Ventricular fibrillation

Video summary

Ventricular fibrillation, also called v-fib or just VF, is when there's quivering of ventricular muscle fibers because they're not contracting at the same time. This results in failure to pump oxygenated blood to the brain, which within minutes can lead to sudden cardiac death. Prompt defibrillation and advanced cardiac life support measures need to be initiated to restore normal heart rhythm and prevent mortality.

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Introduction0:00–0:25

. With ventricular fibrillation, ventricular refers to ventricles, the heart's main pumping chambers, while fibrillation means quivering of the muscle fibers.
So in ventricular fibrillation, ventricles start firing off 100s of fast and disorganized impulses, causing the ventricles to quiver instead of contracting.
As a result, the heart can't pump blood effectively, cutting off circulation to vital organs. Before we proceed with ventricular fibrillation, let's check how the cardiac conduction system works.

Pathology0:25–1:18

Everything starts with the sinoatrial or essay node located in the upper part of the right atrium, which acts like a conductor in the heart's orchestra.
The essay node sends out an electrical impulse that rapidly spreads through the atria. Causing the atria to contract in perfect harmony, eventually pushing blood into the ventricles.
This is known as atrial depolarization, and on an ECG it appears as the P wave. Next, the electrical impulse reaches the atrioventricular or AV node, located in the lower part of the right atrium, just above the tricuspid valve.

Causes1:18–2:42

The AV node acts as a gatekeeper, slowing down the impulse before it reaches the ventricles. This delay gives the atria enough time to fully contract and fill the ventricles with blood, which is also known as the atrial kick.
On the ECG you can see this brief pause as the PR segment. Together, the P wave and PR segment make up the PR interval.
From the AV node, the electrical impulse travels through the bundle of hiss down to the right and left bundle branches, eventually reaching the perkyi fibers.
Now, once the impulse reaches the perkyi fibers, it's transmitted to the cardiomyocytes, triggering a synchronized contraction of both ventricles that forces blood into the systemic and pulmonary circulations.
This phase, which is known as depolarization of the ventricles, Appears as the QRS complex on the ECG. After the contraction, the ventricles reset electrically so they can relax and fill with blood again.
On the ECG, this phase known as repolarization appears as the T wave. The brief period between depolarization and repolarization, where no electrical changes occur, is called the ST segment.

Functional Reentry2:42–3:17

The cycle then repeats, driven by that same smooth electrical impulse, just like a well coordinated orchestra. Normally the heart's rhythm beats at a steady pace of 60 to 100 BPM, with each beat perfectly synchronized.
But when the SA node loses control, this smooth and steady beat can become too fast, too slow, or irregular, throwing the heart's coordination off track.
This abnormal heart rhythm is known as arrhythmia, which can be further classified as supraventricular and ventricular. Supraventricular arrhythmias arise above the ventricles, for example, in the atria, while ventricular arrhythmias start in the ventricles themselves.

Anatomical reentry3:17–3:34

Within the broader group of ventricular arrhythmias, there's a specific subgroup called ventricular tachyarrhythmias, which includes ventricular fibrillation and ventricular tachycardia.

External Electrical Stimulation3:34–4:31

Now ventricular fibrillation happens when the heart's rhythm completely falls apart. The essay node loses control, and the ventricles start firing off 100s of disorganized impulses per minute.
It's like every musician in an orchestra begins playing their solo. There's no rhythm and no harmony, just noise.
Without a single clean impulse to guide the heart contraction, the ventricles start quivering instead of pumping. As a result, the heart can't pump blood effectively, cutting off the blood supply to vital organs.
Now several things can spark the ventricles to beat this fast. The most important trigger is a premature ventricular contraction, or PVC.
PVCs are early heartbeats that come from an ectopic focus, meaning a tiny group of cells in the ventricles that fire on their own instead of waiting for the signal from the SA node.

ECG Changes4:31–5:15

And if there's a short run of 3 or more PVCs in a row that last less than 30 seconds, we're talking about non-sustained ventricular tachycardia or NSVT.
But here's the thing, in a healthy, electrically stable heart, Both PVCs and non-sustained ventricular tachycardia usually come and go without serious issues.
So it's not the extra beat itself that causes trouble, but the environment where it lands. Conditions that disrupt the flow of electrical impulses through the heart can tip the balance toward electrical instability.

Treatment5:15–11:37

In a heart that's ischemic, scarred, or affected by medications, PVCs can hit during the vulnerable period of the T wave.
At that 0.1 part of the myocardium is excitable and ready to contract, and another part is refractory, meaning it's still recovering and cannot respond to a new impulse.
This timing, which is known as the R on T phenomenon, can trigger ventricular fibrillation. Think of it like an orchestra resetting between sections.
If one musician jumps in early with a loud note while the others are still getting ready, it ruins the timing and throws the whole performance off.
That mistimed note is like an R&T beat. It hits at the wrong moment and can send the heart into chaos.
Once ventricular fibrillation starts, the real issue is what keeps it going. Electrical impulses don't just land on a cardiomyocyte and stop, instead they loop back and keep stimulating the heart tissue.
This looping is called re-entry of an impulse, and it's a key driver of the chaos in ventricular fibrillation. First we have anatomical reentry.
Imagine an electrical impulse traveling through cardiomyocytes until it reaches a structural block like scar tissue left from a previous heart attack.
The impulse can't pass through this area, so it takes a detour through nearby healthy cells. Instead of just going around and continuing forward, the impulse loops back to cardiomyocytes that have just recovered from the impulse, triggering them again.
This looping causes the impulse to keep re-entering the same tissue, creating a self-sustaining circuit. On the other hand, functional re-entry doesn't need a physical block.
Instead, it happens when some cardiomyocytes recover faster than others, creating an uneven electrical playing field. Imagine two neighboring rows of cardiomyocytes.
One row conducts impulses quickly but takes longer to recover, while the other row conducts impulses slowly but recovers faster.
When an impulse reaches this area, it can't pass through the fast conducting row because these cells are still recovering.
Instead, the impulse takes the slow conducting route. By the time it finishes traveling down the slow path, the fast conducting row has repolarized and is ready to conduct again.
At this point, instead of disappearing, the impulse now jumps over and activates the fast row. As it rapidly travels through this path, the slow conducting row is already recovering, setting the stage for the cycle to repeat.
This creates a self-sustaining circuit where the impulse keeps re-entering tissue that has just recovered. Functional re-entry commonly occurs in acute ischemia, where damaged cardiomyocytes conduct impulses slowly but re-polarize quickly.
Additionally, electrolyte imbalances like low potassium or magnesium, and medications that prolong the QT interval can also create this vulnerable setting by disrupting normal electrical recovery.
Prolonging the QT interval is like stretching out the pause between sections in an orchestra concert. It gives someone more time to jump in early with a wrong note and throw off the rhythm for everyone else.
Now when the heart starts quivering, it can no longer pump blood into systemic circulation. No blood to the brain, no blood to the organs, just seconds before unconsciousness sets in.
Usually the first sign is collapse. The person might have been talking, walking, or even sitting quietly, and then within seconds they're unconscious on the floor.
There's no pulse because the heart isn't pumping blood. Blood pressure severely drops, and without immediate intervention, the brain and other vital organs start to shut down.
Diagnosis primarily relies on clinical manifestations and ECG findings. If someone collapses, isn't responsive, and has no pulse, you should assume cardiac arrest.
And in adults, ventricular fibrillation is often the cause. In full-blown ventricular fibrillation, it's not just one re-entry loop, it's dozens of re-entry loops.
These circuits form, collide, break apart, and reform in a constant chaotic electrical storm. On ECG this shows up as a rapid irregular squiggle of low amplitude with no P waves, no QRS complexes, and no T waves, just electrical noise.
Ventricular fibrillation is a cardiac emergency, and the only effective treatment is immediate defibrillation. The goal is to deliver an electric shock that stops the chaotic electrical activity, completely resetting the heart, allowing the essay node to regain control, and restoring a normal rhythm.
All right, as a quick recap. Ventricular fibrillation happens when the SA node loses control and the ventricles start firing off 100s of chaotic impulses per minute, causing them to quiver.
A common trigger is a premature ventricular contraction, which is usually harmless in a healthy heart, but in a heart that's damaged, ischemic, or affected by certain medications, the electrical system becomes unstable, so PVCs can easily spiral into ventricular fibrillation.
On ECG, ventricular fibrillation shows up as a rapid irregular squiggle with no P waves, QRS complexes, or T