A heart monitor is a non-invasive tool used to record the heart’s electrical activity. The heart operates via a precise internal electrical signaling system that coordinates the contraction of its muscle chambers. By placing sensors, called electrodes, on the skin, the monitor captures these electrical impulses and translates them into a visual tracing. This tracing provides a detailed view of the heart’s rhythm and function, allowing healthcare professionals to identify irregularities.
Varieties of Heart Monitoring Devices
The type of heart monitor used is selected based on whether a patient’s symptoms are acute or occur infrequently. A Standard ECG is a brief test, typically lasting only a few minutes, which is useful for diagnosing immediate or constant issues. If symptoms are not constant, an ambulatory monitor is necessary to capture intermittent events over a longer period.
The Holter monitor is a wearable device that records the heart’s activity continuously, usually for 24 to 48 hours. Event recorders are worn for a much longer period, sometimes weeks or months, but only record when activated by the patient when symptoms are felt.
Mobile Cardiac Telemetry (MCT) devices automatically detect and record abnormal rhythms before transmitting the data in real-time to a monitoring center. For the longest-term monitoring, an Implantable Loop Recorder (ILR) is a small device placed just beneath the skin that can continuously record for up to three years.
Detection of Rate and Rhythm Abnormalities
Heart monitors are primarily used to detect abnormalities in the heart’s rate and rhythm, collectively known as arrhythmias. The monitor identifies if the heart is beating too quickly (tachycardia, above 100 beats per minute) or too slowly (bradycardia, below 60 beats per minute).
The devices are highly effective at capturing irregular patterns such as Atrial Fibrillation (Afib), the most common serious arrhythmia. In Afib, the upper chambers beat rapidly and chaotically, a pattern distinctly visible on the ECG tracing. Atrial Flutter is a similar but more organized rapid rhythm in the upper chambers, often appearing as a “sawtooth” pattern on the monitor.
Monitors also detect premature beats, which are extra, early heartbeats that interrupt the normal rhythm. These include Premature Ventricular Contractions (PVCs) from the lower chambers and Premature Atrial Contractions (PACs) from the upper chambers. Capturing these events is important because they can indicate an underlying cardiac issue.
Identifying Failures in the Heart’s Conduction System
Heart monitors can pinpoint specific failures within the heart’s electrical wiring. The heart’s conduction system relies on a signal traveling from the upper chambers (atria) to the lower chambers (ventricles) through the Atrioventricular (AV) node. A heart block, or AV block, occurs when this electrical signal is delayed or completely blocked in its path.
The monitor differentiates between three degrees of AV block. First-degree represents a simple delay in the electrical signal. Second-degree heart block involves some signals failing to reach the ventricles, while Third-degree (complete) heart block means no signals pass from the atria to the ventricles at all. In Third-degree block, the ventricles must generate their own slow, independent escape rhythm, a severe pattern that is clearly identifiable on the tracing.
The monitor can also identify Bundle Branch Blocks, which are delays or blockages occurring lower down in the electrical pathways. The signal is slowed, forcing the impulse to travel a different route to the affected ventricle, making one ventricle contract slightly later than the other. This delay is seen on the ECG as a widened QRS complex, typically longer than 120 milliseconds, which helps determine if the block is in the left or right bundle branch.
Recognizing Electrical Signs of Heart Strain or Injury
Heart monitors are essential for detecting signs of physical stress or damage to the heart muscle. When the heart muscle is deprived of sufficient oxygen, a condition known as myocardial ischemia, its electrical properties change. This lack of blood flow is frequently caused by blocked coronary arteries.
The most recognized sign of strain or injury is a deviation in the ST segment of the ECG tracing. ST segment elevation, where the line is lifted above the baseline, indicates an acute myocardial infarction (heart attack). Conversely, ST segment depression, where the line dips below the baseline, suggests subendocardial ischemia, indicating a lack of oxygen to the inner layer of the heart wall.
T-wave abnormalities are also monitored, as the T-wave represents the heart muscle’s recovery phase. An inverted T-wave, pointing downward instead of upward, is a common finding in myocardial ischemia. These electrical changes provide clinicians with information about the location and severity of the physiological stress on the heart.