Teaching Medicine - Tutorial: Rhythm Diagnostic Criteria

ECG

Level 2

Tutorial: Rhythm Diagnostic Criteria

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Tutorial: Rhythm Diagnostic Criteria

This module will list the basic rhythms, their diagnostic criteria, and their clinical significance .

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Tutorial: Rhythm Diagnostic Criteria Atrial Fibrillation

Lessons

Times Practiced

1284

Cases Completed

1h 24m

Total Time spent

1m 24s

Average Time

Progress

Accuracy

Efficiency

Accuracy

Efficiency

	1	Normal Sinus Rhythm Normal Sinus Rhythm
	2	Sinus Bradycardia Sinus Bradycardia
	3	Sinus Tachycardia Sinus Tachycardia
	4	Re-entry Re-entry
	5	Atrial Fibrillation Atrial Fibrillation
	6	Atrial Flutter Atrial Flutter
	7	Heart Block - First degree Heart Block - First degree
	8	Heart Block - Second degree Type 1 Heart Block - Second degree Type 1
	9	Heart Block - Second degree Type 2 Heart Block - Second degree Type 2
	10	Heart Block - Third degree Heart Block - Third degree
	11	Junctional Rhythm Junctional Rhythm
	12	SVT (supraventricular tachycardia) SVT (supraventricular tachycardia)
	13	VT (Ventricular Tachycardia) VT (Ventricular Tachycardia)
	14	Ventricular Fibrillation Ventricular Fibrillation

Atrial Fibrillation

Atrial Fibrillation (also known as "AF" or "a. fib")

Diagnostic criteria: (boldfaced with * indicates an important feature)

Rate: any
* Rhythm: irregular with no pattern
* P waves: none - a wavy chaotic baseline is present
* PR interval: no P waves
QRS: narrow

Do not confuse atrial fibrillation with ventricular fibrillation. They are very very different.

Electrophysiology

The origin of atrial fibrillation is the atria. That is why the word "atrial" is in the title. This rhythm does not come from the sinus node. One way to think of atrial fibrillation is that there are numerous little chaotic electric circuits within the atria, each forming a random pacemaker:
multiple atrial re-entry circuits

Each of these pacemakers is firing off signals at random down to the AV node. Because these signals are all random, the "baseline" of the ECG appears to be a wavy chaotic baseline. There is no isoelectric baseline in atrial fibrillation.

wavy baseline

Also, there are no P waves. At random locations, it might appear like the occasional P wave can be seen, but these are not P waves; they are random changes in the chaotic baseline that simply mimic a P wave. Do not be tricked. You are smarter than that!

The number of electrical signals being generated in the atria is very high; as high as 300-500 per minute. This is far more than the AV node can conduct, so many of these impulses are blocked by the AV node. This is a good thing; if the AV node conducted all of them, the ventricular rate would be very high and would not have enough time to fill with blood between heartbeats. This would result in an empty beating heart with no blood being ejected.

Frequently, the heart rate with untreated atrial fibrillation is high.

Because these chaotic impulses from the atria bombard the AV node in a random pattern, the AV node conducts a fraction of these impulses also in a random pattern. This is why the ventricular rhythm in atrial fibrillaiton is irregular with no pattern.

Clinical Significance:

Atrial fibrillation is very common. It is more common in older patients.

Some conditions associated with an increase in atrial fibrillation:

any structural heart abnormalities, especially valve diseases and enlarged atria
hypertension
acute myocardial infarction
hyperthyroidism
alcohol consumption

Treatment of atrial fibrillation:

convert back to sinus rhythm with anti-arrhythmic drugs or electrical cardioversion
reduce the ventricular heart rate if too fast, using drugs that reduce AV node conduction (beta blockers, calcium channel blockers, and digoxin)
anti-coagulate because the atria do not mechanically contract and therefore blood can pool and clot in the atria

Examples:

In this example, the rate is slower (probably with drugs) and the wavy baseline is easily seen.
Do you see P waves? No, you do not. Even if you think you do, you still do not.

In this example, the wavy baseline is much less pronounced, but still present. The rhythm is irregular with no pattern so if you thought this looked like a junctional rhythm, the rhythm is a very important detail to help you differentiate them.

This is very fast atrial fibrillation.

So it this. The rhythm almost looks regular, but it is not when you look closely.

The QRS is wide in this example of atrial fibrillation. There are also T wave and ST segment abnormalities. Note that a wide QRS is not a requirement for the diagnosis of atrial fibrillation, but a second problem that causes a wide QRS can co-exist with atrial fibrillation. Therefore, atrial fibrillation does not always have a narrow QRS, but when the QRS is wide, it is caused by a second diagnosis.