ECG and Cardiac Conduction System

These flashcards cover key terms and concepts related to the ECG and cardiac conduction system.

ECG

Electrocardiogram; a recording of the heart’s electrical activity.

Node

A specialized area of cardiac muscle that generates electrical impulses (action potentials).

Sinoatrial (SA) node

The area where a normal heartbeat starts, located in the right atrium.

Pacemaker node

Another name for the SA node.

SA node firing rate

60–100 beats per minute.

Unique feature of SA node

It automatically cycles between depolarization and repolarization.

Atrioventricular (AV) node

The area where the impulse goes after the SA node.

Function of AV node delay

Allows atria to fully contract before ventricles contract.

Length of AV node delay

About 100 milliseconds.

AV node's intrinsic rate

40–60 beats per minute.

SA node failure consequence

The AV node takes over pacing at 40–60 bpm.

Max conduction rate of AV node

About 230 bpm.

Heart efficiency decrease

Around 180 bpm.

AV bundle (Bundle of His)

Where the impulse goes after the AV node.

AV bundle's intrinsic rate

20–40 bpm.

Connection of AV bundle

Connects atria to ventricles.

Structures carrying impulses in ventricles

Right & left bundle branches and Purkinje fibers.

Function of Purkinje fibers

Rapidly conduct impulses for coordinated ventricular contraction.

Papillary muscles contraction purpose

To tighten chordae tendineae and prevent backflow.

P wave representation

Atrial depolarization.

Atria contraction timing relative to P wave

About 25 ms after it begins.

QRS complex representation

Ventricular depolarization.

Visibility of atrial repolarization on ECG

It is hidden by the stronger ventricular signal.

T wave representation

Ventricular repolarization.

P-R interval definition

Time from start of P wave to start of QRS complex.

Prolonged P-R interval indication

A conduction delay/problem.

Q-T interval definition

Time from start of QRS complex to end of T wave.

Q-T interval representation

Ventricular systole.

Prolonged Q-T interval indication

Heart damage or electrolyte imbalance.