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. SSS typically occurs in the elderly. 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)
- Symptoms of bradycardia
- Tachycardia-bradycardia syndrome presents with additional symptoms:
- 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)
- Asymptomatic patients: no pacemaker placement needed
- Initial therapy for hemodynamically unstable patients
- Long-term therapy
- Isolated symptoms of bradycardia; : pacemaker placement
- Tachycardia-bradycardia syndrome requires treatment of both tachycardia and bradycardia.