ThedaCare Health Matters
A-Fib Can Happen Suddenly, Sometimes Without Specific Cause
Normally, the heart rhythm is regulated by a portion of the heart that acts as a natural pacemaker called the sinus node. It is in the upper chambers of the heart called the atria. The atria receive the blood as it returns to the heart and pushes it down to the lower chambers, called the ventricles, which contract and force the blood out of the heart. The sinus node keeps the heart beating regularly. It can increase the rate when it needs to pump more blood or decrease it when the body is resting. The electrical impulse starts in the atria and spreads down to the ventricles through nerve fibers.
Atrial fibrillation (A-fib) is the term to describe when the sinus node is not functioning correctly. The atria are beating erratically with unorganized electrical activity causing the atria to quiver. A-fib is the most common heart rhythm problem. It is reported millions of Americans have A-fib. It occurs in about 2 percent of the population younger than 65 years old and in 9 percent of those over 65.
A-fib can occur suddenly and many times there is no specific cause. When it happens, the ventricles are bombarded with many irregular electrical impulses, which can cause the ventricles to beat quite rapidly and irregularly. This can create a medical emergency if the ventricles beat too fast because the heart may not be able to pump the blood effectively causing low blood pressure and lung congestion. In those instances, the best treatment is to shock the heart to get it back into a sinus rhythm.