An electrocardiogram (ECG or EKG) is a non-invasive medical test that records the heart’s electrical activity. This test helps healthcare professionals assess the heart’s function by visualizing the electrical impulses that control heartbeats. The visual output of an ECG, typically printed on specialized grid paper, provides a fundamental understanding of the heart’s rhythm and overall electrical performance. It is a quick and painless procedure that involves placing electrodes on the skin to detect these electrical signals.
Understanding the ECG Paper
ECG paper is a specialized graph paper displaying the heart’s electrical signals. This paper features a grid pattern composed of both small and large squares. Each large square measures 5 millimeters (mm) by 5 mm, and these larger squares are further subdivided. Within each large square, there are 25 smaller squares, arranged in a 5×5 configuration.
The grid’s axes are specific. The horizontal axis on the ECG paper consistently measures time, allowing for the duration of cardiac events to be determined. The vertical axis, conversely, represents voltage, indicating the amplitude of the electrical signals. This standardized layout ensures consistent interpretation of the heart’s electrical activity.
The Millisecond Values
ECG paper moves at a standard speed of 25 millimeters per second (mm/s), allowing precise time measurements. Each small square on the ECG paper, measuring 1mm by 1mm, represents 0.04 seconds or 40 milliseconds (ms) on the horizontal time axis. This value is derived from the paper speed, as 1 mm of paper passing in a second, at 25 mm/s, equates to 1/25th of a second, or 0.04 seconds.
Each large square, spanning 5 mm horizontally, represents 0.20 seconds or 200 milliseconds. This is five times the value of a small square. Five large squares together account for one full second.
Importance in Heart Rhythm Analysis
The precise millisecond values associated with the ECG grid are central to heart rhythm analysis. Medical professionals rely on these time measurements to accurately calculate various aspects of heart function. For instance, heart rate can be determined by counting the number of large squares between specific points on the ECG tracing.
These time measurements are also used to assess the duration of different electrical events within the cardiac cycle. Key intervals like the PR interval, which reflects the time for electrical signals to travel from the atria to the ventricles, are measured using these squares.
The QRS duration, representing the time it takes for the ventricles to depolarize, and the QT interval, which covers ventricular depolarization and repolarization, are similarly quantified. By evaluating the exact timing of these intervals, healthcare providers can identify whether the heart’s electrical activity is normal or if there are irregularities, such as arrhythmias or other cardiac abnormalities.