Ambulatory diagnosis and management of cardiac arrhythmias can be effectively accomplished using electrocardiographic monitoring devices. Potential indications include palpitations, syncope, antiarrhythmic drug monitoring and arrhythmia surveillance in patients with known arrhythmias.
Zimetbaum and Josephson describe available monitoring techniques and provide recommendations for their uses. The Holter monitor is the prototype continuous electrocardiographic monitor, providing continuous recording of the electrocardiographic signal for 24 or 48 hours. Data are recorded by a microcassette and analyzed using computer software that identifies arrhythmias. Patient-activated event markers allow increased correlation between symptoms and rhythm abnormalities. Strengths of Holter monitoring include simplicity and the lack of need for patient activation. A limitation is the short time span, which may be inadequate to diagnose the cause of symptoms. The patient is also required to keep a diary, which may be forgotten by the patient.
Transtelephonic electrocardiographic monitors transmit recordings by telephone and convert the signal into a conventional recording. Devices that are applied during the occurrence of symptoms record and save electrocardiographic data prospectively for an average of two minutes. These devices have an extended monitoring ability. The prototype is a credit card–sized monitor applied to the chest wall at the time of the symptom. Continuous-loop event recorders are worn continuously and save data that occurred before and after patient activation. These are commonly beeper-sized devices attached to the patient's belt with two patch electrodes attached to the chest wall. The duration of the saved data is programmable and depends on the type of monitor. A recently available implantable form of continuous-loop event recorder is implanted to the right or left of the sternum and triggered by placing an activator over the recorder.
Transtelephonic monitoring of pacemakers has been available for many years; a transmitter is placed over the skin. Modern pacemakers and defibrillators can store data revealing the number of episodes of irregularities and the therapies delivered.
Palpitations in the presence of substantial structural heart disease may be serious and are more efficiently evaluated by transtelephonic monitoring over two weeks, although a Holter monitor might be adequate in patients having daily symptoms. Syncope is also best evaluated by continuous-loop event recording. In patients with infrequent syncope, an implantable loop recorder appears to be the most diagnostic mode. In surveillance for arrhythmias, monitoring is recommended routinely in postmyocardial infarction patients with decreased left ventricular function, and in patients with idiopathic dilated cardiomyopathy, hypertrophic obstructive cardiomyopathy or congestive heart failure. Documentation of arrhythmia recurrence after medication can be monitored by periodic Holter monitoring when the patient is asymptomatic and by transtelephonic monitoring when the patient is symptomatic.
The authors mention new technology that enables telephonic transmission of a full 12-lead electrocardiogram or 3-lead event recording, blood pressure and pulse oximetry data; this technology will facilitate diagnosis and management of patients in the ambulatory setting. Monitoring heart rate variability (changes in heart rate or R-R intervals modulated by the autonomic nervous system) will also aid in predicting mortality.