Cardiac Monitoring: Present and the Future

Cardiac monitoring means the continuous or intermittent monitoring of heart activity, generally by ECG, with assessment of the patient's condition relative to their cardiac rhythm. It differs from hemodynamic monitoring, which monitors the pressure and flow of blood within the cardiovascular system. Cardiac monitoring with a small device worn by an ambulatory patient is known as ambulatory ECG. Transmitting data from a monitor to a distant monitoring station is known as telemetry or biotelemetry.

Cardiac monitoring is focused on the collection of ECG signal and interpretation of a patient’s heart rhythm. Different technologies have been established to achieve this goal, each with different features and methods for collecting the data. These methods include Short term, intermediate and long term monitoring.

In short-term monitoring, holter monitor and event recorders are used. A Holter monitor is a short-term, continuous monitoring device that tracks the heart rhythm of a patient with small electrodes attached to the skin. The devices are typically worn for 24–48 hours and then returned for download and analysis. It has several shortcomings. Patients may not experience symptoms or cardiac arrhythmias during the usual Holter recording. It has a low diagnostic yield. In several large groups using 12 h or more of ambulatory monitoring, only 4% had recurring symptoms during monitoring. The overall diagnostic yield of Holter monitoring was 19%. Short-term monitoring via 24-hour Holter has low sensitivity and negative predictive value for AF detection. Transtelephonic monitors are a form of non-continuous ambulatory recording that is convenient for patient use. During symptomatic episodes, the patient activates the device, which then records ECG signals. The received signal is then converted to an analog which is transmitted to receiving center. Recording that is displayed or printed as a single lead rhythm strip. Electrocardiographic signals are collected prospectively for 1 to 2 minutes upon patient activation. The major disadvantages are the need for patient activation; missing asymptomatic arrhythmias; and the inability to record events that surround the onset of symptoms. Cardiac Event Monitoring has proven to be a valuable tool in documenting events that had eluded detection by traditional tests (i.e., 12-Lead and 24-Hour Holter Monitoring). It has also proven to be a very cost-effective alternative to long stays in CCU and in-house telemetry monitoring. Because the patient is active and performing routine daily activities, chances of documenting transient problems are greatly enhanced. New technology has also been evolved. These are patches and wrist recorders.

Intermediate-Duration Monitoring involves the use of extended holter and external loop recorders. Extended Holter which provides continuous ambulatory monitoring with data transmission to a central monitoring station staffed by Health Professionals is a useful resource to extend traditional Holter monitoring beyond 48 h. This technique is typically used for 7 to 14 d, and has shown incremental benefit over a standard external loop recorder in diagnosing arrhythmia. An External Loop Recorder continuously records and stores a single external modified limb lead electrogram with a 4- to 18-min memory buffer. After the onset of spontaneous symptoms, the patient activates the device storing the previous 3 to 14 min and the following 1 to 4 min of recorded information. The captured rhythm strip can be uploaded and evaluated, often providing critical information regarding onset and termination of the arrhythmia. New technology in form of vest wearable monitoring systems has been evolved. Intermittent and symptom-based monitoring has a significantly lower sensitivity and negative predictive value for AF detection compared with continuous monitoring.

Long term monitoring involves implantable cardiac monitors and mobile cardiac devices. Implantable or Insertable Monitors – Designed for long-term use, are the gold standard for determining causes of infrequent, unexplained arrhythmias. The small device is placed just under the skin of the chest during an outpatient procedure. The device detects and records abnormal heart rhythms over long periods of time (up to three years) to help determine whether a patient has an abnormal heart rhythm. Mobile Cardiac Telemetry, or MCT, allows for longer term monitoring with the ability for patient or auto-triggered events based on algorithms. Generally, MCT devices “sample” or “trend” ECG samples periodically throughout the day. Cardiac Ambulatory Telemetry (CAT) device, which is designed for longer term monitoring, collects every heartbeat in order to detect elusive arrhythmias. The patient can trigger recordings or the device can auto trigger based on internal algorithms for tachycardia, bradycardia, pause, or atrial fibrillation. Data is transmitted wirelessly for near real-time analysis. Single lead ECG monitoring device with low power consumption could monitor and store patient’s ECG data for 7 days continuously. This device is convenient for long-term wearing with a small volume. Also, this system is equipped with an acceleration sensor and supports Bluetooth 4.0 protocol, could evaluate patient’s dynamic heart rate monitor and sleep quality analysis combined with mobile phone, which is suitable for mobile health and has a huge potential of application. There are several single-lead ECG wearable bands as well as in a pen-styled form-factor that takes ECG recording and display the results using an App. The ECG is obtained by simply placing finger from each hand on the electrodes. Within just a few seconds the ECG appears on the screen and is automatically uploaded wirelessly for remote interpretation.

Longer, continuous monitoring periods result in higher AF detection. Symptoms are insensitive and non-specific for the diagnosis of atrial fibrillation (AF). Extensive Holter monitor recordings are essential to correctly diagnose AF and, subsequently, to inform therapeutic decisions for its management. Pacemakers and implantable cardioverter defibrillators that detect atrial arrhythmias are a valuable resource for the investigation and quantification of AF. The application of these monitoring systems, however, is limited to a relatively small number of patients. Additional monitoring technologies are therefore necessary to detect the large number of asymptomatic AF episodes, as well as their resulting morbidity and mortality. New, non-invasive systems could be a significant alternative of Holter monitoring and Subcutaneous implantable systems, with automated detection algorithms for atrial arrhythmias, represent a new opportunity for long-term rhythm monitoring. This will not only allow to evaluate the efficacy of different therapies but also to refine the future therapeutic management of AF.

By periodically tracking a patient’s heart rhythms, doctors are more likely to discover whether an arrhythmia is causing a patient’s health condition, and then can use the monitors to help manage the patient’s condition. A recent study showed that in patients with implantable long-term heart monitors than non-implantable cardiac monitors; the time to diagnose arrhythmias was reduced by 79%. Long-term cardiac monitors are easy to use which has improved patient compliance. They also have proven to be cost-effective for patients who are experiencing unexplained fainting and palpitations, based on clinical guidelines. Currently, a miniaturized Insertable Cardiac Monitor is designed to help physicians more quickly diagnose irregular heartbeats. It continuously and wirelessly monitors the heart, and sends information to a patient’s physician to help them make an accurate diagnosis and a treatment plan. Periodic long-term cardiac monitoring is an important tool in the clinical assessment of patients with a variety of conditions. It allows the detection of changes in heart rate, rhythm and heart performance parameters, and is essential in the detection of life threatening arrhythmias. Patients who may require cardiac monitoring include those who are haemodynamically compromised and/or at clinical risk of adverse events, for example, patients with Chest pain, Palpitations, Acute Coronary Syndrome – STEMI, NSTEMI, unstable angina, patients undergone ITU, HDU, cardiac surgery, Major trauma, Post cardiac/respiratory arrest, Acute medical conditions , Pulmonary embolus, drug overdose, electrolyte imbalance, Unexplained syncope episodes, Shock and Undergoing a specific treatment Ischemic stroke cause remains undetermined in 30% of cases, leading to a diagnosis of cryptogenic stroke. Paroxysmal atrial fibrillation (AF) is a major cause of ischemic stroke but may go undetected with short periods of ECG monitoring. The Cryptogenic Stroke and Underlying Atrial Fibrillation trial (CRYSTAL AF) demonstrated that long-term electrocardiographic monitoring with insertable cardiac monitors (ICM) is superior to conventional follow-up in detecting AF in the population with cryptogenic stroke.

Extended continuous ambulatory monitoring is more efficient for the detection of arrhythmias, such as atrial fibrillation, than Holter monitors in patients who have recently experienced cryptogenic strokes or transient ischemic attacks (TIA). Remote monitoring has an excellent sensitivity (95%) in detecting atrial fibrillation, a feature made more important by the fact that up to 90% of detected episodes were asymptomatic.

Periodic cardiac monitoring is suitable for patients with infrequent intermittent symptoms possibly related to arrhythmia, or to those in whom an infrequent “silent” arrhythmia is present. Currently, the methods of using a smartphone to detect and monitor atrial fibrillation can be divided into two groups. The first group simply uses a downloadable application and hardware that already exists on modern smartphones, the camera and LED light . The second group uses a pair of external electrodes, either built into the case or as a standalone unit that communicates with an application downloaded to the phone. These devices show promise in arrhythmia assessment, managing patients with AF, and diagnosing AF early in high risk patients.

Continuous and periodic monitoring systems act as the wireless communication between patient and healthcare professional allowing exchange of data from implanted or wearable devices. These data usually include electrocardiographic recordings, which are interpreted and analyzed to detect cardiac abnormalities without physical presence of patients thus revolutionizing the future of cardiac monitoring. Various single lead ECG devices for periodic cardiac monitoring are available that are low cost, lightweight recorder and for use by an average person. The display shows ECG recordings. The software and uploaded ECG recordings are remarkably good, and very useful for reading by a cardiologist or trained personals. ECG recordings are automatically uploaded but they can’t be interpreted without cardiologist. Trained personals are required for ECG interpretation. The implications and potentials of these wearable health monitoring technologies are paramount, for their abilities to detect early signs of health deterioration, notify health care providers in critical situations, find correlations between lifestyle and health issues, and transform health care by providing doctors with multi-sourced, real-time physiological data. ECG monitoring and interpretation have always been tasks conventionally assigned to trained medical care personals. Although being more comprehensive in the related knowledge, the constraints to manpower are also very obvious. Fatigue factors and overwhelming workloads are both possible causes to delayed emergency response that may have reduced the chances for patients’ survival.

By automating this process, the system frees the medical professionals of the tedious tasks to center their attentions on something much more demanding. There is still a significant gap between the existing sensor network solutions and the needs in medical care. More sophisticated algorithms offering a more accurate diagnosis of AF or other severe arrhythmias without the input of a clinician could make screening more affordable, thereby increasing the detection rate by improving patient compliance and reducing the cost, morbidity and mortality rates.