Heart Rhythm Disorders (cont.)
Sinus bradycardia
The heart, its cells and its electricity may come under the many outside influences where it may beat more slowly. Sinus bradycardia (brady=slow + cardia=heart) by definition, is a heart beat
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 like beta blockers or calcium channel blockers.
Vasovagal syncope is an episode of profound sinus bradycardia associated with
a noxious stimulus in which the vagal system of the body kicks in. 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 does 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. It can also
happen when one bears down to urinate or have a bowel movement.
Abnormal rhythms
Rhythm disturbances are classified according to whether they arise from the
atrium or ventricle, are fast or slow, or regular or irregular.
Tachycardia
Rapid heart rates can originate from either the atrium or the ventricle, but
rhythms from the ventricle are more often considered 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.
Next: Ventricular fibrillation »
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