The document provides an overview of the cardiovascular system including the heart, circulation, cardiac muscle contraction, conduction system, cardiac cycle, electrocardiogram (ECG), and ECG leads and placement. Key points include: - The cardiovascular system includes the heart and blood vessels which work together to circulate blood throughout the body to supply nutrients and oxygen and remove waste. - The heart has four chambers (two atria and two ventricles) and is made of cardiac muscle. It pumps blood through two circuits: systemic and pulmonary circulation. - Cardiac muscle contraction is stimulated by electrical impulses that cause calcium release and muscle contraction. - The cardiac cycle coordinates electrical and mechanical events in the heart

1. CARDIOVASCULAR SYSTEM
(CVS)

2. Outline
• Overview of the CVS
• Circulation
• Cardiac Muscle
• Conduction system in the heart
• Cardiac Cycle
• ECG
• ECG leads and their placement

3. CARDIOVASCULAR SYSTEM
• Cardiovascular system includes heart
and blood vessels.
• Heart pumps blood into the blood
vessels.
• Blood vessels circulate the blood
throughout the body.
• Blood transports nutrients and oxygen
to the tissues and removes carbon
dioxide and waste products from the
tissues.

4. HEART
• Heart is a muscular organ that pumps blood
throughout the circulatory system.
• It is situated in between two lungs in the
mediastinum.
• It is made up of four chambers ie,
• two atria and two ventricles.
• The musculature of ventricles is thicker
than that of atria.
• Force of contraction of heart depends
upon the muscles.

5. Heart Chambers

6. CIRCULATION
DIVISIONS OF CIRCULATION
• Blood flows through two divisions of
circulatory system:
1. Systemic circulation
2. Pulmonary circulation.
„SYSTEMIC CIRCULATION
• Systemic circulation is otherwise known as
greater circulation.
• Blood pumped from left ventricle passes
through a series of blood vessels, arterial
system and reaches the tissues.

7. Systemic circu.. Cont’d
• Exchange of various substances between
blood and the tissues occurs at the
capillaries.
• After exchange of materials, blood enters
the venous system and returns to right
atrium of the heart.
• From right atrium, blood enters the right
ventricle.
• Thus, through systemic circulation,
oxygenated blood is supplied from heart to
the tissues and venous blood returns to the
heart from tissues.

8. PULMONARY CIRCULATION
• Blood is pumped from right ventricle to
lungs through pulmonary artery.
• Exchange of gases occurs between
blood and alveoli of the lungs at
pulmonary capillaries.
• Oxygenated blood returns to left atrium
through the pulmonary veins.
• Thus, left side of the heart contains
oxygenated or arterial blood and the
right side of the heart contains
deoxygenated or venous blood.

9. The
Circulatory
System

10. CARDIAC MUSCLE CONTRACTION
Generation and transmission of impulses in cardiac muscle

11. Cardiac muscle
Recap properties;
• Has one nucleus
• Intercalated discs
• Have large mitochondria
• Myogenic
• Straited

12. Funny channels
• Poorly selective cation channels
• Conduct more current as the membrane
potential becomes more negative close to -40
(hyperpolarization)
• Conduct both potassium and sodium ions
• Found in the SAN cells and activity causes the
membrane potential to slowly become more
positive (depolarize) to create a pacemaker
potential

13. The fast Na+ channel
• Voltage-dependent channels
• Functions:
– Permit Na+ to go in
– Keep K+ from going out
– Prevent Ca2+ from getting stuck in the channel and
interfering with Na+ permeability

14. Potassium channels
• Two main types of K+ channels
• Create a transmembrane "leak" of potassium
ions which causes hyperpolarization
• Activated by a specific depolarizing voltage
change
• located mainly inside the cellular membrane

15. Calcium channels
• L-type Ca++ channels (Long-lasting)
• T-type Ca++ channels (Transient)
• Respond to voltage changes across the
membrane differently
• L-type channels
– Respond to higher membrane potentials
– Open more slowly, and remain open longer than
T-type channels.
• Important in sustaining an action potential,
thus the plateau seen in the cardiac muscles

16. Calcium channels
• T-type channels initiate action potentials
• Because of their rapid kinetics, T-type
channels are commonly found in cells
undergoing rhythmic electrical behavior
– Neuron cell bodies involved in rhythmic activity
such as walking and breathing
– Pacemaker cells (SAN and AVN)

17. Cardiac muscle contraction
• Voltage regulated fast Na+ channels open initiating
an action potential
• Wave of depolarization travels down the T-tubules
resulting in the release of Ca++
– 20-30% of Ca++ needed for contraction comes from the
outside of the cells
• Acts as a stimulus for the release of the Ca++ from the sacoplasmic
reticulum
– For calcium to enter the cell, depolarization wave caused
by opening of the Na+ channels, opens the slow Ca++
channels

18. Cardiac Electrophysiology
Action Effect
Depolarization The electrical charge of a cell is altered by a
shift of electrolytes on either side of the cell
membrane.
This change stimulates the muscle cells to
contract
Repolarization Chemical pumps re-establish an internal
negative charge as the cells return to their
resting state.

19. Cardiac muscle contraction

20. Myocardial contraction:
• Heart muscle:
– Is stimulated by nerves and is self-excitable
(automaticity)
– Contracts as a unit
– Has a long (250 ms) absolute refractory period
• Cardiac muscle contraction is similar to skeletal
muscle contraction
• Autorhythmic cells:
– Initiate action potentials
– Have unstable resting potentials (pacemaker
potentials)

21. Sequence of excitation

22. Sequence of excitation
• Sinoatrial (SA) node generates impulses about
75 times/minute
• Atrioventricular (AV) node delays the impulse
by approximately 0.1 second
• Impulse passes from atria to ventricles via the
atrioventricular bundle (bundle of His)

23. Sequence of excitation

24. Sequence Excitation of Cardiac Muscle

25. THE CARDIAC CYCLE

26. Cardiac Cycle
Cardiac Cycle: the electrical, pressure and
volume changes that occur in a functional
heart between successive heart beats.
• Phase of the cardiac cycle when
myocardium is relaxed is termed diastole.
• Phase of the cardiac cycle when the
myocardium contracts is termed systole.
– Atrial systole: when atria contract.
– Ventricular systole: when ventricles contract.

27. Definitions
• Cardiac cycle
– Sequence of events in one heartbeat
• Systole
– Contraction phase (ventricular contraction)
• Diastole
– Relaxation phase (atrial and ventricular relaxation)
• Stroke volume
– Amount of blood ejected from either ventricle in a
single contraction
• Cardiac output
– Amount of blood pumped through the cardiovascular
system per minute (SV x HR)

28. Mechanical Events of the Cardiac Cycle
1. Ventricular Filling Period [ventricular diastole,
atrial systole]
2. Isovolumetric Contraction Period [ventricular
systole]
3. Ventricular Ejection Period [ventricular systole]
4. Isovolumetric Relaxation Period [ventricular
diastole]

29. Cardiac Cycle
• Electrical changes in heart tissue cause
mechanical, i.e. muscle contraction, changes
• Thus, changes in electrical membrane
potential of specific parts of the heart tissue
represent mechanical events in specific areas
of the heart tissue.

30. Electrical Events of the Cardiac Cycle
• Each wave or interval represents
depolarization or repolarization of
myocardial tissue.
• P wave represents depolarization of atria
which causes atrial contraction.
• QRS complex reflects depolarization of
ventricles which causes contraction.
• T wave reflects repolarization of muscle
fibers in ventricles.

31. Cardiac cycle
Has 2major phases: Systole and Diastole
Systole: (contraction-pumping phase of the cycle)
• Atrial systole
• Ventricular systole
• (depolarization-contraction phase)
Diastole: (relaxing-filling phase of the cycle)
• Atrial relaxation & filling
• Ventricular relaxation & filling
• (constitutes cardiac repolarization phase)

32. CARDIAC CYCLE

33. Stroke volume
• The volume of blood ejected in one ventricular
contraction is the stroke volume.
• SV is the difference between the volume of blood
in the ventricle before ejection (end-diastolic
volume) and the volume remaining in the
ventricle after ejection (end-systolic volume).
• Stroke volume is about 70 mL.
• Thus S.V=EDV-ESV

34. Cardiac output
• The total volume of blood ejected per unit
time
• Depends on the volume ejected on a single
beat (stroke volume) and the number of beats
per minute (heart rate).
• approximately 5000 mL/min in a 70-kg man
(based on a stroke volume of 70 mL and a
heart rate of 72 beats/min).
• Thus C.O= S.V x H.R

35. Frank-Starling relationship
• “The volume of blood ejected by the ventricle depends
on the volume present in the ventricle at the end of
diastole”
• The volume present at the end of diastole, depends on
the volume returned to the heart (venous return).
• Therefore, S.V and C.O correlate directly with E.D.V,
which correlates with V.R.
• The Frank-Starling relationship governs normal
ventricular function and ensures that the volume the
heart ejects in systole equals the volume it receives in
venous return

36. Cardiac Cycle
Coordination of :
• Electrical Changes
• Pressure Changes in Left Atria, Left Ventricle
and Aorta
• Ventricular Volume Changes
• Cardiac Valves

37. Cardiac Output
Cardiac Output is the volume of blood pumped each
minute, and is expressed by the following equation:
• CO = SV x HR
• Where:
– CO is cardiac output expressed in L/min (normal ~5 L/min)
– SV is stroke volume per beat
– HR is the number of beats per minute

38. Heart Rate (HR)
Heart rate is directly proportional to cardiac output
• Adult HR is normally 80-100 beats per minute (bpm.)
Heart rate is modified by autonomic, immune, and local factors.
• Example:
1. An increase in parasympathetic activity via M2 cholinergic receptors in
the heart will decrease the heart rate.
2. An increase in sympathetic activity via B1 and B2 adrenergic receptors
throughout the heart will increase the heart rate.

39. Stroke Volume (SV)
• SV = EDV – ESV
• Is determined by three factors: preload, afterload, and
contractility.
• Preload gives the volume of blood that the ventricle has
available to pump
• Contractility is the force that the muscle can create at the
given length
• Afterload is the arterial pressure against which the muscle will
contract.
– These factors establish the volume of blood pumped with each heart
beat.

40. Cardiac Volumes
• SV = end diastolic volume (EDV) - end systolic
volume (ESV)
• EDV = amount of blood collected in a ventricle
during diastole
• ESV = amount of blood remaining in a
ventricle after contraction

42. The ECG
Electrical changes in the heart muscle as recorded
on the body surface

43. Electro-cardiogram
• Is a series of waves and deflections recording the
heart’s electrical activity from a certain “view.”
• Many views, each called a lead, monitor voltage
changes between electrodes placed in different
positions on the body.
• Leads I, II, and III are bipolar leads, which consist
of two electrodes of opposite polarity (positive
and negative). The third (ground) electrode
minimizes electrical activity from other sources.

45. What is an ECG?

47. Limb leads
• Electrodes are placed on
the right arm (RA), left
arm (LA), right leg (RL),
and left leg (LL).
• With only four electrodes,
six leads are viewed.
• Standard leads: I, II, III
• Augmented leads: aVR,
aVL, aVF
• Einthoven’s Triangle

48. Limb leads and augmented leads

49. Standard leads
• Lead I is the voltage between the (positive) left
arm (LA) electrode and right arm (RA) electrode:
– I=LA-RA
• Lead II is the voltage between the (positive) left
leg (LL) electrode and the right arm (RA)
electrode:
– II=LL-RA
• Lead III is the voltage between the (positive) left
leg (LL) electrode and the left arm (LA) electrode:
– III=LL-LA

51. Augmented limb leads
• Leads aVR, aVL, and aVF are the augmented
limb leads.
• Derived from the same three electrodes as
leads I, II, and III
• These use the Goldberger's central terminal as
their negative pole which is a combination of
inputs from other two limb electrodes

53. Precordial leads
• The precordial leads lie in the transverse
(horizontal) plane, perpendicular to the other
six leads. The six precordial electrodes act as
the positive poles for the six corresponding
precordial leads: (V1, V2, V3, V4, V5 and V6).
• Wilson's central terminal is used as the
negative pole

56. ECG leads
• Leads aVR, aVL, and aVF are unipolar leads and
consist of a single positive electrode and a
reference point (with zero electrical potential)
that lies in the center of the heart’s electrical
field.
• Leads V1–V6 are unipolar leads and consist of a
single positive electrode with a negative
reference point found at the electrical center of
the heart.
• Voltage changes are amplified and visually
displayed on an oscilloscope and graph paper.

57. • An ECG tracing looks different in each lead because the
recorded angle of electrical activity changes with each
lead.
• Several different angles allow a more accurate
perspective than a single one would.
• The ECG machine can be adjusted to make any skin
electrode positive or negative. The polarity depends on
which lead the machine is recording.
• A cable attached to the patient is divided into several
different-colored wires: three, four, or five for
monitoring purposes, or ten for a 12-lead ECG.

58. Lead interpretation
• LEADS I,II and VL look at the left lateral surface of the
heart.
• III and VF at the inferior surface.
• And VR looks at the atria.
• AVR and II look at the heart from opposite directions.
• Leads VI and V2 look at the right ventricle.
• V3 and V4 look at the septum between the
ventricles and the anterior wall of the left ventricle.
• V5 and V6 look at the anterior and lateral walls of
the left ventricle.

59. ECG leads

63. Electrical components

64. Methods of counting heart rate
• Heart rate is calculated as the number of
times the heart beats per minute. It usually
measures ventricular rate (the number of QRS
complexes) but can refer to atrial rate (the
number of P waves).
• Method chosen to calculate HR varies
according to rate and regularity on the ECG
tracing

65. Practical sessions

66. Procedure
1. Position patient supine. Ensure a comfortable positioning.
2. Explain procedure to dispel fears or myths. Instruct patient to lie as still
as possible.
3. Attach electrodes
1. Limb leads
1. Right/left arm, right/left leg
2. Precordial leads
1. V1 = 4th intercostal space to right of sternal border
2. V2 = 4th intercostal space to left of sternal border
3. V3 = midway between leads V2 and V4
4. V4 = midclavicular line, above the 5th interspace
5. V5 = anterior axillary line at the same level as V4
6. V6 = midaxillary line at the same level as leads V4 and V5

67. Procedure

69. How to Read an ECG
• Basics
– Always approach ECG reading in a systematic,
stepwise fashion

70. 1. Rate
• To determine the rate you must first know the paper speed
(usually 25mm/sec)
– 5 large blocks = 1 second
– 1 large block = 0.2 second (200 msec)
– 1 small block = 0.04 second (40 msec)
– Rate = (# of QRS) x 60 seconds
# of seconds 1 min

71. 1. Rate (continued)
• If speed is 25mm/sec, it is much easier to estimate the rate
using the rule
“300-150-100 -- 75-60-50”
• Also…depending on the ECG machine, sometimes the HR will
be provided!

72. 2. Rhythm
• Is there a P-wave before every Q and a Q-wave after every P?
– No P-waves
• Narrow complex QRS: Atrial fibrillation
• Wide complex: ventricular rhythm (Idioventricular, Ventricular tachycardia, Ventricular fibrillation)
– P-wave present
• Fixed PR interval
– Normal PR interval
» If P wave is positive in II → Sinus rhythm
» If P wave is negative in II → Junctional rhythm
– Prolonged PR interval
» QRS always present = First degree AV block
» Regularly “dropped” QRS = Second deg. AV block (Mobitz Type II)
– Sawtooth” p-wave pattern = Atrial flutter
• Variable PR interval
– Second degree AV block (Mobitz Type I/Wenckebach)
– Different P-wave morphologies
» Wandering pacemaker
» Multifocal atrial tachycardia
• P-wave and Q-wave independent
– Third degree (Complete) AV block

73. 2. Rhythm

74. 4. P-Wave and PR interval
• P Wave
– P wave represents atrial depolarization
• PR Interval
– PR interval is beginning of P wave to beginning of QRS
– Normal interval is 120-200 milliseconds (3-5 small boxes)
– Why would PR interval be lengthened?...blocks
• 1st degree - consistently lengthened PR
• 2nd degree (Type 1) - Wenckebach
• 2nd degree (Type 2) - will regularly drop beat, PR interval less important
• 3rd degree - no relation between P and QRS, P waves regular, QRS regular and wide
– Why would PR interval be shortened?
• ectopic atrial foci (e.g. wandering pacemaker, multifocal atrial tachycardia)
• accessory tracts, Wolf-Parkinson-White syndrome (WPW)

75. 5. QRS
• QRS Complex
– Normal width is <120 ms (3 small squares)
– What causes widened QRS?
• RBBB (RSR’ in V1; wide S wave in I, V5-6)
• LBBB (wide R in I, V5-6; no Q in I, V5-6; displaced ST and T waves opposite
to major deflection of QRS)
• Ventricular beat
• Accessory tracts
– Detect ventricular hypertrophy by height of QRS
• S in V1 + R in V5 or V6 ≥ 35 mm → LVH
• R in AVL ≥11mm → LVH
• If R wave (any +ve defl’n ) in V1 → Likely RVH

76. 6. ST Segment
• ST Segment
– Elevation = active infarction (vessel occluded),
pericarditis, aneurysm of ventricle
– Look at lead where elevation occurs to determine
vessel occluded
– Depression = ischemia, digoxin toxicity,
hypokalemia, elevated intracranial pressure
– An old MI will be seen as Q wave (1/3 of QRS
complex)

77. 7. T Waves
• T Waves
– Usually will be in same direction as QRS
– T wave inversion caused by ischemia or old
infarction

78. 8. QT Interval
• QT Interval
– From end of QRS complex to end of T wave
– Long QT is >500 ms (QTc >440ms) → can predispose
to Torsades des pointes
– What causes long QT?
• Ischemia
• Electrolyte abnormalities (↓ K, Mg, Ca)
• Congenital
• Drugs (many including antiarrhythmics, quinolones, TCA)