Sinus node dysfunction or heart pacemaker dysfunction is the malfunctioning of the primary pacemaker of the heart, namely, the sinus node, resulting in abnormal arrhythmias, especially slow heart rate or bradycardia.
- Sinus node dysfunction may be asymptomatic or symptoms such as palpitations, fatigue and weakness may be present.
- Diagnosis by physical examination is confirmed by electrocardiography (ECG).
- Fitting an artificial pacemaker permanently is usually the ideal solution.
When the sinoatrial node or sinus node, which is the pacemaker or the starting point of the electrical activity of the heart, becomes dysfunctional, it may precipitate a constantly low heartbeat called sinus bradycardia. When the sinus node completely stops functioning, it is called sinus arrest.
Usually, when the sinoatrial node is dysfunctional, a new area takes over its function. This substitute pacemaker, which may be a point in the atrium or in the atrioventricular node, is termed an escape pacemaker. The location of the escape pacemaker can be another area much lower in the electric circuit of the heart or even in the ventricles.
Prevalent in the older age group, sinus node dysfunction may result from hypothyroidism or the usage of certain drugs. But more often, a definite cause cannot be identified, in which cases it is termed as sick sinus syndrome. Bradycardia-tachycardia syndrome, in which episodes of tachycardia or fast heart rhythms such as atrial fibrillation and flutter alternates with episodes of bradycardia or slow rhythms, is considered a version of sick sinus syndrome.
Symptoms and Diagnosis
Often, sinus node dysfunction is asymptomatic. General weakness and fatigue may be symptoms of a slow heart rate that persists over a long period. An extremely low heart rate may result in fainting. A fast heart rate is often perceived by the person as Palpitations which are usually felt when the heart rate is high. After a bout of fast arrhythmia, the pacemaker may be delayed in restarting the heart before reverting to normal rhythm. This delay often results in fainting.
Sinus node dysfunction is usually diagnosed from characteristic symptoms such as slow and irregular pulse, a pulse that does not vary even on exertion, or highly fluctuating pulse irrespective of there being no change in activity. Electrocardiography, especially continuous monitoring with a portable Holter monitor helps confirm the diagnosis.
Treatment
An artificial pacemaker, which helps to increase the heart rate, is permanently attached to prevent a slow heart rhythm. If episodes of fast rhythm also occur, Antiarrhythmic drugs that slow the heart are given.
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