Sick Sinus Syndrome

Aka: Sick Sinus Syndrome, Tachycardia-Bradycardia Syndrome, Bradycardia-Tachycardia Syndrome, Tachy-Brady Syndrome, Sinus Node Dysfunction

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II. Definitions

  1. Sinus Node Dysfunction (Sick Sinus Syndrome, Tachy-Brady Syndrome)
    1. Disorder interfering with sinus node pacing function

III. Epidemiology

  1. Incidence: 0.8 per 1000 person years
  2. Prevalence: 1 in 600 cardiac patients over age 65 years
  3. Peaks at ages 70 to 89 years old
    1. Mean age: 68 years old (median 74 years old)

IV. Causes: Intrinsic

  1. Older age (over 65 years)
    1. Sinoatrial Node age-related idiopathic degenerative fibrosis (most common cause)
      1. Peri-myocardial accumulation of elastic fiber, fatty tissue, fibrous tissue (increases with age)
    2. Sinoatrial Node inherited ion channel dysfunction (e.g. Brugada Syndrome)
      1. May be comorbid with Sinoatrial Node degenerative fibrosis
    3. Sinoatrial Node remodeling (delayed cardiac tissue voltage transmission)
      1. Congestive Heart Failure
      2. Atrial Fibrillation
      3. Muscular Dystrophy
      4. Cardiomyopathy
        1. Myocarditis (e.g. Diphtheria, typhoid)
        2. Rheumatic Fever
        3. Chagas Disease
      5. Infiltration
        1. Connective Tissue Disease
        2. Hemochromatosis
        3. Sarcoidosis
        4. Amyloidosis
    4. Sinus node artery atherosclerosis (from proximal right Coronary Artery)
      1. Less common contributing factor (<33%)
      2. Embolization of the Sinoatrial Node artery
      3. Transient Sinus Node Dysfunction may occur with Myocardial Infarction (increased vagal tone)
  2. Children and young adults
    1. Follows Congenital Heart Disease surgical correction
      1. Atrial Septal Defect
      2. Transposition of the Great Vessels
    2. SA Node artery deficiency
    3. Genetic ion channel disorders
      1. Brugada Syndrome
      2. HCN4
      3. SCN5A

V. Causes: Extrinsic (may also mimic Sick Sinus Syndrome)

  1. Obstructive Sleep Apnea
  2. Vagal tone increased
    1. Athletes
    2. Sleep state
    3. Postmyocardial Infarction
  3. Autonomic Dysfunction
    1. Carotid Sinus Hypersensitivity
    2. Neurocardiogenic Syncope
    3. Vasovagal Syncope
  4. Metabolic disorder
    1. Hyperkalemia
    2. Hypokalemia
    3. Hypocalcemia
    4. Hypothermia
    5. Hypothyroidism
    6. Hypoxia
  5. Medications and toxins
    1. Antiarrhythmics (Class I and Class II)
    2. Amiodarone
    3. Amitriptyline
    4. Beta Blockers
    5. Cimetidine
    6. Nonhydropyridine Calcium Channel Blockers
    7. Digoxin
    8. Lithium
    9. Marijuana
    10. Nicotine
    11. Sympatholytic medications (Anesthesia)
  6. Structural or Physiologic Disorder Risk Factors
    1. Diabetes Mellitus (Diabetic atrial Myopathy)
    2. Hypertension

VI. Associated Conditions

  1. Atrial Fibrillation
  2. Atrioventricular Node Block

VII. Symptoms (associated with sinus pause or Bradycardia)

  1. Near Syncope or Syncope (50% of cases)
  2. Palpitations
  3. Angina Pectoris
  4. Fatigue
  5. Confusion or Altered Level of Consciousness
  6. Exercise intolerance
  7. Transient Light Headedness (may be described as Dizziness)
  8. Vague gastrointestinal symptoms

VIII. Signs: Monitor rhythm while performing procedures

  1. Valsalva response absent or minimal (no pulse increase)
  2. Carotid massage induces Sinus Arrest >3 seconds

IX. Diagnosis

  1. Sick Sinus Syndrome requires correlation of Bradycardia and sinus pauses with symptoms
  2. Asymptomatic Bradycardia alone is insufficient to make the diagnosis of Sick Sinus Syndrome
    1. Consider other causes of Sinus Bradycardia
    2. Consider Obstructive Sleep Apnea

X. Diagnostics: Monitoring

  1. Correlate symptom diary with ambulatory monitoring
    1. External Patch Recorder (e.g. Zio monitor) or Holter Monitor
      1. Continuous monitoring (Preferred) for 7-14 days
      2. Consider repeating if non-diagnostic initially
    2. Event Monitor
      1. Consider for non-diagnostic Holter Monitor or less frequent symptoms
  2. Other EKG testing to consider
    1. Electrophysiology (less commonly indicated)
    2. Exercise Stress Test (if Exercise related)
      1. Chronotropic incompetence
        1. Inadequate Heart Rate response to Exercise (maximum Heart Rate <80% of predicted)
        2. Common for Sick Sinus Syndrome patients to fail to reach a Maximal Heart Rate over 120 bpm
  3. Transthoracic Echocardiogram Indications (structural heart disease suspected)
    1. Congestive Heart Failure
    2. Left Bundle Branch Block
    3. Mobitz II AV Block
    4. Third Degree Atrioventricular Block

XI. Diagnostics: EKG Findings

  1. Atrial Bradyarrhythmia (inappropriately)
    1. Sinus Bradycardia (<50 bpm)
    2. Sinus pauses > 3 sec
    3. Sinus Arrest
      1. May present as Junctional Rhythm or junctional escape beats
    4. Sinoatrial Exit Block
      1. May be associated with Tachycardia-Bradycardia Syndrome and Supraventricular Tachycardia
    5. Second Degree Heart Block (Mobitz Type I or II)
    6. Atrial Fibrillation with slow ventricular response
  2. Tachycardia
    1. Atrial Fibrillation
    2. Atrial Flutter
    3. Atrial Tachycardia (Narrow Complex Tachycardia)
  3. Tachycardia-Bradycardia Syndrome (present in >50% of Sick Sinus Syndrome cases)
    1. Alternating Tachycardia-Bradycardia
    2. Typically associated with Atrial Fibrillation or Atrial Flutter and higher risk of Cerebrovascular Accident

XII. Differential Diagnosis

  1. Physiologic responses (consider in asymptomatic Bradycardia)
    1. See Sinus Bradycardia
    2. Increased vagal tone during sleep (especially athletes)
    3. Obstructive Sleep Apnea
  2. Metabolic disorder
    1. Hypothyroidism
    2. Hypothermia
    3. Hypoxia
    4. Hyperkalemia
  3. Miscellaneous disorders
    1. Cardiomyopathy
    2. Collagen vascular disease
    3. Metastatic cancer
  4. Medications
    1. Digoxin
    2. Quinidine
    3. Amiodarone
    4. Beta Blockers
    5. Diltiazem
    6. Verapamil
    7. Clonidine

XIII. Labs

  1. Basic metabolic panel (chem8)
  2. Hemoglobin A1C
  3. Thyroid Stimulating Hormone (TSH)

XIV. Complications

  1. Cerebrovascular Accident (due to Thromboembolism)
    1. Associated with Tachy-Brady Syndrome and typically Atrial Fibrillation or Atrial Flutter
    2. Consider Anticoagulation (see below)
  2. Atrioventricular Block
    1. Prevalence: 0.5 to 1.5% of patients annually, ultimately affecting 50% of Sick Sinus Syndrome patients
  3. Myocardial Infarction
  4. Congestive Heart Failure

XV. Management

  1. See Symptomatic Bradycardia
  2. Hospitalization Indications
    1. Hemodynamic instability
      1. Hypotension (e.g. systolic Blood Pressure <90 mmHg)
      2. Ventricular Arrhythmia
    2. Severe symptoms
      1. Recurrent Syncope
      2. Angina
  3. Comorbidity management (see extrinsic factors above)
    1. Obstructive Sleep Apnea (i.e. CPAP)
    2. Hypothyroidism (i.e. Levothyroxine)
    3. Correction of Electrolyte abnormalities (e.g. Hypokalemia)
  4. Permanent implantable demand ventricular Pacemaker
    1. See Pacemaker for indications
    2. Sick Sinus Syndrome accounts for >50% pacers placed
    3. Dual chamber pacing is preferred
      1. Longterm 50% risk for Atrioventricular Block in Sick Sinus Syndrome
      2. However right atrial pacing is preferred over right ventricular pacing
        1. Right ventricular pacing is associated with decreased Cardiac Function and Arrhythmias
    4. Alternatives for those refusing Pacemaker placement
      1. Oral Phosphodiesterase Inhibitors (e.g. Cilostazol, Theophylline) are positive chronotropes
  5. Tachyarrhythmia control (use only with Pacemaker)
    1. Beta Blocker
    2. Calcium Channel Blocker
    3. Digoxin
  6. Anticoagulation with Coumadin
    1. See Anticoagulation in Atrial Fibrillation
    2. Indications
      1. Atrial Fibrillation or Atrial Flutter
      2. Tachycardia-Bradycardia Syndrome

XVI. Prognosis

  1. Best prognosis with Sinus Bradycardia only (no Tachycardia or tachy-brady)

XVII. References

  1. Faddis in Ahya (2001) Washington Manual, p. 153
  2. Behrman (2000) Nelson Pediatrics, p. 1422-3
  3. Wagner (2001) Marriott's Electrocardiography, p. 402
  4. Adan (2003) Am Fam Physician 67(8):1725-38 [PubMed]
  5. Keller (2006) Am J Crit Care 15(2):226-9 [PubMed]
  6. Kusumoto (2019) J Am Coll Cardiol 74(7): e51-6 +PMID:30412709 [PubMed]
  7. Hawks (2021) Am Fam Physician 104(2):179-85 [PubMed]
  8. Semelka (2013) Am Fam Physician 87(10): 691-6 [PubMed]

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