Understanding a Normal Electrocardiogram (ECG)

Introduction

A normal electrocardiogram (ECG or EKG) is an essential tool in evaluating heart health. It records the electrical activity of the heart and helps identify normal heart function as well as potential cardiac abnormalities. In this short lecture, we will review the basic components of a normal ECG, its significance, and how it is interpreted.

What is an ECG?

An ECG is a graphical representation of the electrical impulses in the heart. These impulses trigger heartbeats and ensure the proper coordination of heart muscle contraction. A normal ECG consists of several key waves and intervals that represent different phases of the heart’s electrical cycle.

Components of a Normal ECG

A standard ECG consists of the following components:

• P wave: Represents atrial depolarization (the electrical triggering of the atria to contract).
• PR interval: The time between the onset of atrial depolarization and the start of ventricular depolarization.
• QRS complex: Represents ventricular depolarization (the electrical triggering of the ventricles to contract).
• ST segment: Reflects the period between ventricular depolarization and repolarization.
• T wave: Represents ventricular repolarization (recovery phase of the ventricles before the next beat).
• QT interval: Measures the total time of ventricular depolarization and repolarization.

Normal ECG Values

A normal ECG usually follows these parameters:

• Heart rate: 60-100 beats per minute (in a healthy adult at rest).
• PR interval: 120-200 milliseconds.
• QRS duration: Less than 120 milliseconds.
• QT interval: Varies with heart rate but typically falls within normal corrected values (QTc < 450 ms in men, < 460 ms in women).
• P wave: Should be smooth and upright in most leads.

Why is a Normal ECG Important?

A normal ECG confirms that the heart's electrical system is functioning correctly. It helps rule out arrhythmias, electrolyte imbalances, or structural heart diseases. Abnormal variations may indicate problems such as atrial fibrillation, heart attack, or conduction disorders.

Conclusion

A normal ECG is a sign of a well-functioning heart. However, ECG interpretation requires expertise due to the possible variations in readings. If any abnormalities are found, further tests such as echocardiography or stress testing may be necessary.

Source recommendations

1. American Heart Association Guidelines on Electrocardiography

1. https://www.heart.org/en/health-topics/heart-attack/diagnosing-a-heart-attack/electrocardiogram-ecg-or-ekg
2. https://www.ahajournals.org/doi/10.1161/circulationaha.108.191095
3. https://pubmed.ncbi.nlm.nih.gov/19281932/
4. https://www.ahajournals.org/doi/10.1161/circulationaha.108.191098
5. https://pubmed.ncbi.nlm.nih.gov/10483977/

2. European Society of Cardiology Guidelines for ECG Interpretation

1. https://www.escardio.org/Guidelines/Clinical-Practice-Guidelines
2. https://pubmed.ncbi.nlm.nih.gov/12269267/
3. https://www.escardio.org/Guidelines/Clinical-Practice-Guidelines/Neonatal-Electrocardiogram-Guidelines-for-the-interpretation-of-the
4. https://academic.oup.com/eurheartj/article-abstract/39/16/1466/2965923
5. https://pubmed.ncbi.nlm.nih.gov/21602522/