What are Beta Blockers?

by admin on May 10, 2010

Beta blockers are a class of drugs that are most commonly used to treat heart problems; short for Beta- adrenergic blocking agents. These drugs prevent epinephrine (adrenaline) and norepinephrine (noradrenaline) from binding to the beta cells located on your nerves resulting in slowed transmission of nerve impulses to the heart (Beta 1 receptors – there are three different beta receptors located on cells – 1, 2 and 3). Once nerve impulses are slowed, the heart requires less blood and oxygen to function, slowing heart rate and preventing blood vessel constriction. Under normal circumstances, when beta 1 cells are stimulated, heart rate increases, and your blood vessels constrict to allow more blood to flow to your skeletal muscles. This is an important adaptation in our bodies, readying them for fight or flight when faced with imminent danger; your heart beats faster, bringing a fresh supply of oxygen to your skeletal muscles, allowing you to run or fight; an evolutionary adaptation. At the same time, blood flow is redirected away from your digestive system as your body needs to worry about the immediate danger in front of it, not with everyday functioning; where you have trouble figuring out priorities, your body decides for you!

The problem with this system, and thus one of the reasons why Beta blockers are prescribed, is that if your heart muscle is damaged, or if you have arrhythmias, or one of many other heart conditions, any increase in workload puts  you at risk for sustaining further heart damage. Beta blockers have negative inotropic and chronotropic effects:

What is an Inotropic Effect?

Inotropic refers to the strength at which a muscle contracts. A negative inotrope decreases the strength of a muscle contraction and a positive inotrope increases the strength of a muscle contraction. Beta blockers are negative inotropes – if your heart doesn’t beat as “hard” it is less likely to break down. Drugs like Milrinone have the opposite effect; they increase the contractility of the heart and are used in some cases of congestive heart failure.

What is a Chronotropic Effect?

Chronotropic refers to the speed at which the heart beats. Negative chronotropic agents, such as beta blockers, decrease the hearts contraction rate.

In summary beta blockers work to decrease heart rate (beats per unit time) and the strength of the heart contraction protecting it from incurring further damage.

Leave a Comment

Previous post:

Next post: