Sick sinus syndrome, also referred to as sinoatrial disease or sinus node dysfunction, is caused by impairment of sinus node automaticity (automaticity is defined as the ability of a cell to initiate an electrical impulse) or of conduction of impulses generated by the sinus node to the surrounding atrial myocardium. It can lead to sinus bradycardia, sinoatrial block or sinus arrest.

In some patients, atrial fibrillation, flutter or tachycardia may also occur. The term ‘bradycardia–tachycardia’ (often abbreviated to ‘brady–tachy’) syndrome applies to these patients. AV re-entrant tachycardia is, however, not part of the bradycardia–tachycardia syndrome.

Sick sinus syndrome is a common cause of syncope, dizzy attacks and palpitation. Though found most often in the elderly, it can occur at any age.

Causes

The cause is usually idiopathic fibrosis of the sinus node. Cardiomyopathy, myocarditis, cardiac surgery, antiarrhythmic drugs and lithium toxicity can also cause the syndrome. Rarely, the disorder can be familial.

ECG characteristics

Any one or more of the following can occur. They are often intermittent, normal sinus rhythm being present for most of the time.

Sinus bradycardia

Sinus bradycardia is a common finding (Figure 16.1).

Sinus arrest

Sinus arrest occurs due to failure of the sinus node to activate the atria. The result is absence of normal P waves (Figures 16.2, 16.3).

Sinoatrial block

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