Atropine is an anticholinergic medication that may be administered in a variety of medical situations. Anticholinergic drugs block the action of acetylcholine, a neurotransmitter found in many places throughout the body. Atropine is often used during surgical procedures performed under general anesthesia. People having an asthma attack or being treated for a cardiac arrest may also receive atropine. Due to atropine's various uses, it is important to understand the effect this medication has on the heart.
Parasympathetic Nervous System
A division of the body's nervous system called the parasympathetic nervous system, or PNS, controls heart rate. The vagus nerve is the specific part of the PNS that controls the heart. It releases acetylcholine, a neurotransmitter that acts on the cells of the heart to control the heart rate. Stimulation of the heart by the vagus nerve results in a slow, steady heart rate.
How Atropine Works
Atropine inhibits the activity of acetylcholine. When atropine is introduced to heart cells, it blocks them from being activated by acetylcholine released from the vagus nerve. In the medical setting, atropine is most commonly used to block the effects of too much vagal stimulation. In other words, administering atropine helps counteract an abnormally slow heart rate.
When people receive atropine, they experience a temporary elevation in heart rate. The effect typically lasts 2 to 6 hours. If there is chronic use or an overdose of atropine, the heart may beat too fast. This is called tachycardia, which is defined as a heart rate greater than 100 beats per minute.
The authors of a 2004 study published in the journal "Continuing Education in Anesthesia, Critical Care and Pain" reported that atropine may temporarily lower heart rate before an increase occurs. The authors speculate that this effect occurs because atropine may transiently increase the amount of acetylcholine available for use by the heart nerves, leading to temporary slowing of the heart rate. This effect of atropine on heart rate remains an area of active research.