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Causes
By Mayo Clinic staff
Your heart is made up of four chambers — two upper chambers (atria) and two lower chambers (ventricles). The rhythm of your heart is normally controlled by the sinoatrial node (SA node) — or sinus node — an area of specialized cells located in the right atrium. This natural pacemaker produces the electrical impulses that trigger each heartbeat. From the sinus node, electrical impulses travel across the atria to the ventricles, causing them to contract and pump blood out to your lungs and body.
A normal sinus node paces your resting heart between 60 and 100 beats a minute. If you have sick sinus syndrome, your sinus node isn't functioning properly, so your heart rate may be too slow (bradycardia) or too fast (tachycardia) or irregular.
Types of sick sinus syndrome and their causes include:
- Sinoatrial block. Electrical signals move too slowly through the sinus node, causing an abnormally slow heart rate.
- Sinus arrest. The sinus node activity pauses.
- Tachycardia-bradycardia syndrome. The heart rate alternates between abnormally fast and slow rhythms, often with a long pause (asystole) between heartbeats.
What makes the sinus node misfire?
Diseases and conditions that cause scarring or damage to your heart's electrical system can be the reason. Scar tissue from a previous heart surgery also may be the cause, particularly in children. Sick sinus syndrome may also be set off by medications, such as calcium channel blockers or beta blockers used to treat high blood pressure, heart disease or other conditions. However, in most cases, the sinus node doesn't work properly because of age-related wear and tear to the heart muscle.
- Sick sinus syndrome. Heart Rhythm Society. http://www.hrspatients.org/patients/heart_disorders/sick_sinus/default.asp. Accessed March 19, 2009.
- Ferri F. Sick sinus syndrome. In: Ferri FF. Ferri's Clinical Advisor 2009. St. Louis, Mo.: Mosby; 2008. http://www.mdconsult.com/das/book/body/127077711-3/819048192/1701/546.html#4-u1.0-B978-0-323-04134-8..50022-7--cesec438_11555. Accessed March 19, 2009.
- Bradyarrhythmias. In: Libby P, et al, eds. Braunwald's Heart Disease: A Textbook of Cardiovascular Medicine. 8th ed. Philadelphia, Pa.: Saunders Elsevier; 2007. http://www.mdconsult.com/book/player/book.do?method=display&type=aboutPage&decorator=header&eid=4-u1.0-B978-1-4160-4106-1..X5001-8--TOP&isbn=978-1-4160-4106-1&uniq=127077711#lpState=open&lpTab=contentsTab&content=4-u1.0-B978-1-4160-4106-1..50038-8--cesec163%3Bfrom%3Dindex%3Btype%3DbookPage%3Bisbn%3D978-1-4160-4106-1. Accessed March 12, 2009.
- Arnsdorf MF. Manifestations and causes of the sick sinus syndrome. http://www.uptodate.com/home/index.html. Accessed March 19, 2009.
- Dual-chamber pacemakers for symptomatic bradycardia due to sick sinus syndrome and/or atrioventricular block. Rockville, Md.: Agency for Healthcare Research and Quality. http://www.guideline.gov/summary/summary.aspx?ss=15&doc_id=8124&nbr=4526. Accessed March 19, 2009.
- What is a pacemaker? National Heart Lung and Blood Institute. http://www.nhlbi.nih.gov/health/dci/Diseases/pace/pace_all.html. Accessed March 19, 2009.
- Arnsdorf MF. Treatment of the sick sinus syndrome. http://www.uptodate.com/home/index.html. Accessed March 19, 2009.
