Basics of Electrocardiography

Vocabulary flashcards covering essential terms and concepts introduced in the lecture on electrocardiography.

Electrocardiography

A noninvasive medical procedure that records the electrical activity of the heart.

Electrocardiograph

The medical device used to perform electrocardiography and generate an ECG/EKG tracing.

ECG / EKG

Abbreviation for electrocardiogram; ‘K’ reflects the German word for heart (Kardio).

Electrode

A small sticky sensor attached to the skin that detects electrical potentials from the heart.

Lead (ECG)

The difference in electrical potential recorded between two electrodes, producing one tracing.

Baseline (Isoelectric line)

The horizontal line on an ECG indicating no significant change in the heart’s electrical state.

Waveform

Any deflection above or below the baseline that represents a significant electrical change.

P wave

ECG waveform produced by depolarization of the atrial myocardium.

QRS complex

Large ECG deflection representing rapid depolarization of the ventricular myocardium.

T wave

ECG waveform generated by repolarization of the ventricular myocardium.

Atrial depolarization

Electrical event corresponding to the P wave that initiates atrial contraction.

Ventricular depolarization

Electrical event represented by the QRS complex that triggers ventricular contraction.

Ventricular repolarization

Electrical recovery phase shown as the T wave on the ECG.

Atrial repolarization

Electrical recovery of the atria, usually hidden within the QRS complex on a normal ECG.

SA (Sinoatrial) Node

Primary pacemaker of the heart; its firing initiates each cardiac cycle and precedes the P wave.

AV Node Delay

Brief pause in conduction at the atrioventricular node, reflected in the P-R segment.

Contractile cells

Cardiac muscle cells (≈99%) whose coordinated electrical changes create detectable ECG waves.

Conductive cells

Specialized myocardial cells (≈1%) forming the conduction system; their signals are usually too small to appear as separate waves.

Plateau phase

Phase of the cardiac action potential with minimal voltage change, seen as a return to baseline.

R-R interval

Time between successive R peaks; used to calculate heart rate.

Q-T interval

Duration from the start of QRS to the end of T; equals the full ventricular action potential and contraction time.

T-Q interval

Period from the end of the T wave to the next QRS onset; represents ventricular diastole and filling time.

P-R segment

Baseline period between the end of the P wave and start of QRS; largely reflects AV node delay.

S-T segment

Baseline period between the end of QRS and start of T wave; corresponds to the ventricular plateau phase.

Sinus rhythm

Normal heart rhythm governed by the SA node, typically 60–100 beats per minute at rest.

Tachycardia

Resting heart rate exceeding 100 beats per minute; often shortens the T-Q interval.

Bradycardia

Resting heart rate below 60 beats per minute; often lengthens the T-Q interval.

Diastole

Phase of ventricular relaxation and filling, mainly occurring during the T-Q interval.

Action potential (cardiac)

Rapid change in membrane voltage of cardiac cells that triggers contraction; length mirrors contraction duration.

Noninvasive procedure

A diagnostic test that does not require incisions or insertion of instruments into the body, such as an ECG.