How To Interpret ECG Readings: An Overview

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On average, senior medical students miss between 26% to 62% of acute myocardial infarctions. This inaccurate ECG interpretation can result in severe consequences for patients. This is why medical practitioners need more training in these areas of study.

Learning how to interpret ECG readings can reduce medical errors and malpractice lawsuits. This skill set requires a lot of training and textbook reading to perfect, but for now, let's start from the basics. With that in mind, keep reading to get an overview of how to comprehend ECG readings.

What is an ECG?

An EKG/ECG reveals the electrical activity of the heart muscle. It varies over time, which is why it's printed on paper to help with interpretation. This helps show providers the snapshot of a short period of time.

EKGs help identifies heart attacks, electrical dysfunction, and other heart conditions. They are often used in conjunction with an echocardiogram to make the proper diagnosis.

Check the Patient First

Before analyzing an ECG reading, you must first assess the patient. There are several questions you have to consider to get an accurate overview of the situation. Answering these questions can increase the accuracy of your reading:

  • Is the patient's skin dry and warm or wet and cold?
  • What is their skin color?
  • Are they experiencing chest or arm pain?
  • What time of day does the discomfort often occur: morning, afternoon, or night?
  • Would they characterize it as a mild pressure or a sharp, stabbing pain?
  • Are there any tearing feelings?
  • Do they smoke or have ever smoked? How many packets per day, if so?
  • Can you palpate their peripheral pulses?
  • Is your patient conversing with you, or are they battling for air?
  • What is the filling rate of their capillary?
  • Are there any existing cardiac conditions?
  • What is their physical activity baseline?
  • Have they ever received an EKG?
  • Were they previously diagnosed with any cardiac diseases?
  • Do they feel nauseous, dizzy, lightheaded, or exhausted?

A piece of paper with a trace does not give enough information. This is mainly because the average heart rate for an athlete is 38 beats per minute. That is pretty low for the average human heartbeat, which is 60-100 beats per minute.

If you combine symptoms from the patients and the reading, then that's another story. For example, chest discomfort, shortness of breath, and an abnormal ECG interpretation can give the whole story. This means we must prepare for a third-degree heart block and put in an emergency pacemaker.

Interpret ECG Reading by Knowing What's Normal

A typical cardiac rhythm consists of P, QRS, and T waves. You must understand the normal amplitude, deflection, and length of each component.

Amplitude quantifies the voltage of the beat and is determined by the height of the wave. Deflection determines where the leads come from, and duration is how long something is. Here are other average values to check out:

What Is a Typical Heart Rate for an Adult?

The normal heart rate is between 60-100 bpm. If the patient's heart beats for more than 100 bpm, then this is known as tachycardia.

If their heart beats less than 60 bpm, then it's bradycardia. Remember that athletes tend to have a lower heart rate, so you must assess for other symptoms.

Direction and Heart View

The twelve leads reveal the heart's electrical activity from various angles. Consider each lead a unique picture of the heart you attempt to decipher.

There are six limb leads (I, II, III, AVR, AVL, and AVF) and six precordial leads (V1 to V6). The limb leads provide a vertical picture of the heart, while the V leads shows the horizontal perspective. Here are more insights on the lead placements:

  • V1: on the right sternal boundary at the fourth intercostal space (ICS).
  • V2: Fourth ICS, along the left side of the sternal boundary
  • V4: Fifth ICS, midclavicular line
  • V6: Fifth ICS, line midaxillary  
  • V5: Fifth ICS, anterior to the axillary line  
  • V3: halfway between V2 and V4

So why are these leads and directions important? This helps you analyze the images and determine which heart regions have the issue.

Utilize a Systematic Method

Always approach the analysis of a 12-lead EKG/ECG in a step-by-step, systematic manner. Here are the steps and factors to consider:

  • Check if the patient is bradycardic, tachycardic, or normal
  • Assess if their heart rhythm is regular or irregular
  • Count the number of squares inside a single R-R interval
  • Calculate heart rate by dividing 300 by this value
  • Determine the number of complexes on the rhythm strip
  • Multiply the number of complexes by six
  • Determine if the rhythm is quick or slow, erratic or regular
  • Examine the ST segments for any elevations or depressions

You can use a piece of paper to jot down your thoughts about the segments. Prepare to notify your team if you can determine elevation or depression without using a piece of paper.

Understanding the Rhythm of the Heart 

Rhythms above the atria are often over 60 and aberrant when the heart rate is rapid. This indicates a potential atrial flutter, atrial fibrillation, or supraventricular tachycardia. When the rate is irregular, rhythms performed below the atria are slower and more likely to be unstable, like a heart block.

Be aware of any medication your patient is taking. Many cardiac drugs, like beta-blockers, can slow down the heart rate. It's vital to assess whether a person's heart rate is:

  • Regularly irregular (i.e. a recurrent pattern of irregularity)
  • Irregularly irregular (i.e. completely disorganized)

Mark out multiple consecutive R-R intervals on paper, then move them down the rhythm strip. This is to test whether succeeding intervals are identical.

Are You Ready to Interpret Some ECG Readings?

An accurate ECG reading can save lives, but it requires some attention to detail. By understanding how to read them, we can catch potential heart problems before they become deadly. While this may seem daunting at first, with a little practice and some help, you can be an expert at no time. Check out our best-selling EKG book and EKG Workbook on Amazon.

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