Abnormal EKGs

Abnormal rhythms

In general, the frequency of the QRS wave—how many of them per minute—reflects the heart rate. For example, everybody has what’s called a sinus rhythm, which is the normal heart rate. For some people, it’s low (usually athletes), and for some people, it’s high. What happens if your heart rate goes high? We call that tachycardia. It is a high heart rate. You would expect to see more cardiac cycles on the EKG paper. That’s what we see here.

Notice the background of this diagram—it’s EKG paper, so we are talking about the same intervals. If your heart rate dips below normal, that’s called bradycardia, a low heart rate. You would see fewer cardiac cycles per minute. You can also have an abnormal rhythm, where each of the QRS waves is not spaced out equally. For example, you might get a heat wave and then another one right after. That’s an abnormal rhythm.

Junctional Rhythm

The P wave corresponds to the SA node depolarizing or firing an action potentialA rapid, temporary electrical charge that travels along neurons, allowing signal transmission. and spreading throughout the atria. When a patient has a non-functional SA node, there is no P wave on the EKG.  It’s just not there.  The heart can still contract, because the AV node is setting the rhythm.  In this case, we’d call this a junctional rhythm.  It can be a challenge to differentiate the P and T wave, something that can only be refined by experience.  Just don’t feel badly if you can’t tell yet. 

Afib and Vfib

Afib and Vfib are bad.  These events are when there are action potentials happening randomly.  These action potentials are not happening in a way to provide the heart with that functional synctium.  The SA node could be misfiring, the AV node could be misfiring, or even the AV bundle and branches.  No matter which structure of the cardiac conductionThe transmission of nerve impulses along neurons. system, it is misfiring.  If the SA node is misfiring, the AV node will be setting the pace of the QRS wave.  The P wave on an EKG reflecting atrial fibrillation will be all over the place.  There will be too many and they will not be of equal heights.  What happens is the atria are not playing nice with the vents and squeezing blood into them.  Blood gets caught in the atria, creating blood clots.  This is why blood thinners are used for afib.

Vfib is similar.  This is when the vents aren’t playing nice.  The QRS wave is unpredictable in height and frequency.  This obscures the P wave despite the factA statement based on direct observation that is repeatedly confirmed. that the atria are probably working correctly.

Heart Blocks

Heart blocks are difficult to understand, even for me.  The name refers to a block between the atria and ventricles. It may also indicate a problem with the AV bundle, both AV branches, one AV branch, or the Purkinje fibers.  This is why there are so many heart blocks.  Discussing diagnoses with these heart blocks is beyond this class. Let’s just look at the EKGs here. We can compare them to a normal EKG.  This will help us narrate these features.  Take a look at all 3 of the 2^nd degree heart blocks. 

They all involve this really long interval here.  At first, you might think it’s an interval between a T wave and a P wave, but it isn’t.  Look.  There are two P waves.  P waves reflect atrial contraction. The QRS reflects ventricular contraction. In this one cardiac cycle, the P wave indicates atrial contractions. The QRS reflects ventricular contraction. Therefore, there are two atrial contractions. Every ventricular contraction is accompanied by two atrial contractions.  That is….not right.  For these first two types of 2^nd degree heart block, it seems like this double contraction happens occasionally. However, for this 3^rd type of second degree heart block, it seems to happen in every cardiac cycle. These are all just observations of the EKG with connection to the events happening.

PVC

Premature ventricular contractions (PVCs) are another anomaly. These contractions affect the QRS wave, making it look distorted. PVCs may occur due to delays in the heart’s pumping rhythm, often from external stimulants like caffeine. They are not usually harmful in a healthy heart.

Ventricular Septal Defect

Sometimes surgery for a VSD can just do more damage than good.  Because the AV bundle and both branches innervateTo invade a tissue with nervous tissue is to innervate it. the interventricular septum, they are at risk.  If they become completely disconnected, the atria will contract without regard for the ventricles. If they are already disconnected at birth, the atria will contract without regard for the ventricles. The ventricles will contract without regard for the atria.  The SA node will set the sinus rhythm for the atria, making them contract at about 80 beats per minute.  The AV bundle will set the rhythm for the ventricles at about 40 bpm. This rate is pretty much half of what the SA node is doing.  We have the top half of the heart contracting at twice the rate of the bottom half.  The atrial contraction is represented by the P wave. The ventricular contraction is represented by the QRS wave. We’d have 2 P waves for each QRS wave.