If there is one thing we afibbers have in common is our obsession with our hearts. And if you’re anything like me, you use your Kardia Mobile heart monitor on a fairly regular basis to get an ECG reading of your heart. If you’re not using the Kardia device I’ll bet you get at least one ECG done a year when you visit your doctor.
It has always driven me crazy that I don’t know what an ECG really is or what I’m looking at when I look at one. I hate it when I’m in the dark and don’t understand something. My ignorance on this topic has driven me to spend time learning more about ECGs so I at least have a basic understanding.
The first thing I did was purchase the book, “A 1st Book on ECGs – 2014,” by Ken Grauer, M.D.
As it says on the front book cover, it’s a book “for beginning and novice interpreters – and others who just want to know.” I’ve been very impressed with the book so far and I highly recommend it to people with atrial fibrillation if they want to have a better understanding of ECGs.
Why You Should Care About Understanding ECGs if You Have Atrial Fibrillation
As I mentioned in the opening paragraph of this article, if you have atrial fibrillation there is a good chance you take ECGs using a consumer-grade heart monitor such the Kardia Mobile or you have one done by your doctor at least once a year. Wouldn’t you feel more empowered if you at least had a general understanding of what an ECG is and what your ECG readings mean?
Second, as an afibber there is a very good chance you battle (or will battle) other arrhythmias such as PVCs, PACs, SVT, and even atrial flutter. Let’s face it, we have defective hearts so our tickers don’t always tick the way they should. If you can learn to at least spot common arrhythmias such as PVCs and PACs it’s going to give you peace of mind.
How so? Well let’s say your heart just doesn’t feel right so you take an ECG reading with the Kardia Mobile. It flags it as “possible atrial fibrillation” or “unclassified.” That alone is probably going to freak you out. But what if you could look at your ECG and guesstimate that you’re only having a few PVCs or PACs because you have a basic understanding of reading ECGs? You’re probably going to be more at ease.
I say “guesstimate” because I don’t expect you’ll become an expert ECG interpreter. In fact, you may never be able to 100% accurately interpret your ECG. Most of us won’t. You’ll still need to verify your ECG readings with your doctor or take advantage of the ECG interpretation services provided through the Kardia Mobile app. While you wait for verification, however, you can have peace of mind knowing that it’s probably just benign PVCs or PACs.
I always tell people who are newly diagnosed with a-fib that the first thing they need to do is empower themselves by getting educated on ALL aspects of atrial fibrillation – and that includes familiarizing yourself with ECGs. With that said, let’s dive in…
ECG or EKG? ECG is the abbreviation for ElectroCardioGram. EKG is the abbreviation for ElektroKardioGram, which is the German spelling. They are one in the same. It seems the general public tends to use EKG while nurses, doctors, etc. prefer ECG. Take your pick.
Electrical System of the Heart
From this point forward I enlisted the help of a resident physician who has extensive knowledge with ECGs and ECG interpretation to help me finish this article. Parts of it may get a little technical but hang in there. It will hopefully make sense!
Before we dive into the ECG, it’s important to understand how the heart works. Something has to trigger or stimulate the heart to get it to work. That “trigger” is an electrical signal that originates from the heart’s natural pacemaker, the sinoatrial node, or SA Node. The SA Node is found at the top of the right atrium. When the heart muscle is electrically stimulated, it contracts.
The signal goes from the SA node and travels across the atria (top two chambers of the heart) along the anterior internodal tract, middle intermodal tract, posterior internodal tract, and Bachmann’s bundle causing the atria to contract.
The electrical signal then moves to the atrioventricular node, or AV Node, where there is a pause. Then the electrical signal travels across the ventricles (bottom two chambers of the heart) along the left and right bundle branches causing the ventricles to contract. This pause between the stimulation of the atria and ventricles causes the atria to contract first, followed by the ventricles.
What is an ECG?
The ECG measures electrical impulses from the heart which represent various stages of cardiac stimulation. When using a portable ECG device like the Kardia Mobile, you are completing a circuit across your heart with a negative side on one finger and a positive side on the other finger. Heart muscle cells are negatively and positively charged as the heart beats, so the state of electrical activity in the heart can be gauged using this circuit. This is the same principle used by ECG measurements in a hospital setting.
The Normal ECG and Your Heart Beat
Remember, the ECG is an electrical recording of the conduction across your heart. When enough electrical potential is reached by the heart muscle cells, they will recruit the rest of the muscle cells around them and contraction will occur.
Let’s take a look at this ECG:
Image Source: By Created by Agateller (Anthony Atkielski), converted to svg by atom. (en:Image:SinusRhythmLabels.png) [Public domain], via Wikimedia Commons
The P wave represents the electrical activity of the atria, with contraction of both atria as the electricity spreads from the sinoatrial node between the P wave and R wave “PR interval”. Then as the electrical activity moves to the atrioventricular node, there is a pause between the P wave and the Q wave which allows the ventricles to fill.
The QRS wave or “complex” represents the portion of the ECG where electrical activity spreads from the atrioventricular node to the ventricles. The Q wave is the first downward stroke and is often not present. This is followed by the R wave which the first upward stroke, then the S wave which is the second downward stroke.
Between the R and S waves the first heart sound “thump” is heard as the A-V valves (tricuspid and mitral valves) close and the aortic and pulmonary valves open with a slight delay. There is then a pause after the QRS complex as the ventricle muscle contracts and blood rushes out the aorta into the body and the pulmonary artery into the lungs.
The T wave follows this pause. This is the portion of the ECG where the ventricle begins to recharge (but is still contracted). At the end of the T wave, ejection of blood from the ventricle has completed. The second heart sound “thump” is then audible as the aortic and pulmonary valves close and the A-V valves open, again with a slight delay.
Between the end of the T wave and the next P wave, the A-V valves stay open and the ventricles relax as they fill with blood. Then the cycle repeats itself, with the atria contracting after the P wave and so on.
I don’t know if you caught that but the sound you hear when your heart beats – the “thump thump” – is actually the valves in your heart closing!
This entire electrical process is called the cardiac cycle and is represented in the diagram below:
Every heart beat is one cardiac cycle and is represented by the P, Q, R, S, and T waves on an ECG. Adults will have 60-100 cardiac cycles per minute, or 60-100 beats per minute, which is your resting heart rate.
Here is a great video that explains the electrical process and the ECG:
Normal Variation in ECG Patterns and ECG Types
Keep in mind again that you are closing a circuit when placing your fingers on a portable ECG. Positive charge is displayed in the up direction, while negative charge in the down direction. Switching the side your fingers are placed on the Kardia Mobile monitor may flip the appearance of the graph, as instead of going negative to positive charge you are now going positive to negative.
In other words, if you hold the monitor one way you’ll get an ECG you’re accustomed to seeing like this:
If you turn the monitor around so that the end of the monitor you placed your right fingers on are now on the left side with your left fingers on it, you’ll see an upside down ECG like this:
If you look at your ECG from the Kardia Mobile app and it’s upside down you’ll now understand what’s going on. Fortunately, the Kardia app has a feature that allows you to invert your upside down ECG reading so no matter how you hold it you can always get a “normal looking” ECG.
Leads vs. Electrodes
One distinction that needs to be made before continuing is that a lead and the actual electrodes placed on your body to do an ECG reading are different. A “lead” is a single ECG picture. For instance, single lead devices will have two electrodes at least, or in the case of Kardia devices two contact points (your left and right fingers).
A traditional 12-lead ECG that your doctor will conduct requires 10 electrodes placed on the body. The following diagram demonstrates where the 10 electrodes are placed:
These are the angles measured in a traditional 12-lead ECG:
The following ECG strip is a read-out from this placement of 10 electrodes. This is the way that ECGs are read in the clinical setting and it provides a more complete picture of what is happening. The 12 leads, or “ECG pictures,” are shown in the ECG strip marked as I, II, II, aVR, AVL, aVF, V1, V2, V3, V4, V5, V6.
Consumer devices like the Kardia will show a single lead readout only, which is best approximated by the “Lead I” readout in the upper left-hand corner of the diagram above. The Lead I readout from a device like the Kardia simulates the placement of “RA” and “LA” electrodes on your body except with the Kardia you are placing your right and left fingers on two electrodes. The RA and LA electrode placement are shown in the electrode placement diagram shown earlier.
In the consumer device realm, as lead number increases more angles are measured over the heart. There are also 3 and 4 lead consumer devices, while 5 lead “Holter” monitors will often be sent home with patients. The number of electrodes will depend on how many of the leads are calculated versus direct measurement, which is entirely based on the software and manufacturer.
Each lead you add will build more and more of the picture obtained by a traditional 10 electrode 12 lead ECG and become increasingly useful to yourself and clinicians. The best way to think of this is as each angle or picture is added you move from a one dimensional to a two or three dimensional representation of the heart, and abnormalities can be more easily pinpointed.
The Value in Understanding the Basics of ECGs
With a basic understanding of ECGs you’ll have a better understanding of what’s going on with your heart when you review your own ECG using portable ECG devices such as the Kardia Mobile. You may even be able to determine if certain abnormal rhythms are present so you can notify your doctor accordingly.
It’s important to note, however, that these single lead devices like Kardia DO NOT replace the traditional 5-lead Holter monitor or the 12 lead ECG your doctor would provide. In fact, they are inferior in that they don’t provide the detail a doctor will need to provide a specific diagnosis. They are only a starting point for you and your doctor.
The idea is you learn the basics of ECGs so that you can have a better understanding of what’s going on with your heart and so you can have an intelligent discussion with your doctor. In short, knowing the basics of ECGs can empower you and make you a more informed patient!
Be sure to read my other post on basic ECG interpretation of common arrhythmias.