In ambulatory ECG registration the patient's heart is continuously monitored during daily activities with a portable ECG-recorder. It is used for the investigation of cardiac arrhythmias (tachy- and bradycardias) or disturbances of consciousness.
The most commonly used devices are a Holter monitor (1-2 days), an event recorder (2-4 weeks) and an implantable loop recorder (12-36 months).
A "negative" Holter recording does not exclude severe arrhythmias, if there were no symptoms during the recording. On the other hand, a normal rhythm during typical symptoms excludes arrhythmia as an aetiological factor and helps to redirect the investigations to other causes.
Indications
Investigation of tachycardia episodes
Investigation of symptoms suggesting bradycardia or pauses (suspicion of malfunction of the sinus node or the atrioventricular (AV) node)
Investigation of a feeling that the heart is "skipping beats" or beating unevenly (e.g. number of extrasystoles)
Assessment of the efficacy of antiarrhythmic drugs (e.g. in atrial fibrillation, extrasystoles)
Assessment of the ventricular rate in patients with permanent atrial fibrillation
Investigation of unclear episodes of disturbed consciousness, dizziness or convulsions
Investigation of a cryptogenic stroke
In exceptional cases, ambulatory ECG monitoring can also be used for:
diagnosis and monitoring of ischaemia;
investigation of pacemaker malfunction and optimization of the settings;
medical surveillance of people with hazardous occupations (such as pilots).
You should be cautious about ordering "therapeutic" Holter investigations because the use of ambulatory ECG recording without a specific indication may lead to problems in interpretation of the clinical significance of the findings.
Choice of method
When choosing the method of ambulatory ECG recording, the frequency of symptoms and whether the patient is capable of switching ECG recording on when symptoms appear are essential.
Three-channel recording is normally used for ordinary Holter recording (1-2 days), with electrodes attached in standard places on the patient's chest. It is most suitable for examining symptoms occurring nearly every day.
Today, there are systems where recording can be performed by a health centre, for example, and a cardiologist can check it via Internet and give instructions for treatment. This improves the availability of ambulatory ECG recording.
Recording can be continued for several weeks, if necessary, by using special electrodes or attaching the recorder over the patient's heart ("patch Holter").
Event ECG recording (2-4 weeks) is mainly used for examining paroxysmal tachycardia. It is by nature poorly fitted for examining asymptomatic arrhythmias. In addition, its use is restricted by the fact that the patient needs to activate recording when symptoms occur.
The patient carries a small recorder, and ECG recording can be activated by pressing the recorder with the thumb when symptoms occur, for example.
Recordings are usually sent for analysis through the mobile phone network or through a wireless Internet connection. There are also smartphone applications available for this purpose.
An implantable loop recorder (1-4 years) is used more rarely. The device is implanted under the skin on the patient's chest for continuous monitoring of the heart rhythm. These devices are mainly used for examining rarely occurring unclear attacks of unconsciousness.
When predefined criteria (such as a certain length of pause or a certain heart rate) are met, the device will record an ECG for subsequent analysis. The patient can also switch on ECG recording when typical symptoms appear.
Pacemakers and implantable cardioverter defibrillators monitor the heart rhythm continuously. They can record the ECG automatically during an attack or when activated by the patient; this function should be utilized when investigating the symptoms of patients with such devices. Nevertheless, the devices should not be implanted just for diagnosis.
Recently, mobile phone applications and portable devices for self-monitoring of heart rhythm have become available to patients. These are particularly suitable for the screening of atrial fibrillation, and patients should be encouraged to use them. If the device does not register ECG, the diagnosis must be confirmed by another method.
Interpretation
Ambulatory ECG recording should be interpreted by a cardiologist or other physician who is well acquainted with the use and interpretation of the method.
The cardiologist/other physician should be familiar with the limitations and sources of error associated with automatic methods of analysis (artefacts, classification of wide complex extrasystoles, etc.). All abnormal findings should be checked manually.
The information collected by ambulatory ECG recording must always be interpreted in relation to the patient's age, cardiovascular and other diseases as well as symptoms.
Without sufficient history (appropriate referral) and a carefully filled symptom diary, it may not always be possible to make a conclusive statement on the pathological significance of the findings.
Atrial fibrillation is an exception to this, since due to the risk of thrombosis it is always a significant finding, irrespective of symptoms (see further information below).
Typical findings and their clinical significance
The doctor in charge of the patient usually receives only a statement and some printouts of sections that are most essential for the interpretation. Here are some guidelines for the interpretation of common findings.
Even healthy, asymptomatic persons are often found to have single extrasystoles and short episodes of tachycardia (3-10 beats).
When examining Holter recordings you should be aware that computer-based analysis programmes always interpret a wide complex beat as a ventricular extrasystole.
Frequent ventricular extrasystoles (> 3 000-5 000/day) usually warrant ensuring whether the heart is structurally and functionally healthy. The most common further examinations are echocardiography, exercise stress testing and coronary CT angiography.
Frequent atrial extrasystoles (P-on-T) may signify latent susceptibility to atrial fibrillation.
Regardless of the symptoms, persistent wide or narrow complex tachycardia always requires more specific cardiological examinations and treatment.
The clinical significance of a single sinus pause or occasional AV conduction disorders depends on the associated symptoms.
Asymptomatic bradycardia is usually not an indication for the implantation of a pacemaker but even short pauses (2 to 3 seconds) that cause severe symptoms may be such an indication.
Nocturnal sinus bradycardia, short sinus pauses and Mobitz 1 type AV conduction disorders are normal phenomena in young, healthy people.
ST-T-changes found in ambulatory ECG monitoring should always be interpreted with caution. The diagnosis of ischaemia can be improved by using a 12-lead Holter device.
A "negative" Holter recording does not exclude severe arrhythmias, if there were no symptoms during the recording. On the other hand, a normal rhythm during symptoms excludes arrhythmia as an aetiological factor and helps to redirect the investigations to other causes.