Ambulatory ECG monitors

Ambulatory electrocardiography (AECG) monitoring allows the noninvasive evaluation of a suspected arrhythmia during normal daily activities. It aids in the diagnosis, documentation of frequency, severity, length of episodes, and correlation of an arrhythmia with symptoms such as palpitations, lightheadedness, or overt syncope. AECG monitoring can be extremely helpful in excluding an arrhythmia as a cause for a patient’s symptoms if there is no associated event during monitoring. AECG monitoring can also be used to assess antiarrhythmic drug response in patients with defined arrhythmias. Occasionally, AECG monitoring is used in other situations such as risk stratification in patients with nonischemic cardiomyopathy or preoperative evaluation for vascular surgery of patients who cannot exercise. The current major indications for AECG monitoring are given in Box 6.1 .

The major types of AECG monitoring include Holter monitors, event monitors, ambulatory telemetry, patch monitors, implantable loop recorders (ILRs), and commercially available smartwatches/wristbands. The type and duration of monitoring are dependent on the frequency and severity of symptoms. Most modern devices have the capability for transtelephonic transmission of ECG data during or after a detected arrhythmia. Each system has advantages and disadvantages; selection must be tailored to the individual. With any system, however, patients must record in some fashion (e.g., diary, electronically) symptoms and activities during the monitored period.

• Holter monitors : A Holter monitor constantly monitors and records two to three channels of ECG data for traditionally 24 to 48 hours with older monitors of the past decade, and up to 2 weeks with some newer models. It is ideal for patients with episodes that occur daily, every 2 to 3 days, or quantitation of premature ventricular contractions (PVCs)-related cardiomyopathy.

• Event monitors : An event monitor constantly monitors two to three channels of ECG data for 30 to 60 days (most commonly up to 30 days). However, it will only record events when the patient experiences a symptom and presses a button that triggers the event monitor to store ECG data 1 to 4 minutes before and 1 to 2 minutes after the event. Some event monitors will also store arrhythmias that are detected by the monitor itself, based on preprogrammed parameters. An event monitor is appropriate for patients with episodes that occur weekly, biweekly, or monthly. “Event monitors” per se are less commonly used in contemporary practice, given that monitors with greater memory capabilities that now continually record and store arrhythmias are available.

• Ambulatory real-time cardiac monitors : Ambulatory real-time cardiac monitoring has various monitors. It has been termed ambulatory telemetry, real-time continuous cardiac monitoring, or mobile cardiac telemetry (MCOT). Ambulatory telemetry is a monitoring system that continuously records a one- to three-lead strip for 14 to 30 days. Depending on the vendor, the ECG data are either stored for offline interpretation or instantaneously transmitted for interpretation by a monitoring technician. In cases where the rhythm is monitored by a technician in real time, the patient or physician can be contacted immediately after an arrhythmia has been detected to minimize delays in treatment. No patient action is necessary for an arrhythmia to be stored, and patient compliance can easily be assessed. These features facilitate the detection of silent or asymptomatic arrhythmias. MCOT is also appropriate for evaluation of a source of cryptogenic stroke or quantification of arrhythmia burden.

• Adhesive patch electrocardiographic monitors : Adhesive patch monitors self-adhere to the chest wall and are worn continuously for several weeks. Advantages include the ability for the patient to continuously wear the device and not have to connect and disconnect wire leads. Some models can wirelessly transmit triggered events related to ECG data to central monitoring station that can alert physicians to review online for real-time analysis. Presently available devices only provide a single ECG channel.

• Implantable loop recorders: An ILR is an invasive monitoring subcutaneously implanted device allowing long-term monitoring and recording of a single ECG channel for over a year (a battery life of 2–3 years). ILR records events similar to an event monitor based on patient’s symptoms or automatically based on heart rate. It is best reserved for patients with more infrequent episodes occurring >1 month apart from each other.

• Commercially available smartwatches or wristbands (e.g., Apple Watch): Commercially available smartwatches or wristbands use automated algorithms to analyze photoplethysmography (PPG) and optical sensors (e.g., blood flow or pulse irregularity) to identify arrhythmias, particularly supraventricular tachycardia or atrial fibrillation. However, the positive predictive value of these devices remains suboptimal and, as of 2021, there are currently no US Food and Drug Administration (FDA)–approved clinical indications (though this may change over time). Smartwatches or wristbands can be considered for monitoring arrhythmic sources in individuals with symptomatic (e.g., palpitations) or symptomatic atrial fibrillation recurrence ( Fig. 6.1 ).

  

An ILR is placed subcutaneously below the left shoulder or overlying the fourth anterior intercostal spaces. Previous devices required a small surgical incision for placement. The more recent, smaller version of the device is placed via a <1-cm incision and a syringe-like device. As discussed above, it continuously monitors bipolar electrocardiographic signals for up to over 1 year. The patient may use a magnetic activator held over the device to trigger an event at the time of symptoms. In addition, the device automatically records episodes of bradycardia and tachycardia. The older device is then interrogated with an external programmer and recorded events reviewed in a similar manner to a permanent pacemaker. The newer device wirelessly connects to a patient monitor. After a diagnosis is obtained, the device is surgically extracted. In patients with unexplained syncope, an ILR yields a diagnosis in more than 90% of patients after 1 year. An example of an older and more recent generation ILR is shown in Fig. 6.2 . A representative printout of ILR interrogation is shown in Fig. 6.3 .

Most modern pacemakers or implantable cardioverter defibrillators (ICDs) will detect and store arrhythmias. The number and type of arrhythmias detected depend on the number of leads, algorithms, device type, and programming, as well as manufacturing specifications. Detected arrhythmias can be reviewed upon device interrogation.