How to Read an EKG
Medical cardiogram printed on paper on the table, disturbing news about the health of the heart

How to Read an EKG

An electrocardiogram, also known as an EKG or ECG, indicates the electrical signals in your heart. It’s a simple, painless, and important medical test used to immediately identify heart difficulties and observe a patient’s heart’s conditions. Typically, an EKG technician performs the test, but sometimes nurses will perform them.

Here are the steps to take to read an EKG accurately:

Assess Your Patient

Asking for the patients’ information is the primary step to properly read an EKG. This assessment will help you properly analyze what’s on the patient’s EKG result. Initially, you must confirm the patient’s name and date of birth on the EKG before checking the physical state of the patient. Subsequently, ask a few questions regarding their medical history to see if they have underlying conditions that may affect their heart.

Here are some common assessment questions and key points that will help you properly read an EKG:

  • Is the patient’s skin dry and warm or damp?
  • Are they experiencing chest pain?
  • Is the patient struggling to catch their breath?
  • Are you able to examine pulses by touch?
  • What is their normal level of physical activity?
  • Has anyone in their family been diagnosed with a heart condition?
  • Does the patient have an underlying heart condition?
  • Are they currently taking any medications?

It’s important to remember an EKG reading alone does not provide enough information to make a diagnosis. A healthy athlete may have a resting heart rate between 30 and 40 BPM (the average heart rate is usually between 60 and 80 BPM), but if they are struggling to breathe and have chest pain, they need further medical attention.

Monitor Heart Rate

The three main components of an EKG are the P wave (depolarization of the atria), QRS complex (depolarization of the ventricles), and T wave (repolarization of the ventricles). For each component, you must know the following information:

  • Amplitude: What is the voltage of the beat? This is measured by the vertical axis.
  • Deflection: Which lead is it coming from?
  • Duration: How long is the component? This is measured on the horizontal axis.

Next, you can start monitoring their heart rate to determine if it is normal or not. Here is the normal heart rate range for the average adult:

Normal: 60-100 BPM

Tachycardia: more than 100 BPM (abnormally fast heart rate)

Bradycardia: less than 60 BPM (abnormally slow heart rate)

Identify Heart Rhythm

There are two types of heart rhythm: regular and irregular. To determine the patient’s rhythm, measure the distance between the P waves and QRS complexes to see if they have any gaps. If the distances are consistent, the heart rhythm is regular. If there are gaps, the heart rhythm is irregular.

Irregular rhythms can be classified into two categories: regularly irregular and irregularly irregular. Regularly irregular indicates there is a recurrent pattern, whereas irregularly irregular means the heart rhythm is totally disorganized.

Some of the possible associated conditions for irregular heart rhythms are:

  1. Tachycardia (Atria)
    • Atrial fibrillation
    • Atrial flutter
    • Supraventricular tachycardia
    • Wolff-Parkinson-White syndrome
  2. Tachycardia (Ventricles)
    • Ventricular tachycardia
    • Ventricular fibrillation
    • Long QT syndrome
  3. Bradycardia
    • Sick sinus syndrome
    • Conduction block
  4. Premature heartbeats

Evaluate Cardiac Axis

The cardiac axis provides an impression of the overall direction of electrical movement inside the heart. You get positive deflection if the path of electrical activity is toward the lead, comparatively, you get negative deflection when electrical activity is far from a lead. You must evaluate the cardiac axis to accurately read an EKG by checking leads I, II, and III. The three outcomes you will find are:

  1. Normal cardiac axis
    • For healthy people, the axis lies approximately within -30° and +90º.
    • Lead II has the highest positive deflection as opposed to Leads I and III.
  2. Right axis deviation
    • Right axis deviation (RAD) includes the course of depolarization having more declined to the right, within +90º and +180º.
    • Lead III has the highest positive deflection and Lead I must be in negative deflection.
  3. Left axis deviation
    • Left axis deviation (LAD) includes the course of depolarization having declined to the left, within -30° and -90°.
    • Lead I have the highest positive deflection.

Examine P Waves

Normally, P waves are followed by a QRS complex. If you look at the electrical activity and notice a flatter baseline between the QRS complex, then the P waves are absent.

Examine P waves by checking if:

  • P waves are present in the graph
  • It is followed by a QRS complex
  •  The P waves seem normal in duration, shape, and direction

If the P wave is absent, check if there is an atrial activity. You can identify atrial activity with these indicators:

  • Sawtooth baseline indicates flutter waves
  • Chaotic baseline indicates fibrillation waves
  • Flatline indicates there is no atrial activity

Analyze PR Interval

PR Interval is the period from the start of the P wave (atrial depolarization) to the start of the QRS complex (ventricular depolarization). Normally, the PR interval must be within 120-200 ms or three to five small squares.

A prolonged PR interval is higher than 200 ms and implies the possibility of an atrioventricular delay (also known as an AV block or heart block), which is the partial or complete interruption of impulse transmission from the atria to the ventricles. There are three subtypes of an AV block: 

  • First-degree AV block: Sinus beat with labeled 1st-degree heart block (340 ms).
  • Second-degree AV block: The longest PR interval before the dropped beat is 340 ms, while the shortest PR interval after the dropped beat is 280 ms.
  • Third-degree AV block: Happens on any part from the AV node down producing entire blockage of conduction.

Assess QRS Complex

The QRS complex is one of the most essential parts to check on an EKG. While evaluating a QRS complex, you must be aware of the following aspects:

  • Width: Narrow QRS complexes are less than 120 ms and broad QRS complexes are greater than 120 ms.
  • Height: This can be described as “small” or “tall.” Small complexes are less than 5 mm in the limb leads or less than 10 mm in the chest leads. Tall complexes indicate ventricular hypertrophy.
  • Morphology: To assess morphology, these individual waves of the QRS complex should be evaluated:
    • Delta wave: A garbled upstroke in the QRS complex usually correlated with a brief PR interval.
    • Q-waves: Any negative deflection that is followed by an R wave.
    • R and S waves: The R wave is the initial upward deflection after the P wave and S wave is the downward deflection after the R wave.
    • J point segment: The crossing between the end of the QRS complex (S wave) and the start of the ST segment.

Evaluate ST Segments

The ST segment is the section of the EKG connecting the end of the S wave and the start of the T wave. For healthy patients, the ST segment is a flat, isoelectric line. Abnormalities are seen if the line is elevated or depressed.

  • ST-elevation is when it is greater than 1 mm in two or more adjacent limb leads or greater than 2 mm in two or more chest leads. The elevation is commonly produced by acute full-thickness myocardial infarction.
  • ST depression can be identified when the ST segment is less than or equal to 0.5 mm in two contiguous leads, which indicates myocardial ischemia.

Examine T-waves

The T-wave exhibits the fast repolarization of contractile cells and its variations happen in a broad range of situations. T-wave alterations are common. The shift from the ST segment to the T-wave must be calm, not unexpected.

  • Normal T waves are insignificantly asymmetric, with a more precipitous descending slope.
  • Tall T are greater than 5 mm in the limb leads or 10 mm in the chest leads. A tall T wave can be associated with hyperkalemia or hyperacute STEMI.
  • Biphasic T waves have two peaks and can indicate ischemia and hypokalemia.

Document Your Findings

Once you have read an EKG, you must document your interpretation in the patient’s notes. Include the date and time the EKG was performed, the indication for the EKG, your impression, and your plan going forward.

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