Introduction to ECG | The Basics | ECG Paper, PQRST wave, Rate, Rhythm, Axis and Interval

Summary

This introductory lesson covers the basics of ECG interpretation, focusing on how ECG paper is structured and the significance of the PQRST waves. It explains the method to determine heart rate, rhythm, axis, and intervals from an ECG reading. The instructor goes over key concepts like calculating heart rate using QRS complexes, recognizing sinus rhythms, and analyzing axis deviation. The lesson also touches on the importance of intervals such as the PR and QT intervals, offering practical tips for beginners. The session ends with a preview of future lessons on heart conditions and ECG interpretation.

Takeaways

• 📊 ECG paper is composed of small boxes grouped into larger boxes, with each large box representing 0.2 seconds and each small box representing 0.04 seconds.
• ⏱ The horizontal axis of ECG paper represents time, while the vertical axis represents voltage (in millimeters).
• 🔍 The PQRST wave sequence is crucial for interpreting ECGs: P-wave indicates atrial depolarization, QRS complex indicates ventricular depolarization, and T-wave indicates ventricular repolarization.
• 💡 The presence and pattern of P-waves preceding QRS complexes help determine the type of cardiac rhythm, such as sinus rhythm, tachycardia, or bradycardia.
• 📈 Heart rate can be calculated from ECG using methods like counting QRS complexes and multiplying by 6, or using formulas involving the number of large boxes between R-waves.
• 🔎 Determining cardiac rhythm involves checking if each QRS complex has a preceding P-wave, which indicates a sinus rhythm.
• 📍 The axis or mean vector of depolarization can be assessed by examining the most positive QRS complexes in different leads and comparing them to leads I and II.
• 🕰 The PR interval, measured from the start of the P-wave to the start of the QRS complex, should normally be between 0.12 to 0.20 seconds.
• 📏 The QRS duration, indicating the time for ventricular depolarization, should typically be less than 0.12 seconds.
• 📉 The QT interval, which can be complex to calculate, is generally assessed using formulas and is different for males and females, with normal values being less than or equal to 0.44 seconds for males and 0.45 to 0.46 seconds for females.

Q & A

What does the horizontal axis of an ECG paper represent?

The horizontal axis of an ECG paper represents time. Each small box on the horizontal axis denotes 0.04 seconds, and each large box (made up of 5 small boxes) represents 0.2 seconds.

What does the vertical axis of an ECG paper represent?

The vertical axis of an ECG paper represents voltage. Each small box vertically denotes 1 millimeter, and each large box represents 5 millimeters of voltage.

What is the P wave in an ECG, and what does it represent?

The P wave in an ECG represents atrial depolarization, which is the electrical activity that leads to the contraction of the atria.

What is the QRS complex, and what does it signify?

The QRS complex represents ventricular depolarization, which is the electrical activity leading to the contraction of the ventricles.

How can you calculate heart rate from an ECG using the QRS complexes?

One method is to count the number of QRS complexes in 10 seconds and multiply it by 6 to get the heart rate in beats per minute. Alternatively, you can use other methods like dividing 300 by the number of large boxes between R waves.

What does a prolonged PR interval indicate?

A prolonged PR interval, which is longer than 0.20 seconds, could indicate an AV block, a type of heart conduction problem.

What is the normal duration for a QRS complex?

The normal duration of a QRS complex is generally less than 0.12 seconds. Some guidelines suggest a normal range of 0.07 to 0.10 seconds.

What is the difference between sinus bradycardia and sinus tachycardia?

Sinus bradycardia refers to a heart rate of fewer than 60 beats per minute, while sinus tachycardia refers to a heart rate of more than 100 beats per minute. Both rhythms have a QRS complex that is preceded by a P wave.

How do you quickly determine if the heart’s axis is normal from an ECG?

To quickly determine if the heart’s axis is normal, check leads I and II. If both have positive R waves, the axis is likely normal. If lead I is positive and lead II is negative, it may indicate a left-axis deviation.

What is the QT interval, and why is it important to monitor?

The QT interval represents the time from the beginning of ventricular depolarization (Q wave) to the end of ventricular repolarization (T wave). It’s important because prolonged QT intervals can be a sign of increased risk for dangerous arrhythmias, especially in patients taking certain medications.