Electrocardiography Essentials

Thirty vocabulary flashcards covering fundamental electrocardiography terms, lead systems, machine settings, waveform components, and heart-rate calculation methods.

Electrocardiogram (ECG / EKG)

A graphic recording of the heart’s electrical activity produced by a galvanometer to evaluate cardiac function and detect disorders.

12-Lead ECG

Standard test using 10 electrodes to view the heart’s electrical activity from 12 different angles for a complete assessment.

Electrode

Disposable sensor with conductive gel placed on the skin to pick up and transmit the heart’s electrical impulses to the ECG machine.

Standard (Bipolar) Leads

Leads I, II, III that measure current flow between two limbs in two directions, each yielding a positive deflection.

Augmented (Unipolar) Leads

Leads aVR, aVL, aVF that record electrical activity from one limb compared with a zero-voltage reference; machine boosts signal 50%.

Chest (Precordial) Leads

Positive unipolar leads V1–V6 positioned across the chest to record the heart’s horizontal plane activity.

Einthoven’s Triangle

Imaginary triangle formed by Leads I, II, III around the heart; right-leg lead serves as ground.

Gain (ECG Machine)

Control that adjusts waveform height (voltage); normal setting is 10 mm/mV.

Paper Speed (ECG)

Rate at which ECG paper moves—standard 25 mm/sec; 50 mm/sec for tachycardia/pediatrics, 12.5 mm/sec for bradycardia.

Artifact

Any interference or abnormal mark on an ECG tracing caused by external factors rather than cardiac activity.

Somatic Tremor

Jittery baseline artifact from muscle movement such as shivering, anxiety, or Parkinson’s disease.

AC Interference

60-cycle electrical artifact from nearby equipment or wiring, creating a thick, uniform baseline.

Wandering Baseline

Slow shift of the isoelectric line due to loose electrodes, patient movement, or dirty lead wires.

P wave

First upward deflection representing atrial depolarization triggered by the SA node.

QRS Complex

Combination of Q, R, S deflections signifying rapid ventricular depolarization.

T wave

Upward deflection following QRS that represents ventricular repolarization.

U wave

Small upward deflection after the T wave indicating Purkinje fiber repolarization; prominent in hypokalemia.

ST Segment

Flat line from end of QRS to start of T wave, showing early ventricular repolarization; deviation suggests ischemia or MI.

PR Interval

Time from start of P wave to start of QRS (0.12–0.20 sec) reflecting AV node conduction.

QT Interval

Interval from start of QRS to end of T wave, encompassing ventricular depolarization and repolarization.

Polarization

Resting state of myocardial cells with no electrical activity detected.

Depolarization

Electrical activation of myocardial cells leading to contraction.

Repolarization

Recovery phase where myocardial cells return to their resting state.

Normal Sinus Rhythm (NSR)

Regular rhythm 60–100 bpm with normal P, QRS, and T waves.

Bradycardia

Heart rate below 60 bpm; normal in athletes but may indicate pathology in others.

Tachycardia

Heart rate exceeding 100 bpm.

Arrhythmia

Irregular heart rhythm characterized by varying intervals between beats.

R-R (300) Method

Heart-rate calculation for regular rhythms: 300 divided by the number of large boxes between two R waves.

1500 Method

Precise rate calculation for regular rhythms: 1500 divided by the number of small boxes between two R waves.

6-Second Method

Rate calculation for irregular rhythms: count R waves in 30 large boxes (6 sec) and multiply by 10.