11/13/24 - Cardiac Physiology (Part 2) Lecture Questions

What is meant by electrical activity in the heart?

Pacemaker and Cardiac Potentials

What is meant by mechanical activity of the heart?

Cardiac Cycle — all events that occur in the heart, per heartbeat

How are electrical events in the heart related to mechanical events?

Electrical events ALWAYS precede and proceed mechanical events

What are the two types of Cardiac Cells?

Which type makes up the majority of Cardiac Cells?

1. Cardiac Contractile Cells / Cardiomyocytes — makes up 99% of Cardiac Cells

2. Pacemaker / Autorhythmic Cells — makes up 1% of Cardiac Cells

What is the purpose of Cardiac Contractile Cells?

What do they create?

Purpose is to carry out mechanical work, such as contraction of the Myocardium which generates a force that pumps blood throughout the body

Creates Cardiac Action Potentials

What is the purpose of Pacemaker Cells?

What do they create?

Purpose is to set the heart rate; makes up the conduction system that initiates and conducts A.P. that spread throughout the system

Creates Pacemaker Potentials

What sets the pace of the heart beat when the SA node is not functioning?

AV Node sets the pace

What sets the pace of the heart beat when the SA Node is okay but the AV Node is damaged?

What is this called?

Atria will be controlled by the SA Node, while the Ventricles will be controlled by the Purkinje Fibers

Called a complete Heart Block

What sets the pace of the heart beat when the Purkinje Fibers depolarize faster than the SA Node?

What causes this to happen?

What does this cause?

Heart will beat based on the rate of the Purkinje Fibers

Caused by Ectopic Focus — abnormal areas of the heart are excited

Causes premature ventricular contractions

How are Pacemaker Cells and Cardiac Contractile Cells connected?

1. SA Node is primarily composed of Pacemaker Cells

2. Pacemaker Cells undergo spontaneous depolarizations to create Pacemaker Potentials

3. Pacemaker Potentials travel to Cardiac Contractile Cells via Gap Junctions

4. Cardiac Contractile Cells contract

5. Pacemaker Potentials also travel to adjacent Pacemaker Cells

6. Adjacent Pacemaker Cells undergo electrical conduction to set the heart rate

What does AV Nodal Delay allow for?

Allows the Ventricles to completely fill up with blood by giving the Atria time to contract and push the remaining 20% of blood out

What happens to Ventricles when they are excited?

How are action potentials spread to the Ventricular Muscles to allow for contraction?

They contract

Spread via the Purkinje Fibers

Where does the Interatrial Pathway occur?

Internodal Pathway?

Interatrial —> Left Atrium

Internodal —> AV Node

How do A.P. travel from cell to cell?

Jump from Gap Junction to Gap Junction

What is the RMP of Pacemaker Cells?

RMP is around 60 mV and 70 mV; it is unstable and often spontaneously depolarizes

What happens during each phase of a Pacemaker Potential?

1. Slow Depolarization — Funny Na+ channels open and close quickly, V.G. T-type Calcium channels open and close quickly

2. Rapid Depolarization — V.G. L-Type Calcium channels open

3. Repolarization — V.G. Potassium channels open, V.G. L-Type Calcium channels close

What does the T stand for in T-Type Calcium Channels?

L in L-Type Calcium Channels?

T — Transient / brief

L — Long-lasting

What happens during each phase of a Cardiac Potential?

1. Rapid Depolarization — V.G. Na+ channels open due to Positive Feedback

2. Brief Repolarization — Na+ channels close, V.G. K+ channels open

3. Plateau — Slow L-Type Calcium channels open, K+ channels stay open

4. Repolarization — Calcium channels close

5. Return to rest — K+ channels close

Do Cardiac Potentials have refractory periods?

Why or why not?

Can the heart undergo summation?

No

Heart has to fully relax before it can begin contracting again

No, no summation

What is an Electrocardiogram (ECG / EKG)?

External measure that records the spread of electrical activity through the heart

What does the P-wave represent on an ECG?

QRS-Complex?

T-wave?

P-wave — Atrial Depolarization / Contraction

QRS-Complex — Ventricle Depolarization / Contraction

T-wave — Ventricle Repolarization / Relaxation

Why do we not measure Atrial Repolarization / Relaxation on an ECG?

The QRS-Complex that shows Ventricle Depolarization / Contraction is so large it masks the Atrial Repolarization / Relaxation

What does the R-R segment measure?

P-Q?

Q-T?

T-Q?

R-R — count heart beats

P-Q — Atrial Contraction

Q-T — Ventricular Contraction

T-Q — Ventricular Relaxation

What does Sinus Tachycardia indicate?

Fast HR (> 100 bpm)

What does Sinus Bradycardia indicate?

Slow HR (< 60 bpm)

What does Ventricular Fibrillation indicate?

Increase in HR with erratic contraction