ECG and the Heart’s Internal Conduction System Guided Notes Name:______

Do Now

What is an action potential and where do they occur?

Intrinsic conduction system

Interestingly, all the cells of the conduction system are

______.

That is, all will depolarize at a certain rate.

The ______has the fastest rate of

depolarization, though, so it sets the pace for the entire heart.

Quick Review – Intrinsic Conduction System

What is the function of

-AV node

-Gap junctions

-SA node

-Purkinje fibers

Name 3 differences between cardiac and skeletal muscle contraction & explain why each is important to cardiac function.

ECG

ECG Questions

What is responsible for the delay between P wave and QRS complex?

What is responsible for the delay between T wave and next P wave?

Examine this normal ECG.

When would the ventricles be in systole?

When would they be in diastole?

When would the heart sounds occur, and what do the heart sounds correspond to?

ECG abnormalities

Examine these ECG readouts, and identify how they differ from a normal ECG.

a)

b)

c)

d)

Descriptors –

Name / Characteristic ECG / Cause(s)
AV block / In severe cases, there is NO relationship between P waves and QRS complex. QRS still occurs due autorhythmic cells in AV node, but at a slower rate. / Damage to AV node, such as from reduced blood flow (ischemia) or fibrosis.
Treatment: dual chamber artificial pacemaker- one that ‘listens’ to the SA node and sends a signal to the AV node
Atrial fibrillation / Wavy baseline, no regular p waves
QRS normal shape but occurs randomly
Looks messy / Heart is doing uncoordinated, ineffective contraction due to lack of blood, excess alcohol, or infection
Tachycardia / Heart beats faster than normal (more than 100 bpm) / Exercise, drugs
Bradycardia / Heart beats slower than normal (less than 60 bpm) / Many conditions, including heart damage, medications, etc,

Regulation of Heart Rate

Earlier, we said that the SA node depolarizes at a rate of ~75 beats per minute, and that this acts as a pace maker for heart contraction.

Does this mean our hearts always beat at ~75 bpm?

What are the two branches of the autonomic nervous system, and how do they affect heart rate?

Other factors that influence heart rate

Age (fastest in fetus, young children)

Gender (faster in females)

Temperature (faster in heat)

Exercise (faster with exercise)

Ions imbalances & medicines (faster or slower)

Weak / damaged heart (can be either faster / slower)