Usual ECG (electrocardiogram) is recorded over a short period of time, typically within one minute. Certain abnormalities which can be detected by ECG may not occur during the short period of recording. Heart rhythm disorders which are intermittent, may not be recorded on the clinic ECG. Some ECG changes may occur only during certain activities. These can never be recorded in an ECG taken while lying down in the ECG room. The solution to record these is an ambulatory ECG or Holter monitoring. Holter monitors were huge devices earlier, almost to be carried in rucksack! But with advancement of micro-electronics, they are just the size of a mobile phone. The recorders can be kept in a belt pouch and leads can be attached over the chest. Number of electrodes depends on how many channels of ECG you need to record. Most recorders have a battery life of 24 to 48 hours of recording and a still higher standby time available for downloading the data to a Holter analyzer. Holter analyzer is a computer with an appropriate software application to which Holter data is downloaded for analysis. Automatic printouts are available after the analysis. The medical technician who analyzes it can review the representative ECGs for each abnormality and verify accuracy, to avoid false reporting by the software. Supervising physician can also oversee the technician’s report.
Who needs a Holter?
As it is already discussed, it is those who have intermittent heart rhythm disorders who benefit from Holter. Those with palpitation, dizziness or blackouts may benefit from ambulatory ECG monitoring. Stroke patients who are suspected to have a rhythm disorder known as atrial fibrillation (AF) also benefit from ambulatory ECG monitoring. Documentation of AF can be done by automatic analysis supplemented by manual inspection of the tracings. Those with AF will benefit from medications which prevent blood clotting (anticoagulants).
How can you correlate symptoms with the abnormalities on Holter?
Holter monitors have event marker buttons which the user presses when there is any symptom. This marking is available on the tracing during review so that exact correlation with symptom is possible. Keeping a diary of activities during the recording period is useful to find out the correlation between activities of daily life and the abnormalities if any.
What if Holter does not pick up any abnormality?
Either you repeat it on another day or longer term event monitors can be used. Event monitors do not record the whole ECG data, but keeps on monitoring and storing in a temporary memory. When ever a significant event is detected or the user presses the event marker button, data preceding the event as well as a short period of forward recording goes into a permanent memory, which can be retrieved during analysis. Event monitors can be used typically for one week to three months. Event monitors are also called external loop recorders. Still longer periods lasting up to 3 years is possible with implantable loop recorders.