Cardiac Conduction System & ECG

Vocabulary flashcards covering the components, steps, timing, and ECG wave representations of the cardiac conduction system.

Cardiac Conduction System

signals that controls the heartbeat by traveling through the heart to cause different parts to contract and relax.

SA node

Located in the right atrium near the opening of the vena cava;

the natural pacemaker of the heart that generates electrical impulses spontaneously

Gap junctions

Structures found within the intercalated discs of cardiac cells that allow electrical impulses to spread from one cardiac muscle cell to another.

AV node

Site where the electrical impulse is delayed to allow the atria to contract and empty all blood into the ventricles before the ventricles contract.

AV bundle / bundle of His

Conduction pathway located in the interventricular septum

Bundle branches

Branches that carry the impulse through the interventricular septum toward the apex of the heart.

Purkinje fibres

Fibres that conduct electrical impulses throughout the whole ventricular myocardium causing the ventricles to contract.

Electrocardiogram (ECG)

A test measuring electrical impulses that trigger the heartbeat, detecting the heart's electrical rhythm and producing a tracing.

Sinus Rhythm

The normal rhythm of the heart (about $60\text{-}100 / \text{min}$ ) where electrical stimuli are initiated in the SA node and conducted through the AV node, bundle of His, bundle branches, and Purkinje fibres.

P wave

The ECG wave representing the event where an electrical impulse is generated at the SA node, causing contraction of the atria.

Isoelectric line

A flat segment on an ECG with no signal, occurring when the impulse is delayed at the AV node or stops during the ST segment.

Q wave

The ECG wave representing the impulse traveling through the bundle of His, producing a small voltage change opposite to main conduction.

R wave

The ECG wave representing the impulse traveling through bundle branches, where the thick left ventricles produce a large voltage change.

S wave

The ECG wave representing the impulse traveling upward through Purkinje fibres in the opposite direction to main conduction.

ST segment

The flat, isoelectric segment on an ECG where the impulse stops, allowing the ventricle to fully contract and move all blood.

T wave

The ECG wave representing ventricular cell repolarisation from the bottom of the heart to the top, allowing the heart to relax.