Sick sinus syndrome is a group of abnormal heartbeats (arrhythmias) presumably caused by malfunction of the sinus node, the heart's "natural" pacemaker.
Sick sinus syndrome is more common in elderly adults, where the cause is often a non-specific, scar-like degeneration of the conduction system. Cardiac surgery, especially to the atria, is a common cause of sick sinus syndrome in children.
Ischaemia, infarction or generalised degeneration of the sinus node tissue. Other factors include negatively chronotropic drugs (drugs thats slow the heart rate), hypothyroidism and hypokalaemia.
In SSS, the sinus node fires at a reduced rate causing a pathological sinus bradycardia. The long interval between sinus depolarisations may allow supraventricular tachycardias to emerge heralding the development of the tachy-brady syndrome.The irregular slow heart rhythm can predispose to clot formation and emboli that can cause cerebrovascular accidents (stroke) and myocardial infarctions (heart attacks).The electrocardiogram image below exhibits the alternating patterns of bradycardia and tachycardia.
Blood tests should investigate electrolyte imbalance and thyroid hormone deficiency.
If the patient remains in a state of bradycradia, the risk of cardiac arrest is increased with the increased risk of developing spontaneous tachyarrhythmia. If the patient is symptomatic or has suffered an episode of tachyarrhythmia, they should be considered for cardiac pacing using an implanted pacemaker device. Mortality is increased because of complications such as myocardial infarction and thrombo-embolic disease.
The mainstay of treatment is ventricular pacing for bradyarrhythmias (slow pulse rate) for pauses of 2-3 seconds or more. Attempting to increase heart rate with drugs such as isoprenaline is usually ineffective, except as a short term emergency measure (eg while preparing for emergency pacing).Permanent pacing allows more aggressive treatment of tacharrhythmias because the ventricle is prevented from beating too slowly.
Hurst's The Heart 8th Edition, McGRAW-HILL 1994. Kumar and Clark, Clinical Medicine 4th Edition, W.B SAUNDERS 1998. MEDLINE Plus.
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