Basic ECG/EKG Interpretation of Common Arrhythmias

In a previous post I covered the basics of an ECG. In this post I’m going to discuss the most common heart arrhythmias my readers seem to encounter. Atrial fibrillation is the obvious one but the others include atrial flutter, SVT, PVCs, and PACs.

I’m a strong believer in empowering patients by arming them with information to help them better manage their health. This post will be particularly helpful for those of you that have the Kardia Mobile heart monitor as it might help you recognize the most common abnormal heart rhythms outlined earlier.

Please note, this post barely covers the basics of ECG interpretation. Doctors, nurses, and technicians that interpret ECGs for a living have had years of experience and have viewed thousands of ECGs in their careers. This post is less than 1,800 words in length so by no means am I implying that you’ll be able to read this post and interpret your own ECGs! Furthermore, you should never make medical decisions based on your own ECG interpretation (unless you are trained to interpret ECGs). Always consult with your doctor before making any medical decisions!

What I Want to Accomplish with This Blog Post

My goal with this post is two-fold. First, I want to show you what these common arrhythmias look like on an ECG. If you know what they look like you may be able to spot them on your own ECG and a result you might have a little more peace of mind.

For us afibbers, our hearts just don’t function like normal hearts. When we’re not battling afib we are likely battling other arrhythmias such as PVCs and PACs. When our hearts don’t feel right we reach for the Kardia Mobile monitor and take a reading to see what’s going on. If we’re having anything but a normal rhythm it will say “Possible Atrial Fibrillation” or “Unclassified.”

Which is it then – atrial fibrillation or some other arrhythmia? Panic sets in and before you know it your heart is pounding harder and racing faster than ever. Instead, what if you could look at your ECG and identify what you believe are “just PVCs and PACs?” You’d probably feel more at ease, right?

Now having said that I DO NOT recommend you rely on your own interpretation! In this same example, rest easy assuming you’re just having PVCs and PACs but by all means confirm that with your doctor or by using the Kardia app’s ECG analysis service! You are not an expert on ECG interpretation and analysis so do not make medical decisions without your doctor!

The second goal of this post, and the most important, is I hope this post (as well as my previous post on ECGs) motivates you to seek out more information on ECG interpretation. Knowledge is power and the more you know about ECGs and interpreting them (even on a novice level) the better off you’ll be – especially if you’re going to be using the Kardia Mobile or similar device.

Lead II vs Lead I ECG Tracings

Consumer ECG devices such as the Kardia Mobile monitor are single lead devices and therefore only provide Lead I ECG tracings. When you have an ECG done at your doctor’s office they use a 12 lead ECG. A 12 lead ECG provides 12 different tracings which includes Lead I and Lead II.

It’s not important in this post to know all the ins and outs of Lead I vs. Lead II tracings. The important take away is that the ECG for a Lead I ECG strip from a device like the Kardia will look different than a Lead II ECG strip from a 12 lead ECG as you’ll see in the examples to follow. For each ECG image shown in this post, it is clearly labeled as “Lead I” or “Lead II” so you know what type of ECG you’re looking at.

All the Lead II images provided in this blog post are provided courtesy of LifeInTheFastLane.com. They have an awesome ECG library and were kind enough to allow me to use their images.

Normal Sinus Rhythm (NSR)

Before we look at ECG examples of abnormal rhythms let’s take a look at an ECG for normal sinus rhythm (NSR), which is a normal heart beat.

Lead I Example of NSR (from the Kardia Mobile device)

Lead II Example of NSR

See Normal Sinus Rhythm on LifeInTheFastLane.com

Atrial Fibrillation (A-Fib)

For us afibbers, this is familiar territory. Recall from my previous article that electrical impulses for the atria normally originate in the SA node. Instead, afibbers have electrical impulses that originate primarily from the pulmonary veins which overwhelm the rhythm set by the SA node.

The ECG for a-fib can look differently depending on how fast the a-fib is going. What you need to look for is an abnormality in the P waves which are truly fibrillary waves, appearing out of rhythm with the QRS complex. Here’s what a-fib looks like on Lead I and Lead II:

Lead I Example of Atrial Fibrillation (from Kardia Mobile device)

Lead II Example of Atrial Fibrillation

See Atrial Fibrillation on LifeInTheFastLane.com

Atrial Flutter

When the SA node conducts electrical impulses to the atria, the signals become “trapped” and circulate rather than propagating out to the rest of the heart. Sometimes these signals can begin in the atria themselves as well. This results in the atria conducting very rapidly in comparison to the ventricles, sometimes as much as 200-400 beats a minute. The ventricles will pick up any signals up until roughly 180 beats a minute, and after that they will “block” heart beats.

This will usually happen every second atrial beat (2:1) but there can be as many as four atrial beats per QRS complex (4:1). In single lead ECG devices multiple P waves may be noted or due to the angle it may be difficult to see the P waves at all. In the following lead II example you can observe an atrial flutter with 3:1 heart block. Note the saw-tooth pattern as well, which can be observed sometimes.

Lead II Example of Atrial Flutter

See Atrial Flutter on LifeInTheFastLane.com

Many of the same issues that a-fib sufferers can develop are shared by atrial flutter. However, atrial flutter is much faster and because of this can be very dangerous for those that have abnormalities in the conduction system of their heart. The fear is that the impulses from atrial flutter can sometimes bypass the “block” mentioned earlier, resulting in very rapid ventricular beats that can be fatal.

Supraventricular Tachycardia (SVT)

There are many types of SVT, but the cause is deranged electrical activity in the top part (atria) of the heart. The origin is described in the name as well, “supra” meaning above and “ventricular” the ventricles. Sometimes this is due to the atria firing such as in atrial fibrillation or atrial flutter, other times the AV node itself fires. The following is an example of how SVT may look, involving rapid QRS complexes that are narrow. Note that in this example of the T waves are hiding in the P waves.

Lead II Example of SVT

See SVT on LifeInTheFastLane.com

These rhythms can be a consequence of long-standing atrial fibrillation or other rhythm abnormalities. Episodes can last minutes to days, with symptoms that include dizziness, shortness of breath, palpitations, chest pain or loss of consciousness.

Premature Atrial Contraction (PAC)

These are instances where the atria are conducted prematurely during the cardiac cycle. They are related to atrial fibrillation and atrial flutter because they are due to a region of the atria conducting a heart rhythm before the next normal heart beat. They can be identified by normal rhythm that occurs prematurely starting with a P wave. Every second beat in this rhythm strip is a PAC, delineated by an arrow (and highlighted). Note the RR interval being significantly longer after each PAC and the P wave appearing differently as the SA node resets.

Lead II Example of PAC

See PACs on LifeInTheFastLane.com

Lead I Example of PAC (from Kardia Mobile)

PACs can originate from one area of the atria “unifocal” or in multiple areas “multifocal.” The examples above are unifocal PACs.

PACs are usually asymptomatic and of little concern in healthy individuals. However, they can be a starting point for atrial fibrillation or atrial flutter to occur in patients that suffer from these conditions.

Premature Ventricular Contraction (PVC)

While PACs originate in the atria, PVCs originate in the ventricles. Specifically, they occur in the fibers that lead into the ventricles from the right and left bundle branches. There are two PVCs in the rhythm strip shown below delineated by arrows, each with different origins within the ventricles (hence why they appear differently).

These are “multifocal” PVCs, meaning they originated from multiple areas of the ventricles. Note each PVC has no P wave and occurs right after the previous beat’s T wave. This indicates that the beat, electrically, did indeed begin in the ventricles. Note also that the RR duration is double normal while the heart resets itself in a full compensatory pause.

Lead II Example of Multifocal PVCs

See PVCs on LifeInTheFastLane.com

PVCs may occur regularly as well, such as in this example of ventricular bigeminy where every other beat is a PVC.

Lead II Example of Ventricular Bigeminy (PVCs occurring every other beat)

Lead I Example of Ventricular Bigeminy (from Kardia Mobile)

Lead II Example of Ventricular Quadrigeminy (PVCs occurring every fourth beat)

Like PACs, PVCs can also trigger episodes of atrial fibrillation or atrial flutter. Most of the time these are benign, but in the setting of having the diagnosis of these conditions it can be concerning. They can also occasionally occur during a-fib, though it is very difficult to determine these beats during an episode. Multifocal PVCs have an inherently increased risk because there is more danger of triggering arrhythmias.

Concluding Remarks on Basic ECG Interpretation

I hope this blog post provides a good starting point for interpreting ECGs for the most common arrhythmias we afibbers will likely experience. I encourage you to dive even deeper in to ECG interpretation – specifically the arrhythmias outlined here: atrial fibrillation, atrial flutter, SVT, PVCs, and PACs. The more you know, the more empowered you will be!

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