6. ecg

What does an ECG measure?

The electrical activity of the heart

What causes the P wave on an ECG?

Atrial depolarization

What causes the QRS complex?

Ventricular depolarization

What causes the T wave?

Ventricular repolarization

What electrical event is not visible on the ECG?

Atrial repolarization (masked by QRS)

What is the 5 big block rule on ECG paper?

5 big squares = 1 second

How do you calculate heart rate using the 3-second method?

Count QRS in 3 seconds, multiply by 20

How do you calculate heart rate using the 6-second method?

Count QRS in 6 seconds, multiply by 10

What is the physiological basis of ECG waves?

They reflect ion movement during cardiac action potentials

What initiates the heartbeat?

Sinoatrial (SA) node

What is the path of the cardiac conduction system?

SA node → AV node → Bundle of His → Bundle branches → Purkinje fibers

What is the role of the AV node?

Delays signal to allow atria to contract before ventricles

What is depolarization?

A positive shift in membrane potential due to Na⁺/Ca²⁺ influx

What is repolarization?

Return to resting potential, usually via K⁺ efflux

Where do you see the longest action potential duration in the heart?

Ventricular cardiomyocytes