heart and blood vessel disorders
Sinus Node Dysfunction
Introduction
Sinus node dysfunction is an abnormality in the natural pacemaker of the heart that causes a slow heart rate. People may have no symptoms, or they may feel weak or tired or have palpitations. Electrocardiography is used to make the diagnosis. A permanent artificial pacemaker is usually needed. (See also Overview of Abnormal Heart Rhythms .) Dysfunction of the heart’s natural pacemaker (the sinus or sinoatrial node) may result in a persistently slow heartbeat (sinus bradycardia) or complete cessation of normal pacemaker activity (sinus arrest—see figure). When activity ceases, another area of the heart usually takes over the function of the sinus node. This area, called an escape pacemaker, may be located lower in the atrium, in the atrioventricular node, in the conduction system, or even in the ventricle. All types of sinus node dysfunction are more common among older people. Some drugs and an Hypothyroidism (hypothyroidism) can cause sinus node dysfunction. However, the cause is usually unknown. When the cause is unknown, the disorder is called in which periods of slow heart rhythms (bradycardia) alternate with periods of fast atrial arrhythmias (tachycardia), such as Atrial Fibrillation and Atrial Flutter . Sinus node dysfunction affects mainly older people, especially those with another heart disorder or with Diabetes Mellitus (DM) . The most common cause is formation of scar tissue (fibrosis) in the sinus node. The cause of fibrosis is usually unknown, but known causes of sinus node dysfunction include drugs (for example, beta-blockers and other drugs used for abnormal heart rhythms), excessive impulses from the vagus nerve, which inhibit the heartbeat, and many disorders that limit blood flow (for example, 