Classical system and Einthoven's triangle
Standard recording is based on the classical Einthoven's triangle. Electrodes are attached to the right arm, left arm, and left leg, forming a closed circuit that encloses the heart. Potential differences are recorded as three standard leads. The position of the organ directly depends on the person's body type — for example, in hypersthenics, due to a high diaphragm, the heart lies more horizontally compared to normosthenics and asthenics.
Considerations for implants, dressings, and amputations
Anatomical changes and medical devices require adjustment of attachment points:
- In patients with breast implants, chest leads V3 through V6 are shifted inferiorly along the same vertical lines (midclavicular, anterior axillary, and midaxillary).
- In patients with limb amputations, electrodes are placed as distally as possible on the stump, or alternative systems — such as Mason-Likar or Khan — are used.
- With compression bandages on the limbs, electrodes are placed on exposed areas or directly over the garment (temporarily lowering it is acceptable); on the chest, as close as possible to standard points.
- In the presence of external fixation metal devices, electrodes are attached proximal to the structures.
The main rule: any shift in electrode placement must be clearly stated in the report, and during serial monitoring, electrode positions must remain consistent.
Non-standard conditions and dextrocardia
Sometimes the procedure is performed under specific conditions:
- In cases where moving the patient to the examination couch is impossible, recording in the sitting position is permitted (the patient is asked to lean back as far as possible, and a corresponding note is made in the report).
- In patients with dextrocardia, the limb cables are swapped (red is attached to the left, and yellow to the right), and chest points are placed in mirror image, labeled as V2R–V6R.
For continuous monitoring in ambulances or intensive care units, compact 3- and 5-lead systems are used, expanding auscultation capabilities.
In dextrocardia, remember the "mirror": right becomes left (red and yellow are swapped, and chest leads are labeled with an R suffix).
Class and exam questions
How to place electrodes in the presence of breast implants?
Chest electrodes V3–V6 are shifted inferior to the implant projection on the anterior chest wall, maintaining the same vertical lines (midclavicular, anterior axillary, and midaxillary).
What to do when recording an ECG in a sitting patient?
This method is permitted if moving the patient to the couch is impossible. The patient is asked to lean back, and the non-standard position must be documented in the test results comment.
What changes are made in dextrocardia?
The red electrode is moved to the left arm, the yellow to the right, and the chest leads are placed in mirror image, labeled as V2R–V6R.
What else to study on this topic
- Alternative Mason-Likar lead systems
- Specifics of Khan leads
- Differences between 3-channel and 5-channel rhythm monitoring
- Principles of augmented limb leads and Wilson's chest leads
- Basics of vectorcardiography
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