Reviewing the ECG of the Holter monitor

The patient comes back with a completed Holter monitor recording. How do you get started reviewing hours of ECG records? To what extent can you trust the analyzer software? Our expert explains the cornerstones of Holter interpretation, including finding the baseline ECG rhythm, looking for pauses, brady- and tachycardias, and reviewing fragments associated with symptomatic episodes.

Holter monitoring is an essential tool in every clinician’s kit. This course will give you the confidence to select the best type of ECG monitor for your patient’s clinical indication, maximize diagnostic yield, and identify and troubleshoot the most common problems. You’ll learn how to correlate your patient’s symptoms with the rhythm strip and confidently report your findings. Become a master in Holter monitoring and confidently analyze and report monitoring results with this course.

When it comes to downloading and analyzing the ECG, it is best to take a structured step-by-step approach. A lot of the modern Holter analysis systems will auto-analyze the recording as it is downloaded. They also have a variety of functions to help you review the recordings such as stop, start, and pause functions. These allow you to play back selected portions of the ECG. You can also zoom in and zoom out on selected ECG strips and you can choose to run the strip at different speeds. All of these functions are there to assist you. However, ultimately you are the operator. So where do we start?

Firstly, we begin with a symptom diary. Most analysis systems will let you add symptom events onto the recordings. So, there is a clear time when the patient has had a symptom. This is the first step. Knowing a patient had a symptomatic episode is the most important factor before we start reviewing the recording. Once you have entered any symptomatic episodes, you are ready to start running the recording. A lot of Holter software will highlight beats which it thinks are abnormal. Generally, a Holter system will decide beats are normal by assessing the amplitude, width, and duration. The software will create a normal template and generally if a beat does not match the normal template, the software will identify that beat as abnormal, or an arrhythmia.

The single most important aspect when reviewing the ECG is to note what the analyzer is showing while looking at the ECG for yourself as it runs. The analyzer is there to help guide you. It is not there to report the recording on its own. So, at the start of the Holter recording, what is the patient's baseline rhythm that you see? Is it normal sinus rhythm? Atrial fibrillation? Is there a bundle branch block morphology? Or is the QRS width normal? It will be important as you review the ECG to note any initial abnormalities.

Also, what we look for at the start of the recording, is whether the waves and intervals have normal durations. Is the PR interval normal? Are the QRS duration and the QT interval normal? Are there any baseline abnormalities evident, such as the delta wave and a short PR interval of Wolff Parkinson White syndrome? Once we've established the initial baseline rhythm, we go on to look for any episodes of tachycardia or bradycardia that we may want to assess in more detail.

During these episodes, is that rhythm still sinus? Or is there evidence of atrial ventricular arrhythmias or any evidence of atrioventricular block? What was the patient doing at the time? Is the rhythm appropriate for the context such as sinus tachycardia when exercising, or sinus bradycardia when sleeping? Are there any pauses during review? Did they occur during daytime hours? Or nocturnally? Are they sinus pauses? Or is there AV block? Was the patient symptomatic to pause and if so, for how long?

Generally, most cardiac electrophysiologists consider six seconds as diagnostic and in the context of AV block rather than sinus pauses. If it is a young patient, you should consider that they might simply have a high vagal tone. We are also looking for premature complexes, both atrial and ventricular. When you see premature beats, you need to identify whether they are coming from the atria or the ventricles. As well as identifying the origin of premature complexes, we also want to know how many there were during the recording, and whether the patient was symptomatic to them.

The analyzer software will normally count the total number of premature complexes, both atrial and ventricular, and provide you with the absolute number of each. It will also provide the proportion of total heartbeats that they account for expressed as a percentage. This is the overall burden. However, it's important to ensure that the software is identifying premature beats correctly. Otherwise, the automated data will be misleading.

If a recording demonstrates frequent premature ventricular complexes or PVCs, it is important that the review states whether they are unifocal or multi-focal, unifocal PVCs are coming from the same focus and if the patient is symptomatic, to these ablation can be considered. Ablation is technically more challenging when the PVCs are coming from different areas. Are there any arrhythmias demonstrated such as supraventricular tachycardia? From a diagnostic perspective, it is important to state whether the tachycardia is of abrupt or gradual onset, and also how the rhythm terminates.

If there are episodes of paroxysmal atrial arrhythmias such as atrial fibrillation or atrial flutter, how long do the episodes last? What is the overall AF or atrial fibrillation burden expressed as the percentage of the recording which the patient spends in AF? This is important when trying to decide whether a patient may need anticoagulation and also in monitoring their response to treatment. So, to summarize, we have established that reviewing a Holter requires structure.

Firstly, assess the symptom diary. If the patient had symptoms, ensure that the ECG findings at the time of the relevant symptoms are noted. Check the rhythm and beat morphology at the start of the recording and note any baseline abnormalities. Ask yourself if they are appropriate for the context. For example, exercise, rest, or sleep. Diagnose beat morphologies and check for pauses. Don't forget to establish whether they are intermittent or constant. And as always note frequency onset and offset of each individual event as they occur.