Which phase of the cardiac cycle does this picture show? How can you be sure?

Think about it…

• What do you suspect happens to the coronary blood vessels as the heart goes through the cardiac cycle?– What would happen to them during

systole?– What would happen to them during

diastole?

Coronary Blood Vessels• Feed the cardiac muscle

with oxygen rich blood• The coronary vessels

branch off of the base of the aorta

• Only fill with blood when the pressure inside of the aorta is low and the blood flows back towards the heart

https://www.youtube.com/watch?v=tBQa8IBzP6I&feature=related

What happens to a heart if it can’t get enough oxygen?

HEART ATTACK

Why?

https://www.youtube.com/watch?v=eTKICIpShaA&feature=related

Intrinsic Conduction

System of the Heart

Heart Beat Control… Why Necessary?

• Cardiac muscle cells contract spontaneously do not require a stimulus from the nervous system to contract

• Atrial cells contract 60x/min.• Ventricular cells contract 20-40x/min.

– heart needs a control system to coordinate pumping heart would be inefficient w/o it

Heart Regulation2 systems regulate heart activity:• Autonomic nervous system: increases and

decreases heart rate – Discussed in nervous system

• *Intrinsic conduction system (AKA nodal system):• Special heart tissue cross between muscle & nervous

tissue• Sets rhythm for heart• Causes controlled contraction (depolarization) from atria to

ventricles

How Does Heart Contract?

1. Sinoatrial (SA) node in the right atrium sends an electrical signal to the atria

*causes atria to contract together

SA node = pacemaker

How Does Heart Contract?

2. After the signal to contract travels through the atria it goes to the atrioventricular (AV) node

(Allows mini pause in signal so atria can finish contracting)

How Does Heart Contract?

3. AV node releases signal to atrioventricular (AV) bundle aka bundle of His

Right & left bundle branches

Purkinje fibers

How Does Heart Contract?

4. As electrical signal spreads through the Purkinje fibers contraction begins in apex and travels toward the atria

Pushes blood into the

aorta and to body

Conduction System Video

http://www.nhlbi.nih.gov/health/health-topics/topics/hhw/electrical.html

Aligns electrical system with an EKG

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter22/animation__conducting_system_of_the_heart.html

General animation of electrical conduction system

Practice• Using your index cards and NO notes,

show how the electrical impulse is carried through the heart starting with the “pacemaker”.

• When you have finished and have been checked, use a piece of chalk to draw where atrial and ventricular contraction occur.

EKG/ ECG

• Electrocardiogram is a way to measure the electrical activity in the heart

• Shows– How fast your heart is beating– Whether the rhythm of your heartbeat is steady or

irregular– The strength and timing of electrical signals as they pass

through each part of your heart

http://www.nhlbi.nih.gov/health/health-topics/topics/hhw/electrical.html

Reading EKG’s

• P wave = SA node firing = happens immediately before atria contract

• QRS complex = AV node firing = happens immediately before ventricles contract

• T wave = ventricles preparing for another impulse

Sample

1. Identify the P, Q, R, S, and T waves. 2. Look to the left of each QRS and identify the P wave. Is the P wave present (+) or absent (-): ______3. Is there a 1:1 ratio of P waves to QRS waves? ____________ …so is this regular or not? __________4. What is the rate of the heart? ______________5. Diagnosis/Conclusions: __________________________________________________________

Tachycardia

The heart’s rate is more rapid than normal (over 100 beats/min)

Bradycardia

The heart rate is significantly lower than normal (less than 60 beats/min)

Atrial Fibrillation

Atria contract more often than the ventricles

One of these things is not like the other!

Sinus Arrest

SA node fails to fire and the heart doesn’t beat.

Sleepin’ on the job

Fibrillation

•The heart is not beating in a coordinated manner

•Muscle cells are contracting but are not in synch inefficient pumping of blood

•Can lead to cardiac arrest

Asystole• There is no electrical activity in heart (no

contraction)• Cannot be revived!

More Practice• Add the P, Q, R, and S cards to

the index cards to show which actions of the electrical system create the types waves seen on an EKG

• Try to do this without your notes!