ECG rate and rhythm

Video summary

The heart is a muscle that regularly beats to pump blood throughout the body. An electrocardiogram (ECG) is a test that records the electrical activity of the heart, which shows how fast and strong the heartbeats are.

The heart rate refers to the number of contractions of the heart per minute. This one can vary according to an individual's age, but usually, the normal heart rate for adults falls between 60 and 100 beats per minute. The rhythm refers to the pattern of electrical impulses that cause the heartbeat. The normal cardiac rhythm is a regular sinus rhythm, which means that each heartbeat follows a predictable pattern. There may be abnormal rhythms, such as atrial fibrillation and ventricular fibrillation, both serious and life-threatening conditions.

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Introduction0:00–0:54

An electrocardiogram or ECG or electrocardiogram or EKG in German is a tool that allows us to visualize the heart's electrical activity.
A 12 lead ECG uses multiple electrodes placed around the body, which are combined in specific ways to create electrical views of the heart, called leads.
There are 6 chest leads and 6 limb leads, and each one captures the heart's activity from a different angle. With each heartbeat, the ECG records the electrical signals, including depolarization, which is the activation of the heart muscle.
And repolarization, which is the recovery phase. Now, to read an ECG there are a few key elements to keep in mind.

Heart Rate0:54–5:43

One of which includes figuring out the rate and rhythm. There are a couple of ways of figuring out the heart rate on an ECG, but before we proceed, we need to define what you're looking at.
On an ECG strip, each heartbeat shows up as a QRS complex, which represents the electrical activity when the ventricles contract.
The tallest and most noticeable part of this complex is the R wave, which is usually easiest to spot and count, especially in lead two.
The first method to calculate heart rate is the box method. Because you count the number of boxes between heartbeats.
Each small box represents 0.04 seconds, and each big box is five small boxes, so a big box equals 0.2 seconds. So to calculate the heart rate, you count the number of small boxes between two R waves in lead two.
Let's say there are 4 big boxes and 1.5 small boxes between two R waves. Since we have 4 big boxes, that means 4 times 5, plus that extra 1.5, which gives us 21.5 small boxes.
Since each small box equals 0.04 seconds, we multiply 21.5 by 0.04, meaning there are 0.86 seconds between heartbeats. So, one heartbeat happens every 0.86 seconds.
Now, to get that heart rate in beats per second, we take the inverse. We divide one by 0.86, which gives us about 1.16 beats per second.
Next, to get the heart rate in BPM, multiply this number by 60, because a minute has 60 seconds. So 1.16 times 60 equals around 70 BPM.
Now, moving on to the 2nd method. Here, instead of counting the small boxes, you can count the number of big boxes and divide 300 by that number.
Why 300? Well, because there are 300 big boxes in one minute.
If we do the math, 60 seconds divided by 0.2 seconds per big box equals 300. In our example, we have about 4.3 big boxes between our waves, so we should divide 300 by 4.3, which is around 70 BPM.
The same answer. Now, if the distance between two R waves is exactly one big box, then the heart rate would be 300 BPM.
If R waves are two big boxes apart, the heart rate is 150 BPM. Three big boxes apart is 100, 4 is 75, 5 is 60 BPM, and so on.
Remembering these numbers makes it easier to quickly estimate the heart rate. For example, if you see 3 to 4 big boxes between R waves, you can tell the heart rate is somewhere between 75 and 100 BPM.
Another way to figure out the heart rate is the R wave method. Here, you count the number of R waves in 10 seconds of the ECG strip, then multiply that number by 6.
Why by 6, you ask? Well, because 10 seconds times 6 equals 60 seconds, or 1 minute.
And we want BPM, not per 10 seconds. So, if you count 15 R waves, the heart rate is 15 times 6, which equals 90 BPM.
This method is especially useful for irregular rhythms, where the distance between heartbeats keeps changing. Because the spacing between R waves varies so much, the other methods don't work well.
Now that we know how to measure heart rate, let's talk about rhythm. On a normal ECG each heartbeat follows a smooth, predictable pattern.
First, there's the P wave, then the QRS complex, and finally the T wave, all spaced evenly. Almost like they were copied and pasted one right after another.
This steady pace shows that the heart rhythm is regular. But when the beats come early or late, the rhythm becomes irregular.
To check this, focus on RR intervals, which refer to the distance between the peaks of consecutive R waves in QRS complexes.
If the RR intervals are consistent, the rhythm is regular. However, if they stretch, Or shrink, the rhythm is irregular.
Now, when rhythms are irregular, they fall into specific patterns. Some are regularly irregular, meaning there's a repeating pattern to the irregularity.
Others are irregularly irregular, completely random, with no pattern whatsoever. Complete chaos.
Finally, there's occasionally irregular rhythm, which is mostly regular, but with random interruptions. These interruptions are usually ectopic beats, which come from abnormal spots in either the atria or ventricles.

Rhythm5:43–7:59

Once you figure out whether the rhythm is regular or irregular, the next step is to check the PQRS relationship. Normally, the sinoatrial or SA node acts as a natural pacemaker that fires a signal that initially travels through the atria, causing them to contract.
On the ECG this contraction shows up as the P wave. Next, the signal continues through the atrioventricular or AV node, down the bundle of hiss, through the bundle branches, eventually reaching perkinji fibers.
This path carries the signal from the essay node to the ventricles, triggering their contraction, which shows up as the QRS complex.
Now, in normal sinus rhythm, you should see one P wave before every QRS complex, and every P wave should be followed by a QRS complex.
Also, the PR interval, which is the time between the start of the P wave and the start of the QRS complex, should stay consistent from beat to beat.
If this 1 to 1 relationship breaks down, it usually means one of two things. Either another area of the heart has started firing signals, overriding the rhythm the SA note is orchestrating, or the normal signal is getting blocked somewhere along its way.
Let's start with ectopic beats, or in other words, cases where abnormal spots in the heart begin firing electrical signals.
First, let's start with premature atrial contractions, or PACs. In this case, the P wave changes shape with each beat.
For example, one might be upright, while the other is inverted. This suggests that the signal isn't coming from the SA node, but from an ectopic focus somewhere else in the atria.
However, the signal still travels through the AV node down its normal path, so the QRS complex remains unchanged. On the flip side, we have premature ventricular contractions, or PVCs.
In this case, the ectopic focus comes from the ventricles and completely bypasses the normal conduction system. Since this signal is not coming from the atria, there's no P wave preceding the QRS complex, and the QRS complex itself is completely disorganized and wide.

Review7:59–14:01

The complex is followed by a compensatory pause, because the heart requires a brief break to recover its normal rhythm. Keep in mind that PVCs are common, and most people have them occasionally.
However, if they are frequent or come in runs, that's when we worry. Speaking of runs, if a person experiences 3 or more PVCs in a row at a rate over 100, that's ventricular tachycardia, or VTAC.
This is where things get serious, because VTA can quickly deteriorate into ventricular fibrillation, where the heart just quivers instead of pumping.
All right, so those are problems with abnormal firing. But in some cases, the SA node works just fine, but the signal gets blocked along its usual path.
This brings us to conduction blocks. First, we have AV blocks, where the signal struggles to pass through the AV node.
First-degree AV block is like a traffic slowdown. Every signal gets through, but it takes longer than usual.
The ECG shows this delay is a prolonged PR interval, greater than 0.20 seconds. Also, each P wave is followed by a QRS complex, meaning each atrial beat leads to a ventricular beat.
In 2nd-degree AV block, some signals pass through the AV node, while others don't. So the ventricles occasionally miss a beat.
Here, we have two subtypes. In Mobit's type 1, the AV node gets progressively tired, causing each signal to take more time to pass through.
On ECG you'll notice the PR interval getting longer with each beat until the AV node completely blocks the signal. As a result, the ECG will show a P wave with no following QRS complex.
Then the cycle starts again. On the other hand, in Mobit's type 2, The PR intervals remain steady, and each P wave precedes a QRS complex.
But suddenly, with no warning, the AV node blocks the signal entirely. This leaves the ventricles silent for a beat, so the ECG misses a QRS complex.
Finally, 3rd degree AV block or complete heart block occurs when the electrical connection between the atria and ventricles completely breaks down.
The atria and ventricles start beating independently, like two people dancing to completely different songs. On the ECG You'll notice P waves and QRS complexes marching along with no coordination.
Finally, we have bundle branch blocks. In this case, the signal passes through the AV node just fine, but then hits a roadblock in one of the bundle branches.
The ventricles still depolarize, but they take longer than usual. On the ECG this delay shows up as a wider QRS complex, lasting more than 0.12 seconds, or over three small boxes.
Finally, let's talk about two common types of atrial arrhythmias, including atrial flutter and atrial fibrillation. In atrial flutter, a single ectopic focus in the atria fires at about 200 to 350 times per minute.
Creating the characteristic sawtooth pattern on ECG. But the AV node can't keep up.
So, it only lets every 2nd, 3rd, or 4th signal pass through. This is called the conduction ratio.
For example, a 2:1 conduction ratio means that every second signal passes through the AV node. So if the atria beats 300 times per minute, and the AV node conducts every other signal, the ventricles beat at 150 times per minute.
This filtering action by the AV node protects the ventricles from beating extremely fast. Now, to calculate the atrial rate, use the same box method, but count P waves instead of R waves.
If they're one big box apart, that's 300 times per minute, which is typical for flutter. Next, is atrial fibrillation, where multiple areas in the atria fire chaotically at 350 and 450 BPM.
It's like popcorn popping, totally random. As a result, the atria never depolarizes as they should.
So, there are no distinct P waves, just a wavy, erratic baseline. These chaotic signals from the atria bombard the AV node, but only some get through the ventricles.
On an ECG this creates an irregularly irregular rhythm with no pattern to the RR intervals. All right, there's a quick recap.
For regular rhythms, One quick way to estimate heart rate is to divide 300 by the number of big boxes between R waves. For irregular rhythms.
We count all the R waves in a 12th strip and multiply by 6. On the flip side, to check if the rhythm is regular or irregular, look at the RR intervals.
Consistent spacing between them suggests the rhythm is regular, while variations between them imply irregular rhythm. Finally, there's occasionally an irregular rhythm, which is mostly regular, but with random interruptions, like from ectopic beats.