Cardiac Conduction System and Electrocardiogram (ECG)

Vocabulary flashcards covering key terms related to the cardiac conduction system and ECG findings from the lecture notes.

Sinoatrial (SA) node

Located in the right atrium near the entrance of the superior vena cava; the natural pacemaker that initiates heartbeat and sets heart rate; its electrical impulses spread through the atria to cause atrial contraction.

Atrioventricular (AV) node

Located in the right atrium near the atrioventricular valve; the electrical gateway to the ventricles and delays impulses to allow atrial contraction and ventricular filling.

Atrioventricular bundle (bundle of His)

Transmits impulses from the AV node to the ventricles; divides into right and left bundle branches toward the apex.

Right bundle branch

Conducts impulses to the right ventricle along the right pathway toward the apex.

Left bundle branch

Conducts impulses to the left ventricle along the left pathway toward the apex.

Purkinje fibers

Specialized conducting fibers that spread impulses through the ventricles to trigger ventricular contraction.

Electrocardiogram (ECG or EKG)

A composite recording of all cardiac action potentials; each wave or segment corresponds to a specific event in the cardiac electrical cycle.

P wave

Atrial depolarization produced when the SA node fires, preceding atrial contraction.

PR interval

From the start of the P wave to the start of the QRS complex; reflects conduction through the AV node.

QRS complex

Ventricular depolarization; Q wave = septal depolarization, R wave = depolarization of the main ventricle mass, S wave = depolarization toward the base.

Q wave

Depolarization of the interventricular septum.

R wave

Depolarization of the main mass of the ventricles.

S wave

The last phase of ventricular depolarization moving toward the base of the heart.

Atrial repolarization

Occurs during the QRS complex but is obscured by the large QRS; repolarization of atrial muscle.

ST segment

Plateau phase of ventricular action potentials when the ventricles are contracted and pumping blood.

T wave

Ventricular repolarization, immediately before ventricular relaxation (diastole).

Atrial systole

Atrial contraction that starts about 100 ms after the start of the P wave.

Cardiac cycle

The repeating sequence of electrical and mechanical events that make up every heartbeat.