exam 1

What does “P” stand for on an EKG strip?

Atrial depolarization

What does “QRS stand for on an EKG strip?

Ventricular depolarization

What does “T” stand for on an EKG strip?

Ventricular repolarization

RECOVERY

What does AVR measure in an EKG?

The AVR lead records the heart’s electrical activity (voltage) from the right arm’s perspective compared to a central point.

Where is the AVR central point?

Between the left arm and left leg

What does AVF measure in an EKG?

The AVF lead records the heart’s electrical activity (voltage) from the left leg’s perspective compared to a central point.

Where is the AVF central point?

Between the right arm and left arm

What does AVL measure in an EKG?

The AVL lead records the heart’s electrical activity (voltage) from the left arm’s perspective compared to a central point.

Where is the AVL central point?

Between the right arm and left leg

What are the 3 types of leads of an EKG?

Precordial (chest, V1-V6), augmented (limb, AVR AVL AVF), and standard (limb, I II III)

What are the 3 fascicles of the left bundle branch?

The anterior, posterior, and septal branches

Which fascicle of the L bundle branch is the longest and thinnest?

The anterior fascicle

Which fascicle of the L bundle branch is shorter and thicker?

The posterior fascicle

In what direction does the electrical impulse spread through the heart wall?

From the endocardium (inner layer) to the myocardium (muscle layer) and then outward toward the epicardium

What is the conduction pathway?

SA Node → AV node → Bundle of HIS → bundle branches → Purkinje fibers

SA Node

Known as the pacemaker of the heart. Normally produces the electrical event that initiates the heartbeat. Located just below the opening of the SVC

AV Node

Composed of 3 layers: the upper, middle, and lower, which have unique conduction characteristics. Lies on the floor of the RA just medial to the mitral valve (bicuspid/L AV) and just above the ventricle

Bundle of His

Passes from the walls of the RA through a small opening in the fibrous skeleton to reach the IV septum

Bundle branches

Divides further into 3 divisions: the septal fascicle, the anterior fascicle, and the posterior fascicle

Purkinje fibers

Consist of countless tiny fibers that spread out widely like twigs of a tree branch. It’s a network. Conducts impulses rapidly through the muscle to assist in its depolarization and contraction, resulting in ventricular depolarization starting in the endocardium and proceeding outward to the epicardium

Normal rate for the SA node

60-100bpm

Normal rate for the AV node

40-60bpm

Purkinje fibers bpm

20-40bpm

What is the function of the intraatrial conductive pathway?

It carries the electrical impulse across the IAS to the LA, allowing both atria to contract together

What pathway do impulses take after leaving the AV node?

From the AV node, impulses travel through the Bundle of His (AV bundle), then to the R and L bundle branches, which carry the signal toward the ventricles for contraction.

Septum

Separates the heart into two functional units

• interatrial- separates the atria

• interventricular- separates the ventricles

What do the 2 upper chambers (atria) do?

Collect blood and deliver to the ventricles

What do the 2 lower chambers (ventricles) do?

Pump blood to the lungs (pulmonary circuit) and body (systemic circulation)

Which ventricle has the highest pressure?

The left ventricle has the highest pressure of all heart chambers

RV is closer to _____

LV is closer to ______

Right ventricle is closer to the front of the left chest

Left ventricle is closer to the side of the left chest

Heart valves function

Permit, control, and maintain blood to flow through the heart in only one direction

What does “AV valves” mean? What is another name for each of them?

Atrioventricular valves

R AV valve - tricuspid

L AV valve - mitral/bicuspid

Where are the AV valves located?

Between the atria and ventricles (separates them)

Does the tricuspid valve (TV) have cusps of leaflets? How many?

Cusps; 3

When is the tricuspid valve open?

During diastole

Does the mitral valve (bicuspid) have cusps of leaflets? How many?

Leaflets; 2. Anterior & posterior mitral leaflets.

When is mitral valve open?

During diastole

What does “SL valves” mean?

Semilunar valves

What valves are the semilunar valves?

Aortic & pulmonic

When are SL valves open?

During systole

Where is the thebesian valve located?

Near the entrance of the coronary sinus

Where is the eustachian valve located?

Near the entrance of the IVC. Once the fetus is born, it goes away (rudimentary)

What is the function of the valves of the heart?

To control and maintain blood flow through the heart/body

What blood does the RA receive and what circuit does it pass the blood to?

The RA receives deoxygenated blood from the body and passes it toward the lungs via pulmonary circuit

What blood does the LA receive and what circuit does it pass the blood to?

The LA receives oxygenated blood from the lungs and passes it toward the body via systemic circuit

What are the 3 layers of the heart?

Epicardium, endocardium, myocardium

What is the order of the blood flow?

SVC → IVC → coronary sinus (CS) → RA → tricuspid valve (TV, r av valve) → RV → pulmonic valve (PV) → main pulmonary artery (MPA) → lungs → 4 pulmonary veins → LA → mitral valve (bicuspid) → LV → aortic valve (AoV) → ascending aorta → aortic arch → descending aorta → body

What is the double-layered sac that surrounds/protects the heart?

The pericardium

What does the pericardium prevent?

Prevents friction, trauma, and infection

What does the pericardium provide?

Provides friction

How much fluid is normally found in the pericardial cavity?

10-50mL (cc) of fluid

• cc = cubic centimeter. It’s used in medicine for liquid volume and 1cc equals 1mL

What structure can a dilated coronary sinus be confused with?

It may resemble the descending aorta due to its posterior location and circular appearance

What are the 3 main branches of the aortic arch?

Brachiocephalic (innominate) artery, left common carotid artery, and left subclavian artery

What arteries branch off of the brachiocephalic (innominate) artery?

Right common carotid artery and right subclavian artery

Which is the higher pressure chamber?

The LV is a higher pressure chamber than the RV

What is each small box on the EKG paper equal to?

0.04 sec/min

What is the cardiac cycle?

One complete contraction and relaxation of the heart

Stroke volume

The amount of blood ejected from the heart each minute

Cardiac output

The amount of blood pumped into the aorta/from the heart in one minute

• heart rate x stroke volume = cardiac output

What does Frank Starling’s law state?

That the greater the stretch of the cardiac muscle the greater the contraction.

What type of relationship is described by Frank Starling’s law?

A length-tension relationship

Where is the SA node located?

In the anterior portion of the RA

What does the anterior & posterior descending coronary arteries feed?

The Bundle of HIS

Where does the R coronary artery usually supply blood to?

The AV node

Excitability (key property of myocardial cells)

Each cell will respond to an electrical stimulus

Automaticity (key property of myocardial cells)

The ability to generate an electrical impulse independently (without outside nerve stimulation)

What gases are transported through the circulatory system?

Oxygen & carbon dioxide

• it carries o2 to tissues and removes co2 from tissues

Myocytes

Heart cells; working cells

Where are myocardial cells located?

Located in the myocardium

Where are myocardial intercalated discs located?

At the junctions where myocardial cells branches join

Why do myocardial cells act as a single unit?

Rapid movement of electrical impulses from one cell to adjacent cells allows my oxygen to act as a single unit, ENABLING COORDINATED CONTRACTION OF THE ENTIRE GROUP OF CELLS

How are myocardial cells shaped?

They are cylindrical and branching at their ends. They are interconnected (forming a network), allowing coordinated contraction of the heart muscle

Where is the nucleus located in myocardial cells?

Myocardial cells usually contain one centrally located nucleus (in the middle of the myocardial cell).

What is the plasma membrane of the myocardial cells?

The sarcolemma is the plasma membrane in which the myocardial cells are enclosed in

What are the protein filaments that make up myocardial cells?

Actin & myocin

What type of filament is actin?

Thin filament

What type of filament is myosin?

Thick