EKG Part 1

Review of information from GDoc named "EKG 7/14/25"

Who invented the EKG/ECG and when?

Willem Einthoven in 1903

What can be diagnosed from and EKG?

• Myocardial infarction

• Arrhythmia/disrhythmia

• Hypertension

• Pulmonary embolism

• Coronary artery disease

Where is the heart located?

In the mediastinum within the thoracic cavity

Pacemaker cells

• under normal circumstances, the electrical power source of the heart

• Located in SA and AV nodes

Electrical conducting cells AKA specialized muscle cells

• the hard wiring of the heart

• Found in the myocardium

Myocardial cells

• the contractile machinery of the heart

• found in the myocardium

What are electrical impulses

waves

Where does the P wave occur?

In the atria and it is triggered by the SA node

Where does the QRS complex occur?

In the ventricles

Where does the T wave occur?

In the ventricles

What are the layers of the heart from outer to inner?

Epicardium → myocardium → endocardium

Epicardium

• outer layer of the heart that covers the heart and attaches to the pericardium

• Thin, serous (watery) membrane

Myocardium

• middle layer of the heart that contracts to pump blood into the arteries

• Thick layer of cardiac muscle

Endocardium

• inner layer of the heart that lines the interior chambers and valves

• Thin layer of epithelial cells that is continuous with the lining of the blood vessels

The right side of the heart pumps what kind of blood?

Deoxygenated blood

Right atrium

upper right chamber that receives deoxygenated blood from the body via both the superior and inferior vena cavas and pumps it into the right ventricle

What is the largest vein in the body?

The vena cava

Right ventricle

Lower right chamber that receives blood from the right atrium and pumps it into the pulmonary artery, which carries ti to the lungs to be oxygenated

The left side of the heart pumps what kind of blood?

Oxygenated blood

Left atrium

Upper left chamber that receives oxygenated blood from the lungs via the pulmonary veins and pumps it into the left ventricle

Left ventricle

lower left chamber that receives blood from the left atrium and pumps it into the aorta

What is the largest chamber of the heart and why?

• left ventricle

• due to the force required to pump the blood into the arterial system

Septa

A partition between the right and left sides of the heart that is mostly made of myocardium

Interatrial septum

Between atrium

Interventricular septum

Between ventricles

Tricuspid valve

• closes when the right ventricle contracts and prevents blood from flowing back into the right atrium

• Located between the right atrium and left ventricle

• AV valve with 3 cusps

Bicuspid/mitral valve

• closes when the left ventricle contracts and prevents blood from flowing back into the left atrium

• Located between the left atrium and left ventricle

• AV valve with 2 cusps

Right semilunar valve

• closes when the right ventricle relaxes and prevents blood from flwoing back into the right ventricle

• Located at the entrance to the pulmonary artery

• 3 cusps

Left semilunar valve

• closes when the left ventricle relaxes and prevents blood from flowing back into the left ventricle

• Located at the entrance to the aorta

• 3 cusps

Sinoatrial (SA) node

• Pacemaker of heart

• Located in upper wall of the right atrium

Internodal pathway fibers

• relay the impulse to the atrioventricular (AV) node

• Located in the wall of the right atrium

Atrioventricular (AV) node)

• picks up the impulse from the internodal pathway fibers, slows ti down while the atria finish contracting, and then relays it through the bundle of His

• Located on the floor of the right atrium

AV bundle AKA bundle of His

• relays impulse throughout the ventricular walls by means of bundle branches and purkinje fibers

• Located in the top of the interventricular septum

Purkinje fibers

• lead off left and right bundle branches

• can make the U wave

Are heart contractions synchronized?

• YES

  • Atria contracts simultaneously 

  • Followed by the contraction of both ventricles

• It is achieved by the electrical conduction system

“Lubb” heart sound

• 1st heart sound (S1)

• Ventricles’ contraction (systole)

  • Action phase (depolarization)

  • P wave

  • QRS wave

• Atrioventricular valves close

Systole

Ventricles contracting/depolarizing

“Dubb” heart sound

• Second heart sound (S2)

• Beginning of ventricular relaxation (diastole)

  • Repolarization (relaxation)

  • T wave

  • U wave

• Semilunar valves close

Diastole

Ventricles relaxing/repolarizing

Murmurs

abnormal heart sounds due to a faulty valve action

Cardiac cycle

• one complete contraction (systole) and subsequent relaxation (diastole)

• About 0.8 seconds long

• One heartbeat

Cardiac output

• The total amount of blood moved throughout the body in 60 seconds

• AKA pulse rate

Describe the process of atrial depolarization in order

1. SA node fires spontaneously (an event not visible on the EKG)

2. depolarization of the atrial myocardial cells

3. atrial contraction

4. P wave

If you split the P wave in half, what would the left side of the P wave represent?

Right atrial component/contractions

Describe the physiologic delay in conduction

Depolarization is briefly held up at the AV node (allowing the atrium to finish contracting before the ventricles begin to contract) → no detectable electrical activity → PR segment

Where on a complex (cardiac cycle/heartbeat) would you find ATRIAL REPOLARIZATION?

When the ventricles are DEPOLARIZING (non-visible in the QRS Complex)

Describe the parts of the ventricular conduction system

• Bundle of His (emerges from the AV node)

• Left and Right bundle branch

• Terminal Purkinje fibers

Describe ventricular depolarization

Ventricular depolarization → ventricular contraction → QRS complex

P wave

• The first electrical impulse is shown on an EKG

• Represents atrial contraction

• Impulse leaving the SA node (atrial depolarization)

Q wave

• a downward deflection ONLY if it is the first wave of the complex

• Septal depolarization

R wave

the first upward deflection

R’ (R prime)

present if there is a second upward deflection (a break in the R wave)

S wave

the first downward deflection following an upward deflection

What is the first downward and upward deflection?

The S wave

If there is no Q wave, what is the first downward deflection?

The S wave

QS wave

present if the entire configuration consists solely of one downward deflection

T wave

Absolute refractory, waiting for the SA node to fire

Describe ventricular repolarization

A brief/absolute refractory period → repolarize → T wave

Brief/absolute refractory period

resistant to further stimulation

Atrial repolarization

• Coincides with ventricular depolarization

• Hidden by the much more prominent QRS complex (not seen on the EKG graph)

Interval

has at least 1 wave and 1 flat line

Segment

the flat line between the waves

PR interval (PRI)

• start of atrial depolarization to the start of ventricular depolarization

• P wave and the straight line connecting it to the QRS complex

PR Segment

• end of atrial depolarization to the start of ventricular depolarization

• End of the P wave to the start of the QRS complex

ST Segment

• end of ventricular depolarization to the start of ventricular repolarization

• End of the QRS complex to the beginning of the T wave

QT Interval

• beginning of the ventricular depolarization to the end of ventricular repolarization

• Includes the QRS complex, the ST segment, and the T wave

QRS Interval

• ventricular depolarization

• QRS complex alone without any connecting segments

What part of the nervous system influences the SA and AV nodes

The autonomic nervous system

How does the current between nodes change from vagal stimulation?

It slows down, prolonging the delay

How does the current between nodes change from sympathetic stimulation?

A fight-or-flight response speeds it down through the AV node

What is the normal heart rate range?

60 to 100 bpm

What is the perfect heart rate in a normal adult?

72 bpm

What is the average cardiac output?

5 to 6 liters per minute

Arrhythmia/Disrhythmia

an irregularity in the heart’s rate or rhythm

What are two types of arrhythmia?

Bradycardia and tachycardia

Bradycardia

a slow rate, less than 60 beats per minute

Tachycardia

a fast rate, over 100 beats per minute

Extrasystoles AKA Etopic beats

extra beats before the normal beat

Fibrillations

rapid, uncoordinated contractions; can result in a lack of pumping action