RRB ECG Technician key terms

The heart's natural pacemaker, a small cluster of specialised cells in the right atrium that spontaneously depolarises at roughly 60 to 100 times per minute and sets the normal rhythm.

A relay station of specialised conducting cells between the atria and ventricles that delays the electrical impulse briefly, allowing the atria to empty before the ventricles contract.

The continuation of the AV node into the interventricular septum, which splits into right and left bundle branches and carries the impulse rapidly toward the ventricles.

Fast-conducting fibres spreading through the ventricular walls that distribute the electrical impulse to ventricular muscle, producing rapid, coordinated contraction.

The first deflection on an ECG, a small rounded wave representing atrial depolarisation; its shape, width and height help identify atrial enlargement or an ectopic atrial pacemaker.

The time from the start of the P wave to the start of the QRS complex, normally 0.12 to 0.20 seconds; prolongation suggests delayed conduction through the AV node.

The sharp deflection representing ventricular depolarisation, normally narrow (under 0.12 seconds); widening suggests a conduction delay such as bundle branch block or a ventricular origin.

The deflection after the QRS complex that reflects ventricular repolarisation; it is normally upright in most leads and can become inverted, flat or peaked in ischaemia and electrolyte disturbance.

The flat section between the end of the QRS complex and the start of the T wave; elevation or depression relative to baseline is a key sign of myocardial injury or ischaemia.

A normal rhythm originating in the SA node, showing upright P waves before every QRS complex at a regular rate between 60 and 100 beats per minute.

A sinus rhythm slower than 60 beats per minute; it may be normal in athletes or during sleep but can cause dizziness and low blood pressure when the rate is inadequate.

A sinus rhythm faster than 100 beats per minute, typically a physiological response to fever, pain, exercise, anxiety, anaemia or hypovolaemia rather than a primary rhythm disorder.

An irregularly irregular rhythm with absent P waves and fibrillatory baseline activity, caused by chaotic atrial activation; it carries a risk of clot formation and stroke.

A rhythm in which R-R intervals vary unpredictably from beat to beat with no repeating pattern, the classic hallmark of atrial fibrillation.

Deriving beats per minute from an ECG, commonly by dividing 300 by the number of large squares between R waves, or by counting QRS complexes in a 10-second strip and multiplying by six.

The distance between two consecutive R waves, used to judge rhythm regularity and to calculate heart rate; it should be measured consistently across the strip.

A consistent prolongation of the PR interval beyond 0.20 seconds in which every P wave is still followed by a QRS complex; usually benign but worth documenting.

Delayed conduction down the right or left bundle branch, producing a widened QRS complex (0.12 seconds or more) with a characteristic pattern in the chest leads.

An early beat arising from ventricular muscle, shown as a wide, bizarre QRS complex without a preceding P wave, often followed by a compensatory pause.

A run of three or more consecutive ventricular beats at a fast rate, appearing as wide QRS complexes; it is a medical emergency because it can deteriorate into ventricular fibrillation.

Chaotic, disorganised electrical activity with no identifiable P waves, QRS complexes or T waves and no effective cardiac output; it requires immediate defibrillation and cardiopulmonary resuscitation.

Upward displacement of the ST segment above the isoelectric line, suggesting acute transmural myocardial injury; it demands urgent medical review and repeat tracing.

Inadequate blood flow to heart muscle, which on ECG commonly appears as ST depression, T wave inversion or flattening in the affected leads without necessarily showing infarction.

Death of heart muscle due to blocked coronary blood flow, shown on ECG by ST elevation, pathological Q waves or new T wave changes depending on the stage and site.

An abnormally deep or wide Q wave, often indicating previous full-thickness myocardial infarction in the territory of the leads where it appears.

The geometric arrangement of the three limb leads I, II and III, which view the heart from three directions and together form the basis of the frontal plane recording.

Six frontal-plane leads: bipolar I, II and III plus augmented aVR, aVL and aVF, formed from electrodes on the arms and legs; lead II is commonly used for rhythm monitoring.

Six unipolar precordial leads V1 to V6 placed across the chest, which record the heart's electrical activity in the horizontal plane and help localise ischaemia or hypertrophy.

Correct positioning of electrodes for a 12-lead ECG, including limb electrode sites and the standard V1 to V6 chest positions; errors cause misdiagnosis and must be avoided.

The rectangular pulse at the start of a tracing showing that 1 millivolt equals 10 millimetres vertically, allowing correct interpretation of wave heights and amplitudes.

The rate at which the ECG paper or digital display advances, standardly 25 millimetres per second, which fixes the time scale used to measure intervals and rate.

Slow up-and-down drift of the tracing caused by patient movement, breathing, poor electrode contact or loose cables; it can mimic or hide ST segment changes.

Rapid, fuzzy, irregular oscillation on the tracing produced by muscle activity such as shivering, tension or talking, which can obscure small waveforms.

Any unwanted disturbance of the isoelectric line, including drift, tremor or electrical interference, that reduces tracing quality and must be corrected before interpretation.

Regular high-frequency fuzz at 50 or 60 hertz caused by nearby electrical equipment or poor electrode contact, producing a thick, unreadable baseline on the ECG.

The quality of the electrical connection between skin and electrode; cleaning the skin, clipping hair and using fresh gel or pads improves contact and reduces artefact.

Precautions when a shock may be delivered, including ensuring nobody touches the patient or bed, oxygen is moved away, and the operator announces and confirms 'clear' before discharge.

Practices such as hand hygiene, clean or disposable electrodes, and disinfection of cables and machine parts between patients to prevent transmission of microorganisms in the ECG room.

Explaining the purpose, procedure and privacy aspects of an ECG to the patient and obtaining voluntary agreement before recording, respecting the right to refuse or ask questions.

Protecting the patient's dignity and personal health information during ECG recording by using screens or curtains, exposing only necessary skin, and keeping records confidential.