrome may also be characterized by sinus block, atrial fibrillation, and other arrhythmias.

Sinus node block

Similarities

Both may manifest as palpitations, chest tightness, even dizziness, precordial pain, fainting, etc.

Both can have ECG manifestations of sinus atrial block.

Differences: Sick sinus node syndrome is characterized by slow arrhythmia, but can also manifest as slow-fast syndrome.

Treatment

If there are no symptoms, no treatment is necessary and regular follow-up is sufficient. In symptomatic patients, a permanent pacemaker is usually implanted if an association between symptoms and bradycardia is established.

Treatment of causes

Treatments are tailored to the cause of the problem.

These include improving myocardial blood supply, increasing myocardial nutrition, correcting electrolyte disorders, and treating drug overdose.

For those with myocarditis/cardiomyopathy, treatment for the underlying heart disease is needed.

Treat metabolic disorders such as hypothyroidism.

The use of a ventilator during sleep is recommended for patients with severe sleep apnea.

In recent years, it has been reported that heart rate can be increased in some patients by removing the cardiac ganglion plexus.

Discontinue medications that cause sinus node suppression, such as beta-blockers, calcium channel blockers, and digoxin;

Symptomatic treatment

Bradyarrhythmias

Scopolamine, ephedrine and isoproterenol can be used to correct hemodynamic disturbances due to bradyarrhythmias, usually only as a temporary measure.

If severe sinus bradycardia or sinus arrest occurs only after the termination of atrial fibrillation, atrial flutter, or atrial tachycardia (the so-called fast-slow syndrome), catheter ablation may be used to treat the tachyarrhythmia first.

In the vast majority of patients, after correction of tachyarrhythmia, symptoms such as dizziness and fatigue can be reduced or even disappear.

Tachyarrhythmia

Tachyarrhythmias are generally left untreated, and drugs that slow down the heart rate and conduction are avoided as much as possible.

When tachycardia occurs, antiarrhythmic drugs alone may aggravate bradycardia. If tachycardia occurs after pacemaker implantation, antiarrhythmic drugs may be used at the same time.

Pacemaker implantation

Implantation of a pacemaker is the best solution for this disease.

Implanting a pacemaker, which is an instrument placed in the heart that controls the heart rate, can temporarily or permanently increase the heart rate and reduce the risk of serious conditions.

Precautions for using a pacemaker

Try to stay away from electronic devices such as cell phones.

Stay away from magnetic cards, magnets, induction cookers, and other items with magnetic properties.

Avoid magnetic resonance imaging tests.

Seek medical attention if there is any abnormality in function.

For those who have undergone pacemaker therapy, catheter ablation may be considered if medications do not satisfactorily control episodes of atrial fibrillation.

Prognosis

Cure

Asymptomatic patients usually do not require treatment and clinical observation is sufficient.

The long-term prognosis for patients treated with pacemakers is good.

Those with severe heart disease have a poor prognosis.

Hazards

Symptoms, if left untreated, may lead to syncope, etc., affecting the patient’s life.

In severe cases, A-s syndrome may occur and even lead to death.

Frequent episodes of atrial fibrillation, the possibility of complication of embolism is higher, affecting the patient’s prognosis.

After the installation of pacemakers, there are restrictions on the places of activities, daily necessities and so on.

Daily life

Daily life

Reasonable diet

Ensure adequate intake of protein, unsaturated fat, vitamins, minerals, dietary fiber and water. You may choose soybean products, dairy products, lean meat, fish (may be 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 6 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 foods such as chili peppers, coffee, strong tea and mustard.

Improve lifestyle habits

Quit smoking and stay away from “second-hand smoke”.

Quit drinking.

Ensure adequate sleep and avoid staying up late.

Exercise in moderation, choose fast walking, jogging, tai chi, swimming, square dancing, cycling and other sports, or follow the doctor’s instructions to choose sports, avoid excessive exercise. If you feel uncomfortable during exercise, you should stop and rest immediately.

Pay attention to safety

If dizziness occurs, sit down or lie down immediately to avoid falling.

Regular follow-up

Follow your doctor’s instructions for regular follow-up; if symptoms do not improve, or new symptoms appear, consult a doctor promptly.

Prevention

Treatment of underlying diseases

Such as coronary heart disease, myocarditis, cardiomyopathy, hyperkalemia and other diseases.

Reasonable use of medication

Use the medication according to the doctor’s prescription. Seek medical advice if you feel unwell during the medication period.

Reasonable diet to prevent heart disease

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

Avoid diets high in salt, sugar and fat, and try to avoid pickled, smoked, barbecued and fried foods.

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