Ambulatory ECG Monitoring

Long term ECG recording is used to assess or monitor a patient’s heart rhythm and conduction over and extended period of time. It is also employed to gauge the risk stratification of a population, and to monitor the efficacy of prognostic medical therapy on known rhythm abnormalities.

There exist many different brands of ambulatory ECG (AmbECG) recorder, but there are, for all intents and purposes, three main varieties;

  • Full-disclosure recorders (Holter)
    • Documents every beat produced by the patient in the given time period
  • Event recorders
    • Either uses an algorithm to record what is deemed abnormal, or controlled by the patient themselves, when they experience symptoms
  • Implantable Loop Recorders (ILR)
    • Surgically implanted, longer term recording that transmits abnormal rhythms to a care centre to be analysed remotely

A general recommendation is to use AmbECG if a patient suffers from unexplained;

  • syncope
  • near-syncope
  • episodic dizziness
  • recurrent palpitations

Symptom manifestation is key when deciding which type of monitor to use;

  • Daily, or near-daily symptoms;
    • 24-7day Holter full-disclosure recording
  • Less frequent;
    • Event monitor
    • ILR

Holter Monitoring

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  • 24hr – 7 days
  • 2 or 3 channel recording
  • Records every cardiac cycle
  • Patient event button
  • Software generally includes analysis algorithms for (at least):
    • Events (both software and patient determined)
    • Heart rate variation (HRV)
    • R-R interval
    • ST segment
    • QTc

Patients should be advised against removing the electrodes. For 24hr recording, inform the patient that they may not shower or bathe, rather they must wash around the electrodes.

In the case of 48hr recording and longer, extra electrodes should be provided, and an assurance that the patient knows they must replace the electrode pads after washing, so showing the patient where to apply the replacement stickers is important.

Event Monitoring

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  • 2-4 weeks, but sometimes up to 3 months
    • Used for paroxysmal symptoms
  • 2 channel recording
  • Records abnormal rhythms automatically
    • Sets “normal” rhythm, and records deviations
  • Patient event button
  • Differing memory capacities between device brands
    • Some offer 10 patient activations, others more
  • Recordings transmitted wirelessly, or physically at the end of recording period

As with Holter monitoring, extra electrodes should be provided, and an assurance that the patient knows they must replace the electrode pads after washing, so showing the patient where to apply the replacement stickers is important.

Implantable Loop Recorder

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  • Used to monitor for years
  • Subcutaneous monitor
    • Placed in the subclavicular region
    • Relatively risk-free; 1.5% of patients suffer infection, 0% mortality
  • Similar mechanics to the event recorder
  • Wireless data transfer
    • Transfer station provided with monitor

Patients should be instructed how to transfer data to the issuing care trust. Storage is limited, so manual transfer should be done weekly. Potentially serious arrhythmic recordings are sent automatically by the monitor, when it is in range of the transmit station.

Indications for AmbECG Implementation

The evidence classification table these guidelines refer to, can be found here

Class I

  • Unexplained:
    • Syncope
    • Episodic dizziness
    • Recurring palpitations

Class IIb

  • Unexplained:
    • Episodic shortness of breath
    • Chest pain
    • Fatigue
    • Neurological events wherein transient AF/Flutter is suspected
  • When non-cardiac condition is being treated, yet symptoms persist:
  • Near-syncope
  • Syncope
  • Episodic dizziness
  • Palpitations

Class III

  • After causes have been identified via physical examination, history or lab tests:
    • Near-syncope
    • Syncope
    • Episodic dizziness
    • Palpitations
    • Cerebrovascular accidents with no other evidence of arrhythmia

Holter Monitoring:

  • Daily or near-daily symptoms, in line with classifications

Event Monitoring:

  • Symptom frequency making 24hr – 7 day recording unlikely to be diagnostic
  • Non-diagnostic Holter recording, with continuation of symptoms
  • Cryptogenic stroke

Implantable Loop Recorder

  • Serious symptoms occurring less than monthly
  • After non-diagnostic, shorter-term recording, with continuation of symptoms

AmbECG used in Risk Assessment

Post-MI 

Patients for whom a myocardial infarction has been survived are under greater threat of ventricular arrhythmia, coronary heart disease and subsequent sudden cardiac death, so may undergo AmbECG monitoring to assess their risk.

Treatment can be used to assess PVCs, specifically their frequency and focal origin.

On its own, AmbECG is only around 5-15% accurate, but when combined with monitoring of LV function, the predictive value jumps to 15-34%

Hypertrophic Cardiomyopathy

Due to the increased risk of syncope and sudden death in HCM patients, AmbECG can offer prognostic information, but due to conflicting studies linking heart rate variation to ventricular arrhythmia, and treatment reducing mortality, it is currently unclear as to whether routine ambulatory monitoring is beneficial.

Pre and Postoperative

Although preoperative monitoring of patients with known BBB is recommended, there is currently no data citing it as being beneficial, or indicative of suitability.

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