- Clinical science
Sick sinus syndrome (SSS) refers to the dysfunction of the sinoatrial node and is responsible for several types of arrhythmia. It comprises bradyarrhythmias (e.g., sinus bradycardia, sinoatrial pauses, blocks, and arrest), and may alternate with supraventricular tachyarrhythmias, in which case it is referred to as tachycardia-bradycardia syndrome. The most common SSS arrhythmias are sinus bradycardia and non-respiratory sinus arrhythmia. Depending on the extent of bradycardia or tachycardia, the condition may be asymptomatic or present with symptoms such as palpitations or dyspnea. More serious manifestations, such as lightheadedness and syncope, are indications for pacemaker placement.
- Degeneration and fibrosis of the sinoatrial node and surrounding myocardium (most common cause)
- Medications (e.g., β-blockers, digoxin, non-dihydropyridine calcium channel blockers such as verapamil and diltiazem)
- Less common causes
Symptoms vary or may be entirely absent depending on the extent of bradycardia or tachycardia.
- Symptoms of bradycardia
- Tachycardia-bradycardia syndrome presents with additional symptoms:
- Non-respiratory sinus arrhythmia, bradycardia, sinus arrest, sinoatrial pauses, or SA block
- In cases of tachycardia-bradycardia syndrome: atrial tachycardia, atrial flutter, or atrial fibrillation
- Holter monitor: detects bradycardic episodes and sinus pauses However, the duration of a relevant sinus pause is not defined. Pauses that may cause clinical symptoms are presumed to have a duration of more than three seconds.
- Exercise stress testing; : shows an inadequate increasing heart rate during physical activity (also called chronotropic incompetence)
- Atropine challenge test: shows an inadequate increasing heart rate after administration of atropine.
- Electrophysiology studies: may show prolonged sinus node recovery time.
Management depends on the symptoms of each patient, most notably on the length of sinus pauses.
- All patients: address reversible causes (e.g., side effects of medication or coronary ischemia)
- Asymptomatic patients: no pacemaker placement needed
Initial therapy for hemodynamically unstable patients
- First-line: atropine
- Temporary cardiac pacing
- Long-term therapy
- Isolated symptoms of bradycardia; : pacemaker placement, e.g., AAI or DDD pacemaker
- Tachycardia-bradycardia syndrome requires treatment of both tachycardia and bradycardia.
- Initial therapy for hemodynamically unstable patients