Sick sinus syndrome electrocardiogram

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Overview

Sick sinus syndrome is a collection of heart rhythm disorders that include sinus bradycardia, sinus pauses and sinus arrest. Sick sinus syndrome can evolve towards causing atrial fibrillation, atrial flutter, ectopic atrial tachycardia, sinus node reentrant tachycardia, and tachycardia-bradycardia.

Electrocardiogram

Ambulatory monitoring of the electrocardiogram (EKG) may be necessary because arrhythmias are transient. The EKG may show any of the following:

• Inappropriate sinus bradycardia
• Sinus arrest
• Sinoatrial block
• Atrial fibrillation with slow ventricular response
• A prolonged asystolic period after a period of tachycardias
• Atrial flutter
• Ectopic atrial tachycardia
• Sinus node reentrant tachycardia
• Tachycardia-bradycardia

Electrophysiologic tests are no longer used for diagnostic purposes because of their low specificity and sensitivity. Cardio-inhibitory and vasodepressor forms of sick sinus syndrome may be revealed by tilt table testing.

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Shown below is an EKG demonstrating sick sinus syndrome. Atrial fibrillation is present (an irregularly irregular rhythm) which stops abruptly due to sinus arrest.

Copyleft image obtained courtesy of ECGpedia, http://en.ecgpedia.org/wiki/Main_Page

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Shown below is an EKG showing the termination of a supraventricular tachycardia at about 130/min. which terminates and leaves a pause and then sinus bradycardia. This is a from of "tachy/brady" syndrome where a tachycardia is followed by a bradycardia.

Copyleft image obtained courtesy of ECGpedia, http://en.ecgpedia.org/wiki/Main_Page

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For more EKG examples of sick sinus syndrome click here.

Guideline

2018 ACC/AHA/HRS Guideline on the Evaluation and Management of Patients With Bradycardia and Cardiac Conduction Delay

Term	Definition
Sinus Node Dysfunction	Sinus bradycardia: Sinus rate <50 bpm
	Ectopic atrial bradycardia: Atrial depolarization attributable to an atrial pacemaker other than the sinus node with a rate <50 bpm
	Sinoatrial exit block: Evidence that blocked conduction between the sinus node and adjacent atrial tissue is present. Multiple electrocardiographic manifestations including “group beating” of atrial depolarization and sinus pauses.
	Sinus pause: Sinus node depolarizes >3 s after the last atrial depolarization
	Tachycardia-bradycardia (“tachy-brady”) syndrome: Sinus bradycardia, ectopic atrial bradycardia, or sinus pause alternating with periods of abnormal atrial tachycardia, atrial flutter, or AF. The tachycardia may be associated with suppression of sinus node automaticity and a sinus pause of variable duration when the tachycardia terminates.
	Chronotropic incompetence: Broadly defined as the inability of the heart to increase its rate commensurate with increased activity or demand, in many studies translates to failure to attain 80% of expected heart rate reserve during exercise.
	Isorhythmic dissociation: Atrial depolarization (from either the sinus node or ectopic atrial site) is slower than ventricular depolarization (from an atrioventricular nodal, His bundle, or ventricular site).