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What is a Normal ECG Reading?

Published in Cardiology 2 mins read

A normal ECG reading, also known as an electrocardiogram, indicates that the heart's electrical activity is within expected ranges. This encompasses several key intervals and waves, each representing a specific phase of the cardiac cycle. It's important to remember that "normal" can vary slightly depending on individual factors, so interpretation always needs to be done by a qualified healthcare professional.

Here's a breakdown of typical normal values:

  • Heart Rate: Typically between 60 and 100 beats per minute (bpm).

  • Rhythm: Should be a regular sinus rhythm, meaning the electrical impulse originates from the sinoatrial (SA) node, the heart's natural pacemaker.

  • Waves and Intervals: These represent different phases of the heart's electrical cycle:

    • P Wave: Represents atrial depolarization (contraction). Normally smooth and upright.

      • Duration: Less than 120 milliseconds (0.12 seconds).
    • PR Interval: Represents the time it takes for the electrical impulse to travel from the atria to the ventricles.

      • Duration: 120-200 milliseconds (0.12-0.20 seconds).
    • QRS Complex: Represents ventricular depolarization (contraction).

      • Duration: Less than 120 milliseconds (0.12 seconds).
    • ST Segment: Represents the period between ventricular depolarization and repolarization (relaxation). Should be flat (isoelectric) and at the baseline.

    • T Wave: Represents ventricular repolarization. Usually upright and asymmetrical.

    • QT Interval: Represents the total time for ventricular depolarization and repolarization. The duration varies with heart rate and should be corrected using formulas such as Bazett's formula (QTc). The corrected QT interval (QTc) is usually considered normal if:

      • QTc: Less than 450 milliseconds in men
      • QTc: Less than 460 milliseconds in women

Here's a table summarizing the normal ECG values:

ECG Component Normal Value
Heart Rate 60-100 bpm
Rhythm Regular Sinus Rhythm
P Wave < 120 ms
PR Interval 120-200 ms
QRS Complex < 120 ms
ST Segment Isoelectric (at baseline)
QTc Interval < 450 ms (men), < 460 ms (women)

It's crucial to understand that these are general guidelines. A cardiologist or other trained healthcare professional will interpret the ECG in the context of the patient's medical history, symptoms, and other test results. Minor variations may be normal for a particular individual.