Electric Impulse

What is the purpose of an electrical impulse in the heart?

It causes atrial and ventricular contraction.

Where is the sinoatrial (SA) node located?

In the right atrium.

What is the SA node?

The pacemaker of the heart; it starts the electrical impulse.

What happens when the SA node starts an impulse?

The impulse spreads through the myocardial cells of both left and right atria.

What does atrial electrical activity cause?

Atrial contraction, which pushes blood into the ventricles.

What does the P wave represent?

Atrial depolarization/activation from the SA node.

What happens after the impulse passes through the atria?

It gathers at the AV node.

What is the pathway of the electrical impulse after the AV node?

AV node → bundle of His → interventricular septum → ventricular walls.

What does ventricular electrical activity cause?

Ventricular contraction.

What does the QRS complex represent?

Ventricular depolarization/activation. (The electroactivity that showers down)

What are the atria doing during the QRS complex?

Relaxing/repolarizing.

What does the T wave represent?

Ventricular repolarization and relaxation (diastole).

What is an arrhythmia?

An abnormal heart rhythm that may require an ECG/EKG to evaluate.

What happens during ventricular systole?

The ventricles contract and eject blood.

What does S1 (“lub”) represent?

Closure of the AV valves at the start of ventricular systole.

Why is S1 / “lub” heard?

Blood hits the closing AV valves creates the sound.

What does S2 (“dub”) represent?

Closure of the semilunar valves at the end of ventricular systole.

What is the order of the main heart sounds?

S1 = lub → ventricular systole → S2 = dub→beginning of ventricular diastole

What is S3?

A rarely heard sound that may occur during early ventricular filling.

What is S4?

A rarely heard sound caused by the atria pushing the last bit of blood into the ventricles.

When is S4 heard?

Just before S1