Heart Rhythm Disorders (cont.)

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Sinus bradycardia

The heart, its cells, and its electricity may come under the many outside influences causing it to beat more slowly. Sinus bradycardia (brady = slow + cardia = heart) by definition, is a heartbeat generated by the SA node at a rate slower than 60 beats per minute. This may be normal in people who are active and athletic or in patients taking medications designed to slow the heart such as beta blockers and some calcium channel blockers.

Vasovagal syncope is an episode of profound sinus bradycardia associated with a noxious stimulus that causes the vagal system of the body to kick in and slow the heart rate. While the sympathetic system of the body is mediated by adrenaline, the parasympathetic system is mediated by the vagus nerve and the chemical acetylcholine, which promotes the exact opposite body reaction than adrenaline. In some people, exposure to pain or a difficult emotional situation can stimulate the vagus nerve, slow the heart, and dilate blood vessels (veins), causing cardiac output to decrease and making a person feel lightheaded or faint. The vagus nerve also can be stimulated to slow the heart when one bears down to urinate (micturition syncope) or have a bowel movement.

Abnormal heart rhythms

Rhythm disturbances are classified according to whether they arise from the atrium or ventricle, are fast or slow, or regular or irregular.


Rapid heart rates can originate from either the atrium or the ventricle, but rhythms from the ventricle are more often life threatening. The initial approach to rapid heart rates is to quickly identify the rhythm, and if blood pressure is maintained and there is no evidence of a failing heart, then treatment is directed to rate control with the eventual return of the heart back to normal sinus rhythm. If, however, there is evidence that the heart is failing because of the rapid rate, then emergency measures, including using electricity to shock the heart back into a regular rhythm, may be necessary.

Medically Reviewed by a Doctor on 1/30/2015

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