01Purpose and principlesWhat the assessment is for and the core concepts behind it.
Ambulatory monitoring is a sampling problem. Diagnostic yield depends more on matching recording duration to symptom frequency than on choosing the most familiar device.
Continuous patch or Holter systems quantify rhythm throughout wear; event and external loop systems store selected episodes; an implantable loop recorder continuously overwrites memory and stores automatically detected or patient-marked events over years.
The goal is a defensible symptom-rhythm correlation or exclusion of arrhythmia during a typical event, not simply finding isolated ectopy.
Key points
- Choose the monitor from event frequency: short continuous recording for daily events, longer external recording for less frequent events and an implantable recorder for infrequent unexplained syncope.
- NICE recommends 24-hour ambulatory ECG when suspected paroxysmal AF episodes are less than 24 hours apart or asymptomatic episodes are suspected.
- For suspected paroxysmal AF with episodes more than 24 hours apart, use longer ambulatory ECG, event recording or another appropriate ECG technology.
- In suspected arrhythmic syncope, ambulatory ECG is first-line; do not put tilt testing ahead of rhythm monitoring.
- A symptom diary with exact clock time, activity and symptoms materially improves interpretation.
- Patient-triggered devices miss asymptomatic events and events causing immediate loss of consciousness; auto-trigger capability matters.
- A negative short recording is non-diagnostic when the target event did not occur.
02Indications, selection and cautionsWhen it is useful, when urgency changes and important limitations.
Symptomatic pauses, high-grade AV block or profound bradycardia require prompt specialist assessment and may lead to pacing.
A broad-complex sustained tachycardia, especially with syncope or structural heart disease, needs emergency assessment rather than routine report follow-up.
An irregularly irregular narrow-complex rhythm without consistent P waves should be confirmed on an interpretable ECG strip; device algorithms alone can generate artefact.
A typical event during documented sinus rhythm makes an arrhythmic cause less likely, provided recording quality was adequate.
Premature beats are common; quantify burden, complexity, symptoms and structural-heart context before assigning significance.
03Method and interpretationA systematic approach to the test and its findings.
Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.
- 01
24–48-hour continuous ECGFirst step - Why
- Capture daily palpitations, frequent presyncope or suspected frequent/asymptomatic AF.
- Interpretation and limitations
- A negative study is useful only if a representative symptom occurred or the clinical question was arrhythmia burden.
- 02
Multi-day patch monitor - Why
- Increase continuous sampling for symptoms occurring every few days.
- Interpretation and limitations
- Check analyzable wear time, event markers and raw strips for algorithm-labelled arrhythmias.
- 03
External event or loop recorder - Why
- Capture symptoms separated by days to weeks.
- Interpretation and limitations
- Auto-trigger helps capture asymptomatic rhythm and events that impair the patient's ability to activate the device.
- 04
Implantable loop recorder - Why
- Investigate infrequent recurrent unexplained syncope or selected cryptogenic events over long periods.
- Interpretation and limitations
- Review stored electrograms, programming and symptom timing; false detections from undersensing or oversensing are common.
- 05
Echocardiography and baseline ECG - Why
- Identify structural disease and fixed electrical abnormalities that alter risk.
- Interpretation and limitations
- Abnormal structure or baseline conduction disease lowers the threshold for urgent electrophysiology assessment.
04Clinical next stepsHow the result changes management or prompts escalation.
01Preferred routeIntermittent palpitationsFirst stepPreferredNo diagnostic rhythm on a resting ECG+
- 1Clarify frequency, duration, regularity, triggers and associated syncope or chest pain; obtain baseline ECG and relevant blood tests.
- 2Select continuous 24-hour monitoring for daily or very frequent episodes and longer patch or event recording for less frequent episodes.
- 3Require raw ECG confirmation of algorithm-detected AF or tachycardia.
- 4EscalationEscalate sustained arrhythmia, pre-excitation, high-grade conduction disease or symptoms with haemodynamic compromise.
02AlternativeSuspected paroxysmal AFAlternativeAF is suspected but absent from a 12-lead ECG+
- 1Use 24-hour monitoring when episodes are less than 24 hours apart or asymptomatic episodes are suspected.
- 2Use longer ambulatory or event monitoring when symptomatic episodes are more than 24 hours apart.
- 3Confirm AF on an interpretable ECG trace before applying the AF treatment pathway.
- 4Once confirmed, assess stroke and bleeding risk and address rate or rhythm symptoms under NICE NG196.
03EscalationInfrequent unexplained syncopeEscalationSuspected arrhythmic syncope occurs less often than every 2 weeks+
- 1Complete red-flag assessment, 12-lead ECG and structural evaluation; urgently refer when high-risk features are present.
- 2Offer an implantable event recorder when arrhythmia remains suspected and events are infrequent, as recommended by NICE CG109.
- 3Programme auto-activation and teach patient or witness activation and wound care.
- 4Review transmissions after symptoms and act urgently on significant pauses, block or ventricular arrhythmia.
05Risks, monitoring and follow-upComplications, safety checks and further assessment.
- Check skin tolerance, device adhesion, battery and analyzable recording time.
- Reconcile symptom diary times with device clock and stored electrograms.
- For implantable recorders, monitor wound healing, remote connectivity and alert programming.
- Review clinically important alerts through an agreed pathway with documented response times.
- Stop or change strategy when a representative symptom-rhythm correlation answers the question.
06Special situationsVariants, exceptions and circumstances that change the usual approach.
Frequency chooses duration
A technically excellent 24-hour Holter is the wrong test for a symptom occurring every 6 weeks.
Raw strips outrank labels
Motion artefact, undersensing and ectopy can fool automated AF, pause and tachycardia detection.
No event means no exclusion
A normal trace without the patient's usual symptom does not exclude a paroxysmal arrhythmia.
ILR is diagnostic, not protective
An implantable loop recorder records rhythm but does not pace or terminate tachyarrhythmia.
Symptom-free arrhythmia matters
AF or ventricular arrhythmia may be clinically relevant even without a diary marker; interpret duration and context.
07Common pitfallsFrequent interpretation and management errors.
- 01
Defaulting every patient to a 24-hour Holter regardless of symptom frequency.
- 02
Accepting a smartwatch or device label as AF without an interpretable ECG trace.
- 03
Using ambulatory monitoring instead of admission for high-risk syncope.
- 04
Calling a negative study reassuring when no typical event occurred.
- 05
Failing to tell the patient how and when to mark symptoms or seek emergency help.