Cardiac telemetry monitoring provides a continuous, remote view of a patient’s heart activity, often used in hospital settings. This technology uses electrodes placed on the chest to sense the heart’s electrical signals, transmitting them to a central screen. Telemetry tracks the heart’s rhythm and rate over time to identify abnormal patterns, such as irregular heart rhythms (arrhythmias). This data enables early diagnosis and intervention.
Understanding the Telemetry Display
The electrical signals picked up by the electrodes (leads) are translated into a wavy line graph displayed on the telemetry screen. This graph, known as an electrocardiogram (ECG or EKG), uses a standardized grid system. The horizontal axis represents time, while the vertical axis measures the voltage of the electrical impulse.
The grid is composed of small squares (1mm x 1mm) and larger squares (five small squares wide and high). Horizontally, each small square represents 0.04 seconds, making one large square equal to 0.20 seconds. Vertically, each small square represents 0.1 millivolt (mV) of electrical potential. This standardization allows for accurate measurement of the timing and strength of the heart’s electrical events.
Decoding the ECG Wave Components
The wavy line displayed on the monitor is composed of three primary electrical deflections, each corresponding to a specific mechanical action of the heart muscle. The first small, rounded bump is the P wave, which represents the electrical activation (depolarization) of the atria. This depolarization originates in the heart’s natural pacemaker and causes the upper chambers to contract.
Following the P wave is the QRS complex, a sharp, taller spike that signals the depolarization of the ventricles (the heart’s large lower chambers). This electrical event is stronger than the P wave because the greater ventricular muscle mass leads to the powerful contraction that pushes blood out to the body.
The final major component is the T wave, a smooth, broad hump that represents the repolarization (electrical recovery) of the ventricles. This recovery phase allows the ventricles to relax and refill with blood before the next heartbeat.
Calculating Heart Rate and Assessing Regularity
After identifying the basic wave components, the heart rate and its consistency must be determined. For regular rhythms, a quick estimation method uses the large squares between two consecutive R waves (the tall peaks of the QRS complex). Since 300 large squares represent one minute, dividing 300 by the number of large squares between two R waves approximates the rate in beats per minute. For example, four large squares between R waves equals a rate of approximately 75 beats per minute (300/4 = 75).
For irregular rhythms, the six-second method is used for a more accurate rate calculation. This involves locating a six-second segment (30 large squares) on the rhythm strip. By counting the number of QRS complexes within this segment and multiplying that count by ten, the average heart rate for one minute is calculated.
Consistency of the rhythm is assessed by measuring the R-R interval, which is the distance between consecutive R waves. If the R-R intervals are equal across the entire strip, the rhythm is considered regular.
Recognizing Basic Rhythm Deviations
The normal pattern is called Normal Sinus Rhythm, characterized by a regular rhythm between 60 and 100 beats per minute, where every QRS complex is preceded by a P wave. Deviations from this pattern are often visually distinct.
An overly fast rate, known as tachycardia, is noticeable because the R waves are packed close together, indicating a rate over 100 beats per minute. Conversely, bradycardia is a slower-than-normal rate, where the R waves appear widely spaced, falling below 60 beats per minute.
Another common visual change is ectopy, which manifests as an occasional, strange-looking beat interrupting the regular sequence. Premature Ventricular Contractions (PVCs) are a type of ectopic beat characterized by a QRS complex that appears wider and more bizarre than the normal complexes. These isolated, early beats originate lower in the heart and disrupt the underlying regularity.