What is Electrocardiography, ECG or EKG?
It is a medical device used to monitor the electrical and muscular activity of the heart within a certain timeframe. It is a non-invasive medical diagnostic tool and the report produced by this medical device is called an electrocardiogram (ECG or EKG).
What is an ECG machine used for?
A trained doctor looking at an ECG report (electrocardiogram) can interpret the following information:
- Information about the rate and rhythm of heartbeats
- Know the size of the heart and the position of the heart chambers
- Health of the heart muscles and its natural electrical systems
- Check for effects or side effects of medications on the heart
- Check for heart abnormalities caused by other health conditions
How is a ECG test done?
An electrocardiogram can be done at a clinic or hospital. A nurse or technician often conducts the ECG test.
- Usually the patient is placed lying in the face upward (supine) position. Slightly elevated positions are also possible if required for better patient comfort.
- Depending on the type of ECG test to be conducted, the number of electrodes placed on the skin can vary with regard to the number of leads connected to the machine. Common lead variants are 3 and 12. Other combinations like 5 and 15 are also possible.
- Before attaching the electrodes to the skin surface, the skin area is cleaned and any excess hair is removed for more secure placement of the electrodes.
- The electrodes are placed in position and they are connected by wires to the ECG machine.
- Once the machine operator makes sure that the patient is relaxed and comfortable, the machine is activated and it prints out a report (electrocardiogram)
- Normally the machine prints a report for 10 seconds and then the test is over.
- The report is directed back to the physician who requested the test.
Invention of the ECG machine
Dutch physician Willem Einthoven is considered as the father of the modern day ECG machine. He invented the string galvanometer in 1901 and this lead to the invention of the first practical clinical ECG machine around the same time.
He was also the first to coin the term “electrocardiogram” in 1893. Most of the working principles and methods of reading an electrocardiogram still in use to this day were originally conceived by Willem Einthoven. For his invention, he received the 1924 Nobel Prize in Physiology or Medicine.
Here is a list of 10 types of ECG devices that has been used in the health industry
ECG machines vary in size, shapes and functionality. They all work on the same working principles and are used for patient monitoring and checking for heart abnormalities.
Depending on their intended application, they can vary in the type of data they can output, record or monitor.
Telelectrocardiogram
The first ECG machines were very large and bulky, weighing around 275 Kgs (600 lbs). It was not possible to bring these machines to the patient's bedside.
Doctors had to connect the electrodes to the patient and the information would be transmitted (telemetry) to the ECG machine in another room with the help of connecting cables.
A modern day version of this concept with a twist is the portable handheld devices like Cardiac Event Recorders. The ECG device is with the patient and the doctor is at a distance. These devices can transmit the reordered ECG data via internet to the doctor's office for detailed analysis.
In the early days, the hands and feet of the patient were placed in buckets filled with sodium chloride for conduction.
One of the greatest innovations in the development of ECG machines came in 1940s with the invention of electrodes that could be attached to the skin surface of the patient.
These electrodes conducted and relayed the electric signals through attached cables to the ECG machine. Nowadays ECG machines use disposable electrodes in the form of self-adhesive patches.
Wireless ECG
Left: Low cost compact wireless ECG sensor. © Isansys Lifecare.
This is a modern day innovation of the traditional clinical ECG machine with similar functional capabilities. Electrodes do not have wirers directly attached to the recording or monitoring machine. These electrodes can transmit the signal wirelessly over to the receiver in the ECG machine.
Wireless ECG machine can offer more flexibility for the patients. This is especially useful when combined with a treadmill test where the lack of cables can offer more freedom of movement during the test.
12 lead ECG test - standard ECG machine
This is the modern adaptation of the original Willem Einthoven ECG machine based on the Einthoven’s Triangle principles. It is the standard ECG machine used in clinical settings today. In 1942 Emanuel Goldberger added 3 more leads know as augmented limb leads (aVR, aVL and aVF) to Willem Einthoven's limb leads (I, II & III) and six chest leads (V1, V2, V3, V4, V5 & V6) forming the basis of the 12 lead ECG.
The 12 leads provide 12 different views of the heart from different angles and this help the doctor visualize the location of the abnormality in the patient’s heart. A 12 lead ECG is critical for doctors to make the right decision when diagnosing or monitoring a patient.
It important to note that a 12 lead ECG has just 10 physical electrodes placed on the skin surface at various positions. 4 electrodes are placed on the hands and feet of the patient. 6 electrodes are placed on the chest of the patient. The 12 views (12 leads) are derived from the combination of electric signals from these 10 electrodes by the ECG machine.
3 lead ECG monitoring
A 3-lead ECG is used for continuous monitoring of heartbeat, heart rate, and heart rhythm in critical situations like when the patient is under anesthesia, in surgery or being transported in an ambulance to a health center.
3-lead ECG monitoring requires the use of 4 electrodes that are placed on each of the limbs. It is also used in combination with other medical devices like an echocardiogram (Ultrasound scan of heart).
5 lead ECG monitoring
Occasionally a 5 lead ECG is also used for monitoring purposes. It uses 4 electrodes like a 3 lead ECG with an additional 5th electrode placed on the chest. Usually these devices do not produce a print out of the electrocardiogram and may not store the information for further review.
3 and 5 lead variations of ECG monitoring does not provide detailed views like a 12 lead ECG, but is most often sufficient for monitoring purposes. A 12 lead ECG is the standard equipment of choice for diagnosing heart disease in a clinical situation.
Holter Monitor Test
Abnormal heart behavior can be often unpredictable and infrequent making it difficult to monitor these instances properly in a clinical setting using a standard ECG machine.
Holter Monitor is a portable ECG monitor that can be worn by a patient for duration of 24 to 48 hours while the device continuously monitors the heart rhythm. It has fewer leads than a normal clinical ECG machine. The patient is free to move around and go around their usual daily routines.
This medical device is useful for detecting abnormalities in heart rhythm that could be easily missed during a clinical ECG test, which last less than a minute. The device is returned to the doctor at the end of the monitoring period and the data from the device is retrieved and analyzed.
Cardiac Event Recorder
Sometimes the symptoms may not appear during the ECG and a Holter Monitor test. In such cases, the doctor may suggest a Cardiac Event Recorder than can be worn continuously for an extended period of time (2-4 weeks). The device is the size of a deck of cards and cables to the recording device connect the electrodes. Unlike the Holter Monitor, an Event recorder does not continuously record the heart rhythm.
When the patient is experiencing the symptoms, he or she can activate the recorder and the device will record the incident. Depending on the model of the device, multiple events can be recorded in the internal memory.
The data can be transferred to the consulting doctor for detailed analysis and the doctor can make a more an accurate diagnosis based on data obtained during the abnormal incident.
Cardiac Loop Recorder
A loop recorder is a compact USB pen drive sized medical device to monitor the heart function. It can be attached to the surface of the skin around the area of the patient's heart. It continuously records the heart rhythm for a certain duration, depending on the memory capacity of the device and when the device memory is full, it starts overwriting from the beginning of the recording. Hence the name, loop recorder.
An event recorder can miss the starting of an abnormal heart activity due to the delay in initiating the record function. A loop recorder has a record button when pressed can save the immediate few minutes prior to the start of the abnormal heart activity and continue recording for few additional minutes and then stop recording. This way the entire episode is captured and not overwritten.
When the patient experiences an abnormality the recorder can be set to automatically record the incident or can manually instruct the device to record the incident.
A loop recorder can be worn for many days or weeks (up to 30 days), while the patient goes around their routine day-to-day activities. It can be removed during showering or swimming.
Implantable Loop Recorder (ILR)
ILR is a miniature loop recorder that can be implanted between the chest skin and the rib cage, above the heart. Like the loop recorder it can be programmed to automatically start recording when an abnormality is detected is detected in the heart rhythm.
It can also be activated by an external trigger device that the patient can carry around in the form of a wrist band or a remote control.
This is more suitable for patients who experience symptoms that cannot be monitored easily within the 30 days’ period of a normal external loop recorder. The device can have a battery life of up to 3 years and is very suitable for long term continuous monitoring in high-risk patients.
Stress ECG
Stress ECG is also known as Cardiac stress test or treadmill test. In patients that can walk, the test is conducted on a treadmill. The patient is connected to an ECG monitoring machine and is asked to start walking on the treadmill. As the test progresses, the intensity of the physical activity is increased. Patients with walking disability can use hand pedaling stationary bike. In some cases, a pharmaceutical drug is used to simulate the same effect in disabled patients.
It is a test designed the study how the patient's heart can cope up with added external stress. Any abnormalities detected on the ECG during the test can be an indication of underlying heart disease.
The test is useful for overall assessment of a person's health and is often used by professionals like Aviators and Astronauts during their routine health checkups.
