What Is Holter Monitoring?
Ambulatory Cardiac Monitoring
Holter monitoring is considered one of the types of longer-duration ambulatory monitoring as compared with the brief 10-second snapshots an electrocardiogram (ECG) provides. As such, recordings can continue uninterrupted for 24-48 hours. This on-going monitoring has two American Heart Association-sanctioned indications:
- Transient, unexplained palpitations
- Mysterious episodes of dizziness, passing out (syncope), or near-syncope
Aside from these official indications, vascular specialists also find it useful for the following:
- To assess the efficacy of treatment in patients with atrial fibrillation (AF) and observe for covert episodes of it
- To monitor cardiomyopathy patients (ventricular hypertrophy, congenital heart disease, etc.)
- For close surveillance of patients who had recently experienced acute coronary syndrome (ACS)
- To identify “silent” myocardial ischemia
The Holter monitor consists of an array of 3 external electrodes connected to a shoulder strap-carried monitor. The monitor is small enough to allow going about day-to-day tasks, which offers the advantage of identifying events that would ordinarily go hidden or unprovoked by bedrest or the sedentary non-activity other more cumbersome arrangements (e.g., 12-lead ECG) would create. The monitor is returned to the physician’s office for review of the data recorded during the 24-48 hours it was being collected.
Other Cardiac Monitors
When Holter monitoring indicates the need for continuous monitoring or when the 24-48 hours of data fail to identify on-going, intermittent complaints, longer monitoring is effected by implantable (under the skin) loop recorders, about the size of a small thumb drive, which can wirelessly stream the day’s data to the physician over the Internet every evening during sleep. Alternately, a small patch–the Zio patch–can be used. These small devices do not render the data a 3-lead Holter monitor can, but are suitable for continuous, unobtrusive cardiac surveillance; even with their limitations, they can provide helpful–even crucial–data.
Many normal fluctuations in cardiac activity can occur as a result of vagal stimulation, athleticism, medication side effects, or orthostatic- or respiratory-mediated blood pressure changes, and the continuous monitoring provided by Holter monitors and other devices can separate these normal variations from true cardiac pathology.