Cardiovascular Medical Device Series: Introduction and Technical Trends in the Cardiac Monitoring Industry
Author: Emeli (Li) Zhang
Finished by April, 2016
Cardiac monitoring devices are designed for continuous monitoring of cardiac activities using electrocardiogram (ECG). Cardiac arrhythmias may occur in different clinical conditions where the electrical impulse pathway is abnormal and life-threatening arrhythmia can cause sudden cardiac death or cardiac arrest. Arrhythmic events often occur intermittently or in a transient manner. A patient whoever experienced arrhythmic events may be at risk for threatening conditions in future. So monitoring and recording of cardiac activities/ECG is valuable and can be used by a physician to achieve timely and accurate diagnosis or to determine the cause of the symptoms on patients. In addition, cardiac monitoring devices can also be used to monitor and evaluate the efficacy of therapeutic treatments such as device-based therapy (e.g. pacemakers and ICDs) and medication (e.g. anti-arrhythmic drugs).
Cardiac monitoring device can be externally worn or implantable subcutaneously, and can monitor and record cardiac rhythm intermittently or continuously. Advances in wireless monitoring and telemedicine with medical data streaming via mobile internet revolutionized the clinical practice in cardiology. The cardiac monitoring devices can be categorized as Holter monitors, cardiac event recorders, mobile cardiac telemetry (MCT) or mobile cardiac outpatient telemetry (MCOT), and implantable cardiac monitoring (ICM). The multi-parametric patient monitors are excluded in this report. It was forecasted that the North American cardiac monitoring device market is to reach $1.4 billion by the year 2020 .
Holter monitors are portable devices with wires connected to electrodes/sensors that are attached to the chest via sticky pads. A Holter monitor can continuously monitor the heart rhythm and record the ECG signals for 24 to 48 hours. One of the limitations is that the patients are required to make a note of symptoms. In addition, the short monitoring duration can be not sufficient if symptoms occur infrequently. The device has no real-time analysis and interpretation. Fig. 1. shows a hotter monitor with ECG reading.
Wireless Holter monitors still need wires that connect the device to the electrodes being attached to the chest. This type of Holter monitors use wireless cellular technique streaming the recorded signal to a central station accessible by your doctor. It can record ECG signals for a preset duration but the patient is still asked to make a note with the time of symptoms.
With FDA approval in 2009, Zio Patch (iRhythm Technologies, San Francisco, CA) is a small, water-proof one lead continuous ECG monitor that can be worn for up to 14 days. Then the device is mailed to iRhythm for a comprehensive analysis. Comparing with conventional Holter monitors with multi-channels, Zio Patch only offers 1 lead, yielding reduced sensitivity; nevertheless, the longer monitoring duration facilitates Zio Patch to detect more arrhythmic activities than a Holter monitor. The relatively long monitoring duration and comfort of use may outweigh the limitation, making it an alternative to Holter monitors. Fig. 2. shows the Zio Patch applied to a patient.
An event recorder is also a portable device attached to patient with wired electrodes patched to the chest or through a wrist band. But it does not record cardiac activities continuously and it only record ECG signals for a fixed amount of time that is programmable after being activated. There are two types of event recorders including a symptom event monitor and a memory looping monitor. The former only store data for a period of time when the user presses the button to activate it. And the latter can record the signal for a period of time covering the time before and during a symptom, assuming that the user activate the device when feeling the symptom. Some of these deices can have automatic triggering when detecting irregular heart rates. Event recorder can be used for monitoring and recording ECG signals for 14-30 days. Data are transmitted to a central station and could be uploaded to any computer for analysis and interpretation. In comparison to Holter monitors, event recorders are smaller and can record cardiac activities for a longer time. However, there might be issues occurring when continuously wearing the devices such as lead irritation and poor chest contact during the movement. For the devices with no need to wear continuously such as wristbands or handheld event recorders, the arrhythmias might already terminate before or when the device is attached to the chest.
Mobile Cardiac Telemetry
Mobile cardiac telemetry or mobile cardiac outpatient telemetry devices are also external monitors and are developed to overcome the limitations of conventional ambulatory monitors such as Holter monitors and event recorders. With MCT/MCOT monitors worn, the devices can continuously provide real-time ECG monitoring up to 30 days and can automatically detect cardiac arrhythmias such as bradycardia, tachycardia and cardiac arrest through the sensor with 3 channels ECG capability. The latest MCT/MCOT monitors have a small sensor attached to the chest and the sensor remotely transmits recorded signals to the monitor with built-in mobile technology where the received signals are analyzed and the monitor automatically transmit the data to a central station for clinical follow-up.
The NUVANT MCT system (Corventis Inc. Sant Paul, MN, USA) got the FDA approval in 2010 for marketing and sales in the US market. NUVANT is composed of a wearable sensor and a portable transmitter. Once the sensor attached to the chest, it is automatically activated and starts monitoring cardiac activities, only transmit signals to the central station when arrhythmias in a pre-defined select list detected). Fig. 3 is a diagram showing how NUVANT is applied to a patient.
In June, 2014, Medtronic acquired Covent’s for more than $150 million. And Medtronic launched the SEEQ CMT system in Sep, 2014. SEEQ is an external, wireless, water-poof, adhesive monitor that can be used for continuous ECG monitoring for up to 30 days and allow an automatic data transmission with a button allowing patients to alert the monitoring central station when the patient have symptoms.
Implantable Cardiac Monitoring
Implantable cardiac monitors are designed for long-term monitoring and recording of ECG signals up to 3 years, which can help to determine the causes of cardiac arrhythmias. The ICM devices are placed under the skin and automatically record signals in a continuous manner. Currently. the clinical use of the ICM devices includes the evaluation of causes for transitory symptoms and study on symptomatic arrhythmias. The Reveal LINQ ICM system (Medtronic) got the FDA approval in Feb. 2014. It is the smallest ICM with the features introduced above are very beneficial for patients with infrequent cardiac arrhythmias that are usually undetectable with short-term external cardiac monitors.
 Engel, Jonathan M., et al. "Comparison of arrhythmia prevalence in NUVANT Mobile Cardiac Telemetry System patients in the US and India." Engineering in Medicine and Biology Society (EMBC), 2014 36th Annual International Conference of the IEEE. IEEE, 2014.