Atrial flutter

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Introduction0:00–0:31

. With atrial flutter, atrial refers to the two upper chambers of the heart, while flutter describes the rapid wave of electrical activity that causes the atria to contract quickly, almost like their flapping.
During atrial flutter, the atria can contract at rates between 250 and 350 BPM. 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.

Physiology0:31–1:15

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.
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.

Pathology1:15–4:05

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.
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 hits and ensuring coordinated ventricular contractions.
Now once the impulse reaches the Berkindji 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 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.
With atrial flutter, a rogue electrical impulse arises in the atria and overrides the essay note, throwing off the rhythm of the whole orchestra.
The usual trigger is a premature atrial contraction, which is an early heartbeat that comes from an ectopic focus. An ectopic focus refers to a tiny group of cells in the atria outside of the essay node that fires on its own instead of waiting for the signal from the essay node.
Premature atrial contractions often occur due to atrial irritation, which can result from electrolyte imbalances and stimulants like caffeine.

ECG Changes4:05–6:04

Even though they are often harmless, if these early heartbeats hit at just the right time, they can set off a re-entrance self-sustaining circuit, which is one of the main ways atrial flutter occurs.
Now, based on where this re-entry circuit forms, atrial flutter is divided into two main types. Type one or typical atrial flutter is the most common form in the lower part of the right atrium between the opening of the inferior vena cava and the tricuspid valve.
There is a band of tissue called the cavo tricuspid isthmus. This area conducts impulses a bit slower than the surrounding tissue.
That difference in conduction speed creates the perfect setup for a reentrance circuit. Here's how it works.
Once cardiomyocytes contract, they need time to recover and reset electrically before contracting again. During this recovery period, new impulses won't trigger them, but when an impulse travels through the slow area of the cavo tricuspid isthmus, cardiomyocytes have more time to reset.
So once the impulse passes through, it can loop back and stimulate them again. This allows the impulse to loop continuously, usually in the counterclockwise direction around the tricuspid valve.
Now while everyone has a cavo-tricuspid isthmus, atrial flutter only occurs when there is stress on the atria. Anything that stretches or enlarges the atria creates a perfect setup for these re-entrance circuits to form, including high BP, valvular heart disease, coronary artery disease, and scarred tissue from prior cardiac surgery.
In contrast to type 1, which occurs only in the right atrium, type 2 or atypical atrial flutter can involve either atrium, especially the left.

Symptoms6:04–6:27

It's typically associated with scar tissue, usually from prior cardiac interventions and structural heart conditions. One common example is mitral valve disease, which puts pressure on the left atrium, leading to stretching and fibrosis.

Complications6:27–6:27

Complications6:27–6:47

In this type, the impulse encounters a region it can't pass through. So instead of disappearing, the impulse detours through the nearby cardiomyocytes.
However, rather than moving forward, it circles back and reactivates cells that have just recovered. You can think of it like trying to stop a row of falling dominoes.

Treatment6:47–7:34

As you reset one end, the wave loops back around and knocks it over again. In both types, the ultimate result is a self-sustaining circuit.
The impulse keeps cycling through the same pathway, causing the atria to contract at extremely rapid rates, around 250 to 350 times per minute.
However, for ventricles to contract, the impulses must pass through the AV node, which acts as a gatekeeper. So when an impulse reaches the AV node, only one impulse can pass at a time.
Once one signal passes, the gatekeeper blocks the pathway for a moment. This block is the AV node's refractory period, which is relatively long.

Review7:34–12:51

While blocked, any new impulses coming from the atria bounce off. When the refractory period ends, the gatekeeper opens the pathway, and the next impulse can pass through.
That's why even if the atria are firing 300 times per minute, only every second or third impulse gets through, slowing the ventricular rate to around 100 to 150 BPM.
Keep in mind that even this heart rate is still too fast for the ventricles to function efficiently, which is why atrial flutter is classified as supraventricular tachycardia, meaning the fast rhythm originates above the ventricles.
This rapid beating of the atria ultimately affects the atrial kick. 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.
And that's not all. With less blood entering the ventricles, cardiac output can drop by as much as 30%.
But when it comes to these complications, keep in mind that the bigger troublemaker is atrial fibrillation, not atrial flutter.
Now, moving on to clinical manifestations, these individuals often experience palpitations, shortness of breath, or fatigue, especially during exertion.
Some describe a fluttering or pounding sensation in the chest or even in the neck. When the ventricular rate becomes too fast, there's less time for the ventricles to fill between beats, eventually reducing cardiac output, and reduced cardiac output leads to lower BP and symptoms like lightheadedness and syncope.
Also on physical examination, you might notice a rapid, often regular or regularly irregular pulse. Interestingly, BP can still appear normal, especially in early stages.
Diagnosis primarily relies on ECG findings. With typical atrial flutter, you'll notice the absence of normal P waves because the SA node is no longer controlling the heartbeat.
Instead, the nonstop depolarization around the atria creates F waves, or electrical flutter, which takes on a sawtooth pattern.
F waves are more visible in leads 23, and AVF. Sometimes F waves aren't as easy to spot because the rapid QRS complexes can hide them.
Fortunately, we can temporarily slow conduction down through the AV node and reduce the number of impulses that reach the ventricles.
By spacing out impulses, we give the flutter waves room to show themselves. First, we can use carotid sinus massage, which stimulates the vagus nerve and boosts parasympathetic activity.
Another option is adenosine, which is a short-acting medication that temporarily blocks the AV node conduction. Finally, if the AV node is letting impulses through at regular intervals, the RR interval will remain consistent.
So in a 2:1 conduction ratio, you'll see 2 flutter waves for every QRS complex. Keep in mind that other conduction ratios like 3:1 and 4:1 can also occur.
But sometimes the AV node can have variable conduction, meaning the number of atrial impulses that get through changes beat to beat.
In this case, the rhythm will appear as regularly irregular. On the flip side with atypical flutter, the re-entrance circuit is somewhere else.
In other words, you'll notice a more variable ECG pattern and not the classic sawtooth appearance. The first line treatment for atrial flutter, especially the typical type, is catheter ablation.
It destroys the cavo tricuspid isthmus and breaks down the re-entrance circuit around the tricuspid valve. If ablation isn't possible, the goal is to slow down the ventricular rate using medications like beta blockers or calcium channel blockers.
Anticoagulation is also essential to reduce the risk of blood clots and stroke. All right, as a quick recap.
Atrial flutter is a type of supraventricular arrhythmia, where the atria contract rapidly, usually between 250 and 350 BPM.
Typical flutter happens when a re-entrance circuit loops around the tricuspid valve, creating a classic sawtooth pattern on ECG.
Atypical flutter involves other circuits, often near scarred atrial tissue, leading to more variable ECG