Given the widespread availability and use of smartphones worldwide, there has been interest in using these devices to record ECG data in real time. As an example, the AliveCor heart monitor incorporates two electrodes; when at least one finger from each hand is placed onto each of the two electrodes, the electrical signals are converted to ultrasound signals. These signals are then transmitted to the smartphone’s microphone and a single lead (analogous to lead I) ECG tracing is generated, which can then be downloaded wirelessly using any browser for immediate remote interpretation. In a recent study, the monitor could detect atrial fibrillation (AF) and flutter with 100% sensitivity and 97% specificity; furthermore, 98% of patients found the monitor easy to use. Because the patient owns the monitor, this system offers the opportunity to visualize ECG data in real time for as long as the patient retains the monitor and smartphone.

This is the standard AECG and most commonly used in practice. It is a continuous ECG (single or multi-lead) recorder with patient activated event markers. It is important for a patient to keep a diary. It lacks wireless transmission. The device is battery operated and data are recorded on digital media, which is removed at the end of recording period, downloaded and analyzed by proprietary algorithms. However,
though effective for assessing ectopy and heart rate trends, the short recording period may miss infrequent symptoms.

In an extension of this continuous monitoring concept, “patch ECG monitors” constructed with embedded electrodes, with or without wireless data transmission, are a new class of compact, lightweight AECG recording devices, which remove the need for patient cable wires. They can record one or two lead electrogram from two closely spaced electrodes worn continuously for up to 14 days. They are comfortable to wear and do not interfere with patients’ daily routines since by being water resistant and can remain on the patient during showering and exercise. Patients can press a button to mark symptomatic episodes. Proprietary algorithms diagnose cardiac rhythms based on beat-by-beat QRS detection. They provide up to 7 to 14 days of continuous ambulatory monitoring.

Information from Holter and patch recordings is only available after return of the device, downloading and analysis. In the case of the patch, this may be >2 weeks after application. Transtelephonic AECG systems (event recorders and ambulatory cardiovascular telemetry) provide closer to real time monitoring and analysis than Holter or patch recorders.

These are indicated for infrequent symptoms. There are two varieties. Simpler non-looping post-event recorders are not used continuously and do not require chest electrodes. Rather, these portable devices with built-in electrodes are applied directly on the chest (or held by both hands) to record a very brief duration single lead ECG signal during symptoms. When a symptom occurs, the patient presses a button to activate ECG storage. Patient activated post-event recorders have the potential to transmit the “near real time” event ECG data, provided patients recognize symptoms and activate the recording in a timely fashion. These are therefore best for symptoms that are prolonged enough to permit recording, and do not interrupt consciousness.

Intermittent auto-triggered loop recorders are typically single bipolar lead devices. They need to be worn continuously by the patient and are attached to the chest by a variety of carrier systems that include wire-electrodes. Upon event detection, ECG data are stored for a predefined amount of time prior to the event (looping memory) and a period of time after the activation. ECG tracings lasting from few seconds to several minutes (in some cases up to one hour, to include the onset and offset of arrhythmias) can be acquired over a period of a few days to a few weeks; both symptomatic and asymptomatic arrhythmias (by means of auto-trigger functions) can be identified. Thus, these systems are well suited to identify infrequent rhythm disorders such as pauses, bradycardia, supraventricular and ventricular arrhythmias.

Ambulatory cardiovascular telemetry devices combine and extend the benefits of Holter recorders and event recorders. Worn continuously, these devices are capable of real-time streaming, transmitting a loop or a single event electrogram directly to the reading center via a wireless link. Newest iterations can accomplish this using a patch-based method (see Fig. 11-2); additionally, some systems can connect to any WiFi access point to transfer data. These telemetry devices may be equipped with real-time signal processing
algorithms providing detection of cardiac arrhythmias. The ECG data are processed at a reading center by trained technicians. A daily report is provided to the physician, even in the absence of an arrhythmia. Alarms are pre-specified by the prescriber and notified to the caregivers immediately. These devices capture asymptomatic and symptomatic events and provide the benefit of real-time, comprehensive data without requiring the patient to participate in the process of data transmission. Compared with AECG recorders, these devices allow immediate transmission of information; compared with looping event recorders, they gather more information and allow remote data transfer while overcoming the technical challenges of data transmission. This large amount of real-time data affords a higher diagnostic yield than standard devices but places a potential burden on the clinician who must be available to review large amounts of information (e.g., daily) at any time of the day or night.

The selection of appropriate technology has to take into account diagnostic power, monitoring and risk stratification accuracy with consideration about cost-effectiveness, patient acceptance, degree of automaticity, and local availability and experience, as well as, symptom frequency, the overall patient clinical condition and the probability of life threatening arrhythmia. Holters and loop recorders are inexpensive and readily available. Short duration recordings (24 to 72 hours) Holter recordings are best suited for patients with very frequent symptoms. The need for ECG resolution may direct choice of a 12-lead Holter versus patch electrode based Holter system. For less frequent episodes, patient-activated event and loop recorders can be used for several weeks at a time. These devices are particularly useful to capture ECG recordings during symptomatic events and clarify the arrhythmic basis for unexplained or ambiguous symptoms. Auto-triggered devices have higher diagnostic yield than standard 24 hours Holter monitors and 30-day loop recorders. Patch monitors and ambulatory cardiovascular telemetry monitors are the most complete outpatient ECG recording and increases the likelihood for detecting arrhythmia as well as quantifying burden during the duration of recording. The choice of device may also be influenced by the number of recording ECG leads available. Sometimes a single ECG lead may be enough to establish the connection between the symptom and the cardiac rhythm (e.g., complete heart block). Most patch ECG monitors, event recorders, and telemetry monitors available today feature only a single lead derived from either two closely spaced embedded or wired electrodes. However, 12 lead monitoring may be necessary for diagnosing arrhythmia origin (and thus guide interventional procedures) or diagnosis (e.g., Brugada syndrome).