The value of monitoring in-context to a lifestyle, over a longer period, increases the chance of capturing the ECG at times of symptoms. However, so that the procedure is minimally invasive to that lifestyle, the equipment required to carry out the monitoring must be portable and lightweight. An ambulatory ECG will therefore record the ECG for much longer than a 12-lead, but will use fewer leads.
In addition to monitoring the ECG, symptoms should be recorded in a diary to aid the task of diagnosing their cause.
Ambulatory electrocardiography falls into one of two categories:
- continuous (Holter monitoring) and
- intermittent (event monitoring).
For patients suffering from intermittent symptoms, the chances of an event during the few minutes of a resting ECG test are very small. In this case a Holter test is used to monitor cardiac activity continuously for 24 hours, which greatly increases the chances of detecting the cause of the symptoms.
Conventional devices store the ECG on tape or smart cards for later analysis by a technician using a computer.
The Cardionetics C.Net5000 fits into this category, however due to its automated classification of arrhythmia it produces an instant report, and does not require any further analysis on a computer. The C.Net5000 is designed for primary care use.
For patients who do not present their symptoms as regularly as once per day, a longer term test is required. Intermittent recorders are symptom-driven and fit into two categories:
- Loop recorders are connected to the patient for up to 7 days and store the previous 20 minutes of ECG data in a loop. When the patient experiences symptoms they press a button and the data is recorded for later analysis.
- Event recorders are not connected to the patient but are placed on the chest during a symptom. They have electrode contacts built into the casing to detect the ECG. These devices are useful to detect very intermittent events that last for several seconds. Otherwise they can be missed as it takes time to find, position and activate the recorder.
When to use Ambulatory Electrocardiography
- Patients with unexplained syncope, near syncope, or episodic dizziness with no obvious cause.
- Patients with unexplained recurrent palpitation.
- Patients with episodic cardiac symptoms: shortness of breath; chest pain; fatigue.
- Patients with episodic neurological symptoms with suspected atrial fibrillation or flutter.
- Patients with syncope, presyncope, dizziness or palpitation, which persist despite treatment of another suspected cause.
- To assess antiarrhythmic drug response in individuals in whom baseline frequency of arrhythmia has been well characterised as reproducible and of sufficient frequency to permit analysis.
- To detect proarrhythmic responses to antiarrhythmic therapy in high-risk patients.
- For the evaluation of frequent symptoms of palpitation, syncope, or near syncope, to assess pacemaker and implantable cardiac defibrillator devices.
- For the assessment of arrhythmia risk after myocardial infarction.
For more information on indications for ambulatory electrocardiograpy, see: Crawford et al, ACC/AHA guidelines for ambulatory electrocardiography: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Committee to Revise the Guidelines for Ambulatory Electrocardiography). J Am Coll Cardiol 1999;34:912-948. View