Introduction to EKG Interpretation

Before diving into EKGs, it’s imperative to refresh on the basics of cardiac conduction as well as the anatomy of the heart. The heart comprises four chambers with two pairs of atria and ventricles. In between the chambers of the heart, there are valves that open and close based on when the atrium and ventricles are contracting.

Clinicians may evaluate the sounds of the heart to detect a heart murmur utilizing a stethoscope. The normal heart will make an iconic “lub dub” sound as it beats. The “lub” sound corresponds with the closing of the mitral and tricuspid valves at the start of systole (ventricles contracting). The “dub” sound corresponds with the closure of the aortic and pulmonic valves.

The contraction of the heart is due to the flow of electrical conduction from the sinoatrial node (SA node), commonly called the pacemaker. The SA node fires at about 60-100 bpm in a normal healthy adult. This is called normal sinus rhythm and corresponds with the client’s heart rate. From the SA node, electricity flows into the atrioventricular node (AV node).

Occasionally, the SA node may fail due to certain medical conditions. From this, the AV node can become the new pacemaker that fires at 40-60 bpm. Therefore, the SA node is sometimes called the backup pacemaker.

Electricity then flows into the bundle of His, then into the Purkinje fibers, which are responsible for squeezing the ventricles. Purkinje fibers also contain pacemaker cells which may serve as the last backup for electrical conduction in the heart, firing at 40-60 bpm.

Reading EKGs can be challenging but proves to be an important part of daily medical practice. A firm understanding of EKGs can enable nurses and other practitioners to help detect and manage clients with cardiac abnormalities. Hopefully, reviewing this NCLEX® Review of EKGs will aid in understanding this critical aspect of practice.

Atrial Fibrillation (A Fib) Pathophysiology

The most common rhythm you’ll see in a clinical setting is atrial fibrillation (A Fib). Atrial fibrillation is the rapid firing of impulses in the right atrium with about 350 to 650 beats or impulses per minute.

Impulses are regulated by the atrioventricular (AV) node, which mainly controls the number of impulses that pass along the ventricles. Without the AV node (and if the ventricles are beating at 650 a minute), there’s not enough time to repolarize and get blood inside the ventricles. This results in almost a full contraction.

This scenario is similar to administering potassium directly to your heart which would cause full contraction. This means the heart will contract and no longer open. If that happens, the heart will no longer receive and circulate blood with oxygen.

So, the main thing you must remember is that your heart’s primary function is to distribute oxygenated blood throughout the body and the AV node is there to regulate the number of impulses that are coming inside the heart.  

Pooling of Blood

If the chamber is full of blood, it starts pooling in the atriums. Pooling will cause the blood to eventually dry up and start forming fibrinogen and fibrin, which is also known as a clot. 

Clot formation will block the atriums entirely or will be sent out to the system as tiny clots, which are the leading causes of cerebrovascular accident (CVA), myocardial infarction (MI), or deep vein thrombosis (DVT). Clots are deadly enough to shut down the lungs in a condition known as pulmonary embolism (PE).

A Fib Causes

Ischemia

Ischemia occurs with decreased oxygenation to the heart. Ischemia usually happens with myocardial infarction, which is mainly caused by decreased oxygen levels in the heart. This can lead to necrosis.

Lung disease is another viable reason for ischemia. The decreased oxygen going inside the lungs can deliberately affect how the heart receives oxygen. Very little (or no oxygen at all) will lead to organ failure, and eventually death.

Valve Disease

The chambers’ inability to open and close at a certain period results in heart valve disease. When this happens, it can adversely affect the heart. If there are not enough succinct pumps going to the heart, it will result in decreased cardiac output.

Cardiac output is the amount of blood pumped by the heart in a whole minute. If the heart isn’t contracting efficiently, it is not filled adequately, the contractions will fail as well. Without a normal cardiac output, the body will not receive a satisfactory amount of blood and oxygen required for proper functioning.

Atrium Complications

When there are issues concerning the atriums of the heart, blood will not be pushed down all the way to the ventricles because the atriums are not contracting properly. There will be minor contractions, but they are not enough to sustain the needs of the heart.

A Fib Nursing Interventions

• Administer anticoagulants, antiplatelets, and calcium channel blockers as ordered.
• Provide oxygen.
• Monitor vital signs.

How to Read EKG Rhythms (in 5 Steps)

Reading EKGs can be challenging, especially when attempting to do so without training. Nevertheless, reading EKGs has become a common practice for nurses and clinicians daily. Electrocardiograms portray several waves that correspond with the depolarization and contraction of different parts of the heart.

Overall, the EKG monitor will reveal several waves which can be read as PQRST. The P-wave corresponds with the depolarization and squeezing of the atrium, the QRS-wave signifies the squeezing of the ventricles, and the T-wave demonstrates the relaxation and repolarization of the ventricles.

To read EKGs you can use a five-step process to assess a client’s cardiac condition:

Step 1: Calculate the sinus rate 

To determine the sinus rate, count the R peaks, then multiply by ten. This will represent the number of beats per minute as the monitor will only display a few seconds worth of electrical impulses. 

When interpreting this information, it’s important to know that the normal sinus rhythm (NSR) usually leads to 60-100 pulses per minute. Normal sinus brady represents a slow rate when < 60 bpm. Normal sinus tachy is described as > 100.

Step 2: Assess the rhythm

The rhythm should be regular and evenly spaced out between peaks. When the pattern reveals abnormally spaced out pulses, the client may have an arrhythmia. Here you should assess all of the waves, including the presence and regularity of the P and QRS waves.

Step 3: Assess the P-wave

Determine if the P-wave looks normal – this will get easier with practice. Abnormalities in the P-wave may suggest abnormalities with atrial depolarization. The duration that is usually observed should be <0.12 seconds.

Step 4: Assess the PR interval 

The PR interval includes the P-wave as well as the PR segment. Measured from the beginning of the P-wave to the first part of the QRS complex. A normal PR interval will be shown as < 5 mini boxes with a normal reading between 0.12-0.20 seconds. PR intervals are shorter with faster heart rates signifying a sympathetically mediated upregulation of AV nodal conduction. Short PR intervals may suggest Wolff-Parkinson-White syndrome, long PR intervals may represent AV node blockage.

Step 5: Asses the QRS complex 

This represents the time for the ventricles to depolarize and contract. The QRS duration normally takes 0.06-0.10 seconds, which is not influenced by heart rate. Increased voltage may indicate left or right ventricular hypertrophy.

Example Questions for NCLEX^® Review for EKGs:

EKG Rhythm Nursing Interventions

There are several nursing interventions to keep in mind concerning EKG analysis. The main goal is to restore the heart to a normal rhythm. There are many potential causes of EKG abnormalities so treating the underlying issues should be the primary approach. 

Reporting abnormalities to clinicians is also an important intervention to aid in diagnosing cardiac abnormalities.

When clients present with a normal sinus brady (< 60bpm) several interventions may be made. After confirmation of normal sinus brady, the client should be assessed for signs and symptoms of low perfusion (low oxygenation).

Two key signs include pale dusty skin and cyanotic blue lips. This suggests evidence of hemodynamic instability. A key treatment for clients showing these signs is atropine. This should upregulate sympathetic tone and improve the normal sinus brady. Other potential options clients can take includes dopamine or epinephrine to improve blood flow and tissue perfusion.

It is also imperative to recognize that clients with normal sinus brady may exhibit these symptoms due to drug overdose. Certain drugs that can cause this complication are those that are negative chronotropic, which decreases heart rate.

Examples of medications that can achieve this effect include beta-blockers, certain calcium channel blockers (e.g. verapamil, diltiazem), and digoxin. Therefore, withholding the medications that can contribute to this side effect or reducing the dose is the main intervention.

Clients that present with normal sinus tachy the main approach is to determine the underlying etiology. On rare occasions, clients with sinus tachycardia may have hypotension or shock related to fluid depletion. These clients should be admitted and assessed for potential heart failure, hypoxia, or for other potential conditions. 

Sinus tachycardia may present in clients in clients with acute myocardial ischemia. Less severe causes of tachycardia can include fear, anxiety, or due to potential medications.

Treating clients with tachycardia often involves discontinuation or reduction in the dose of certain medications. For clients whose rhythm does not appear to be resolved through these measures – it’s reasonable to initiate a trial of beta blockers.

For clients with persistently symptomatic tachycardia may benefit from the addition of ivabradine, which helps to further decrease heart rate. Another potential treatment includes catheter ablation, where small scars are created on the heart tissue to slow the electrical signals.

Common Diseases that Impact EKG Interpretation

There are many potential diseases that can impact EKG readings. Therefore, it’s critical to review the types of disease states and situations that can contribute to these abnormalities.

Arrhythmia 

Arrhythmias can be caused by a variety of conditions including medications, genetic abnormalities, or structural abnormalities of the heart. Certain medications may increase the odds of having an arrhythmia by prolonging the QT interval. 

Examples of drugs that can contribute to QT prolongation include: antidepressants, fluoroquinolones, macrolides, antipsychotics, amiodarone, and antihistamines.

Treating arrhythmia can often be complex with multiple therapeutic considerations. Occasionally clients will not be eligible to have their arrhythmia cured, so they may have their heart rate suppressed instead of rhythm correction. Either cardioversion can achieve rhythm correction via electrical shock or via certain medications (e.g. amiodarone).

Electrolyte imbalances

Electrolyte imbalances can contribute to abnormalities in the EKG reading. Several electrolytes may alter the heart’s conduction, including potassium, sodium, calcium, and magnesium. Therefore, assessing the client’s electrolyte levels is an important intervention to consider before looking for other etiologies.

Myocardial infarction & ischemia 

EKG abnormalities are likely in clients who are having a heart attack. In these clients you can observe acute ST-elevation myocardial infarction (STEMI). However, it’s possible for clients to be having no ST-elevation despite showing signs of a heart attack as well. Myocardial ischemia and infarction can also lead to EKG changes such as T-wave inversion.

EKG Interpretation Conclusion

EKGs are a very important diagnostic tool to use when evaluating clients for many kinds of medical conditions. Reading EKGs can prove to be a complicated process that will often become easier with continued practice. This includes myocardial infarction, electrolyte imbalances, and arrhythmias. 

For this reason, it is imperative to refer to this NCLEX® Review for EKGs to aid in studying for the NCLEX® exam and for daily practice.

References:

1. Basic Heart Sounds. http://www.stethographics.com/main/physiology_hs_introduction.html. Accessed April 12, 2020.
2. UpToDate. https://www.uptodate.com/contents/ecg-tutorial-basic-principles-of-ecg-analysis Accessed April 12, 2020.
3. UpToDate. https://www.uptodate.com/contents/sinus-bradycardia April 12, 2020.
4. UpToDate. https://www.uptodate.com/contents/sinus-tachycardia-evaluation-and-management April 12, 2020.
5. Johnson J. Abnormal EKG: Results, causes, and treatment. Medical News Today. https://www.medicalnewstoday.com/articles/324922. Published April 9, 2019. Accessed April 12, 2020.
6. UpToDate. https://www.uptodate.com/contents/arrhythmia-management-for-the-primary-care-clinician?search=arrhythmia-management-for-the-primary-care-&source=search_result&selectedTitle=1~150&usage_type=default&display_rank=1 Accessed April 12, 2020.