Cardio Functioning Exam 1

The heart is located in the…

Mediastinum

The heart is enclosed and held in place by the ___

What are the 3 layers of it?

1. Pericardium

2. fibrous & Serous (Parietal and Visceral)

The visceral and parietal layers are separated by the…

serous cavity which is a fluid-filled space

The outside of the heart is covered by the:

1. Fibrous Pericardium

2. Parietal Serous Pericardium

3. Visceral Serous Pericardium (Epicardium)

The wall of the heart has 3 layers:

1. Epicardium (visceral serous pericardium)

2. Myocardium (heart muscle; striated)

3. Endocardium (lines chambers & valves)

Are the left and right ventricles the same size? and Do they output the same amount of blood?

NO! The left ventricle is much thicker because it builds more pressure in order to send to the rest of the body; where the right only send blood to the lungs

YES! they output the same amount of blood… the left only is thicker due to increased pressure of push out

The valves of the heart open and close in response to…

pressure changes as the heart contracts and relaxes

Job of Right and left atrioventricular valves (tricuspid & bicuspid)

Prevents back flow from the ventricle into the atria

Job of Right and left semilunar valves (pulmonary & aortic)

Prevents back flow from the arteries into the ventricles

Jobs of the fibrous skeleton of the heart:

• Forms the foundation for which the heart valves attach

• Prevents overstretching of the heart valves

• Acts as an electrical insulator (prevents retrograde current flow from ventricles to atria

Pathway of Electrical System of the heart

1. SA Node (pacemaker) ———> Bachmann’s Bundles

2. 3 Internodal tracts

3. AV Node (Delay)

4. Bundle of HIS

5. Bundle Branches

6. Purkinje Fibers

Intrinsic rates

SA node = 60 - 100

Atrial muscle = 60 - 80

AV Node = 40 - 60

Ventricular muscle = 20 - 40

Overall delay of the heart

0.06 - 0.10 sec

Blood has to flow from…

High to low pressure

Blood vessels pressure ranked from highest to lowest

Arteries

Arterioles

Capillaries

Venules

Veins

Job of arterioles

control how much blood enters tissues

Cardiac Output defined

the amount of blood the heart pumps out in a minute

• CO = HR x SV

MAP formula

MAP = CO x TPR

what is TPR?

essentially how difficult it is for blood to move through blood vessels

• Arteriole diameter is biggest factor (Vasoconstriction → vessels narrow / vasodilation → vessels widen)

Why are cardiac cells auto rhythmic?

Some cardiac cells can create their own electrical signal without needing a nerve to tell them when to fire

2 types of cardiac cells

1. Slow-response cells = pacemaker cells

2. Fast-response cells = contractile cells

Where can Slow-response cells be found and how do they function?

found mainly in the SA and AV nodes

They do not have a stable resting membrane potential… Instead they slowly drift toward threshold on their own

• starting potential ~ -60mV

• Threshold ~ -40mV

Phases of Slow-response cells

Phase 4 → Phase 0 → Phase 3

(Threshold -60 — -45)

Phase 4 = Pacemaker potnetial

• Membrane becomes slowly less negative due to Na+ entering (“Funny Currents”)

Phase 0 = Depolarization

• Ca+ enters

• Membrane becomes more positive

Phase 3 = Repolarization

• K+ leaves

• Membrane becomes negative again

Where can Fast-response cells be found and how do they function?

Found in the atria and ventricles

Their job is to contract and pump blood.

• They have a stable resting membrane potential

• Resting potential = -90mV

• Threshold = -70mV

Phases of Fast-response Cells

Phase (4) 0 → 1 → 2 → 3 → 4

(Threshold -90 — -70)

Phase 4 = Resting

• Around -90mV

• Cell is waiting for another signal

Phase 0 = Depolarization

• Na+ rapidly enters

• Voltage shoots upward

Phase 1 = Early repolarization

• Na+ channels close

• small amount of K+ leaves

Phase 2 = Plateau (No net change in charge)

• Ca+ enters

• K+ leaves

Phase 3 = Repolarization

• Ca+ channels close

• K+ leaves

P Wave

Atrial contraction (depolarization)

QRS Complex

Ventricular contraction (depolarization)

T Wave

ventricular diastole (repolarization)

PR Interval

Represents the time it takes the electrical system to travel from the atria through the AV Node and toward the ventricles

• Atrial to ventricular conduction

ST Segment

The ventricles are fully depolarized

• corresponds roughly to the period when the ventricles are contracting/ejecting blood

QT Interval

Represents essentially the entire period of ventricular electrical activity

• Ventricular depolarization + repolarization

The SA node is the heart’s…

It determines___ _____ by controlling …

1. natural pacemaker

2. Heart rate by controlling how frequently the heart depolarizes

How does the sympathetic pathway affect heart rate?

Sympathetic "(“Speed Up”) → increases HR

Pathway:

• Sympathetic stimulation → norepinephrine → B1 receptors → increase in cAMP → faster SA node depolarization → increase HR

Mechanism of sympathetic affect on HR

1. Sympathetic nerves release NE

2. NE binds to B1-receptors on SA node cells

3. This increases cAMP

4. More ion movement occurs, especially increased Na+/Ca2+ activity

5. The SA node reaches threshold faster

6. More action potentials per minute → heart rate increases

How does the parasympathetic pathway affect heart rate?

Parasympathetic (“Put on the brake”) → decreases HR

Pathway:

• Parasympathetic stimulation → acetylcholine → M2 receptors → decrease in cAMP + increase in K+ efflux → slower SA node depolarization → decrease in HR

Mechanism of parasympathetic affect on HR

1. Parasympathetic nerves releases ACh

2. ACh binds to M2 muscarinic receptors

3. This decreases cAMP and increases K+ leaving the cell

4. The SA node becomes more negative/slower to reach threshold

5. Fewer action potentials per minute → heart rate decreases

What are the bipolar limb leads?

What are the augmented leads?

• Both represent FRONTAL Plane

Bipolar → Lead I, II, & III

Augmented → aVR, aVL, aVF

What are the precordial/chest leads?

• Represent horizontal Plane

Leads V1 thru V6

Lead I

Negative → Right arm

Positive → Left arm

Direction → Right to Left

Lead II

Negative → Right arm

Positive → Left leg

Direction → Right to Left leg

Lead III

Negative → Left arm

Positive → Left leg

Direction → Left arm → left leg

Rule of thumb of electrical activity direction

Moving toward the positive electrode produces an upward/positive ECG deflection

Moving away from the positive electrode produces a downward/negative deflection

Lead aVR

Positive → Right arm

Direction → toward right shoulder

Lead aVL

Positive → Left arm

Direction → toward left shoulder

Lead aVF

Positive → Left leg

Direction → Downward toward feet

Heart Locations based on 12 Lead locations

Septal → V1-V2

Anterior → V3-V4

Lateral → I, aVL, V5-V6

Inferior → II, III, aVF

What is the Hex-axial system?

The system is used to determine the heart’s mean electrical axis, usually referring to the mean QRS axis

• It uses the 6 limb leads: I, II, III, aVR, aVL, & aVF

What is the normal QRS axis?

About -30 degrees to +90 degrees

What do the 4 quadrants and what do they display?

0^o to +90^o → Normal

-30^o to -90^o → Left axis deviation

+90^o to +180^o → Right axis deviation

-90^o to ±180^o → Extreme axis

ECG paper basics

1 small box - 0.04 sec

one large box (5 small boxes) - 0.20

5 large boxes - 1 sec

5-step ECG Interpretation

1. Rate

2. Rhythm

3. Axis

4. Hypertrophy

5. Infarction

Rate

Determine Heart Rate

• 300 Method

• count # of small boxes from R - R then divide 1500 by that

Rhythm

is it regular?

• Equal R - R intervals = regular

• Unequal R - R intervals = irregular

is it sinus rhythm?

• P wave → QRS → T wave

Axis

Use the hex-axial system

Lead I aVF Interpretation

+ + Normal

+ - Left axis deviation

- + Right axis deviation

- - Extreme axis

Hypertrophy

definition = enlarged/thickened cardiac muscle

More cardiac muscle means:

• More electrical activity → larger voltage/amplitude

• Ex. Left ventricular hypertrophy can produce unusually large QRS voltages

Infraction / Ischemia

Looks for abnormal changes in

• ST segment

• T wave

• Q waves

ST depression can indicate ischemia or other conditions

T-wave abnormalities can also indicate abnormal ventricular repolarization

Pathologic Q waves can be evidence of prior myocardial infarction