Atrial fibrillation

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Introduction0:00–0:20

. With atrial fibrillation or afib, atrial refers to the atria or the upper two heart chambers, while fibrillation refers to rapid, uncoordinated, and irregular contractions of the heart muscle fibers.
So in atrial fibrillation, which is the most common type of cardiac arrhythmia, the atrial muscle fibers fire electrical signals randomly, causing the atria to quiver instead of contracting normally.

Pathophysiology0:20–0:58

First, let's check how the cardiac conduction system works. Everything starts with the sinoatrial or SA node located in the upper part of the right atrium, which acts like a conductor in the heart's orchestra.
The SA node sends out an electrical impulse that rapidly spreads through the atria, causing them 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.

ECG Changes0:58–1:49

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 perkinji fibers.
However, not all impulses from the atria make it to the bundle of hiss. This is because our gatekeeper, the AV node, carefully regulates the flow of impulses to the ventricles, particularly during its refractory period.

Risk Factors1:49–2:32

During this time, the AV node is recovering from the previous impulse and is temporarily unable to transmit new signals.
This system acts as a filter preventing excessive or chaotic ectopic atrial impulses from reaching the bundle of his and ensuring coordinated ventricular contractions.
Now once the impulse reaches the perkinji 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.

Multiple Wavelet Theory2:32–3:18

After each 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. 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, you can easily confirm if a rhythm is regular by looking at the RR interval, which remains the same between each consecutive beat.

Automatic Focus Theory3:18–3:52

Now in atrial fibrillation, instead of a single conductor leading the orchestra, dozens of rogue musicians start playing their own tunes at different tempos.
This chaotic rhythm can occur due to structural changes that stretch the atrial walls, including valvular heart disease, particularly the mitral valve disease, but also due to coronary artery disease and cardiomyopathy.
Additionally, important risk factors to keep in mind include age over 65, diabetes, hypertension, hyperthyroidism, acute infections, and electrolyte imbalances.

Atrial Fibrillation Progression3:52–3:52

Atrial Fibrillation Progression3:52–4:59

Regardless of the underlying cause, numerous ectopic electrical impulses, often originating from the pulmonary veins, flood the atria with chaotic signals.
As a result, the essay node is no longer in control, so the atria lose their usual rhythm and begin to fibrillate or quiver.
Without effective atrial contraction, the atrial kick is lost. Less blood fills the ventricles and more remains pooled in the atria, especially in the left atrial appendage.
And when blood sits still, it starts to clot. If one of those clots breaks loose and enters the ventricle, it can reach the systemic circulation, potentially reaching the brain and causing ischemic stroke.
But that's not all. With less blood entering the ventricles, cardiac output can drop by as much as 30%.
Over time, repeated episodes of fibrillation can result in atrial fibrosis or permanent scarring of the atrial tissue. This scarring can lead to electrical and structural remodeling of the atria, making future episodes of arrhythmia more likely to occur.

Symptoms4:59–5:21

Now, even though the atria may fibrillate at rates exceeding 200 BPM, the ventricular rate typically remains lower. This is because the chaotic impulses reaching the AV node usually hit during its refractory period when it's temporarily unresponsive.

Complication5:21–5:48

As a result, impulses can't pass through to the ventricles. The actual ventricular rate in atrial fibrillation can vary.
It depends on things like how long the AV node stays in that refractory state, how frequently impulses are coming from the atria, and the balance between the sympathetic and parasympathetic nervous systems.

Diagnosis5:48–6:06

When the sympathetic system is more active, it enhances AV node conduction, thereby increasing the ventricular rate. This is common in hyperthyroidism, stress, and exercise.
On the flip side, when the parasympathetic system dominates, it slows down AV node conduction, resulting in a slower ventricular rate.

Treatment6:06–9:17

This is common during sleep. Now all that quivering in the atria leads to classical clinical manifestations which include palpitations.
Chest discomfort, shortness of breath, and poor exercise tolerance, it's like the heart is trying to keep up with a frantic drummer, leaving the person feeling tired and lightheaded.
Some individuals may feel fine at rest but become quickly exhausted during physical activity. On physical examination you will notice an irregularly irregular pulse and normal BP.
However, in more severe cases, atrial fibrillation can compromise the heart's pumping ability, which can result in low BP or even acute heart failure.
Diagnosis relies primarily on ECG, which characteristically shows the absence of P waves because the SA node is no longer controlling the heartbeat.
Instead, the atria fire chaotically. Instead of clear P waves, you might see coarse or fine fibrillatory waves.
Another key finding is the irregularly irregular rhythm, which is a hallmark of atrial fibrillation. This means the time between each ventricular beat, which represents the RR interval, is unpredictable and constantly changing because the AV node receives random electrical impulses from the atria at irregular intervals, allowing only some impulses to pass through to the ventricles.
However, if your patient reports symptoms consistent with atrial fibrillation, but the ECG reveals no abnormalities, you should think of paroxysmal atrial fibrillation.
This type of atrial fibrillation is characterized by episodes that spontaneously resolve within 7 days. In this case, a standard ECG might miss the abnormal rhythm, so you will need to obtain an extended monitoring with a Holter monitor which records the heart rate and rhythm over 24 to 48 hours while the person goes about their daily activities.
This increases the chance of catching the abnormal rhythm. As far as the treatment goes, the aim is to restore the normal heart rhythm using cardioversion, which can be either electrical with a synchronized shock or pharmacological with anti-arrhythmic medications.
Next, we want to control the heart rate and give the ventricles enough time to fill using medications like beta blockers.
Next, we can destroy the small areas in the heart that are generating abnormal impulses using catheter ablation. Finally, since there's a risk of blood clots, don't forget anticoagulation therapy.
All right, as a quick recap, in atrial fibrillation, which is the most common type of cardiac arrhythmia, multiple ectopic impulses flood the atria, causing them to quiver over time.
Repeated episodes of fibrillation can result in fibrosis, which can cause both electrical and structural remodeling of the atria, making future episodes of arrhythmia more likely to occur.
Diagnosis primarily relies on ECG findings which reveal the absence of P waves with coarse or fine fibrillatory waves and unpredictable RR