Holter Monitoring

Holter monitoring is continuous recording of the electrocardiogram while the patient goes about daily life. A small portable recorder is worn on a belt or around the neck and connected to 3 to 12 electrodes on the chest.

It records for 24 to 48 hours, and patch recorders can record for 7 to 14 days. The patient keeps a diary of symptoms and activities, so the rhythm at the time of symptoms can be checked.

It finds arrhythmias that come and go, which are missed by a 10 second ECG. Typical findings are atrial fibrillation, supraventricular tachycardia, ventricular ectopy, pauses and heart block.

It is useful when symptoms occur daily. In 24 hours, the yield is about 10 to 15% for symptom rhythm correlation, and it falls when symptoms are weekly or less often. For longer events, an event recorder or implantable loop recorder is used.

The test is safe, painless and cheap. Palpitations affect up to 16% of people who consult a doctor, and syncope affects about 1 in 5 over a lifetime.

Detection of atrial fibrillation after a stroke increases from about 5% at 24 hours to about 15% with 7 days or more of monitoring.

Indications.

• Palpitations, dizziness, presyncope or syncope that may be arrhythmic.
• Unexplained stroke or transient ischaemic attack, for atrial fibrillation.
• Known atrial fibrillation or other arrhythmia: rate control, burden and response to treatment.
• Frequent ventricular ectopy (burden) and non-sustained ventricular tachycardia, and monitoring after myocardial infarction or in cardiomyopathy.
• Assessment of antiarrhythmic drugs and pro arrhythmia.
• After ablation or cardioversion, for recurrence.
• Pacemaker and defibrillator function (sensing and pacing), and suspected device malfunction.
• Suspected myocardial ischaemia (silent or vasospastic angina), with ST analysis.
• Heart rate variability in research, and unexplained breathlessness.
• Sleep: nocturnal bradycardia and pauses.

Contraindications and precautions.

• No contraindication. Allergy to electrode adhesive is the most frequent problem.
• The skin is cleaned and dried, and chest hair may be clipped. Electrodes are fixed firmly to avoid noise.
• The patient should avoid water on the recorder and electrodes. Showers are limited unless the device is waterproof.
• Magnets, electric blankets, mobile phones at close range and metal detectors can cause interference.
• The recorder should be worn day and night, and the patient should do usual activities and exercise.
• The diary is completed with time, symptom and activity. A button is pressed at the time of symptoms.
• The device must be returned on time. Lost data are not recoverable.
• Pacemaker patients need the recorder set to detect pacing spikes.

Preparation and technique.

No fasting is needed. Electrodes are applied to prepared skin on the chest (usually five electrodes for three channels, or ten for 12 leads) and connected to the recorder. Signal quality is checked.

The patient receives instructions about the diary, event button, bathing and what to do if an electrode comes off. Symptoms are recorded with the time.

After 24 to 48 hours (or longer for patch recorders), the device is returned and the data are downloaded.

The software detects beats and arrhythmias, and a technician and doctor review the full recording. The report gives the heart rate range, pauses, ectopic beats, runs of tachycardia, atrial fibrillation burden, ST changes and the rhythm at the time of diary entries.

Normal appearances.

• Sinus rhythm throughout, with a mean heart rate of 60 to 90 beats a minute, minimum 40 to 50 during sleep, and maximum 120 to 180 during activity.
• Sinus bradycardia of 40 to 50 during sleep is normal, especially in the young and in athletes. Pauses of up to 2 seconds are normal, and up to 3 seconds in sleep.
• Isolated atrial or ventricular ectopic beats are common. Under 1% of beats (or under 1000 a day) is generally normal.
• Occasional first degree block and second degree block type 1 (in sleep) can be normal in young adults and athletes.
• No sustained arrhythmia and no ST shift of over 1 mm.

Interpretation.

• Atrial fibrillation: irregular rhythm without P waves, with burden reported as the percentage of time. Any episode of 30 seconds or more is significant, and rate control is judged from the mean and maximum heart rates.
• Supraventricular tachycardia: sudden onset and offset of regular narrow complex rhythm. Symptoms match when the diary entry coincides.
• Bradycardia and pauses: sinus pauses of over 3 seconds (while awake), sinus arrest, or high grade atrioventricular block suggest conduction disease and need pacing review.
• Ventricular ectopy: burden over 10 to 15% of total beats is linked to cardiomyopathy. Non-sustained ventricular tachycardia (3 or more beats under 30 seconds) is significant with structural heart disease.
• Sustained ventricular tachycardia (30 seconds or more) or ventricular fibrillation: an emergency.
• Heart rate response: chronotropic incompetence (peak rate under 100 despite activity) and inappropriate sinus tachycardia (mean rate over 90).
• ST depression of 1 mm or more for 1 minute or longer, with symptoms or without, suggests ischaemia. Vasospastic angina typically occurs at night or at rest.
• Symptom correlation: sinus rhythm during symptoms excludes an arrhythmic cause for those symptoms and is useful. A normal result during no symptoms does not exclude arrhythmia.
• Device function: failure to capture, failure to sense or pacing at the wrong rate.
• Artefact: a diary entry that matches movement noise is not an arrhythmia.

Critical values and findings needing immediate action.

• Sustained ventricular tachycardia or ventricular fibrillation: urgent admission, defibrillation capacity, and cardiology.
• Pauses over 5 to 6 seconds, or complete heart block with symptoms: urgent pacing assessment.
• Atrial fibrillation with a fast ventricular rate or pre-excitation: urgent rate control and cardiology.
• Long QT with runs of polymorphic ventricular tachycardia: stop causative drugs, correct electrolytes, and urgent treatment.
• Frequent ST depression with symptoms: urgent evaluation for ischaemia.
• Syncope with a documented bradyarrhythmia: urgent referral for pacing.

Limitations and artefacts.

• A 24 to 48 hour recording misses infrequent episodes, and a normal result is common. Longer monitoring is needed when symptoms are less frequent than daily.
• Many patients have no symptoms during the recording, so the symptom rhythm link is lost.
• Artefacts from loose electrodes, movement, muscle activity and interference mimic pauses, tachycardia or ventricular tachycardia. Full review of the tracing is essential.
• Automated analysis misclassifies beats, so manual review of events is needed.
• Two or three leads give limited ST analysis, and the results are less reliable than an exercise test.
• Diaries are incomplete. Symptoms can occur without a clear cause.
• Detected abnormalities such as ectopy and short runs of tachycardia may be benign, and the clinical context decides.
• Skin irritation and discomfort can limit wear time.
• Data loss from battery failure or electrode detachment.
• Findings do not show structural heart disease, so echocardiography is needed.

Special groups.

• Children: smaller electrodes, and a diary kept by a parent. Normal heart rates are higher.
• Athletes: bradycardia and pauses can be normal.
• Pregnant women: palpitations are common, and monitoring is safe.
• Patients with stroke: prolonged monitoring (7 to 30 days) for atrial fibrillation.
• Patients with pacemakers or defibrillators: device interrogation gives more information.
• Patients with infrequent symptoms: event recorder or implantable loop recorder.
• Regions: Holter monitors are available in few centres, and results may take weeks. Clinical history, 12-lead ECG, pulse palpation and portable devices are used, and symptom triggered recording is a practical option.

Follow up tests.

• 12-lead ECG.
• Event recorder or patch monitor.
• Implantable loop recorder.
• Echocardiography.
• Exercise stress test.
• Electrophysiology study.
• Thyroid function, electrolytes, full blood count and renal function.
• Cardiac MRI for cardiomyopathy.
• Tilt table test for suspected reflex syncope.
• Referral to cardiology or an arrhythmia clinic.