🩺 12-Lead ECG Acquisition

A 12-lead ECG (Electrocardiogram) is a non-invasive diagnostic test that records the electrical activity of the heart over time via electrodes placed on the skin. It provides a 'snapshot' of the heart from 12 different perspectives (leads), allowing for the diagnosis of ischaemia, arrhythmias, and conduction abnormalities. Precise electrode placement is critical to ensuring an accurate interpretation. It is a fundamental tool in the assessment of acute chest pain and cardiovascular stability.

Chest pain or suspected acute coronary syndrome (ACS). Palpitations, syncope, or dizziness suggestive of arrhythmia. Monitoring of patients on medications known to prolong the QT interval (e.g., certain antipsychotics or macrolides). Pre-operative assessment for patients with known cardiovascular disease or major surgery. Assessment of electrolyte imbalances (e.g., hyperkalaemia) or metabolic disturbances. Monitoring of known conditions like heart failure or hypertension.

There are no absolute contraindications to performing an ECG as it is a non-invasive, low-risk procedure. However, patient refusal is a contraindication. Care should be taken in patients with significant skin breakdown or burns where electrode adhesive might cause further damage. In emergency settings (e.g., cardiac arrest), the primary focus is resuscitation/defibrillation, but a 12-lead ECG is obtained as soon as a rhythm is stabilised (ROSC).

ECG machine (calibrated to 25mm/sec and 10mm/mV). 10 electrode leads (wires). Disposable adhesive electrode pads. Skin preparation wipes (or gauze for drying). Razor for chest hair removal (if necessary). Patient gown and a private environment with a couch. Printout paper compatible with the machine.

Introduce yourself, verify patient identity, and explain the procedure. Ensure the patient is supine with their chest exposed and limbs relaxed. Clean or shave the skin at lead sites if necessary. Apply the four limb electrodes (RA-Red, LA-Yellow, LL-Green, RL-Black) to the fleshy parts of the limbs. Apply the six chest electrodes (V1-V6) using precise anatomical landmarks. Connect the lead wires to the electrodes. Ask the patient to remain still. Press the 'start' or 'acquire' button on the ECG machine. Review the quality of the trace for artifact or lead reversal. Print the ECG, label it with the patient's details (if not digitised), and document if the patient was symptomatic.

A systematic approach is essential: check the patient's name, date, and time. Assess the rate (usually 60-100 bpm) and rhythm (is every P-wave followed by a QRS?). Determine the axis (normally -30 to +90 degrees). Examine individual components: P-wave (atrial depolarisation), PR interval (0.12-0.20s), QRS complex duration (<0.12s) and morphology (looking for Q-waves or RSR' patterns), ST-segment (elevation >1mm in limb leads or >2mm in chest leads is significant for STEMI), T-waves (inversion or peaking), and the QTc interval. Always compare with previous ECGs to identify new changes.

Incorrect lead placement (specifically V1 and V2 too high in the 2nd intercostal space) can mimic pathological patterns like Brugada syndrome or RBBB. Swapping the limb leads (e.g., LA/RA) is a frequent error that results in an extreme axis deviation and an inverted P-wave and QRS in Lead I. Placing electrodes over bony prominences rather than fleshy areas leads to poor contact and increased 'noise' or artifact. Failing to ensure the patient is relaxed and warm can lead to somatic tremor, which obscures fine details like P-waves or ST-segment changes.

Always ensure patient privacy by using curtains and a gown, and explain that you will need to place stickers on their chest, wrists, and ankles. Correct landmarks: V1 (4th ICS, right sternal edge), V2 (4th ICS, left sternal edge), V4 (5th ICS, mid-clavicular line), V3 (between V2 and V4), V5 (5th ICS, anterior axillary line), V6 (5th ICS, mid-axillary line). Remember 'Ride Your Green Bike' (Red, Yellow, Green, Black) for limb leads starting from the Right Arm and going clockwise. Advise the patient to lie still, breathe normally, and not talk during the recording. Record the presence of chest pain at the time of the trace on the paper.

Aligned with MLA 'Clinical Skills' (Procedural/Diagnostic): 12-lead ECG. Students must know the precise anatomical landmarks for V1-V6. Recognition of 'Red Flag' ECG patterns (STEMI, Ventricular Tachycardia, 3rd-degree Heart Block) is a core MLA requirement. Knowledge of how to reduce artifact and ensure a 'clean' trace is vital for clinical practice.