EKG Interpretation: Atrial Fibrillation and Atrial Flutter

In this video we’ll be looking at how to interpret an EKG strip, specifically atrial flutter and atrial fibrillation. If you haven’t already, you may want to watch our video on basic EKG interpretation first—it goes into more detailed steps of how to read an EKG strip and is a good refresher.

Interpreting EKG Strips

First we’ll go over a simplified five-step approach to interpreting all EKG strips:

1. What is the heart rate? Count how many R waves in 6 seconds (this is the ventricular heart rate – the QRS complex represents the ventricles contracting).
2. Are there P waves present? Count how many in 6 sec. (this is the atrial heart rate – remember the P wave represents the atria contracting).
3. Are the P waves regular? Measure with calipers or a paper.
4. Are the R waves regular? Again, measure with calipers or a paper.
5. How long is the PR interval? (Normally 0.12-0.20 sec./3-5 small squares) & what is the width of the QRS complex? (normally 0.06-0.12 sec/1.5-3 boxes).

Evaluating a Normal Sinus Rhythm

Let’s evaluate a normal sinus rhythm using these six steps:

1. What is the heart rate? Count how many R waves in six seconds and multiply by 10, or count how many in three seconds and multiply by 20. Here we have 4 R waves in three seconds, times 20, equals 80 bpm (remember normal HR falls between 60-100).
2. Are there P waves present? Since we have three seconds here, we’ll multiply the number of P waves by 20, so four P waves times 20 shows an atrial rate of 80 bpm.
3. Are the P waves regular? Start from the beginning of one P wave to the beginning of the next P wave, measuring with calipers or a paper. In this case, the P waves do measure out to be regular distances apart.
4. Are the R waves regular? Do this again for the R waves and they also measure out equal or almost equal distances apart. There might be a slight variation in length and that is okay, we have to allow for some fluctuation in heart rate.
5. How long is the PR interval? The PR interval (normally 0.12-0.20 sec./3-5 small squares) represents the time it takes an impulse to travel from the sinus node to the ventricles. In this normal sinus rhythm, the PR interval does fall in the normal range.
6. What is the width of the QRS complex? This represents the contraction of the ventricles (normally 0.06-0.12 sec/1.5-3 small squares) and the QRS complex is within the normal range here.

Atrial Flutter

Atrial flutter occurs when the electrical impulses of the heart take an abnormal path through the atria, usually circulating around the tricuspid valve in the right atrium. The atria discharge between 240 to 400 regular impulses every minute. These atrial contractions produce flutter (F) waves that have a sawtooth appearance.

With such rapid atrial contractions, the AV node slows them down, often with every second or third contraction reaching the ventricle. The ventricles often respond to the impulses at a regular rate, therefore the QRS complexes are usually normal and regular. The number of F waves to QRS complexes is expressed as a ratio. For example, in atrial flutter with an atrial rate of 280, and a ventricular rate, or pulse rate, stuck at 70, it is referred to as 4:1 A-V conduction.

Atrial flutter usually indicates underlying disease and may show symptoms of palpitations, shortness of breath, anxiety, or weakness.

Evaluating Atrial Flutter

Now we’ll use the six-step approach to evaluate atrial flutter:

1. What is the heart rate? Counting the R waves (QRS complexes) in six seconds, there are 7, so \(7\times 10=\) a ventricular rate of 70 bpm.
2. Are there P waves present? No, only saw-toothed flutter (F) waves The atrial rate can be figured out by counting the number of F waves in the six seconds and multiplying by 10. There are 28 F waves, so the atrial rate is 280 bpm.
3. Are the P waves regular? There are no P waves, so this doesn’t apply.
4. Are the R waves regular? This is the interval from one R wave to the next. If you use calipers or a paper to mark the beginning of the QRS complex to the beginning of the next QRS complex, you see that the QRS complexes or R waves occur at regular intervals. However, sometimes they can be irregular also.
5. How long is the PR interval? Since there are no P waves, it is not measurable.
6. What is the width of the QRS complex? They are all normal, falling between 0.06-0.12 sec.

Atrial Fibrillation (AFib)

Instead of one impulse moving through the heart as it should, many impulses begin in the atria and fight to get through the AV node. The atria depolarize chaotically at rates of 350-600 beats per minute. These extra impulses trying to get through the AV node cause the atria to fibrillate (quiver and twitch) in a fast and disorganized way.

This chaotic electrical activity results in a chaotic waveform between the QRS complexes. The P waves are absent and are replaced by lowercase “f” waves. No P waves mean there are no PR intervals. The rapid electrical activity overwhelming the AV node causes impulses to enter the ventricular conduction system at irregular points without a discernible pattern, resulting in an “irregularly irregular” ventricular rhythm (R waves).

This irregular heart rhythm can cause symptoms such as shortness of breath, exercise intolerance, heart palpitations, or weakness, but some people experience no symptoms at all. However, if left untreated, the side effects can be life-threatening, leading to stroke or heart failure.

Evaluating Atrial Fibrillation

Now we’ll use the six-step approach to evaluate atrial fibrillation:

1. What is the heart rate? Counting the R waves (QRS complexes) in 6 seconds, there are 7, so \(7×10=\) a ventricular rate of 70 bpm.
2. Are there P waves present? No, only fibrillatory (f) waves The atrial rate is impossible to determine, but is very fast, most certainly >350 bpm.
3. Are the P waves regular? There are no P waves, so this doesn’t apply.
4. Are the R waves regular? If you use calipers or a paper to mark the beginning of the QRS complex to the beginning of the next QRS complex, you see that the QRS complexes or R waves occur at irregular intervals.
5. How long is the PR interval? Since there are no P waves, it is not measurable
6. What is the width of the QRS complex? They are all normal, falling between 0.06-0.12 sec.

Both atrial flutter and AFib are common abnormal heart rhythms. They are both types of supraventricular tachycardia, which means a rapid heart beat occurring above the ventricles. In AFib, the heart beats fast and in no regular pattern or rhythm. With atrial flutter, the heart beats fast, but in a regular pattern—the “sawtooth” pattern.

Review

Let’s do a quick comparison to review.

In atrial flutter, the atrial rate is between 240-400 bpm. In AFib, we are not able to determine the atrial rate. Neither arrhythmia has P waves. Atrial flutter has sawtooth flutter (F) waves and AFib has fibrillatory (f) waves. The R waves in atrial flutter are usually regular, but in AFib they are irregular. Neither arrhythmia has a PR interval, but the QRS width on both is normal.

 
For more videos on EKGs, check out our EKG playlist.