Sick sinus syndrome (SSS) is a condition characterized by a decline in sinoatrial node function due to its pathology, resulting in various arrhythmias. Patients may experience more than one type of arrhythmia at different times and often have concurrent atrial automaticity abnormalities. Some patients also have atrioventricular conduction disorders.
Etiology
Various pathological processes, such as sinoatrial node fibrosis and fatty infiltration, sclerosis and degeneration, amyloidosis, hypothyroidism, and certain infections (brucellosis, typhoid), can damage the sinoatrial node, leading to pacemaker and conduction dysfunction. Reduced blood supply to the sinoatrial node artery, as well as nerve and atrial muscle disorders around the sinoatrial node, are also causes of SSS. Carotid sinus hypersensitivity, cerebrovascular accidents, hyperkalemia, increased vagal tone, and certain antiarrhythmic drugs such as digitalis glycosides and acetylcholine can inhibit sinoatrial node function and should be differentiated.
Clinical manifestations
Patients may experience symptoms of insufficient blood supply to organs such as the heart and brain related to bradycardia, including episodic dizziness, amaurosis fugax, palpitations, malaise, and reduced exercise tolerance. Severe cases may present with angina, heart failure, transient loss of consciousness, or syncope, and even sudden death. If tachycardia occurs, symptoms such as palpitations and angina may occur.
Electrocardiogram features
Key ECG features include:
- Persistent and significant sinus bradycardia (below 50 bpm) not caused by medication
- Sinus pause or arrest, and sinoatrial block
- Coexistence of sinoatrial and atrioventricular blocks
- Bradycardia-tachycardia syndrome, where bradycardia alternates with atrial tachyarrhythmias (atrial flutter, atrial fibrillation, or atrial tachycardia)
Other ECG changes in SSS include:
- Slow ventricular rate during atrial fibrillation without antiarrhythmic drugs, or sinus bradycardia and/or first-degree AV block before and after episodes
- Chronotropic incompetence, with insignificant heart rate increase after exercise
- Junctional escape rhythms
Diagnosis
Diagnosis is confirmed by typical ECG findings or a clear correlation between clinical symptoms and ECG changes. Single or multiple Holter monitoring or event recorders can be used to establish this relationship. Recording significant bradycardia or cardiac arrest during symptoms like syncope provides strong evidence.
Treatment
If patients have no symptoms related to bradycardia, treatment is not necessary; regular follow-up is sufficient. Symptomatic SSS patients should receive permanent pacemaker implantation.
In patients with bradycardia-tachycardia syndrome, using anti-tachycardia drugs alone may exacerbate bradycardia, so these medications are typically used after pacing therapy. In some patients, after correcting tachyarrhythmias (catheter ablation of atrial fibrillation), bradyarrhythmias (including sinus arrest and sinus bradycardia) and their symptoms may improve or even subside, possibly eliminating the need for a permanent pacemaker. Additionally, due to the increased risk of thromboembolism from atrial flutter or fibrillation in these patients, anticoagulation therapy should be considered.