What are the diagnosis and management of Sick Sinus Syndrome (SSS)?

From the Guidelines

Sick sinus syndrome should be managed with permanent pacemaker implantation, specifically a dual-chamber pacemaker, as it has been shown to be highly effective in relieving symptoms and improving quality of life 1. The diagnosis of sick sinus syndrome is based on a combination of clinical evaluation and electrocardiographic findings, including unexplained bradycardia, sinus pauses, sinus arrest, or alternating bradycardia and tachycardia (tachy-brady syndrome). Initial evaluation includes:

• A 12-lead ECG
• Ambulatory ECG monitoring (Holter or event monitor)
• Sometimes exercise testing Laboratory tests should be performed to rule out reversible causes like electrolyte abnormalities, hypothyroidism, or medication effects. Management depends on symptom severity and underlying causes. For asymptomatic patients, observation may be sufficient. However, for symptomatic patients, permanent pacemaker implantation is the definitive treatment, typically a dual-chamber pacemaker (DDD mode) or rate-responsive single-chamber pacemaker (AAIR mode) 1. Before pacemaker implantation, temporary measures include:
• Atropine (0.5-1 mg IV) for acute symptomatic bradycardia
• Isoproterenol infusion (2-10 μg/min) in emergency situations Medications that exacerbate bradycardia should be discontinued, including beta-blockers, calcium channel blockers, digoxin, and antiarrhythmics. For patients with tachy-brady syndrome, antiarrhythmic medications may be needed after pacemaker implantation to control tachyarrhythmias. The underlying pathophysiology involves degenerative fibrosis of the sinoatrial node, leading to impaired automaticity and conduction, which explains the variable presentation from bradycardia to tachyarrhythmias due to compensatory mechanisms. According to the 2018 ACC/AHA/HRS guideline, dual-chamber pacemakers are recommended for treating symptomatic bradycardia due to sick sinus syndrome without atrio-ventricular block 1.

From the Research

Diagnosis of Sick Sinus Syndrome

• Sick sinus syndrome refers to a collection of disorders marked by the heart's inability to perform its pacemaking function, and diagnosis may be challenging 2.
• Diagnosis is ultimately made by electrocardiographic identification of the arrhythmia in conjunction with the presence of symptoms 2.
• If electrocardiography does not yield a diagnosis, inpatient telemetry monitoring, outpatient Holter monitoring, event monitoring, or loop monitoring may be used 2.
• Autonomic blockade is commonly employed as a test of sinus node dysfunction, and combined autonomic blockade and electrophysiological tests can be of great value in unmasking the severity and degree of intrinsic dysfunction 3.
• Intrinsic heart rate obtained by autonomic blockade is the best and most simple method for the diagnosis of intrinsic sinus node dysfunction 3.

Management of Sick Sinus Syndrome

• Treatment of sick sinus syndrome includes removing extrinsic factors, when possible, and pacemaker placement 2.
• Pacemakers do not reduce mortality, but they can decrease symptoms and improve quality of life 2.
• The mainstay of treatment is atrial or dual-chamber pacemaker placement, which generally provides effective relief of symptoms and lowers the incidence of atrial fibrillation, thromboembolic events, heart failure, and mortality, compared with ventricular pacemakers 4.
• Pacemaker implantation is the first-line treatment for symptomatic patients with SSS and documented bradycardia history 5.
• Catheter ablation may also be used as an alternative second-line therapy for some patients with SSS and AF 5.

Clinical Presentation and Complications

• Patients with sick sinus syndrome may experience syncope, pre-syncope, palpitations, or dizziness; however, they often are asymptomatic or have subtle or nonspecific symptoms 2, 4.
• Cerebral hypoperfusion is most common, with syncope or near-fainting occurring in about one-half of patients 2.
• Sick sinus syndrome coexisting with atrial fibrillation forms the basis of bradycardia-tachycardia syndrome, and the combination of these diseases will adversely affect the condition of patients and the efficiency of subsequent treatment 5.
• Age-related interstitial fibrosis is considered to be the common pathophysiological mechanism between SSS and AF 5.