Other monitoring

Continuous ambulatory ECG monitoring: Holter monitoring

• Holter monitoring: Ambulatory ElectroCardioGraphy (AECG) was first introduced by Holter in 1961
• Continuously records the patient’s ECG (via electrodes on the chest) over anything from 24 hours to 7 days, on a digital recorder
• The patient’s history is essential to determine if this test will prove informative

Indications

To determine if there is any relationship between transient (at least once/day) symptoms and underlying cardiac arrhythmias. Symptoms may be:

• Syncope or near syncope
• Dizziness
• Palpitations

Other indications include:

• To determine if there are conduction disturbances e.g. sinus node disease or AV (atrio-ventricular) block
• To assess ventricular rate control in atrial fibrillation
• To assess response to antiarrhythmic drug therapy
• To analyse the performance/function of pacemakers and other implantable devices
• To assess parameters of heart rate (HR) variability (this can be a predictor of mortality in cardiac patients at high risk.) (Ref: ACC/AHA 1999)

Analysis

• The ECG recording captures a continuous reading of heart rate and rhythm, provides a note of the HR variability; the number and frequency of extrasystoles; pauses (sinus arrest or asystole); tachyarrhythmias such as atrial fibrillation; or bradyarrhythmias such as heart block.
• The patient keeps a diary – notes activities and symptoms
• Computer and software programmes analyse the data at high speed
• A critical element is review of the analysis by a physiologist or clinician
• Motion artefact can present a problem

Possible diagnostic findings may be:

• Typical symptoms occur at the same time as a documented arrhythmia
• Symptoms occur even though there is no arrhythmia evident
• The patient is asymptomatic during an arrhythmia
• The patient is asymptomatic during the monitoring time period and no arrhythmias are evident

Advantages:

• Ease of use
• Precise quantification

Disadvantages:

• Short duration of monitoring, therefore, if no symptoms or arrhythmia experienced during this time, of no value

Intermittent ambulatory electrocardiography (AECG)

One type of AECG recorder is a hand-held patient-activated event monitor. The patient places the event monitor, which has 4 contact points, on their chest. It stores 30 seconds of ECG activity when activated by the patient. An example is the “King of Hearts” device.

Another type of AECC is the External loop recorder – with this type of AECG, 2 electrodes are attached to the patient’s chest and it is worn continuously. The electrodes attach to the monitoring device. The loop memory continuously records and deletes ECG. When activated by the patient, typically after symptoms have occurred, 30secs-15mins of pre-activation ECG is stored and can be retrieved for analysis.

The event monitor is better for very fleeting /infrequent symptoms or to capture the onset of a tachycardia.

The data is stored digitally then can be downloaded by the physiologist to be analysed. The data can also be transferred digitally over the Intranet to the physiologist at the hospital.

Indications:

• Patient experiencing intermittent palpitations
• Pre-syncope

Advantages:

• Can be used to monitor the heart rhythm for anything from 1-30 days
• Ease of use
• Not invasive or painful

Disadvantages:

• Dependent on patient activation which means the patient needs to have awareness of their symptoms starting
• Skin electrodes for some types

What is an Implantable Loop Recorder (ILR)?

• A subcutaneous implantable recorder which allows ECG monitoring for up to 18 months. It is usually implanted in the infraclavicular area.
• Consists of a single-lead ECG system, which is initiated by the patient through application of a magnet or it can be programmed to record rhythms automatically , on the basis of pre-programmed rate-limit thresholds.
• It stores the rhythm recorded for several minutes before and after the device is activated.
• Even if no warning, the patient can activate the device following the return of consciousness and it will store a brief period of data from before, during and after.
• The stored recordings can be retrieved by radiotelemetry-based interrogation of the device (as with pacemakers and ICDs).
• An example is the “Reveal Plus” device. (As shown in the image on previous page.)

Indications:

• Recurrent syncope, where initial investigations including Holter monitoring and EPS have not been diagnostic.
• Palpitations that are too infrequent for an event recorder to capture.

Risks / limitations:

• An important limitation of relying on the ILR before providing treatment is that the clinician must wait for the patient to experience another episode of syncope, which may carry some risk of being fatal eg the underlying rhythm may be episodes of asystole. However the risk is considered low in patients without structural heart disease or known familial arrhythmias.
• Infection

Advantages:

• Long period of observation
• No skin electrodes
• ILR can lead to a correct diagnosis, thereby avoiding inappropriate therapy, based on a presumed cause of syncope.

Disadvantages:

• Invasive
• Dependent on patient activation immediately after they regain consciousness, which they may forget to do.