What is a 12-lead ECG?
A 12-lead electrocardiogram (ECG) is a non-invasive diagnostic tool that allows your doctor to analyse and record your heart’s electrical activity. It uses 10 electrodes strategically placed on the body to capture the heart’s electrical activity from 12 distinct angles. For a standard 12-lead ECG, the electrode placements are crucial to the accuracy of the readings.
A 12-lead ECG offers a comprehensive overview of cardiac function and is commonly used to detect and monitor various heart conditions, including:
Abnormal heart rhythms (arrhythmias)
Heart attacks (myocardial infarction)
Electrolyte imbalances and other cardiac abnormalities
This test is a routine but vital tool in both emergency and long-term cardiac care.
What can a 12-lead ECG detect?
A 12-lead ECG can detect:
Heart attacks (myocardial infarction):
The ECG can identify signs of a heart attack by detecting changes in the electrical activity of the heart muscle. An ECG can show signs of damage to the heart from a previous heart attack.
Arrhythmias (irregular heart rhythms):
It can reveal problems with the heart's rhythm, including heart rates that are too fast (tachycardia), too slow (bradycardia), or irregular heartbeats.
Cardiac ischaemia (reduced blood flow to the heart):
The ECG can detect signs of poor blood flow to the heart muscle, which can be a precursor to a heart attack.
Heart valve diseases:
ECG can identify abnormalities in heart valve function.
Heart enlargement:
The test can indicate if the heart chambers are enlarged.
Electrolyte imbalances:
An ECG can detect abnormalities in the heart's electrical activity that may be related to imbalances in electrolytes like potassium and calcium.
Congenital heart defects:
ECG can help identify some types of congenital heart defects present at birth.
Medications and pacemaker function:
ECG can show the effect of medications on the heart and can also help assess the function of pacemakers and implantable cardioverter-defibrillators (ICDs).
If you have any concerns related to the above heart conditions, don’t hesitate to request an appointment with Thomson Medical. Our cardiologists will help you to answer any questions you have and provide you with tailored recommendations.
How does a 12-lead ECG work?
A 12-lead ECG records the heart’s electrical activity using sticky pads (electrodes) placed on the chest, arms, and legs. These electrodes detect small voltage changes as the heart beats and send the signals to the ECG machine. The result is a detailed snapshot of your heart’s rhythm, including:
P wave: Signals from the upper chambers (atria)
QRS complex: Pumping action of the lower chambers (ventricles)
ST-T wave: The heart’s recovery phase
The “12 leads” provide different angles of the heart’s activity, with six chest leads (V1–V6) focusing on the ventricles and six limb leads capturing the overall rhythm and atrial activity.
Why is proper electrode placement important?
Accurate electrode placement ensures reliable ECG interpretation, with chest electrodes (V1–V6) focusing on the heart's lower chambers and limb electrodes assessing the upper chambers. Together, they provide a comprehensive, three-dimensional view of the heart’s electrical conduction.
Misplacement can distort waveforms, leading to misdiagnosis of conditions like heart attacks (myocardial infarction) or enlargement of the heart (hypertrophy). Maintaining onsistency in limb lead positioning and chest lead positioning is important, particularly in paediatric patients or those with anatomical variations.
12-lead ECG placement of electrodes
Each electrode must be positioned precisely to ensure consistent and diagnostically valid recordings of the heart’s electrical activity:
Limb electrodes:
Right arm (RA): Place it on the upper arm, between the shoulder and the elbow.
Left arm (LA): Place it on the upper arm, between the shoulder and the elbow.
Right leg (RL): Place it on the lower leg, between the torso and the ankle.
Left leg (LL): Place it on the lower leg, between the torso and the ankle.
Chest electrodes (Precordial):
V1: Place it on the right side of the chest, at the 4th rib space near the breastbone.
V2: Place it on the left side of the chest, at the 4th rib space near the breastbone.
V3: Place it halfway between where V2 and V4 are located.
V4: Place it on the left side of the chest, at the 5th rib space in line with the middle of the collarbone.
V5: Place it on the left side of the chest, along a line running down from just in front of the armpit, level with V4.
V6: Place it on the left side of the chest, along a line running down from the middle of the armpit, level with V4 and V5.
Note for female patients: For chest electrodes V3 to V6, place them under the left breast.
When should you have a 12-lead ECG?
A 12-lead ECG is recommended in these situations:
Symptoms of heart issues:
Chest pain, tightness, or discomfort (especially if spreading to the arm, jaw, or neck).
Shortness of breath, dizziness, fainting, or unexplained fatigue.
Rapid, irregular, or pounding heartbeats (palpitations).
Risk factors:
Monitoring:
Checking how well heart medications, pacemakers, or implanted devices (e.g., ICDs) are working.
Assessing heart health before/after surgery or during treatment for conditions like electrolyte imbalances.
Emergencies:
Suspected heart attack (e.g., ST-Elevation Myocardial Infarction, a severe type of heart attack caused by a complete blockage of one or more coronary arteries) – requires an ECG within 10 minutes of medical contact.
Overdoses, venomous bites, or syncope (fainting) with unclear causes.
Doctors may also use it routinely for patients with chronic heart conditions or during health check-ups.
Are you experiencing any of the symptoms mentioned above? Request an appointment with us to determine whether a 12-lead ECG is right for you.
How to prepare for 12-lead ECG placement?
Preparing for a 12-lead ECG test is relatively simple. However, as with any test, there are a few things you should take into consideration beforehand:
Shower beforehand and avoid moisturisers, oils, or powders on the skin to ensure electrodes stick to your skin.
Wear loose clothing for easy access to the chest and limbs. Men are usually bare-chested during the test, whilst women can wear a bra, t-shirt or gown where applicable.
Remove jewellery from the neck, wrists, and ankles.
If the electrode must be placed in an area with body hair, you are required to shave the hair.
If you require any further instructions to prepare, your doctor will inform you separately.
How is a 12-lead ECG performed?
You will be asked to lie down, and a cardiac technician will attach 10 electrodes with adhesive pads to the skin on your chest, arms and legs. Men may need their chest hair shaved to allow a better connection.
At this point, the doctor will pay close attention to you to ensure you don't feel any discomfort or stress.
Once all electrodes are applied, your doctor can turn on the ECG machine and begin recording the electrical activity of your heart.
The ECG machine will create a picture on graph paper of the electrical impulses that travel through your heart.
Your ECG pattern will be reviewed by our doctor and kept on file for comparisons with future ECG recordings.
The test usually takes around 10 to 15 minutes to complete.
The procedure is non-invasive and risk-free, with no radiation exposure or known complications. The electrodes (sticky patches) that connect the sensors to your chest do not send out electric shocks. However, you may develop a mild rash or skin irritation where the electrodes were attached.
What happens after a 12-lead ECG?
After completing the test, your doctor will remove the electrodes from your body. Your doctor can print out a tracing from the ECG machine with the information recorded. Results are typically reviewed by a cardiologist and shared with your doctor within 24 hours.
If any abnormalities are detected, further investigations—such as a stress ECG or echocardiogram—may be recommended. Your doctor will contact you to discuss the findings and next steps, if necessary.
Price of a 12-Lead ECG Test in Singapore
The cost for a standard 12-lead ECG test in Singapore typically ranges from about $49.05 to $63.22 SGD at most private clinics and health screening centres. Some comprehensive health screening packages (which include ECG and other tests) start from $428 SGD and include consultations. However, the quoted prices are for the ECG test itself and do not always include consultation or follow-up fees unless specified. Reports are usually ready within 72 hours, with express reports available for an additional fee at some clinics.
FAQ
What does the 12-lead ECG actually refer to?
A 12-lead ECG, as its name implies, is used to measure twelve leads. Depending on which lead shows deviations from a normal ECG, experts can find out things like in which part of the heart muscle an infarction has occurred or whether a heart rhythm problem is coming from the atria or the ventricles.
What is the difference between a normal ECG and a 12-lead ECG?
A standard ECG may use fewer leads (e.g., 3-lead), while the 12-lead ECG provides a comprehensive spatial analysis, essential for diagnosing complex conditions. Moreover, a normal ECG is often used for basic heart monitoring. On the other hand, 12-Lead ECG provides a complete picture of heart activity and is a very important tool in making clinical decisions related to heart disorders
What can you tell from a 12-lead ECG?
A 12-lead ECG, a non-invasive test recording the heart's electrical activity, can reveal information about heart rate, rhythm, and potential problems like arrhythmias, heart attacks, or ischaemia, offering valuable insights into cardiac health.
Who needs a 12-lead ECG?
A 12-lead ECG is recommended for individuals experiencing symptoms like chest pain, shortness of breath, or palpitations, or those with a family history of heart disease, as well as for pre-operative assessments and heart screening.
How to tell if an ECG is abnormal?
An abnormal ECG can show issues with heart rate, rhythm, or waveforms, potentially indicating problems like heart attack, arrhythmia, or heart muscle damage.
Can I wear clothes during a 12-lead ECG?
Loose clothing is acceptable, but chest electrodes require direct skin contact. A gown may be provided.
Can I use lotions or oils before a 12-lead ECG?
No. These interfere with electrode adhesion and signal quality.
Can improper placement affect ECG accuracy?
Yes. Misplaced electrodes may mimic pathological patterns (e.g., false ST changes) or obscure true abnormalities.
How do clinicians ensure accuracy in patients with physical limitations?
Clinicians ensure accuracy in patients with physical limitations by using a multi-faceted approach that includes thorough assessment, open communication, and collaboration within the healthcare team, while also considering the patient's perspective and limitations.
The information provided is intended for general guidance only and should not be considered medical advice. For personalised recommendations and tailored advice, please consult a specialist at Thomson Medical. Request an appointment with Thomson Medical today.
For more information, contact us:
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