A cardiac event monitor is a small, portable device used to record the heart’s electrical activity, or electrocardiogram (ECG), over an extended period as a person goes about their daily life. This monitoring tool is designed to capture irregular heart rhythms, known as arrhythmias, that occur too infrequently to be detected during a brief, in-office ECG test. The device functions as a diagnostic aid, providing physicians with a snapshot of the heart’s rhythm at the exact moment a patient experiences symptoms like palpitations, dizziness, or fainting. Documenting the heart’s behavior during these events helps pinpoint the underlying cause of the patient’s intermittent cardiac concerns.
Event Monitor vs. Holter Monitor
The primary factor determining whether a patient receives an event monitor or a Holter monitor is the frequency of their symptoms. Holter monitors are typically worn for a short duration, usually 24 to 48 hours, and continuously record every single heartbeat during that time. This makes the Holter monitor the preferred choice for patients who experience symptoms on a daily or very frequent basis.
Conversely, an event monitor is used when symptoms are intermittent or infrequent, occurring perhaps once a week or even less often. The device is typically worn for several weeks, often up to 30 days, or until a significant symptomatic event is recorded. The event monitor’s longer wear time is suited for capturing rare arrhythmias, which might include episodes of atrial fibrillation, bradycardia (slow heart rate), or tachycardia (fast heart rate).
The core difference lies in the recording strategy: the Holter records continuously for a short time, while the event monitor records selectively over a long time. This selective approach ensures that when a patient experiences a symptom, the device is ready to capture the relevant cardiac data.
How Event Monitors Capture Cardiac Activity
Most modern event monitors utilize a specialized feature called “looping memory” to ensure the capture of the crucial moments leading up to a symptom. The monitor is constantly sampling and temporarily storing the heart’s electrical activity, typically holding the most recent few minutes of ECG data. This temporary data is continually overwritten until the device is manually activated by the patient.
When a patient feels a symptom, such as fluttering or lightheadedness, they press a button on the device to record the “event.” Because of the looping memory, the recorded strip of ECG data includes the heart rhythm from before the patient pressed the button, during the symptomatic period, and for a short time after the activation. This pre-symptom data is valuable for physicians, as it reveals the exact rhythm change that triggered the patient’s symptoms.
Once the recording is saved, the captured ECG data is transmitted wirelessly via cellular signal or over a phone line to a monitoring center for analysis. Some sophisticated monitors also feature an automatic recording function, which autonomously saves an ECG strip if it detects a rhythm that deviates from pre-set normal parameters, even if the patient does not press the button.
Patient Experience and Daily Use
For models that use electrode patches, the skin must be clean and dry before placement, sometimes requiring the area to be shaved to ensure good contact for the sensors. Patients are typically given extra patches and instructed on how to change them regularly to maintain signal quality and minimize skin irritation from the adhesive.
While wearing the monitor, patients are advised to avoid getting the device wet, meaning they must remove it before showering or swimming. Excessive sweating during strenuous activity can also compromise the adhesion of the electrodes, necessitating a change of patches after exercise. Patients are also instructed to keep the device away from strong magnetic fields and certain electrical appliances, like electric blankets or some razors, as these can interfere with the electrical signal recording.
Maintaining a detailed symptom log or diary is essential for successful monitoring. Each time the patient activates the monitor, they must record the exact date and time, the specific symptoms they felt—such as “skipped beat” or “dizziness”—and what activity they were engaged in at that moment. This meticulous documentation allows the reviewing cardiologist to correlate the patient’s subjective symptoms with the objective electrical data captured by the device.
Interpreting the Data and Next Steps
Once the monitoring period is complete, or an event is transmitted, the recorded ECG data is sent to a monitoring service or directly to the physician’s office for review. A cardiologist or a trained technician examines the strips of heart rhythm, paying close attention to the recordings captured when the patient reported a symptom. The primary goal of this interpretation is to determine if the reported palpitation or dizzy spell corresponds to an actual, identifiable cardiac arrhythmia.
By cross-referencing the patient’s symptom log with the recorded ECG, the physician can confirm a diagnosis of a specific rhythm disorder, such as atrial flutter or a heart block. If the data shows that the patient’s symptoms occurred during a normal heart rhythm, it may provide reassurance and direct the diagnostic process toward non-cardiac causes.
If an abnormal rhythm is identified, the next steps depend on the type and severity of the diagnosis. This may involve prescribing antiarrhythmic medication, recommending lifestyle changes, or planning for further interventions, such as an ablation procedure or the implantation of a pacemaker.