From the Guidelines
Sick sinus syndrome is diagnosed based on several key criteria, including documented episodes of inappropriate sinus bradycardia, sinus pauses or arrest exceeding 3 seconds, and sinoatrial exit block, as outlined in the 2019 ACC/AHA/HRS guideline on the evaluation and management of patients with bradycardia and cardiac conduction delay 1. The primary criteria for diagnosing sick sinus syndrome include:
- Documented episodes of inappropriate sinus bradycardia (heart rate below 50 beats per minute)
- Sinus pauses or arrest exceeding 3 seconds
- Sinoatrial exit block Additional diagnostic features include:
- Alternating bradycardia and tachycardia (known as tachy-brady syndrome)
- Chronotropic incompetence (inadequate heart rate response to exercise or stress)
- Symptoms correlating with these rhythm disturbances, such as dizziness, syncope, fatigue, or exercise intolerance, as noted in the 2019 guideline 2. Diagnosis typically requires electrocardiographic evidence captured on a 12-lead ECG, Holter monitor, event recorder, or implantable loop recorder that demonstrates these abnormalities. The diagnosis is strengthened when symptoms correlate with documented arrhythmias. It's essential to rule out extrinsic causes of sinus node dysfunction, such as medication effects (beta-blockers, calcium channel blockers), electrolyte abnormalities, hypothyroidism, or increased vagal tone, before confirming the diagnosis, as emphasized in the 1991 guidelines for implantation of cardiac pacemakers and antiarrhythmia devices 3, 4. Invasive electrophysiological testing with measurement of sinus node recovery time and sinoatrial conduction time may be performed in uncertain cases, though this is less commonly required with modern ambulatory monitoring techniques.
From the Research
Definition and Causes of Sick Sinus Syndrome
Sick sinus syndrome refers to a collection of disorders marked by the heart's inability to perform its pacemaking function, predominantly affecting older adults 5. The syndrome comprises various arrhythmias, including bradyarrhythmias with or without accompanying tachyarrhythmias. Intrinsic causes of sick sinus syndrome include degenerative fibrosis, ion channel dysfunction, and remodeling of the sinoatrial node, while extrinsic factors can be pharmacologic, metabolic, or autonomic 5, 6.
Symptoms and Diagnosis
Symptoms of sick sinus syndrome are often subtle early on and become more obvious as the disease progresses, commonly related to end-organ hypoperfusion 5. Cerebral hypoperfusion is most common, with syncope or near-fainting occurring in about one-half of patients 5. Diagnosis may be challenging and is ultimately made by electrocardiographic identification of the arrhythmia in conjunction with the presence of symptoms 5, 7, 6, 8.
- Electrocardiographic findings may include sinus bradycardia, sinus arrest, sinoatrial block, and alternating patterns of bradycardia and tachycardia (bradycardia-tachycardia syndrome) 7, 6, 8.
- If electrocardiography does not yield a diagnosis, inpatient telemetry monitoring, outpatient Holter monitoring, event monitoring, or loop monitoring may be used 5.
- Electrophysiologic studies also may be used but are not routinely needed 5.
Treatment
Treatment of sick sinus syndrome includes removing extrinsic factors, when possible, and pacemaker placement 5, 7, 8.
- Pacemakers do not reduce mortality, but they can decrease symptoms and improve quality of life 5.
- Atrioventricular block, chronic atrial fibrillation, and systemic embolism are major pathologic conditions that affect the outcome of the syndrome 8.
- Cardiac pacing is the most powerful therapy; physiologic pacing (atrial or dual-chamber) has been shown definitively to be superior to ventricular pacing 7, 8.