1. Anatomy and Electrophysiology of the Heart1
Anatomy and Electrophysiology of the Heart
Fast & Easy ECGs, 2nd E – A Self-Paced Learning Program
Fast & Easy ECGs, 2E

2. Electrocardiogram
Graphic representation of heart’s electrical activity
often referred to as an ECG or EKG
Instructional point:
It is the electrical activity that causes the heart muscle to contract and pump blood. However, the presence of electrical activity does not guarantee muscle contraction. I
Fast & Easy ECGs, 2E

3. ECG Machine Detects heart’s electrical current activity
Displays it on a screen or prints it onto graph paper
Instructional point:
These impulses, which appear as a series of upward (positive) and downward (negative) deflections (waveforms) are then transferred to the ECG machine where they can be viewed on the screen (referred to as the oscilloscope or monitor) or printed onto graph paper (often referred to as an ECG tracing or strip). I
Fast & Easy ECGs, 2E

4. ECG Machine Identifies irregularities in heart rhythm
Reveals injury, death or other physical changes in heart muscle
Used as an assessment and diagnostic tool
Can continuously monitor heart’s electrical activity
Instructional point:
Irregularities in the heart rhythm are called dysrhythmias. I
Fast & Easy ECGs, 2E

5. What the ECG Won’t Do Does not tell how well heart is pumping
Patient must be properly assessed to ensure heart is functioning mechanically
Instructional point:
Emphasize to the students that electrical activity on cardiac monitor does not guarantee heart is contracting and producing pulse and blood pressure. I
Fast & Easy ECGs, 2E

6. The Heart The pump of the circulatory system
Contraction pushes blood throughout the body to deliver needed oxygen and nutrients to tissues and remove waste products
Depending on body’s requirements heart rate can either be increased or decreased
Instructional point:
The heart rate speeds up during exercise, stress or other strenuous activities and slows down while resting or sleeping. Perfusion describes the circulatory system’s delivery of oxygen and nutrients to the tissues and the removal of waste products. Perfusion is necessary for the body cells to function and survive. The body cells die if there is insufficient blood supply to meet their needs. I
Fast & Easy ECGs, 2E

7. The Heart Shaped like an inverted blunt cone
Base
Shaped like an inverted blunt cone
Base is the larger, flat part
Apex is the inferior end which tapers to a blunt, rounded point
Instructional point:
About two thirds of the heart is situated in the left side of the chest cavity.
Apex I
Fast & Easy ECGs, 2E

8. The Heart
Located between the two lungs in mediastinum behind the sternum
Instructional Point:
Knowing the position and orientation of the heart will help you to understand why certain ECG waveforms appear as they do when the electrical impulse moves toward a positive or negative electrode. The location of the various ECG leads permits us to look at the heart from several different directions. I
Fast & Easy ECGs, 2E

9. The Heart Anterior-posterior orientation in the chest
RV closer to front of left chest
LV closer to side of left chest
Posterior surface
Instructional Point:
Electrodes placed over the right side of the chest view the right ventricle while electrodes placed over the left side of the chest view the left ventricle.
Anterior surface I
Fast & Easy ECGs, 2E

10. The Heart Surrounded by pericardial sac (a double-walled closed sac)
fibrous pericardium
serous pericardium
Instructional point:
The fibrous pericardium is the outer layer while the serous pericardium is the thin transparent inner lining. The space between the two layers is called the pericardial space. It contains a small amount of fluid called pericardial fluid. The pericardial fluid allows the heart to contract and expand within the chest cavity with minimal friction. I
Fast & Easy ECGs, 2E

11. Heart Wall Made up of three layers. Epicardium (outermost)
Myocardium (middle)
Endocardium (innermost)
Instructional point:
The epicardium is the outermost layer, the myocardium is the middle muscular layer and the thickest of the three while the endocardium is the innermost layer. I
Fast & Easy ECGs, 2E

12. Internal Heart Heart consists of four chambers
2 atria collect blood and deliver to ventricles
2 ventricles pump blood to pulmonary and systemic circulation
Septum separates heart into two functional units
Left atrium
Right atrium
Left ventricle
Instructional point:
The atria are thin-walled while the ventricles are muscular. The left ventricle is thicker and more muscular than the right ventricle.
Right ventricle
Ventricular septum I
Fast & Easy ECGs, 2E

13. Heart Valves Permit blood to flow through heart in only one direction
Mitral and bicuspid valves (AV valves) located between atria and ventricles
Aortic and pulmonic valves (semilunar valves) located at base of aorta and pulmonary artery
To demonstrate the heart valves in action show the following animations: The Cardiac Cycle, Mitral Valve Stenosis.
Instructional points:
The atrioventricular valves are the mitral and bicuspid valves while the semilunar valves are the aortic and pulmonic valves. The mitral valve has two cusps while the tricuspid valve has three cusps. Both the aortic and pulmonic valves have three cusps. I
Fast & Easy ECGs, 2E A

14. Skeleton of Heart Forms fibrous rings around AV and semilunar valves
Provides firm support for valves and separates atria from ventricles
Electrically insulates the atria from the ventricles
Instructional point:
The skeleton of the heart allows top and bottom parts of heart to act as separate, sequential pumps and electrically insulates the atria from the ventricles. I
Fast & Easy ECGs, 2E

15. Cardiac Muscles Attached to fibrous connective tissue
Contract ventricles in a wringing motion
Instructional point:
Because of how the heart muscles are arranged it results in the most efficient ejection of blood out of the ventricles. I
Fast & Easy ECGs, 2E

16. Heart Cells Myocardial cells (working cells)
contract to propel blood out of heart’s chambers
Electrical conduction system cells
initiate and carry impulses throughout heart
Instructional point:
Myocardial cells are also referred to as the “working” cells. I
Fast & Easy ECGs, 2E

17. Myocardial Cells Cylindrical and branching at their ends
Intercalated disks and gap junctions allow rapid movement of electrical impulses from one cell to another
Desmosomes hold cells together when heart muscle contracts
Instructional point:
The rapid movement of the electrical impulse from one cell to adjacent cells results in myocytes acting as a single unit permiting coordinated contraction of whole group of cells. I
Fast & Easy ECGs, 2E

18. Working Cells Myocytes Enclosed in sarcolemma
Composed of two protein filaments
Actin (thin)
Myosin (thick)
To demonstrate the actin and myosin in action show the following animation: Sarcomere Shortening.
Instructional points:
Actin and myosin permit muscle fiber to shorten itself and then return to its original length.
Mitochondria are interspersed within cell to provide plentiful supply of energy for muscle contraction. I
Fast & Easy ECGs, 2E A

19. Key Properties of Myocardial Cells
Automaticity
Can produce electrical activity without outside nerve stimulation
Excitability
Ability to respond to an electrical stimulus
Conductivity
ability to transmit an electrical stimulus from cell to cell throughout myocardium
Contractility
ability of myocardial cell to contract when stimulated by an electrical impulse
Fast & Easy ECGs, 2E

20. Polarized State
Inside of myocardial cells more negatively charged in relationship to outside where it is more positively charged
Instructional points:
Difference in electrical charges between inside and outside of cell creates a resting membrane potential.
There is more sodium outside the cell. I
Fast & Easy ECGs, 2E

21. Depolarization
Occurs when positively charged ions move inside cells causing interior to become positively charged
Change in electrical charge over time referred to as cell’s action potential
To demonstrate depolarization show the following animation: “Voltage-Gated Channels and the Action Potential” and Action Potential Propagation.” A
Fast & Easy ECGs, 2E

22. Repolarization Follows depolarization and occurs when:
potassium leaves cell causing positive charge to lower
sodium and calcium are removed by special transport systems
To demonstrate depolarization show the following animation: “Sodium-Potassium Exchange Pump”
Instructional point:
During repolarization sodium and calcium will continue to be removed until the electrical potential inside cell reaches its normal negative charge. I A
Fast & Easy ECGs, 2E

23. Refractory Period Absolute refractory period Refractory period
no stimulus no matter how strong will depolarize cell
Refractory period
a sufficiently strong stimulus will depolarize myocardium
Fast & Easy ECGs, 2E

24. Heart’s Conduction System
Grouping of specialized tissues that carry wave of depolarization throughout heart
To demonstrate heart’s conduction system show the following animation: “Origin of Self Excitability”
Instructional point:
Emphasize to students that in order for any muscle to contract it must first be electrically stimulated. I
Fast & Easy ECGs, 2E A

25. Pacemaker Sites SA node is primary pacemaker site of heart
Other cardiac cells lower in conduction pathway play a back-up role
To demonstrate heart’s conduction system in action show the following animation: “Myocardial cells – conduction system of the heart.”
Instructional point:
The farther from the SA node, the slower the intrinsic rate of the pacemaker site. I
Fast & Easy ECGs, 2E A

26. Coronary Arteries Provide heart with most of its blood supply
Originate from base of ascending aorta
Immediately above leaflets or cusps of aortic valve
Instructional point:
Two major branches of the coronary arteries are the right main coronary artery and the left main coronary artery. I
Fast & Easy ECGs, 2E

27. Blood Flow Pulmonary circulation Systemic circulation
Pulmonary arteries carry deoxygenated blood to lungs
Pulmonary veins carry oxygenated blood back to heart
Systemic circulation
Arteries carry oxygenated blood.
Veins carry deoxygenated blood
Instructional point:
Blood flow through heart occurs as follows:
Deoxygenated blood is returned to right atria where it flows into right ventricle.
Contraction of right ventricle pumps deoxygenated blood into pulmonary circulation where it is oxygenated and waste products are removed.
Blood is returned to left atria and ventricle.
Blood is then pumped through systemic circulation to deliver oxygen to tissues. I
Fast & Easy ECGs, 2E

28. Cardiac Cycle Diastole Relaxation and filling of atria and ventricles
Fast & Easy ECGs, 2E

29. Cardiac Cycle Systole Contraction of atria and ventricles
Results in blood being projected forward
Fast & Easy ECGs, 2E

30. Cardiac Output Amount of blood pumped from the heart in one minute
Expressed in LPM
HR X SV = CO
To demonstrate cardiac output show the following animation: “Mechanical Performance.”
Instructional point:
Stroke volume is the amount of blood ejected from ventricles. I
Fast & Easy ECGs, 2E A

31. CO X PVR = BP Blood Pressure
The force that blood exerts against walls of arteries as it passes through them
Equals cardiac output times peripheral vascular resistance
CO X PVR = BP
Fast & Easy ECGs, 2E

32. Putting it All Together
Cardiac cycle begins with RA and LA receiving blood from systemic and pulmonary circulations
Rising pressure within atria forces tricuspid and mitral valves open
Instructional point:
Approximately seventy percent of the blood coming into the chambers flows passively through the atria and into the ventricles prior to the atria contracting. I
Fast & Easy ECGs, 2E

33. Putting it All Together
Heartbeat initiated by an electrical impulse that arises from SA node
Impulse travels through atria
generates a positive waveform on ECG and contraction of atria
To demonstrate atrial contraction show the following animation: “Contribution of Atrial Contraction to Ventricular Filling.”
Instructional point:
Atrial contraction pushes remaining blood from atria into the ventricles. I
Fast & Easy ECGs, 2E A

34. Putting it All Together
Impulse slows as it passes through AV node from atria to ventricles
Allows atria time to finish filling ventricles
Fast & Easy ECGs, 2E

35. Putting it All Together
Impulse then rapidly travels through His-Purkinje system
Seen as a flat line following P wave
Fast & Easy ECGs, 2E

36. Putting it All Together
Depolarization of septum and ventricular walls generates QRS complex and contraction of ventricles
Instructional point:
Ventricular contraction causes blood to be pushed into pulmonary and systemic circulations. I
Fast & Easy ECGs, 2E

37. Putting it All Together
Repolarization of ventricles is represented on ECG by ST segment and T wave
To demonstrate the electrocardiogram show the following animation: “Electrocardiogram.”
Instructional point:
Atrial repolarization occurs but is hidden by the QRS complex. I
Fast & Easy ECGs, 2E A

38. Influences on Heart
Receptors in blood vessels, kidneys, brain, and heart constantly monitor changes
Baroreceptors identify changes in pressure
Chemoreceptors sense changes in chemical composition of blood
To demonstrate baroreceptors and chemoreceptors show the following animations: “Baroreceptor Reflex Control of Blood Pressure” and “Chemoreceptor Reflex Control of Blood Pressure.” A
Fast & Easy ECGs, 2E

39. Autonomic Nervous System
Helps regulate rate and strength of myocardial contractions
Divided into sympathetic and parasympathetic nervous systems
Instructional point:
Both branches exert their effects via neurotransmitters that bind specific receptors. I
Fast & Easy ECGs, 2E

40. Sympathetic Stimulation
Sympathetic stimulation in the heart produces:
enhancement of myocardial cell excitability
increased rate of pacemaker firing
Increased conduction speed
increased contractility
coronary vasodilation
To demonstrate autonomic nervous system show the following animations: “The Control of the Heart Rate” and “Functions of ANS.”
Instructional points:
Stimulation of the sympathetic nervous system produces what is described as the "fight or flight" response. Sympathetic fibers exert their effect by stimulating special receptors. These receptors are divided into categories depending on their response. The two major categories are alpha and beta receptors. I A
Fast & Easy ECGs, 2E

41. Parasympathetic Stimulation
Parasympathetic stimulation in the heart produces:
slowing of heart rate and AV conduction
Fast & Easy ECGs, 2E

42. Summary
Electrocardiogram detects electrical activity occurring in heart
Nerve impulses stimulate cardiac muscles to contract
Heart consists of two upper chambers, the atria and two lower chambers, the ventricles
Heart is separated into right and left sides by the septum
Coronary arteries perfuse myocardium during diastole
Fast & Easy ECGs, 2E

43. Summary
Sodium, calcium and potassium are key electrolytes responsible for initiating electrical charges
Depolarization of cells occurs when positive electrolytes move from outside to inside cell causing it to become more positively charged
Depolarization of myocardial cells causes calcium to be released and come into close proximity with actin and myosin filaments of muscle fibers leading to myocardial contraction
Fast & Easy ECGs, 2E

44. Summary
Myocardial depolarization progresses from atria to ventricles in an orderly fashion
electrical stimulus causes heart muscle to contract
Other sites in heart can assume control by discharging impulses faster than SA node or stepping in when SA node fails
Fast & Easy ECGs, 2E

45. Summary
Electrical impulse that initiates heartbeat arises from SA node
From there it travels through atria generating a positive waveform on ECG and contraction of atria
Impulse is slowed as it passes from atria to ventricles through AV node
On ECG impulse traveling through His-Purkinje system is seen as a flat line following the P wave
QRS complex is generated and ventricles contract as a result of electrical impulse stimulating ventricles
ST segment and T wave represents repolarization of ventricles
Atrial repolarization occurs but is hidden by QRS complex
Instructional point:
Emphasize that ventricular muscle contraction causes the blood to be pushed into the pulmonary and systemic circulations. I
Fast & Easy ECGs, 2E

46. Summary
Cardiac output is amount of blood pumped through circulatory system in one minute.
Rate and strength of myocardial contractions can be influenced by autonomic nervous system.
Two divisions are the sympathetic and parasympathetic nervous systems.
Fast & Easy ECGs, 2E