Diagnosis via Holter Monitor
The 12-lead electrocardiogram (ECG) is the gold standard by which cardiac health (or the lack thereof) is confirmed. To understand its advantages, it is important to know the differences between electrodes and leads. An ECG with only 3 electrodes has only 3 leads, the leads referring to the “views” from a certain direction determined by an electrical “bridging” between two of the leads. When another 6 electrodes are added to the mix, it is possible for some electrodes to have associations with more than one other electrode, so the lead count increases to 12 in a “round-robin” of sorts. The result is a 360° view of the electrical goings-on of the heart from all directions.
The wave of electrical activity in the heart originates in the atria and travels down the heart’s electrical conduit; it is directional such that there is a synchrony of non-simultaneous contractions in the atria and ventricles to create a vector force outward from the heart, supplying the body with blood and perfusion. The different leads (or views) of an ECG can catch the direction of these electrical waves of stimulus from different viewpoints to create a picture of not only when–but where–difficulties or abnormalities in these waves occur. This identifies where arrhythmias may be originating, where ischemia has occurred, or whether infarction of heart tissue has already happened or is pending.
Data Accrued by a Holter Monitor
Although the data from the 3-electrode Holter monitor is more limited than the 12-lead ECG, it will still render data for a report that will include total heart beats, heart rates (average, minimum, and maximum), any premature supraventricular (atrial or junctional) or ventricular beats, arrhythmias, episodes of prolonged electrical “pauses,” ST segment changes on the ECG indicative of ischemia, and patient “marked” symptomatic episodes for comparing such symptoms with the associated cardiac recording at the time.
Other Types of Monitors
Another type of monitor is the Zio patch, a small, adhesive patch that has the advantage of being temporary, convenient, and yielding up to 14 days of data. Its disadvantage is that only one view (direction, or “lead”) is obtained, making it less thorough than the 3-lead Holter monitor. This limits its effectiveness in identifying ischemia, but it still can render important information on premature beats, arrhythmias, “pauses” in perceived cardiac activity, and patient “marked” episodes for correlation with the simultaneous cardiac electrical activity.
The “loop” recorder is a small device–about the size of a thumb-drive–implanted under the skin with enough battery power to last a few years. Nightly it will send a report wirelessly to a bedside unit that will convey data to a patient’s doctor with a day’s worth of accrued data for evaluation.
While the patch and the implanted loop recorder are small and unobtrusive, their data is more limited than a full 12-lead ECG or the 3-lead Holter monitor, but they offer a last resort to catch pathology in action when even 48 hours of Holter monitoring fails to spot trouble. Patients cannot remain recumbent in an ECG lab for days, and the Holter monitor offers the next best chance to catch an occult, fleeting, or intermittent cardiac event as it happens, even with the limited “view” of one-lead surveillance. When the Holter comes up inconclusive, these other methods can extend surveillance by weeks or even years.
All of these methods allow patient “bookmarking” to tag the simultaneous electrical activity that occurs with suspicious symptoms they want to point out.