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AFib: Pathophysiology & Complications

Instructor: Tari Rajchel

Tari has been a Registered Nurse for 29 years and has her Docotorate in Nursing Practice.

In this lesson, we will discuss the pathophysiology, or functional changes, found in atrial fibrillation by comparing a normal heart to that of a heart experiencing AFib. We will also look at the complications associated with AFib.

Atrial Fibrillation (AFib)

Atrial fibrillation, also known as AFib, is a disturbance in a person's heart rhythm. Normally, a heart contracts, or tightens, and relaxes to a regular steady beat. AFib is an irregular, rapidly beating heart. In this cardiac arrhythmia, the upper chambers, or atria, of the heart quiver or beat irregularly.

AFib Pathophysiology

Let's take a look on how a normal heart functions and how the heart functions during AFib.

Normal Heartbeats

A heart that is beating normally keeps a regular rhythm. Have you ever watched a metronome keep a steady beat? In the heart, the SA node plays the role of the metronome and acts as the pacemaker, producing a steady beat. The SA node sends an electrical impulse through the atria, causing both the right and left atrium to contract and deliver blood to both ventricles. The atrioventricular (AV) node, located between the atria and ventricles, receives an impulse from the SA node. The AV node is what keeps the ventricles in sync with the atria.

Filling and pumping actions in a healthy heart
Heart

Abnormal Heartbeats

Two different scenarios can cause AFib. In the first case, the atria receive early, or premature, impulses from the pulmonary veins. We call this a focal activation, as the impulses start at a specific point. These abnormal impulses cause chaos in the atria because the pulmonary veins are the ones sending the impulses, instead of the SA node. As a result, the atria do not contract as they would in a normal heartbeat and just quiver.

These rapid, chaotic impulses can be as fast as 200-400 beats per minute. The poor AV node floods with impulses and doesn't know what to do. It tries to filter some out, but is instead overwhelmed. This allows rapid impulses to get through to the ventricles, which causes them to beat fast, hence the fast heartbeat.

In the second scenario, multiple areas in the atria send impulses, called multiple wavelets. Imagine being in a crowded room filled with background noise and two different people trying to talk to you at once. This is how the atria feel: they're receiving impulses from multiple places, so instead of contracting, they just start quivering, blood begins pooling, and the ventricles beat irregularly and fast. These events lead to AFib, a disturbance in a person's heart rhythm.

Complications of AFib

While AFib itself isn't fatal, it can cause two major complications: stroke and heart failure. Remember how we said that the atria are quivering and not actually contracting during AFib? Without the contractions, blood pools instead of entering the ventricles, and blood clots can start to form. If one of those clots breaks loose, it can travel throughout the body and cause a blockage.

A stroke occurs when the blood supply to the brain is blocked, such as by a blood clot formed in the heart, which leads to a sudden death of brain cells. People with AFib are about five times more likely to suffer a stroke.

A second complication of AFib is heart failure, again due to the atria's failure to contract. Because the heart is working so hard and beating so fast for long periods of time, the heart muscle keeps getting weaker and weaker. A main symptom of heart failure is shortness of breath, where the lungs and the rest of the body are not getting enough blood to meet their needs. When the heart is not pumping effectively, fluid builds up in the lungs, making breathing difficult.

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