Sinus Node Dysfunction

Sinus Node Dysfunction

  • Refers to problems with sinus node impulse formation and propagation
  • May include sinus bradycarda, sinus pauses or arrest, chronotropic incompetence, and sino-atrial exit block
  • When accompanied by symptoms it is referred to as Sick Sinus Syndrome
  • When associated with periods of paroxysmal supraventricular tachycardia it is referred to as Tachycardia-Bradycardia Syndrome or “Tachy-Brady Syndrome”

Causes of Sick Sinus Syndrome

  • Idiopathic
  • Ischemic heart disease
  • Primary non-ischemic cardiomyopathy
  • Hypertensive heart disease
  • Secondary cardiomyopathy
    • Connective tissue disease
    • Syphilis
    • Metastatic tumor
    • Amyloidosis
    • Myxedema
    • Hemochromatosis
    • Friedreich’s ataxia
    • Muscular dystrophy
    • Scleroderma
  • Mitral valve prolapse
  • Rheumatic heart disease
  • Acute myocarditis
  • Congenital heart disease
  • Familial sinus node disease
  • Surgical injury to the SA node (especially following repair of transposition of the great vessels)
  • Following the Cox-Maze III procedure for management of atrial fibrillation

Tachycardia-Bradycardia Syndrome

  • Observed in 54 to 76% of patients with Sick Sinus Syndrome
  • Not a pure clinical or ECG entity but rather a constellation of cardiac rhythm disturbances and their clinical manifestations
  • Occurs in all age groups but most common in the elderly

Indications for Permanent Pacing

  • Sinus pauses of 3 seconds or greater
  • Sustained symptomatic sinus rates of 40 BPM or less in the awake patient

See also: The basics of paced rhythms.



A Sign of the Times?

Further Reading

Sinus Node Dysfunction at Life in the Fast Lane.

Sick Sinus Syndrome at the Heart Rhythm Society

Click here for a great case from Dr. Smith’s ECG Blog.


Epstein A, DiMarco J, Ellenbogen K et al. ACC/AHA/HRS 2008 Guidelines for Device-Based Therapy of Cardiac Rhythm Abnormalities. Journal of the American College of Cardiology. 2008;51(21):e1-e62. doi:10.1016/j.jacc.2008.02.032.

Hayes D, Lloyd M, Friedman P. Cardiac Pacing And Defibrillation. Armonk, NY: Futura Pub. Co.; 2000.

Surawicz B, Knilans T, Chou T. Chou’s Electrocardiography In Clinical Practice. Philadelphia: Saunders; 2001.

Content Reviewer

Kelly A. Bouthillet, APRN, MSN, CCNS, ACNP-BC (@BarefootNurse24)


About author

Tom Bouthillet
Tom Bouthillet - 25 posts

Tom Bouthillet (@tbouthillet) is Editor-in-Chief of (@ECGTraining) and Fire Captain/Paramedic in South Carolina where he is the Emergency Cardiac Care Program Manager and the STEMI and CARES Site Coordinator of his fire department.

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