Sick sinus syndrome

Sick sinus syndrome is a term applied to a syndrome encompassing a number of sinus nodal abnormalities, including the following:

(1) Persistent spontaneous sinus bradycardia not caused by drugs and inappropriate for the physiologic circumstance

(2) Sinus arrest or exit block i.e. no P wave on ECG for > 2 s.

(3) Combinations of SA and AV conduction disturbances and

(4) Alternation of paroxysms of rapid regular or irregular atrial tachyarrhythmias and periods of slow atrial and ventricular rates (bradycardia-tachycardia syndrome).

More than one of these conditions can be recorded in the same patient on different occasions, and their mechanisms often can be shown to be causally interrelated and combined with an abnormal state of AV conduction or automaticity.

Incidence:

3 in every 10,000 persons are affected. Incidence increases with age, seen more after 65 years of age. Men and women are equally affected.

Patients who have sinus node disease can be categorized as having intrinsic sinus node disease unrelated to autonomic abnormalities or combinations of intrinsic and autonomic abnormalities. Symptomatic patients with sinus pauses or SA exit block frequently show abnormal responses on electrophysiologic testing and can have a relatively high incidence of atrial fibrillation.

In children, sinus node dysfunction most commonly occurs in those with congenital or acquired heart disease, particularly after corrective cardiac surgery. Sick sinus syndrome can occur in the absence of other cardiac abnormalities. The course of the disease is frequently intermittent and unpredictable because it is influenced by the severity of the underlying heart disease. Excessive physical training can heighten vagal tone and produce syncope related to sinus bradycardia or AV conduction abnormalities in otherwise normal individuals.

Pathology:

The anatomic basis of sick sinus syndrome can involve

1) total or subtotal destruction of the sinus node,

2) areas of nodal-atrial discontinuity,

3) inflammatory or degenerative changes in the nerves and ganglia surrounding the node, and

4) pathologic changes in the atrial wall.

5) Fibrosis and fatty infiltration occur, and the sclerodegenerative processes generally involve the sinus node and the AV node or the bundle of His and its branches or distal subdivisions.

6) Occlusion of the sinus node artery may be important.

Symptoms:

1) Palpitations

2) Fainting, near fainting, light-headedness

3) Fatigue and weakness

4) Chest pain

Management:

Diagnosis can be confirmed by doing a Holter monitoring for at least 24 hours.

For patients with sick sinus syndrome, treatment depends on the basic rhythm problem but generally involves permanent pacemaker implantation when symptoms are manifested. Pacing for the bradycardia, combined with drug therapy to treat the tachycardia, is required in those with bradycardia-tachycardia syndrome. The latter also are at greatest risk to develop stroke.

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