In patients with sick sinus syndrome, various types of arrhythmias may be observed at different times.

  A single ECG is generally inadequate for the diagnosis of sick sinus syndrome.

  Definitive diagnosis is made by electrophysiologic study. However,
several ECGs recorded at different times may strongly suggest the diagnosis of sick sinus syndrome.

ECG abnormalities in patients with Sick Sinus Syndrome

  Inappropriate sinus bradycardia (not related to medication use or the patient's physiological status).

  Sinus arrest.

  Sinoatrial exit block.

  Atrial arrhythmias: atrial flutter, atrial fibrillation.

  Consecutive atrial tachycardias and bradycardias (
bradycardia-tachycardia syndrome).

  Atrioventricular (AV) blocks.

Inadequate increase of heart rate: failure to increase heart rate despite pain, fever, etc.

Failure to increase heart rate during exercise.


  Card Electrophysiol Clin 10 (2018) 183-195

ECG 1a. Above is an ECG from a 51 years-old woman. The ECG shows no clear abnormality.
She was admitted to Cardiology clinic with the complaints of attacks of palpitation and near-syncope.
For the last 2 years, she was taking Metoprolol tablets.
A normal ECHOcardiogram ruled out heart failure and valvular heart disease.
Metoprolol was stopped and Holter (ambulatory cardiac rhythm) monitor was requested.

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ECG 1b. The above rhythm tracing is from her Holter recording (while not taking Metoprolol).
A pause of
2.4 seconds of duration was recorded at 07:36 AM (while she was awake).

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ECG 1c. The above rhythm strips are also from her Holter recording.
Sudden increases in heart rate are seen: Atrial tachycardia following sinus braycardia.

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ECG 1d. The two Holter strips above belong to the same patient..
The strips show sinus pauses, each lasting more than 5 seconds. Both pauses follow atrial tachycardias.

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ECG 1e. Above Holter rhythm tracings also belong to the same patient.
Sudden increases and decreases of heart rate are seen.
Consecutive bradycardias and atrial tachycardias: bradycardia-tachycardia syndrome.

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