Sick sinus node syndrome is also referred to as “sick sinus syndrome” or “sick sinus”. The sinus node is located in the upper part of the right atrium of the heart. In layman’s terms, the main function of the human heart is to act like a pump, constantly contracting and diaphrasing at a certain frequency to pump blood to the vital blood vessels and organs throughout the body. This working frequency of the heart is the heart rate (i.e., the number of heartbeats per minute), which is usually between 60 and 100 beats per minute under normal quiet conditions. The sinus node is like the “command” that controls the heart rate, and after it gives the “command”, it has to be transmitted down through the atria, atrioventricular node, and then to the ventricles. In other words, the sinus node is in charge of the rhythm of the heart, the normal “sinus rhythm”. If the sinus node and its neighboring tissues become diseased and thus hypofunctional, it may not be able to produce “instructions” properly, or the transmission of “instructions” may be impaired, resulting in a series of problems and symptoms.
The causes of sinus disease are complex and can be caused either by the sinus node itself or by factors other than the sinus node. The common clinical causes are as follows.
1, coronary artery disease: insufficient blood supply to the sinus node due to coronary atherosclerosis.
2, degenerative lesions: with age, degenerative lesions can occur in the sinus node, causing hypofunction, so patients with diseased sinuses are more common in the elderly.
3, inflammation: various causes of myocarditis, etc. In some cases, sinus node function can be restored after the inflammation is cured, but in some cases the dysfunction will persist.
4, other causes: for example, severe increased vagal excitability, application of certain antiarrhythmic drugs can inhibit sinus node function.
The clinical manifestations of patients with sick sinus are mainly symptoms of insufficient blood supply to the heart, brain and other organs related to bradycardia. In mild cases, there may be dizziness, weakness, slow reaction, memory loss, and in severe cases, blackness, syncope, or even sudden death. If accompanied by premature beats or tachycardia episodes, symptoms such as palpitations and chest pain can occur.
The diagnosis of sick sinus is mainly based on clinical manifestations, electrocardiogram and sinus node function assessment. The duration of sinus disease is long and sometimes progresses slowly, the symptoms vary in severity, and the electrocardiogram is often varied, so a comprehensive analysis is needed in the diagnosis. In addition to the conventional ECG, single or multiple ambulatory ECG follow-ups are often required. If necessary, an atropine test, transesophageal atrial pacing, or electrophysiological examination is also required to help evaluate sinus node function. When analyzing a patient’s profile, it is critical to determine that there is a clear correlation between clinical symptoms and electrocardiographic changes.
From the electrocardiogram and ambulatory electrocardiogram, the diseased sinus often shows the following arrhythmias.
1. persistent and significant sinus bradycardia: the heart rate is often <50 beats/min and is not drug-induced, and the patient has difficulty with a corresponding acceleration of the heart rate during exercise (variable temporal insufficiency), often <90 beats/min.
2. sinus atrioventricular block or sinus arrest.
3, sinus atrial block combined with atrioventricular block.
4, alternating slow arrhythmias with tachyarrhythmias: the latter are mainly atrial fibrillation (AF), atrial flutter (AF) and atrial tachycardia (AF).
The principles of treatment of sick sinus include.
1, etiological treatment.
2, pharmacological treatment: for milder cases, some drugs to increase the heart rate can be applied to improve clinical symptoms, or short-term application of drugs as a transition before pacemaker therapy, such as anticholinergic drugs (atropine, etc.) and adrenergic drugs.
3. Pacemaker therapy: temporary pacing can be performed in emergency situations, and permanent pacemakers are implanted electively in patients with indications.
Permanent pacemakers are an important measure in the treatment of slow arrhythmias. The need for permanent pacemaker implantation in patients with sick sinus depends on the presence of bradycardia and whether this symptom is related to sinus node dysfunction (including chronotropic insufficiency). If these conditions do exist, pacemaker therapy should be considered. As for the type of pacemaker to be implanted, consult with a specialized clinician depending on the patient’s specific condition. Some patients with sinus disease have recurrent tachyarrhythmias such as atrial flutter, atrial fibrillation, and atrial tachycardia, which pose a great problem for the clinical use of anti-tachyarrhythmic drugs (since these drugs can affect the sinus node). In this case, antiarrhythmic drugs can be used more safely after implantation of a permanent pacemaker.
Clinically, there are several situations that should be of concern.
First, there are a few patients who should have received a permanent pacemaker because of the psychological influence of “subjective feeling of being okay” or “being too old to have a pacemaker” or “being too young to have a pacemaker”. “This is undesirable.
Secondly, there are a few patients (often <70 years old) who have a transient sinus node function significantly depressed at the termination of an episode of tachyarrhythmia (atrial tachycardia, paroxysmal atrial flutter or atrial fibrillation, etc.), resulting in a slow arrhythmia such as transient sinus arrest. In such patients, catheter radiofrequency ablation for tachyarrhythmias can be performed first if available (success rate may be around 80%), and the decision to implant a permanent pacemaker will be made after the ablation, depending on the follow-up. However, the specific management plan should still be based on the condition in consultation with a professional physician.
Third, clinically, there are many patients with sinus bradycardia found on ECG during routine physical examination, mostly at 55-59 beats/min, and the patients are asymptomatic. At this point, further tests, such as ambulatory ECG, can be done as appropriate according to the patient’s specific situation. The vast majority of these patients do not fall into the category of sinus disease and usually do not require special management.