ECG'S Made Easy!
Learners seem to fall into two groups when it comes to ECGs, they are either fascinated or terrified by them! Whichever group you fall into, hopefully you'll find the following helpful in your journey into decoding them!
On this page.....
Underlying Principles of an ECG
Trust me, ECG's became a lot less confusing once you understand a little about what exactly their looking at and how they work! This section aims to give you the bare minimum of biology and technical knowledge required to get you started. If your completely new to ECG's (or really confused by them...) I really recommend you start here!
'Oversimplified'
The Plumbing and the Electrics
We can think of the cardiovascular system as the plumbing of the body. The blood vessels are the pipes, allowing the blood to flow around the body, and the heart is the pump that's pushing the blood through the system.
Having a 'pump' that's in good working order is obviously pretty essential. The trouble is the heart its self is hidden inside our chests. What we can see however, is the electrics that power it. The beating of the heart is controlled and regulated by the electrical current that flow trough the muscle.
Cardiac Conduction
refers to the specialised cells that spread across the top surface of the heart, transmitting the electricity that makes it beat. We can easily observe this flow of electricity using an ECG. Monitoring electrical activity allows us to make sure that the electrics are working as they should be, as well as telling us how the heart is behaving eg. is beating quickly or slowly? We can monitor this electrical activity through electrodes on the patients chest.
P, 'QRS' and T
The 'bumps' and spikes represent the different parts of the heart as it contracts.
-The small bumps (p-waves) represent the top chambers (atria) as they contract. Pushing blood into the lower chambers.
-The larger, 'spikey bits' (QRS complexes), represent the bottom chambers of the heart (ventricles) as they contract, pushing blood around the body.
- The second, slightly larger bump (t-wave) represents the the cells involved in transmitting electrical signals 'resetting them self's' (repolarising), so their ready to transmit electricity once again.
Interpreting a 'normal' Sinus Rhythm
It can be very helpful to know what's 'normal' before you start to learn what abnormal!
With this in mind, a normal sinus should be the first rhythm that every learns. Normal sinus represents a heart whose electrics are operating as we'd expect.
'Oversimplified'
we don't have to be an expert in ECG's to have an opinion as to whether they look normal or not.
The rate. To fast? to slow? or just right....
The bottom axis on an ECG represents the passing of time. Do the complex's look unusually close together? Then the rhythm is probably fast (tachycardic). Are the complex's unusually wide apart? Then the rhythm is slow (bradycardic).
Is the rhythm regular?
when operating normally, we expect the sinus node of the heart to produce electrical impulses at very regular intervals. We would therefore expect the p-waves (contractions of the atrium) to be
spaced at regular intervals along the length of the ECG. Are some of the p-waves close together than others? Then the heart is probably in an irregular rhythm. The same logic can be applied to the QRS complexes (ventricular contractions). If there irregularly spaced then the heart can not be considered to be beating regularly.
Is everything in the right order?
If everything is working properly then we would expect the atria to contract first, resulting in a p-wave, followed by the ventricles, resulting a QRS complex. work along the length of the ECG from left to right (like your' reading a sentence). Are there multiple p-waves without a QRS complex? Can you see lots of QRS complexes and no p-waves? Then something isn't right.
If you perform an ECG for a patient it is essential that you show it to someone skilled in interpreting them! Don't just stick them in the notes! something important (potentially life-saving) may be missed!