Normal EKG Variants in the Population

Ian Johnson, PA-C

So you mistakenly did it. You looked at the computer interpretation of your patient’s EKG. The EKG doesn’t look perfect, but is it pathologic? As with most findings in medicine, the most important question to answer is “is the patient symptomatic?”. If the answer is no, then let’s review some findings on EKG that although odd, are considered normal EKG variants, and discuss their implications for your patient and practice.

Sinus Bradycardia and Tachycardia

These findings can be completely normal. With bradycardia we traditionally think of young athletes. Their heart is so effective at pumping blood that sympathetic responses are not triggered to increase chronotropy, the rate at which the heart beats. Even in non-athletes, the heart rate may decrease to as low as 30 bpm while sleeping. Caution, age is a big factor here. If you’re patient is approaching or over age 50, then sinus node dysfunction needs to be on your differential, no matter how good of shape they’re in.

Sinus tachycardia, especially with the rate under 110 at multiple different visits, can be completely normal. That’s right, it’s not necessarily a pheochromocytoma or heavy metal toxicity. It can be completely normal. Again, exercise caution with age or lack of history. However, both of these findings can be considered completely normal in the asymptomatic patient.

Sinus Arrhythmia

Don’t reach for the crash cart yet! Ainus arrhythmia can be a completely normal variant. There are several factors that can cause us in an otherwise healthy individual. One cause can be the respiratory phase, or the normal individual heart rate increases with inspiration and decreases with expiration. Additionally, the SA node Can accelerate or decelerate independent of the respiratory cycle. As long as the P waves are normal and rate is within a normal range, these variations in R to R Interval can be normal- say it with me “as long as your patient is asymptomatic”.

Premature Atrial Contractions and Wandering Atrial Pacemaker

Any atrial tissue can depolarize. Premature atrial contractions occur when another region of the atria depolarizes before the SA node and triggers a premature beat. You’ll find 2 differently shaped p-waves on EKG. A wondering atrial pacemaker is identified by finding at least three different P wave morphologies. This indicates 3 areas of depolarizing foci. While the EKG will show an “irregularly irregular” rhythm, the key here is rate less than 100. We typically see this in young athletes and elderly Populations. Both are normal EKG variants as long as… you get it.

PVCs

But wait! The ventricles can depolarize too! PVC’s, initiated by the Purkinje fibers, and cause this appearance on EKG. Although a little more concerning than their atrial counterparts, PVCs can be a normal variant on EKG. Patients may or may not feel PVCs. More than 1 in an EKG may be concerning and should prompt investigation for electrolyte abnormalities.

Axis Deviation

As with most other anatomical structures, the heart is located differently depending on the individual. Leads 1 and aVF should be compared to determine axis deviation. The QRS complex should be upward in both of these leads. Left access deviation, when extreme, can be concerning for left ventricular hypertrophy, electrolyte abnormalities, or inferior MI. However, if less than -30 degrees and asymptomatic, it’s completely normal. Right access deviation in an adult can be concerning for right ventricular hypertrophy as seen in respiratory disorders, however in children is a very common finding on EKG due to smaller heart size. Indeterminate axis, while rarer, is even less concerning.

Left Atrial Enlargement and Left Ventricular Hypertrophy

Similarly, as above, the findings of left atrial enlargement with characteristic P-wave on EKG or left ventricular hypertrophy as demonstrated through increased conduction are not concerning. Both of these conditions may be present in patients with significant heart disease. However, they are not concerning findings in otherwise young healthy individuals.

Incomplete Right Bundle Branch Block

Impulses that pass through the AV node are normally shared between the left and right heart. These impulses travel within the Purkinje fibers. However, occasionally these fibers are dominant in the left, causing right ventricular depolarization to occur through spread of the left myometrium. This can be a completely normal finding in a healthy individual. Seen as the beginnings of characteristic rabbit ear appearance on EKG of the QRS in complete RBBB, if otherwise healthy, there is no cause for concern.

Intraventricular Conduction Delay

Defined as a QRS wider than 0.12 but with no apparent right bundle or left bundle branch block, can also be completely benign.

1st Degree Heart Block

Oh no! It’s heart block in the first degree! A PR interval greater than 200 milliseconds (1 big box), is usually an incidental finding on ekg. If caused by an electrolyte imbalance or drug overdose, it can be concerning. But if it’s something your patient was born with, move on.

Second Degree Type 1 Block

This can be easily see by an increasing PR interval that eventually triggers a skipped beat. This rhythm resets itself without incident. Make sure you don’t confuse this with a second degree type 2 block, which drops beats without a clear pattern! Type 2 second degree blocks are a big deal!

Benign Early Repolarization

I saved my EKG variant favorite for last, here we go again with those young healthy athletes. Elevated j point and ST elevation with characteristic fishhook appearance on EKG, BER occurs in 1-13% of the population and is significantly higher in male elite athletes. Not so benign… If you’re not an elite athlete however, BER in the inferior or inferolateral leads or globally throughout EKG can be a concerning predictor of vfib or vtach. This relationship is thought to be caused by an ion channel imbalance.

It’s rare to encounter a completely textbook normal EKG in practice. Hope this has been a good review of some common non-concerning findings. Above all, remember these are all only benign or normal variants as long as your patient is asymptomatic.

Learn more about these conditions by taking our live Clinical Skills and Procedure Workshop! The PPE program is specially designed for advanced practice providers.