What are the diagnostic criteria for Sick Sinus Syndrome (SSS)?

From the Guidelines

Diagnosing sick sinus syndrome requires a combination of clinical evaluation and diagnostic tests, with electrocardiography (ECG) being the most important tool, as it can show bradycardia, sinus pauses, sinus arrest, or alternating bradycardia and tachycardia (tachy-brady syndrome) 1. The diagnosis begins with a thorough medical history focusing on symptoms like unexplained fatigue, dizziness, syncope, palpitations, or shortness of breath.

Key Diagnostic Steps

• Physical examination may reveal bradycardia or irregular heart rhythms
• ECG can show characteristic abnormalities, but since arrhythmias may be intermittent, a standard 12-lead ECG might not capture the abnormality
• Prolonged monitoring with a Holter monitor (24-48 hours) or an event recorder (up to 30 days) is recommended for intermittent symptoms
• For less frequent symptoms, an implantable loop recorder may be used for continuous monitoring over months
• Exercise stress testing can assess heart rate response to physical activity
• Electrophysiology studies may be necessary in complex cases to evaluate sinus node function directly
• Laboratory tests should be performed to rule out reversible causes like electrolyte imbalances, medication effects, or thyroid dysfunction
• Echocardiography is also valuable to assess overall cardiac structure and function, as sick sinus syndrome often coexists with other cardiac conditions 1.

Important Considerations

• Invasive electrophysiology studies (EPS) play a very limited role in the assessment of sinus node function 1
• Clinical assessment for structural heart disease and noninvasive assessment of sinus node function with ambulatory monitoring and stress testing are also appropriate in symptomatic patients or those with resting heart rates <30 bpm or pauses >3 seconds 1
• Patients with symptomatic bradycardia not responsive to other measures may need to be treated with a permanent pacemaker, although this is very rarely needed in the athlete 1.

From the Research

Diagnosis of Sick Sinus Syndrome

To diagnose sick sinus syndrome, the following methods can be used:

• Electrocardiographic identification of the arrhythmia in conjunction with the presence of symptoms 2
• Inpatient telemetry monitoring, outpatient Holter monitoring, event monitoring, or loop monitoring if electrocardiography does not yield a diagnosis 2
• Electrophysiologic studies, although they are not routinely needed 2
• Recording of intracardiac electrograms, atrial overdrive pacing, and extrastimulus technique to assess electrophysiologic disorders 3

Key Findings for Diagnosis

Some key findings that can aid in the diagnosis of sick sinus syndrome include:

• Sinus bradycardia, sinus arrest, sinoatrial block, and alternating patterns of bradycardia and tachycardia (bradycardia-tachycardia syndrome) on electrocardiogram 4
• Symptoms such as syncope, pre-syncope, palpitations, or dizziness, although patients may often be asymptomatic or have subtle or nonspecific symptoms 4
• Careful evaluation of symptoms and electrocardiogram, as diagnosis is mainly based on these two elements 5

Challenges in Diagnosis

Diagnosis of sick sinus syndrome can be challenging due to:

• Nonspecific symptoms and elusive findings on electrocardiogram or Holter monitor 4
• Subtle or nonspecific symptoms, especially in the early stages of the disease 6
• The need for careful evaluation of symptoms and electrocardiogram to make an accurate diagnosis 5