1. Electrocardiography for Healthcare Professionals
Kathryn A. Booth
Thomas O’Brien
Chapter 2:
The Cardiovascular System

2. Learning Outcomes
2.1 Explain how circulation occurs in relation to the ECG. 2.2 Recall the structures of the heart including valves, chambers, and vessels. 2.3 Differentiate among pulmonary, systemic, and coronary circulation. 2.4 Explain the cardiac cycle, including the difference between systole and diastole.

3. Learning Outcomes (Cont.)
2.5 Describe the parts and function of the heart and conduction system and how they relate to the ECG.
2.6 Describe the heart activity that produces each part of the ECG waveform.

4. 2.1 Circulation and the ECG
Functions of the heart
Pumps blood to and from all body tissues
Supplies tissues with nutrients and oxygen
Removes carbon dioxide and wastes
LO 2.1: Explain how circulation occurs in relation to the ECG.
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5. 2.1 Circulation Process of transporting blood throughout the body
Depends on:
Electrical activity of heart
Ability of heart to contract
ECG records the heart’s electrical activity
LO 2.1: Explain how circulation occurs in relation to the ECG.
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Circulation depends on the heart’s pumping ability.
The electrical activity of the heart causes the heart to contract.
A knowledge of heart function is an important aspect of understanding the ECG.

6. 2.1 Apply Your Knowledge What is the function of the heart?
ANSWER: To pump blood to and from
body tissues.
LO 2.1: Explain how circulation occurs in relation to the ECG.

7. 2.2 Anatomy of the Heart Key Terms
Aorta
Aortic semilunar valve
Atrium (pl. atria)
Chordae tendineae
Deoxygenated blood
Interventricular septum
Left atrium
Left ventricle
Mitral (bicuspid) valve
Oxygenated blood
LO 2.2: Recall the structures of the heart including valves, chambers, and vessels.
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Aorta: The largest artery of the body, which transports oxygenated blood from the left ventricle of the heart to the entire body.
Aortic semilunar valve: Valve located in the aorta that prevents backflow of blood into the left ventricle.
Atrium (pl. atria): Top two chambers of the heart.
Chordae tendineae: Structures that connect the atrioventricular valves to the papillary muscles and prevent them from opening in the wrong direction.
Deoxygenated blood: Blood that has little or minimal oxygen (oxygen-poor blood).
Interventricular septum: A partition or wall (septum) that divides the right and left ventricles.
Left atrium: The left upper chamber of the heart, which receives blood from the lungs.
Left ventricle: The left lower chamber of the heart, which pumps oxygenated blood through the body. It is the biggest and strongest chamber, known as the workhorse of the heart.
Mitral (bicuspid) valve: Valve with two cusps or leaflets located between the left atrium and left ventricle; it prevents backflow of blood into the left atrium.
Oxygenated blood: Blood having oxygen (oxygen-rich blood).

8. 2.2 Anatomy of the Heart Key Terms (cont.)
Papillary muscles
Pericardium
Pulmonary artery
Pulmonary semilunar valve
Pulmonary veins
Right atrium
Right ventricle
Semilunar valve
Tricuspid valve
Vena cava
LO 2.2: Recall the structures of the heart including valves, chambers, and vessels.
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Papillary muscles: Muscles in the ventricles that anchor the chordae tendineae and atrioventricular valves.
Pericardium: A two-layered sac of tissue enclosing the heart.
Pulmonary artery: Large artery that transports deoxygenated blood from the right ventricle to the lungs; only artery in the body that carries deoxygenated blood.
Pulmonary semilunar valve: Valve found in the pulmonary artery that prevents backflow of blood into the right ventricle.
Pulmonary veins: Transport oxygenated blood back into the left atrium of the heart. These are the only veins that carry oxygenated blood .
Right atrium: The right upper chamber of the heart; receives blood from the body.
Right ventricle: The right lower chamber of the heart, which pumps deoxygenated blood to the lungs.
Semilunar valve: A valve with half-moon-shaped cusps that open and close, allowing blood to travel only one way; located in the pulmonary artery and the aorta.
Tricuspid valve: Valve located between the right atrium and right ventricle; it prevents backflow of blood into the right atrium.
Vena cava: Largest vein in the body, which provides a pathway for deoxygenated blood to return to the heart; its upper portion, the superior vena cava, transports blood from the head, arms, and upper body; and its lower portion, the inferior vena cava, transports blood from the lower body and legs.

9. 2.2 Anatomy of the Heart Lies in center of chest Under sternum
Between the lungs
The size of your fist
Weighs 10.6 oz or 300 grams
LO 2.2: Recall the structures of the heart including valves, chambers, and vessels.
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The heart varies in size and weight depending on a person’s weight, physical condition, and gender.
In most people, two-thirds of the heart lies to the left of the sternum.

10. 2.2 Heart Statistics Average beats Per minute: 72 Per day: 100,000
Per lifetime: 22.5 billion
Average output: 70 mL of blood per beat
Total output = 5 L per minute
LO 2.2: Recall the structures of the heart including valves, chambers, and vessels.
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Each day, the heart pumps approximately 7,250 liters or 1,800 gallons of blood.

11. 2.2 Heart Anatomy Pericardium Pericardial space Epicardium Myocardium
Endocardium
LO 2.2: Recall the structures of the heart including valves, chambers, and vessels.
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Pericardium -Sack of tissue surrounding the heart
Two layers
Parietal layer is the tough outer layer
Visceral or epicardium layer is the inner layer and adheres closely to the heart
Purpose is to protect the heart from infection and trauma
Pericardial space
Between parietal and visceral layers of the pericardium
Contains approximately 10 to 20 mL of fluid
Serves to cushion the heart against trauma
Epicardium – outer layer
Also known as the visceral pericardium
Thin and contains the coronary arteries
Myocardium – middle, muscular layer
Endocardium – inner layer
Lines the inner surfaces of the heart chambers and valves

12. 2.2 Heart Layers
LO 2.2: Recall the structures of the heart including valves, chambers, and vessels.
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13. 2.2 Heart Chambers, Vessels, and Valves
LO 2.2: Recall the structures of the heart including valves, chambers, and vessels.
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14. 2.2 Heart Valves Tricuspid valve Mitral (bicuspid) valve
Semilunar valves
Aortic
Pulmonary
LO 2.2: Recall the structures of the heart including valves, chambers, and vessels.
-----
Tricuspid valve – located between the right atrium and right ventricle
Mitral (bicuspid) valve – located between left atrium and left ventricle
Semilunar valves – located in the pulmonary artery and aorta; prevent blood from backing up into the right ventricle and left ventricle, respectively.

15. 2.2 Major Vessels to and from the Heart
LO 2.2: Recall the structures of the heart including valves, chambers, and vessels.
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Vena cava
Superior vena cava returns blood from upper body to the heart
Inferior vena cava returns blood from lower body to the heart
Pulmonary artery
Carries deoxygenated blood from the right ventricle to the lungs
Pulmonary vein
Carries oxygenated blood from the lungs to the left atrium
Aorta
Carries blood from the left ventricle to the body
First branches from aorta are the coronary arteries
Coronary arteries
Supply blood to the heart muscle

16. 2.2 Oxygenated and Deoxygenated Blood
LO 2.2: Recall the structures of the heart including valves, chambers, and vessels.
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17. 2.2 Apply Your Knowledge
Which valve of the heart lies between the left atrium and the left ventricle?
ANSWER: The mitral or bicuspid valve
LO 2.2: Recall the structures of the heart including valves, chambers, and vessels.
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18. 2.2 Apply Your Knowledge Name the three layers of the heart.
ANSWER: The endocardium, myocardium,
and epicardium
LO 2.2: Recall the structures of the heart including valves, chambers, and vessels.
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19. 2.3 Principles of Circulation Key Terms
Coronary circulation
Pulmonary circulation
Systemic circulation
LO 2.3: Differentiate among pulmonary, systemic, and coronary circulation.
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Coronary circulation: The circulation of blood to and from the heart muscle.
Pulmonary circulation: The transportation of blood to and from the lungs; blood is oxygenated in the lungs during pulmonary circulation.
Systemic circulation: The pathways for pumping blood throughout the body and back to the heart.

20. 2.3 Pulmonary and Systemic Circulation
LO 2.3: Differentiate among pulmonary, systemic, and coronary circulation.
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21. 2.3 Pulmonary Circulation
Blood enters right atrium
Blood passes through the tricuspid valve to the right ventricle
Right ventricle pumps blood to the lungs
Blood returns into the left atrium
LO 2.3: Differentiate among pulmonary, systemic, and coronary circulation.
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Pulmonary Circulation:
Deoxygenated blood enters the right atrium from the superior and inferior venae cavae.
Blood travels through the tricuspid valve into the right ventricle.
The right ventricle pumps the blood through the pulmonary semilunar valve into the pulmonary artery, then into the lungs. In the lungs, the blood is oxygenated.
The blood returns to the heart through the pulmonary veins into the left atrium. The left atrium is the last step of pulmonary circulation.

22. 2.3 Systemic Circulation
Blood enters the left atrium and passes through into the left ventricle
The left ventricle pumps to the aorta
From the aorta, blood circulates throughout the body
Deoxygenated blood returns to the right atrium of the heart
LO 2.3: Differentiate among pulmonary, systemic, and coronary circulation.
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Systemic circulation:
Oxygenated blood enters the left atrium and travels through the mitral valve into the left ventricle.
The left ventricle pumps the blood through the aortic semilunar valve into the aorta.
After traveling through the body, the deoxygenated blood returns to the right atrium of the heart through the superior and inferior venae cavae.

23. 2.3 Coronary Circulation: Arteries
LO 2.3: Differentiate among pulmonary, systemic, and coronary circulation.
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The two main coronary arteries are the left and right coronary arteries.
Branches of the left and right coronary arteries supply blood throughout the heart.
The left artery has more branches than the right because the left side of the heart is more muscular and requires a larger blood supply.

24. 2.3 Coronary Circulation: Veins
Aortic arch
LO 2.3: Differentiate among pulmonary, systemic, and coronary circulation.
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The coronary veins carry deoxygenated blood to the coronary sinus, which empties directly into the right atrium.

25. 2.3 The Heart as a Pump Stroke volume Cardiac output
Amount of blood ejected with each contraction
Varies with gender, size, physical fitness, disease, and genetics
Cardiac output
Volume of blood pumped per minute
Estimated by multiplying heart rate by stroke volume HR × SV = CO
LO 2.3: Differentiate among pulmonary, systemic, and coronary circulation.
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When blood volume decreases, heart rate increases.
When contractile force decreases, stroke volume decreases.
Signs of low cardiac output:
Pallor
Confusion
Low blood pressure
Nausea
Dizziness

26. 2.3 Apply Your Knowledge Great!
Which side of the heart pumps deoxygenated blood?
ANSWER: The right side
LO 2.3: Differentiate among pulmonary, systemic, and coronary circulation.
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Great!

27. 2.3 Apply Your Knowledge Great! How is cardiac output estimated?
ANSWER: By multiplying the heart rate by
the stroke volume
LO 2.3: Differentiate among pulmonary, systemic, and coronary circulation.
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Great!

28. 2.4 The Cardiac Cycle Key Terms
Diastole
Systole
LO 2.4: Explain the cardiac cycle including the difference between systole and diastole.
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Cardiac cycle: The contraction and relaxation of the heart.
Diastole: The phase of the cardiac cycle when the heart is expanding and refilling; also known as the relaxation phase.
Systole: The contraction phase of the cardiac cycle, during which the heart is pumping blood out to the pulmonary (lungs) and systemic (body) circulation.

29. 2.4 The Cardiac Cycle: Diastole
LO 2.4: Explain the cardiac cycle including the difference between systole and diastole.
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30. 2.4 Diastole – Relaxation Phase
Blood returns to the heart via the superior and inferior vena cava
Blood flows from the right atrium into the right ventricle
Blood from the pulmonary veins flows from the left atrium into the left ventricle
LO 2.4: Explain the cardiac cycle including the difference between systole and diastole.
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Blood from the upper body returns via the superior vena cava.
Blood from the lower body returns via the inferior vena cava.
The right atrium fills with blood, pushes open the tricuspid valve, and enters the right ventricle.
Blood returns from the lungs via the pulmonary veins to the left atrium, then forces the mitral valve open to allow blood flow to the left ventricle.

31. 2.4 The Cardiac Cycle: Systole
LO 2.4: Explain the cardiac cycle including the difference between systole and diastole.
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32. 2.4 Systole – Contraction Phase
Contraction creates pressure, opening the pulmonary and aortic valves.
Blood from the right ventricle flows to the lungs.
Blood from the left ventricle flows through the aorta to the body.
LO 2.4: Explain the cardiac cycle including the difference between systole and diastole.
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Contraction of the right ventricle pushes blood into the lungs to exchange oxygen and carbon dioxide.
Contraction of the left ventricle pushes blood through the aorta to be distributed through the body to provide oxygen for tissues and to remove carbon dioxide.
Lubb-dupp sounds:
Lubb is the closing of the mitral and tricuspid valves during systole.
Dupp is the closing of the pulmonary and aortic valves during diastole.

33. 2.4 Apply Your Knowledge
The relaxation phase of the cardiac cycle is known as:
ANSWER: Diastole
LO 2.4: Explain the cardiac cycle including the difference between systole and diastole.

34. 2.5 Conduction System of the Heart Key Terms
Atrioventricular (AV) node
Automaticity
Bachmann’s bundle
Bundle branches
Bundle of His (AV bundle)
Conductivity
Contractility
Excitability
Myocardial
Parasympathetic
Purkinje fibers
Purkinje network
Sinoatrial (SA) node
Sympathetic
LO 2.5: Describe the parts and function of the heart and conduction system and how they relate to the ECG.
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Atrioventricular (AV) node: Delays the electrical impulse to allow the atria to complete their contraction.
Automaticity: The ability of the heart to initiate an electrical impulse without being stimulated by another or independent source.
Bachmann’s bundle: The structure that relays the electrical impulse from the SA node to the left atrium in a normal heart.
Bundle branches: Left and right branches of the bundle of His that conduct impulses down either side of the interventricular septum to the left and right ventricles.
Bundle of His (AV bundle): Located next to the AV node; provides the transfer of the electrical impulse from the atria to the ventricles.
Conductivity: The ability of the heart cells to receive and transmit an electrical impulse.
Contractility: The ability of the heart muscle cells to shorten in response to an electrical stimulus.
Excitability: The ability of the heart muscle cells to respond to an impulse or stimulus; also called irritability.
Myocardial: Pertaining to the heart (cardi) muscle (myo).
Parasympathetic: The part of the autonomic nervous system (ANS) that helps slow the heart rate.
Purkinje fibers: The fibers within the heart that distribute electrical impulses from cell to cell throughout the ventricles.
Purkinje network: Spreads the electrical impulse throughout the ventricles by means of the Purkinje fibers.
Sinoatrial (SA) node: An area of specialized cells in the upper right atrium that initiates the heartbeat.
Sympathetic: The part of the autonomic nervous system that causes an increase in the heart rate.

35. 2.5 Unique Qualities of the Heart
Heart’s unique qualities initiate and control the beating
of the heart:
Automaticity
Conductivity
Contractility
Excitability
LO 2.5: Describe the parts and function of the heart and conduction system and how they relate to the ECG.
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Automaticity – heart’s ability to initiate an electrical impulse
Conductivity – ability of myocardial cells to receive and conduct electrical impulses
Contractility – ability of the heart muscle to shorten in response to an electrical impulse
Excitability – ability of the heart to respond to an impulse or stimulus

36. 2.5 Regulation of the Heart
Autonomic Nervous System (ANS)
Sympathetic branch
Secretes norepinephrine.
Increases heart rate and contractility.
Parasympathetic branch
Secretes acetylcholine.
Decreases heart rate by stimulating vagus nerve.
LO 2.5: Describe the parts and function of the heart and conduction system and how they relate to the ECG.
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The ANS is involuntary – you have no control over it. It secretes norepinephrine automatically when you are under stress or become frightened.
The vagus nerve is the major nerve of the parasympathetic system.

37. 2.5 Regulation of the Heart (cont.)
Other factors that affect heart rate
Exercise
Stress
Body temperature
Blood pressure
Electrolyte levels
LO 2.5: Describe the parts and function of the heart and conduction system and how they relate to the ECG.
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Potassium
Low concentration causes decrease in heart rate
High concentration causes dysrhythmias
Calcium
Low concentration depresses heart activity
High concentration causes longer-than-normal heart contractions

38. 2.5 Pathways for Conduction
SA node
Bachmann’s bundle
AV node
Bundle of His
Bundle branches
Purkinje fibers
LO 2.5: Describe the parts and function of the heart and conduction system and how they relate to the ECG.
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39. 2.5 Sinoatrial (SA) Node and Bachmann’s Bundle
Located in upper portion of right atrium
Initiates the heartbeat
Pacemaker of the heart (60 to 100 beats per minute)
Normal conduction begins in SA node
Bachmann’s bundle
Relays the impulse from SA node to the rest of the left atrium
LO 2.5: Describe the parts and function of the heart and conduction system and how they relate to the ECG.
-----

40. 2.5 Atrioventricular (AV) Node
Located on the floor of the right atrium
Causes delay in the electrical impulse
Can act as pacemaker if SA node is not working
Inherent rate: (40 to 60 bpm)
LO 2.5: Describe the parts and function of the heart and conduction system and how they relate to the ECG.
-----
The AV node slows the electrical impulse, providing three benefits:
Provides for atrial kick
Prevents excessive rate of impulses from reaching the ventricles
Allows ventricles to contract from the bottom up
Atrial kick: Additional blood that travels from the atria to the ventricles before they contract, as a result of the electrical delay caused by the AV node.

41. 2.5 Bundle of His (AV bundle) and Bundle Branches
Located next to the AV node
Transfers electrical impulses from the atria to the ventricles
Bundle branches
Split the electrical impulse down the right and left side
Stimulate left and right ventricles to contract
Stimulate intraventricular septum to contract in left-to-right pattern
LO 2.5: Describe the parts and function of the heart and conduction system and how they relate to the ECG.
-----
The bundle branches are the two branches of the Bundle of His that carry the electrical impulse to both sides of the heart.

42. 2.5 Purkinje Fibers Form the Purkinje network
Electrical pathway for each cardiac cell
Impulse activates left and right ventricles simultaneously
Produce an electrical wave that results in contraction
LO 2.5: Describe the parts and function of the heart and conduction system and how they relate to the ECG.
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43. 2.5 Apply Your Knowledge A. B. C. D. E. I. H. G. F.
Identify each part of the conduction system (A to I), then view the next slide for the answers.
LO 2.5: Describe the parts and function of the heart and conduction system and how they relate to the ECG.
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44. 2.5 Apply Your Knowledge F. SA node A. AV node AV bundleC. D. E. I. H. G. F.
SA node
AV node
AV bundle
Purkinje fibers
Interventricular septum
Bachmann’s bundle
Left bundle branch
Right bundle branch
Apex
LO 2.5: Describe the parts and function of the heart and conduction system and how they relate to the ECG.
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Answers to Slide #44 above.

45. 2.5 Apply Your Knowledge
What is the ability of the heart to generate an electrical impulse called?
ANSWER: Automaticity
LO 2.5: Describe the parts and function of the heart and conduction system and how they relate to the ECG.
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46. Apply Your Knowledge
Which part of the conduction system is known as the pacemaker of the heart?
ANSWER: The sinoatrial or SA node
LO 2.5: Describe the parts and function of the heart and conduction system and how they relate to the ECG.
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47. 2.6 Electrical Stimulation and the ECG Waveform Key Terms
Action potential
Complexes
Depolarization
Interval
Ischemia
Isoelectric
Polarization
Repolarization
Segment
LO 2.6: Describe the heart activity that produces each part of the ECG waveform.
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Action potential: The change in the electrical potential of the heart muscle when it is stimulated.
Complexes: Atrial or ventricular contractions as they appear on the ECG; complete ECG waveforms.
Depolarization: The electrical activation of the cells of the heart that initiates the contraction of the heart muscle.
Interval: The period of time between two activities within the heart.
Ischemia: Occurs when there is a sudden loss or reduction in blood supply (oxygen) to a region of the heart tissue. This occurs due to the presence of atherosclerotic plaque, blood clot, emboli, or even vascular spasm (Prinzmetal’s angina).
Isoelectric: The period when the electrical tracing of the ECG is at zero or a straight line, and no positive or negative deflections are seen.
Polarization: The state of cellular rest in which the inside is negatively charged and the outside is positively charged.
Repolarization: The return of heart muscle cells to their resting electrical state, causing the heart muscle to relax.
Segment: A portion or part of the electrical tracing produced by the heart.

48. 2.6 Electrical Stimulation
Polarization
Cells are at peak resting energy
Depolarization
State of stimulation that precedes contraction
Electrical activation of heart cells
Causes the heart to contract
LO 2.6: Describe the heart activity that produces each part of the ECG waveform.
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In a polarized cell, the inside of the cell is negatively charged compared to the outside of the cell.
Depolarization occurs when the electrical charge is reversed across the cell membrane so the interior becomes positively charged compared to the outside of the cell.
The rapid change of polarization during depolarization is called action potential.

49. 2.6 Electrical Stimulation (Cont.)
Repolarization
State of cellular recovery following contraction
Cell returns to a resting state
Heart relaxes, allowing for refilling of the chambers
LO 2.6: Describe the heart activity that produces each part of the ECG waveform.
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As the cell repolarizes and returns to its resting state, the charges again reverse, so that the inside of the cell is negatively charged compared to the outside of the cell.

50. 2.6 ECG Waveform
Recorded activity of depolarization and repolarization
Isoelectric line or baseline
Labeled P,Q,R,S,T
LO 2.6: Describe the heart activity that produces each part of the ECG waveform.
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The isoelectric line or baseline refers to the tracing when no electrical activity is occurring.

51. 2.6 P Wave First positive deflection
Represents atrial depolarization and atrial contraction
Small compared to other ECG waves
LO 2.6: Describe the heart activity that produces each part of the ECG waveform.
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The atrial kick occurs during the short baseline segment that appears immediately after the P wave.

52. 2.6 QRS Complex QRS complex consists of the Q, R, and S waves Q wave
Represents conduction of impulse down the interventricular septum
First negative deflection, occurs before the R wave
Not always visualized on the ECG
Less than 1/4 the height of the R wave
LO 2.6: Describe the heart activity that produces each part of the ECG waveform.
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The QRS complex represents ventricular depolarization and the resulting ventricular contraction. It reflects the time it takes for an electrical impulse to depolarize the interventricular septum down through the ventricular myocardium, causing the ventricles to contract.
Although atrial repolarization occurs during ventricular depolarization, it is not seen on the ECG because the larger voltage of the ventricular depolarization overshadows the voltage of atrial repolarization. Only the largest voltage is seen on the ECG tracing.

53. 2.6 QRS Complex (cont.) R wave S wave
First positive wave of the QRS complex
Represents conduction of electrical impulse to the left ventricle
S wave
First negative deflection after the R wave
Represents conduction of electrical impulse through both ventricles
LO 2.6: Describe the heart activity that produces each part of the ECG waveform.
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54. 2.6 ST Segment
Measured from end of the S wave to the beginning of T wave
Indicates end of ventricular depolarization and beginning of ventricular repolarization
Normally on isoelectric line
Elevation or depression of ST segment may result from ischemia
LO 2.6: Describe the heart activity that produces each part of the ECG waveform.
-----
The reason this segment is studied in a 12-lead ECG recording is to determine whether there is any ischemia or myocardial (heart) damage.
Ischemia occurs when there is a sudden loss or reduction in blood supply (oxygen) to a region of heart tissue.

55. 2.6 T Wave T wave Represents ventricular repolarization
Normal T wave is in same direction as R wave and
P wave
LO 2.6: Describe the heart activity that produces each part of the ECG waveform.
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Unlike the rounded, symmetrical shape of the P wave, the T wave looks like a mountain with one sloping side, peaking toward the end instead of in the middle.

56. 2.6 U Wave Follows the T wave
Represents repolarization of Bundle of His and
Purkinje fibers
Not seen on all ECGs
Presence can indicate an electrolyte imbalance
LO 2.6: Describe the heart activity that produces each part of the ECG waveform.
-----
The U wave usually deflects in the same direction as the T wave and is more prominent when the heart rate is slow.

57. 2.6 PR Interval
Measured from beginning of P wave to beginning of QRS complex
Normal length of time is 0.12 to 0.20 second
Interval should be consistent.
LO 2.6: Describe the heart activity that produces each part of the ECG waveform.
-----
The PR interval represents the time from initiation of the electrical impulse until the ventricles are stimulated by the impulse to start the contraction.

58. 2.6 QT Interval
Time required for ventricular depolarization and repolarization to occur
Starts at beginning of QRS complex and ends at end of T wave
Includes QRS complex, ST segment, and T wave
Normally measures less than one-half of R-R interval
LO 2.6: Describe the heart activity that produces each part of the ECG waveform.
-----
Factors that can affect the QT interval include:
Heart rate
Coronary artery disease
Electrolyte imbalance
Antidysrhythmic medications
Longer-than-normal QT interval may indicate increased risk for certain ventricular dysrhythmias and sudden cardiac death.

59. 2.6 R-R Interval R-R interval
Time from start of one QRS complex to start of next QRS complex
Used to calculate heart rate
LO 2.6: Describe the heart activity that produces each part of the ECG waveform.
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The R-R interval is used to calculate heart rate because they are the easiest waves to identify, so they can be identified and counted quickly for rapid heart rate calculations.

60. 2.6 J Point Junction of the QRS interval and the ST interval
Represents end of the QRS complex and ventricular depolarization
Important when measuring the length of the QRS complex
LO 2.6: Describe the heart activity that produces each part of the ECG waveform.
-----
The J point is important when measuring the length of the QRS complex and interpreting the ECG tracing. A normal QRS complex is 0.06 to 0.1 second.

61. 2.6 Apply Your Knowledge
Which wave on the ECG waveform represents ventricular repolarization?
LO 2.6: Describe the heart activity that produces each part of the ECG waveform.
ANSWER: T wave

62. 2.6 Apply Your Knowledge
What is the normal length of time for the PR interval?
ANSWER: 0.12 to 0.20 second
LO 2.6: Describe the heart activity that produces each part of the ECG waveform.

63. Chapter Summary
The function of the heart is to pump blood to and from all body tissues.
The heart has three layers and is covered by the pericardium.
The heart consists of four chambers and four valves.
The coronary arteries supply oxygenated blood to the heart.
The coronary veins remove carbon dioxide and wastes.
LO 2.1: Explain how circulation occurs in relation to the ECG.
LO 2.2: Recall the structures of the heart including valves, chambers, and vessels.

64. Chapter Summary (Cont.)
Blood travels, or circulates, through three pathways:
Pulmonary
Systemic
Coronary
The cardiac cycle consists of a contraction phase and a relaxation phase:
Systole
Diastole
LO 2.3: Differentiate among pulmonary, systemic, and coronary circulation.
LO 2.4: Explain the cardiac cycle including the difference between systole and diastole.

65. Chapter Summary (Cont.)
The conduction system of the heart generates and maintains electrical activity.
Unique qualities of heart cells include automaticity, conductivity, contractility, and excitability.
The sympathetic and parasympathetic branches of the autonomic nervous system regulate the heart.
The heart’s conduction system includes the SA node, AV node, bundle of His, bundle branches, and Purkinje fibers.
LO 2.5: Describe the parts and function of the heart and conduction system and how they relate to the ECG.

66. Chapter Summary (Cont’d)
Depolarization causes the heart to contract, and repolarization allows for cellular recovery.
The ECG waveform is created by the various activities of the conduction system.
The ECG waveform includes the P wave, QRS complex, T wave, U wave, PR interval, QT interval, and ST segment.
LO 2.6: Describe the heart activity that produces each part of the ECG waveform.