d o
t o r e g . c o m
Dr. Mete ALPASLAN
Electrode Placement and ECG Recording
ECG is recording of the heart's electrical activity.
Normally intracellular potential is negative and extracellular potential is positive. When electrically stimulated, intracellular potential becomes positive.
The recorded electrical activity is formed by heart muscle (myocardial) cells and Purkinje cells.
The recorded electrical acitivity is directly related to total mass of the cells.
Since Purkinje cells constitute only a very small part of heart's total mass, the ECG mainly represents the electrical activity of heart muscle (myocardial) cells in the same cardiac chamber.
In a healthy adult, left ventricular mass is more than right ventricular mass. Therefore, QRS complex and T wave represents LEFT ventricular depolarization and repolarization, respectively.
Why do we use more than one electrode for ECG recording?
The heart's electrical activity is a three dimensional event.
Several electrodes, each located differently, observe heart from different angles. If electrical activity is perpendicular to a certain lead, it will be recorded isoelectric (it will not be observable) on that lead. Electrode located at a another site may record that electrical activity, thus making it observable.
Color coding of limb lead electrodes
Color coding is used for quick and correct selection of the electrodes.
Different colors are preferred in Europe and U.S.A.
In Europe: red for right arm, yellow for left arm, black for right foot, green for left foot.
In U.S.A.: white for right arm, black for left arm, green for right foot, red for left foot.
Some ECG machines designate chest electrodes with the letter " V ",
some others designate chest electrodes with the letter " C ".
Chest electrodes are placed as follows:
V1: 4th intercostal space, at the right sternal border.
V2: 4th intercostal space, at the left sternal border.
V3: between leads V2 and V4.
V4: At the 5th intercostal space on the midclavicular line.
V5: At the 5th intercostal space on the anterior axillary line.
V6: At the 5th intercostal space on the midaxillary line.
Common misplacement errors of chest electrodes
Placing leads V1 and V2 at the 2nd intercostal spaces.
Placing lead V3 at the right border of the sternum: You can realize this misplacement error by observing that the R wave amplitude increases from lead V1 to lead V2, then decreases at lead V3 and re-increases at lead V4.
Correct electrode placement is crucial for serial ECG recordings of a patient during hospitalization.
Electrode misplacement may result in erroneous appearance of newly developed ST segment depression or elevation.
The recording principle of electrical activity is as follows:
Electrical activity is inscribed positive if it is approaching the electrode, negative if it is going away from the electrode, isoelectric if it moves perpendicular to the electrode.
Sweep speed of ECG
The sweep speed of standard ECG is 25 mm/second.
When the sweep speed is 25 mm/second, one small square on the paper equals to 40 milisecond (0.04 sec), one large square equals to 200 milisecond (0.2 second), five large squares equal to 1 second.
If long strip recording is needed for rhythm monitoring, 5 or 10 mm/second sweep speed is preferred. By this way, long rhythm recording will be possible, permitting the observation of infrequent arrhythmias.
If tachycardia is present, 50 mm/second sweep speed is preferred to see the details. This is especially useful in infants and small children.
References
Am J Emerg Med 2018;36(5):865-870.
Circ Cardiovasc Qual Outcomes 2017 Feb;10(2).
J Electrocardiol 2014 Jan-Feb;47(1):1-6.
Figure 1. The sweep speed of a standard ECG is 25 mm/second.
Figure 2a. Correct placement of chest electrodes is shown above.
Intercostal spaces are palpated.
V1 electrode is placed to the right side of the sternum, at the 4th intercostal space.
Blue vertical line shows the midclavicular line.
Figure 2b. Above is an example of incorrect placement of chest electrodes.
V1 and V2 electrodes should not be placed on the 2nd intercostal spaces.
Figure 2c. Above is another example of incorrect placement of chest electrodes.
Figure 2d. Above is another example of incorrect placement of chest electrodes.
Electrodes from V1 to V4 are placed like a zigzag.
You can suspect this type of malplacement when the R wave amplitude in V1 is bigger than V2,
and the one in V3 is smaller than the one in V4.
Below are examples of faulty precordial electrode placement.
Do not place chest electrodes as below:
ECG 1a. The ECG above belongs to a man who was admitted to the hospital at the 6th hour of acute anterior myocardial
infarction. During recording of the initial ECG, the C1 and C2 electrodes were misplaced at the 2nd intercostal spaces.
Click here for a more detailed ECG
ECG 1b. The ECG was recorded again after placing the leads C1 and C2 to the 4th intercostal spaces (correct placement).
Since the electrodes C1 and C2 are closer to the ventricles now, the amplitude of the S wave increased and the ST segment
is elevated more. This case clearly shows that in patients hospitalized for management of acute coronary syndromes,
the detection of recently developed ST segment deviations rely heavily on correct electrode placement.
Click here for a more detailed ECG
ECG 2a. The ECG above belongs to a 43 years-old asymptomatic woman. There are ventricular couplets and triplets.
However, this is a 10-second recording only. It does not give us an idea about the frequency of the ventricular beats.
Click here for a more detailed ECG
ECG 2b. The above 6-channel rhythm strip was recorded at a calibration of 10 mm/mV but at a sweep speed of 5mm/second.
The above recording shows approximately 1 minute rhythm, which is 6 times longer than the tracing in ECG 2a.
By this way, a longer recording can be accommodated on the standard ECG paper, allowing us to see how frequent
the ventricular couplets and triplets are.
Click here for a more detailed ECG
ECG 3. Above is a one-channel rhythm tracing recorded at a normal speed and calibration (10 mm/mV, 25 mm/sec).
Some ECG machine producers provide this type of printing.
You can select this format to have an idea on the frequency of extrasystoles.
By this way, you can see 60 seconds of rhythm on a single page without sacrificing from the image quality.
Click here for a more detailed ECG
ECG 4a. The ECG above belongs to a 42 years-old healthy woman.
After seeing the ST elevation in lead V2, a doctor referred her to Cardiology outpatient clinic.
We suspected that the leads V1 and V2 were placed above 4th intercostal space.
Click here for a more detailed ECG
ECG 4b. The ECG above belongs to the same woman.
This time leads V1 and V2 were placed at the 4th intercostal space.
ST segment elevation is not seen any more.
Additionally, QRS amplitude in lead V2 is increased when comnpared with the ECG 4a.
Click here for a more detailed ECG
ECG 5a. The ECG above belongs to a 33 years-old anxious man.
His ECHOcardiogram is normal (no structural heart disease).
Leads V1 and V2 show negative T waves due to misplacement of these electrodes.
Leads V1 and V2 were placed under claviculae during recording of the above ECG.
Click here for a more detailed ECG
ECG 5b. The ECG above belongs to the same man. It was recorded one hour before the ECG 5a at a different clinic.
This time leads V1 and V2 were correctly placed at the 4th intercostal space, not under claviculae.
Leads V1 and V2 do not show T wave negativity any more.
This example shows the importance of correct lead placement during close follow-up of patients by ECG.
Click here for a more detailed ECG
ECG 6a. The ECG above belongs to a 59 years-old woman with coronary artery disease. She came to the hospital with the
complaint of chest pain, coronary angiography was performed and then she underwent coronary artery bypass grafting surgery.
A VPC, widespread ST depression and negative T waves are seen in this preoperative ECG.
Click here for a more detailed ECG
ECG 6b. The ECG above belongs to the same woman.
It was recorded after a successful coronary artery bypass surgery (45 days after the ECG 6a).
T wave is positive in lead V1, negative in lead V2 and again positive in leads V3 to V6.
Is this new-onset myocardial ischemia or is there electrode misplacement?
While recording the above ECG, the V2 electrode was misplaced at the 2nd intercostal space, on left side of the sternum.
Click here for a more detailed ECG
ECG 6c. The above ECG belongs to the same woman.
It was recorded immediately after the ECG 6b but this time with correct lead placement.
While recording the above ECG, the V2 electrode was correctly placed at the 4th intercostal space, on left side of the sternum.
Chest leads do not show negative T waves. All chest leads show positive T waves.
No need to worry about myocardial ischemia.
Therefore, correct placement of electrodes is important for correct diagnosis.
Click here for a more detailed ECG
ECG 7a. The ECG above belongs to a 64 years-old woman with coronary artery disease.
ECHOcardiography showed normal left ventricular systolic function with mild left atrial dilation.
This ECG was recorded while the patient was sitting on a chair.
Click here for a more detailed ECG
ECG 7b. The ECG above belongs to the same patient. It was recorded while the patient was lying supine.
As you see, recording an ECG while sitting on a chair complicates diagnosing.
Click here for a more detailed ECG
ECG 8a. The ECG above belongs to a 69 years-old obese woman with systemic hypertension.
Her ECHOcardiography was normal. She has no known coronary artery disease.
Chest leads show non-specific T wave changes.
This ECG was recorded while she was upright and sitting on a chair.
Click here for a more detailed ECG
ECG 8b. The ECG above belongs to the same patient. It was recorded while the patient was lying supine.
Now, the ECG is normal.
As you see, recording an ECG while sitting on a chair complicates diagnosing.
Click here for a more detailed ECG
ECG is recording of the heart's electrical activity.
Normally intracellular potential is negative and extracellular potential is positive. When electrically stimulated, intracellular potential becomes positive.
The recorded electrical activity is formed by heart muscle (myocardial) cells and Purkinje cells.
The recorded electrical acitivity is directly related to total mass of the cells.
Since Purkinje cells constitute only a very small part of heart's total mass, the ECG mainly represents the electrical activity of heart muscle (myocardial) cells in the same cardiac chamber.
In a healthy adult, left ventricular mass is more than right ventricular mass. Therefore, QRS complex and T wave represents LEFT ventricular depolarization and repolarization, respectively.
Why do we use more than one electrode for ECG recording?
The heart's electrical activity is a three dimensional event.
Several electrodes, each located differently, observe heart from different angles. If electrical activity is perpendicular to a certain lead, it will be recorded isoelectric (it will not be observable) on that lead. Electrode located at a another site may record that electrical activity, thus making it observable.
Color coding of limb lead electrodes
Color coding is used for quick and correct selection of the electrodes.
Different colors are preferred in Europe and U.S.A.
In Europe: red for right arm, yellow for left arm, black for right foot, green for left foot.
In U.S.A.: white for right arm, black for left arm, green for right foot, red for left foot.
Some ECG machines designate chest electrodes with the letter " V ",
some others designate chest electrodes with the letter " C ".
Chest electrodes are placed as follows:
V1: 4th intercostal space, at the right sternal border.
V2: 4th intercostal space, at the left sternal border.
V3: between leads V2 and V4.
V4: At the 5th intercostal space on the midclavicular line.
V5: At the 5th intercostal space on the anterior axillary line.
V6: At the 5th intercostal space on the midaxillary line.
Common misplacement errors of chest electrodes
Placing leads V1 and V2 at the 2nd intercostal spaces.
Placing lead V3 at the right border of the sternum: You can realize this misplacement error by observing that the R wave amplitude increases from lead V1 to lead V2, then decreases at lead V3 and re-increases at lead V4.
Correct electrode placement is crucial for serial ECG recordings of a patient during hospitalization.
Electrode misplacement may result in erroneous appearance of newly developed ST segment depression or elevation.
The recording principle of electrical activity is as follows:
Electrical activity is inscribed positive if it is approaching the electrode, negative if it is going away from the electrode, isoelectric if it moves perpendicular to the electrode.
Sweep speed of ECG
The sweep speed of standard ECG is 25 mm/second.
When the sweep speed is 25 mm/second, one small square on the paper equals to 40 milisecond (0.04 sec), one large square equals to 200 milisecond (0.2 second), five large squares equal to 1 second.
If long strip recording is needed for rhythm monitoring, 5 or 10 mm/second sweep speed is preferred. By this way, long rhythm recording will be possible, permitting the observation of infrequent arrhythmias.
If tachycardia is present, 50 mm/second sweep speed is preferred to see the details. This is especially useful in infants and small children.
References
Am J Emerg Med 2018;36(5):865-870.
Circ Cardiovasc Qual Outcomes 2017 Feb;10(2).
J Electrocardiol 2014 Jan-Feb;47(1):1-6.
Figure 1. The sweep speed of a standard ECG is 25 mm/second.
Figure 2a. Correct placement of chest electrodes is shown above.
Intercostal spaces are palpated.
V1 electrode is placed to the right side of the sternum, at the 4th intercostal space.
Blue vertical line shows the midclavicular line.
Figure 2b. Above is an example of incorrect placement of chest electrodes.
V1 and V2 electrodes should not be placed on the 2nd intercostal spaces.
Figure 2c. Above is another example of incorrect placement of chest electrodes.
Figure 2d. Above is another example of incorrect placement of chest electrodes.
Electrodes from V1 to V4 are placed like a zigzag.
You can suspect this type of malplacement when the R wave amplitude in V1 is bigger than V2,
and the one in V3 is smaller than the one in V4.
Below are examples of faulty precordial electrode placement.
Do not place chest electrodes as below:
ECG 1a. The ECG above belongs to a man who was admitted to the hospital at the 6th hour of acute anterior myocardial
infarction. During recording of the initial ECG, the C1 and C2 electrodes were misplaced at the 2nd intercostal spaces.
Click here for a more detailed ECG
ECG 1b. The ECG was recorded again after placing the leads C1 and C2 to the 4th intercostal spaces (correct placement).
Since the electrodes C1 and C2 are closer to the ventricles now, the amplitude of the S wave increased and the ST segment
is elevated more. This case clearly shows that in patients hospitalized for management of acute coronary syndromes,
the detection of recently developed ST segment deviations rely heavily on correct electrode placement.
Click here for a more detailed ECG
ECG 2a. The ECG above belongs to a 43 years-old asymptomatic woman. There are ventricular couplets and triplets.
However, this is a 10-second recording only. It does not give us an idea about the frequency of the ventricular beats.
Click here for a more detailed ECG
ECG 2b. The above 6-channel rhythm strip was recorded at a calibration of 10 mm/mV but at a sweep speed of 5mm/second.
The above recording shows approximately 1 minute rhythm, which is 6 times longer than the tracing in ECG 2a.
By this way, a longer recording can be accommodated on the standard ECG paper, allowing us to see how frequent
the ventricular couplets and triplets are.
Click here for a more detailed ECG
ECG 3. Above is a one-channel rhythm tracing recorded at a normal speed and calibration (10 mm/mV, 25 mm/sec).
Some ECG machine producers provide this type of printing.
You can select this format to have an idea on the frequency of extrasystoles.
By this way, you can see 60 seconds of rhythm on a single page without sacrificing from the image quality.
Click here for a more detailed ECG
ECG 4a. The ECG above belongs to a 42 years-old healthy woman.
After seeing the ST elevation in lead V2, a doctor referred her to Cardiology outpatient clinic.
We suspected that the leads V1 and V2 were placed above 4th intercostal space.
Click here for a more detailed ECG
ECG 4b. The ECG above belongs to the same woman.
This time leads V1 and V2 were placed at the 4th intercostal space.
ST segment elevation is not seen any more.
Additionally, QRS amplitude in lead V2 is increased when comnpared with the ECG 4a.
Click here for a more detailed ECG
ECG 5a. The ECG above belongs to a 33 years-old anxious man.
His ECHOcardiogram is normal (no structural heart disease).
Leads V1 and V2 show negative T waves due to misplacement of these electrodes.
Leads V1 and V2 were placed under claviculae during recording of the above ECG.
Click here for a more detailed ECG
ECG 5b. The ECG above belongs to the same man. It was recorded one hour before the ECG 5a at a different clinic.
This time leads V1 and V2 were correctly placed at the 4th intercostal space, not under claviculae.
Leads V1 and V2 do not show T wave negativity any more.
This example shows the importance of correct lead placement during close follow-up of patients by ECG.
Click here for a more detailed ECG
ECG 6a. The ECG above belongs to a 59 years-old woman with coronary artery disease. She came to the hospital with the
complaint of chest pain, coronary angiography was performed and then she underwent coronary artery bypass grafting surgery.
A VPC, widespread ST depression and negative T waves are seen in this preoperative ECG.
Click here for a more detailed ECG
ECG 6b. The ECG above belongs to the same woman.
It was recorded after a successful coronary artery bypass surgery (45 days after the ECG 6a).
T wave is positive in lead V1, negative in lead V2 and again positive in leads V3 to V6.
Is this new-onset myocardial ischemia or is there electrode misplacement?
While recording the above ECG, the V2 electrode was misplaced at the 2nd intercostal space, on left side of the sternum.
Click here for a more detailed ECG
ECG 6c. The above ECG belongs to the same woman.
It was recorded immediately after the ECG 6b but this time with correct lead placement.
While recording the above ECG, the V2 electrode was correctly placed at the 4th intercostal space, on left side of the sternum.
Chest leads do not show negative T waves. All chest leads show positive T waves.
No need to worry about myocardial ischemia.
Therefore, correct placement of electrodes is important for correct diagnosis.
Click here for a more detailed ECG
ECG 7a. The ECG above belongs to a 64 years-old woman with coronary artery disease.
ECHOcardiography showed normal left ventricular systolic function with mild left atrial dilation.
This ECG was recorded while the patient was sitting on a chair.
Click here for a more detailed ECG
ECG 7b. The ECG above belongs to the same patient. It was recorded while the patient was lying supine.
As you see, recording an ECG while sitting on a chair complicates diagnosing.
Click here for a more detailed ECG
ECG 8a. The ECG above belongs to a 69 years-old obese woman with systemic hypertension.
Her ECHOcardiography was normal. She has no known coronary artery disease.
Chest leads show non-specific T wave changes.
This ECG was recorded while she was upright and sitting on a chair.
Click here for a more detailed ECG
ECG 8b. The ECG above belongs to the same patient. It was recorded while the patient was lying supine.
Now, the ECG is normal.
As you see, recording an ECG while sitting on a chair complicates diagnosing.
Click here for a more detailed ECG