EKG Interpretation, part 10: Other EKG Abnormalities
In this article, we cover some EKG abnormalities that you may see, including a bundle branch block, a sinus pause, escape beats. We also explain the impact of electrolyte imbalances, and cardiac/respiratory disorders on the EKG.
The EKG interpretation video series follows along with our EKG interpretation flashcards, which are intended to help RN and PN nursing students study for nursing school exams, including the ATI, HESI, and NCLEX.
Bundle branch block (BBB)
A bundle branch block (BBB) is an EKG abnormality that occurs when the heart's electrical impulse is delayed in the bundle of His or within the bundle branches.
If you recall from our overview on the steps in the heart conduction system, the electrical impulse originates in the SA node, travels down the AV node, then arrives at the bundle of His, which are a bundle of muscle fibers that transmit electrical impulse. The electrical impulse should transmit through the bundle branches and travel to the ventricular myocardium. If the heart's electrical impulse is delayed within the bundle of His or within one of the bundle branches, it is not arriving at the ventricular myocardium on time to trigger ventricular depolarization (the completed QRS complex).
If the electrical impulse is delayed within the right bundle branch, it is known as a right bundle branch block, and vice versa with the left bundle.
A BBB on an EKG will result in a wide QRS complex, which is over 3 small boxes or greater than 0.12 seconds duration. In the EKG strip shown above, the wide QRS complex indicates a bundle branch block. Because the entire QRS complex represents ventricular depolarization, if the electrical impulse is hung up at the ventricular depolarization step, that's why the QRS complex takes longer to complete (is wide).
If a patient has a bundle branch block but is asymptomatic, then they will usually not require treatment. However, if a patient has a bundle branch block that is symptomatic, they may require an artificial pacemaker or cardiac resynchronization therapy (CRT).
Another EKG abnormality that you should be familiar with is a sinus pause. A sinus pause occurs when the sinoatrial node fails to initiate an impulse. A sinus pause can also occur when the sinoatrial node does initiate an impulse, but the impulse becomes blocked in a way where the atria are prevented from depolarizing.
If you recall from our article on the steps in the heart conduction system, the SA node should initiate an electrical impulse, which stimulates the atria to depolarize, which is then recorded as the P wave.
If you have been following along in this series, you have already seen one type of sinus pause, which occurs during a premature atrial complex.
During a sinus pause, the EKG will skip the P wave, QRS complex, or the T wave. Sometimes after a sinus pause, the EKG will show an escape beat, which we will cover next.
Treatment of a sinus pause is usually not required if the patient is asymptomatic.
An escape beat is an abnormal impulse in the heart that occurs after a sinus pause and occurs late. You can see two examples of an escape beat in this section
A ventricular escape beat can be identified by an abnormally wide QRS complex. A ventricular escape beat is initiated in the ventricle. After the sinus pause, the P wave will be absent, and the QRS complex will be abnormally wide.
A junctional escape beat can be identified by an absent P wave, inverted P wave, or abnormally short PR interval, combined with a normal QRS complex. A junctional escape beat is initiated in the junctional foci at the AV junction.
Treatment of an escape beat is usually not required if the patient is asymptomatic.
Electrolyte imbalances on EKG
Electrolytes are important to overall body functions, including and especially the heart conduction system. Electrolytes are minerals that have electric charge, and the heart relies on them to conduct its electrical impulses to keep itself running. The important electrolytes to know for this section are potassium, calcium, and magnesium.
Need help remembering the normal ranges for these electrolytes? Our Lab Values flashcards for nursing students were purpose-built to help nursing students remember the key labs they need to know throughout their studies and nursing practice. These flashcards cover potassium, calcium, magnesium and many more.
Potassium is an electrolyte important for regulating heart and muscle contractions. The expected range for potassium is 3.5 - 5.0 mEq/L.
If a patient's potassium levels are too high, this is known as hyperkalemia, which can be caused by diabetic ketoacidosis, metabolic acidosis, salt substitutes (which are usually pure potassium chloride), or kidney failure. On an EKG, hyperkalemia can result in a peaked T wave, as well as a wide, flat P wave, or a wide QRS complex.
Calcium gluconate can be used as an emergency treatment for hyperkalemia.
If a patient's potassium levels are too low, this is known as hypokalemia, which can be caused by diuretics like furosemide, GI losses, diaphoresis (sweating), Cushing's syndrome, or metabolic alkalosis. On an EKG, hypokalemia can result in a flattened or inverted T wave, ST depression, a U wave occurring after the T wave, or increased amplitude and duration of the P waves.
Calcium is an electrolyte important for muscle and nerve function. The expected range for calcium is 9 - 10.5 mg/dL.
If a patient's calcium levels are too high, this is known as hypercalcemia, which can be caused by hyperparathyroidism, corticosteroids, or bone cancer. On an EKG, hypercalcemia can cause a shortened ST or QT interval.
If a patient's calcium levels are too low, this is known as hypocalcemia,which can be caused by diarrhea, vitamin D deficiency, or hypoparathyroidism. On an EKG, hypocalcemia can cause a prolonged ST and QT interval.
Magnesium is an important electrolyte for nerve and muscle function. The expected range for magnesium is 1.3 - 2.1 mEq/L.
If a patient's magnesium levels are too high, this is known as hypermagnesemia, which can be caused by kidney disease, or laxatives or antacids containing magnesium. On an EKG, hypermagnesemia can result in bradycardia as well as heart blocks.
Calcium gluconate can be used as an emergency treatment for hypermagnesemia. If a patient's potassium OR magnesium levels are too high, calcium gluconate is the antidote.
If a patient's magnesium levels are too low, this is known as hypomagnesemia, which can be caused by GI losses, diuretics, malnutrition, or alcohol abuse. On an EKG, hypomagnesemia can result in tachycardia, a prolonged QT interval, as well as flattened or inverted T waves.
Magnesium can also be supplemented with magnesium chloride, magnesium oxide, or magnesium gluconate, which are covered in our Pharmacology flashcards for nursing students.
Respiratory & Cardiac disorders that affect EKG
There are several respiratory and cardiac disorders (including life-threatening conditions) that will cause abnormalities on an EKG, including angina, ischemia, myocardial infarction, pericarditis, pulmonary embolism, and chronic obstructive pulmonary disease.
Need to remember these disorders and conditions? They are key ones to know for your Medical-Surgical studies and nursing practice, which is why we cover them in our Medical-Surgical flashcards for nursing students.
Angina is a cardiac disorder marked by chest pain due to ischemic heart disease. If a patient has angina, their EKG strip may show ST depression and T wave inversion.
Ischemia or Myocardial infarction
Ischemia is a reduction in blood flow, in this case to the heart. A myocardial infarction is a sudden blockage of blood flow to the heart, also known as a heart attack. If a patient has an MI, their EKG strip may show ST elevation, T wave inversion, and/or an abnormal Q wave.
Some MIs are Non-ST Elevated Myocardial Infarctions (NSTEMIs), meaning that you wouldnot see ST-segment elevation here, but there is still tissue death occurring!
Pericarditis is inflammation of the pericardium, which is the thin membrane surrounding and protecting the heart. If a patient has pericarditis, their EKG strip may show ST elevation.
Pulmonary Embolism (PE)
Pulmonary embolism (PE) is a cardiac disorder marked by life-threatening blockage in the pulmonary vasculature, which are the blood vessels that transport blood from the heart to the lungs and back again. If a patient has a PE, their EKG may show ST elevation, an inverted T wave, or a right bundle branch block.
Chronic Obstructive Pulmonary Disease (COPD)
Chronic obstructive pulmonary disease (COPD) is the term for a group of respiratory diseases, including emphysema and chronic bronchitis, that lead to airflow obstruction. If a patient has COPD, their EKG may show a peaked P wave, as well as a low-voltage QRS. This means a shorter QRS complex.
In this video, we will be talking about some other EKG abnormalities that you may see, including a bundle branch block, a sinus pause, escape beats. And we will also talk about the impact of electrolyte imbalances on the EKG as well as some key respiratory and cardiac disorders, how those disorders affect an EKG as well.
So one EKG abnormality I'd be familiar with is something called a bundle branch block or BBB.
With a bundle branch block, the electrical impulse is delayed in the bundle of His or within the bundle branches.
This results in a very wide QRS complex. So the QRS complex will be over 3 small boxes in duration or over 0.12 seconds in duration.
If a patient has a bundle branch block but is asymptomatic, then it often doesn't require treatment. However, if the patient has a bundle branch block that is symptomatic, then we can treat that with either a pacemaker or cardiac resynchronization therapy or CRT.
Here you can see in the EKG strip that we definitely have a consistent bundle branch block because that QRS complex is abnormally wide.
Here we have a sinus pause, which is another EKG abnormality to be familiar with. We actually saw one of these when we were talking about premature atrial complexes, or PACs.
So a sinus pause is caused when the SA node fails to initiate an impulse or that impulse somehow becomes blocked such that the atria do not depolarize.
So during the sinus pause, we will not have the P wave, QRS complex, or the T wave. And then after the sinus pause, sometimes we will have what's called an escape beat, which I'll be talking about next.
In terms of treatment, treatment is typically not required when a patient is asymptomatic.
So an escape beat is an abnormal impulse that occurs after a sinus pause and occurs late. So I've included two examples of escape beats here.
One is a ventricular escape beat. We know it's a ventricular escape beat because, as we talked about before, a key characteristic of a ventricular rhythm is an abnormally wide QRS complex.
With the ventricular escape beat, it is initiated in the ventricle.
After the pause, the P wave will be absent, and the QRS complex will be abnormally wide.
With a junctional escape beat, this is initiated in the junctional foci which is at the AV junction, and it causes the P wave following a pause to either be absent, which it is here, or inverted, or it causes an abnormally short PR interval.
So in this case, we just have an absent P wave, and then the QRS complex will be of normal duration when we're talking about a junctional escape beat.
So for asymptomatic patients with escape beats, treatment is not typically required.
All right, now let's talk about how electrolyte imbalances can affect an EKG. The key electrolytes that you need to keep your eye on are potassium, calcium, and magnesium. So all the information I'm going to go over here in this portion of the video can be found on card 39 in my deck, if you are following along.
So if a patient has hyperkalemia, meaning their potassium levels are too high, this can result in a peaked T wave, as well as a wide, flat P wave, or a wide QRS complex.
If the patient has hypokalemia, meaning their potassium levels are too low, this can cause a flattened or inverted T wave, it can cause ST depression. It can also cause the presence of a U wave, which is this little wave that occurs after the T wave, and then lastly, it can caused increased amplitude and duration of the P waves.
For calcium, if the patient has hypercalcemia, which is too high levels of calcium. This can cause a shortened ST and/or QT interval. If their calcium levels are too low, meaning they have hypocalcemia, this can cause a prolonged ST and QT interval.
And then moving on to magnesium. If the patient has hypermagnesemia, meaning their magnesium levels are too high, this can cause bradycardia as well as heart blocks.
And then if they have hypomagnesemia, which means their magnesium is too low, this can result in tachycardia, a prolonged QT interval, as well as flattened or inverted T waves.
And then let's talk about how different cardiac disorders can impact an EKG as well.
So if a patient has angina, this can result in ST depression as well as T wave inversion.
If the patient is experiencing ischemia or a myocardial infarction, this can result in ST elevation, as well as T wave inversion and an abnormal Q wave.
If a patient has pericarditis, this can also result in ST elevation on the EKG. Certain respiratory disorders can also cause EKG abnormalities.
So if a patient has a pulmonary embolism or PE, this can result in ST elevation as well as an inverted T wave or a right bundle branch block.
And then if a patient has COPD, this can result in a peaked P wave as well as a low-voltage QRS. So the QRS amplitude will be lower.
So in my next video, which will be the last video in the series, we will talk about artificial pacemakers, and then we will talk about bradycardia and tachycardia in terms of the symptoms, the causes, and the treatment of those conditions. Thanks so much for watching!
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