Telemetry strips provide a continuous, graphical record of the heart’s electrical activity, tracking the tiny electrical impulses that drive each heartbeat. This monitoring system is commonly used in hospital settings, such as intensive care units, for patients requiring constant surveillance of their cardiac function. Telemetry detects changes in heart rate, rhythm, or conduction. Although the strips may appear complex, they are built upon repetitive, measurable patterns that reflect the heart’s repeating cycle.
The Visual Language of the Strip
The telemetry strip is printed on specialized grid paper, which acts as the foundational ruler for all measurements. This grid is divided into small and large squares, providing a standardized system for analyzing time and voltage.
The horizontal axis measures time, as the paper runs at a speed of 25 millimeters per second. Each small square represents 0.04 seconds, and a large square (five small squares) represents 0.20 seconds. This consistent speed allows the interpreter to accurately measure the duration of electrical events.
The vertical axis measures the voltage, or amplitude, of the electrical impulse, which relates to the strength of the heart muscle’s electrical activity. Standard calibration is 10 small squares vertically representing 1 millivolt of electrical potential.
Decoding the Cardiac Cycle
The strip visualizes the heart’s electrical sequence, where each complete heartbeat is represented by a specific set of waves and intervals. The sequence begins with the P wave, a small, rounded deflection representing atrial depolarization (electrical activation of the upper chambers).
Following the P wave is the QRS complex, a sharp, taller series of deflections signifying ventricular depolarization. This complex is the electrical signal that causes the contraction of the ventricles (the heart’s main pumping chambers). Atrial repolarization occurs during this time but is typically hidden by the larger QRS complex.
The T wave represents ventricular repolarization. The PR interval spans from the start of the P wave to the beginning of the QRS complex, measuring the time for the impulse to travel from the atria into the ventricles (0.12 to 0.20 seconds). The QT interval measures the total time required for the ventricles to depolarize and fully repolarize, extending from the start of the QRS complex to the end of the T wave. A normal QRS complex duration is less than 0.12 seconds.
Systematic Interpretation of Rate and Rhythm
Interpretation begins with determining the heart rate. For regular rhythms, the “300 method” provides a quick estimate by dividing 300 by the number of large squares between two consecutive QRS complexes. A more precise method involves counting the small squares between two QRS complexes and dividing 1,500 by that number.
For irregular rhythms, an average rate is calculated using a 6-second strip (30 large squares). Count the number of QRS complexes within that section and multiply by 10 to obtain the rate in beats per minute.
The next step is assessing rhythm regularity (the distance between consecutive QRS peaks). In a regular rhythm, this distance should be consistent across the strip. Variability in the R-R interval indicates an irregular rhythm where heartbeats are not evenly spaced.
Finally, P waves must be analyzed to ensure they are present, uniform, and correctly paired with a QRS complex. A P wave should precede every QRS complex, indicating the impulse originated correctly in the atria. The measured intervals (PR interval and QRS duration) are then checked against normal limits to identify conduction delays or abnormalities.
Recognizing Common Variations
Deviations from the normal pattern, known as Normal Sinus Rhythm, are identified as variations. Bradycardia is a heart rate below 60 beats per minute, appearing on the strip as an increased distance between QRS complexes. Tachycardia is a rate greater than 100 beats per minute, represented by QRS complexes that are much closer together.
Other variations involve disorganized patterns. An irregular rhythm shows random, inconsistent spacing between QRS complexes, suggesting a loss of organized pacing. Ectopic beats interrupt the regular pattern, presenting as a single, premature QRS complex that appears earlier than expected.