12 Lead ECG: Everything You Need to Know About the Test
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Heart rate monitors are an important tool for gaining maximum benefits in workout sessions or monitoring cardiovascular health for many individuals worldwide. And within heart rate monitors, there are two trendy variants chest straps and wrist-based watches-with respective advantages and disadvantages. Therefore, understanding the advantages and disadvantages of each would help you make informed choices based on your fitness goals, lifestyle, and preferences.
ECG (Electrocardiography)
Before we get started let’s talk about ECG— ECGs are of different types, 3-lead ECG, 5-lead ECG, 12 lead ECG, and Portable ECG machines, These portable ECG machines are a great way to take care of yourself and your family and take their ECG without going to the hospital.
ECG is a non-invasive device that is used to assess the electrical activity of the heart, it is a first-line diagnostic test, recommended by healthcare professionals, to the patient having any symptoms related to heart disease, it detects various heart conditions like arrhythmias, heart attack, palpitations, different ECG waves abnormalities and other heart issues.
12 Lead ECG Electrodes Placement
The 12 lead ECG is performed using 10 electrodes, Precise positioning of electrodes is crucial to ensure trustworthy readings and enable accurate diagnosis. Every electrode plays a distinct role in forming a complete understanding of how the heart functions. It is essential for healthcare professionals to know the location and the method of placement for these electrodes. Let’s investigate the proper positioning of electrodes in a 12 lead ECG.
Chest (Precordial) Electrodes Placement:
- V1 – 4th intercostal (ICS) space on the right sternum
- V2 – 4th ICS at the left sternum
- V3 – Midway between V2 and V4
- V4 – 5th ICS at the midclavicular line
- V5 – Anterior axillary line at same horizontal level as V4
- V6 – Mid-axillary line at same horizontal level as V4 and V5
Limbs Electrodes and Placement:
- RA (Right Arm) – b/w right shoulder and right elbow
- RL (Right Leg) – below right torso and above right ankle
- LA(Left Arm) – b/w left shoulder and the left elbow
- LL (Left Leg) – below left torso and above left ankle
Principle of Electrocardiogram
The cardiac action potential and cardiac conduction serve as the foundation for the 12 lead ECG. The SA node produces the electrical signal for the heart, which travels along the heart’s electrical system causing a change in the electrical charge across the heart muscle cells’ membranes. This alteration in the cardiac electrical activity leads to the uninterrupted progression of the heart’s pumping process.The cardiac signal travels through the heart, diffuses through the neighboring tissue, and ultimately reaches the skin of our body. The electrodes of the ECG machine receive and process the electric impulse in the skin to generate an ECG.
What is a 12 lead ECG?
A 12 lead ECG is a non-invasive device that is used to record heart electrical activity from multiple angles, it consists of 10 electrodes, and these electrodes provide important information for detecting the electrical activity of the heart.
Ten electrodes are placed on the body, typically on the limbs and chest, to monitor the heart’s electrical signals from 12 different perspectives for a duration. The ECG is interpreted by the waves that are P wave, QRS complex, and T wave. The 12 lead ECG consists of the following leads:
- Limb leads: I, II, and III
- Augmented limb leads: aVL, aVF, and aVR
- Precordial leads: V1 to V6
Color Codes of ECG
Color-specific electrodes are utilized in ECGs to reduce errors that may occur when electrodes are attached to the body, with multiple reasons for doing so.
- Standardization: The standardization of colors helps the healthcare provider to know the electrode placement in different ECG machines, which in return helps them to quickly recognize the placement on the body which helps them to run the test smoothly and correctly
- Reduction of Error: When there is a fixed colour for a fixed lead there are very minimal chances of error by the healthcare professionals ensuring the correct placement of electrode and the interpretation of ECG is done correctly.
- Time-Saving: Because of the Standardization of color codes, healthcare professionals don’t have to think where to place which electrodes by recognizing the color, the leads are positioned correctly.
The American Heart Association (AHA)/Association for the Advancement of Medical Instrumentation (AAMI) and the International Electrotechnical Commission (IEC) gave us standardized color codes. They vary with each other, the IEC colour code is commonly used in Europe and other parts of the world, and the AHA/AAMI is mainly used in the USA. The color codes of these two are as follows:
The American Heart Association (AHA)/Association for the Advancement of Medical Instrumentation (AAMI)
- RA (Right Arm): White
- LA (Left Arm): Black
- RL (Right Leg): Green
- LL (Left Leg): Red
- V1 (Precordial): Red
- V2: Yellow
- V3: Green
- V4: Blue
- V5:Orange
- V6:Violet
According to the International Electrotechnical Commission (IEC), the color codes are:
- RA (Right Arm): Red
- LA (Left Arm): Yellow
- RL (Right Leg): Black
- LL (Left Leg): Green
- V1 (Precordial): Red
- V2: Yellow
- V3: Green
- V4: Brown
- V5:Black
- V6: Purple
Electrode Application
Correct placement of electrodes is necessary to achieve precise and dependable 12 lead ECG outcomes. When attaching electrodes, it is important to consider certain factors.
Use Electrode Gel: Utilizing conducting gel or adhesive electrodes is necessary to improve signal accuracy in a 12 lead ECG. To enhance conductivity, make sure to evenly spread the gel on the electrode surface when using it.
The skin should be clean: Properly preparing the skin is essential before placing electrodes. Use alcohol wipes to clean the electrode sites and get rid of oils, dirt, and sweat. This procedure improves bonding and guarantees precise electric signals. In certain situations, it may also be necessary to shave or trim excess hair to ensure the best contact.
Storage of Electrodes: Keep electrodes in a dry area, and avoid exposing them to extreme temperatures. Verify expiration dates before using to confirm their effectiveness. The electrodes will remain in good condition with proper storage, which guarantees dependable performance for ECG procedures.
Connection to ECG: Once the electrodes are in place, make sure to connect the leads from each electrode to the ECG machine securely. Make sure the connections are secure to avoid any disruption or loss of signal. Verify that the ECG machine is correctly adjusted and prepared for recording prior to initiating the procedure.
Waves in a Normal 12 lead Electrocardiogram
During a typical electrocardiogram (ECG), three clear waves can be seen: the P-wave, the QRS complex, and the T-wave. Every wave signifies various stages of the heart’s electrical function, indicating the heart muscles’ movement of contracting and relaxing. Comprehending these waves is essential for analyzing an ECG and identifying different heart conditions.
P-wave: The initial small upward wave in an ECG indicates the depolarization of the atria. It signifies the electrical activity responsible for triggering the contraction of the atria, specifically the impulse initiated and transmitted by the SA node right before and at the beginning of atrial contraction.
QRS-complex: The QRS complex indicates ventricular depolarization. The QRS complex consists of three separate waves on an ECG: the Q wave is the first downward deflection, the R wave is a sharp upward deflection, and the S wave is a sharp downward deflection within the larger triangular wave. The QRS complex aligns with the ventricular depolarization phase.
T-wave: The T-wave is the final wave in the ECG cycle and signifies the ventricles’ repolarization. This stage is crucial for the heart to reset and get ready for the upcoming contraction.
Interpretation of 12 lead ECG
Trained medical personnel are the only ones who analyze and interpret an ECG. The main focus when reading an ECG includes the P wave, QRS complex, T wave, PR interval, QT interval, PR segment, and ST segment. The analysis includes studying the amplitude of every wave, the length of the waves, as well as the length of segments and intervals. Moreover, the ECG also examines the heart rate, rhythm, and axis. Interpreting an ECG report is based on a combination of different factors. A typical ECG will display the following outcomes:
Abnormalities Detected in a 12 Lead ECG
A vital tool in identifying different heart irregularities is a 12 lead ECG (electrocardiogram). It offers a complete look at the heart’s electrical function, enabling medical professionals to detect potential health problems. Here is a more comprehensive examination of some of the main irregularities that can be identified:
1. Arrhythmias: Arrhythmias are heartbeats that are irregular, impacting the heart’s ability to pump blood effectively.
- Tachycardia: Described as a heart rate that is higher than 100 beats per minute. This situation may be caused by various factors such as stress, fever, anemia, or heart issues such as atrial fibrillation. A rapid heart rate could be a typical bodily reaction to physical activity or stress, but it could also signal a potential underlying problem needing additional assessment.
- Bradycardia: This state is identified by a heartbeat that is lower than 60 beats per minute. In well-trained athletes, a slow heart rate may be common, but if experienced with fatigue, dizziness, or fainting, it could be a sign of heart block, hypothyroidism, or other health issues.
- Atrial Fibrillation: This is a frequently seen irregular heartbeat marked by a disorganized and erratic heart rhythm. An electrocardiogram will demonstrate a lack of clearly defined P waves and a QRS complex that is irregularly timed. Atrial fibrillation heightens the likelihood of stroke and necessitates careful handling.
2.ST Segment Elevation Myocardial Infarction (STEMI): An ECG will display notable ST segment elevation, suggesting a total obstruction of a coronary artery. It is essential to act promptly in these situations to reestablish the flow of blood.
3.Non-ST Segment Elevation Myocardial Infarction (NSTEMI): This kind of heart attack might not display ST-segment elevation but could instead exhibit ST segment depression or T wave inversions. These alterations indicate that the heart muscle is lacking oxygen, even though the artery is not entirely obstructed.
4. Conduction Delays
Conduction abnormalities can affect the heart’s rhythm and efficiency.
- First-Degree AV Block: This state is defined by an extended PR interval, showing a slowdown in the electrical transmission from the atria to the ventricles.
- Second-Degree AV Block: This encompasses Wenckebach (Mobitz Type I) and Mobitz Type II. In Wenckebach, the PR interval gradually lengthens until a beat is skipped, whereas Mobitz Type II is more alarming since it can result in sudden complete heart block.
5. Electrolyte Imbalances
Electrolyte levels significantly affect heart function.
- Hyperkalemia: Increased levels of potassium can lead to T waves peaking, QRS complex widening, and eventual absence of P waves. Severe high levels of potassium in the blood can result in arrhythmias that are life-threatening.
- Hypokalemia: Increased levels of potassium can lead to T waves peaking, QRS complex widening, and eventual absence of P waves. Severe high levels of potassium in the blood can result in arrhythmias that are life-threatening.
A 12-lead ECG is a powerful diagnostic tool that can reveal a wide range of cardiac abnormalities, providing essential insights into a patient’s heart health. By recognizing these abnormalities, healthcare professionals can make informed decisions regarding diagnosis and treatment, ultimately improving patient outcomes. Regular monitoring and timely intervention can be crucial in managing existing cardiac conditions and preventing complications.
