M.sc part. 1 seme 2 . This is topic are biochemistry ECG are electro cardio graph this full from of ECG And this topic related a heart function in human body

1. Mechanical and Electrical
Events of the Cardiac Cycle
PEP 3510: Exercise Physiology
PEP 4370: Exercise Management for
Special Populations

2. 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.

3. 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, atrial diastole]

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

6. Electrocardiography
 Two common abbreviations for
electrocardiogram: EKG and ECG.
 EKG comes from German language where
cardiogram is written as kardiogram.
 The ECG records the electrical activity of
the heart.
 Mechanical activity of the heart is sensed by
echocardiography.

7. Electrocardiography
ECG - electrocardiogram
– graphic recording of electrical events
– established electrode pattern results in specific
tracing pattern
– electrical pattern reveals blood supply problems

8. Electrophysiology
 If an electrode is placed so that wave of
depolarization spreads toward the recording
electrode, the ECG records a positive
(upward) deflection.
 If wave of depolarization spreads away
from recording electrode, a negative
(downward) deflection occurs.

9. Electrophysiology

10. Electrophysiology

11. Electrophysiology

12. Electrophysiology
 When myocardial muscle is completely
polarized or depolarized, the ECG will not
record any electrical potential but rather a
flat line, isoelectric line.
 After depolarization, myocardial cells
undergo repolarization to return to electrical
state at rest.

13. Electrical Events of the
Cardiac Cycle
• Sinoatrial (SA) node is the normal pacemaker
of heart and is located in right atrium.
• Depolarization spreads from SA node across
atria and results in the P wave.
• Three tracts within atria conduct depolarization
to atrioventricular (AV) node.
• Conduction slows in AV node to allow atria to
empty blood into ventricles before vent. systole.
• Bundle of His connects AV to bundle branches.
• Purkinje fibers are terminal bundle branches.

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

17. ECG Time & Voltage
• ECG machines can run at 50 or 25 mm/sec.
• Major grid lines are 5 mm apart; at standard
25 mm/s, 5 mm corresponds to .20 seconds.
• Minor lines are 1 mm apart; at standard 25
mm/s, 1 mm corresponds to .04 seconds.
• Voltage is measured on vertical axis.
• Standard calibration is 0.1 mV per mm of
deflection.

19. Basic Electrographic Complexes
• P wave represents depolarization of atria which
causes atrial contraction
• Repolarization of atria not normally detectable on
an ECG
• Excitation of bundle of His and bundle branches
occur in middle of PR interval
• QRS complex reflects depolarization of
ventricles
• T wave reflects repolarization of muscle fibers in
ventricles

20. Electrocardiogram
 Normal P wave has
amplitude of ≤ 0.25 mV
 Q wave is first downward
deflection after P wave;
signals start of ventricular
depolarization
 R wave is positive
deflection after Q wave
 S wave is negative
deflection preceded by Q
or R waves
 T wave follows QRS

22. Standard 12-Lead ECG
 Usually performed when person is resting in
supine position.
 Composed of three bipolar limb leads: I, II,
and III; three augmented voltage leads:
aVR, aVL, aVF; and six chest or precordial
leads: V1 – V6.
 All limb leads lie in frontal plane.
 Chest leads circle heart in transverse plane.

23. ECG Limb Leads

24. ECG Augmented Limb Leads

26. ECG Precordial Leads

28. Standard 12-Lead ECG
 Each lead provides a
different electrical angle
or picture of the heart.
 Anterior part of heart by
looking at V1 – V4.
 Lateral view of heart: I,
aVL, V5 and V6.
 Inferior view of heart: II,
III, and aVF.

29. Exercise 12-Lead ECG

30. 12-Lead ECG
 Limb lead II shows large
R amplitude because left
ventricle current vector
lies parallel with
electrode placement.
 Chest lead V1 has large S
wave because left
ventricle current vector is
directed away from
electrode.

31. 12-Lead ECG Strip

32. Interpretation of ECG:
Rate
First measurement to calculate is heart rate.
PQRST waves represent one complete cardiac
cycle.
1. At standard paper speed, divide 1500 by
distance between R to R waves.
2. Find R wave on heavy line. Count off 300,
150, 100, 75, 60 for each following line.
Where next R lands is quick estimate.
3. Multiply number of cycles in 6 second marks
by 10.

33. Interpretation of ECG: Rate

34. Interpretation of ECG:
Rhythm
• Normal heart rhythm has consistent R-R interval.
• Mild variations due to breathing also normal.

35. Interpretation of ECG: Rhythm
Normal Sinus Rhythm
• Rate: 60-100 b/min
• Rhythm: regular
• P waves: upright in
leads I, II, aVF
• PR interval: < .20 s
• QRS: < .10 s
Sinus Bradycardia
• Rate: < 60 bpm
• Rhythm: regular
Sinus Tachycardia
• Rate: > 100 bpm

37. AV Conduction Disturbances
o Atrioventricular
conduction
disturbances refer to
blockage of electrical
impulse at AV node.
o 1st degree P waves result
in delayed QRS.
o 2nd degree some but not
all P waves have QRS.

38. Arrhythmias
Arrhythmia: an irregular
heartbeat.
• Sinus arrhythmia- P
wave precedes @ QRS
but RR interval varies.
• Premature Atrial
Contraction (PAC)
• Premature Ventricular
Contraction (PVC)

39. Arrhythmias

40. Myocardial Ischemia
ST segment depression.
• Hallmark of myocardial ischemia.
• Reduction of oxygen-rich blood supply alters normal
cellular action causing ST segment displacement ≥ 1
mm below line.
• Upsloping, horizontal, downsloping

41. Illustration References
 McArdle, Katch, Katch. 2000. Essentials
of Exercise Physiology Image Collection,
2nd ed. Lippincott Williams & Wilkins
 Foss and Keteyian. 1998. Physiological
Basis for Exercise and Sport, 6th ed. WCB
McGraw-Hill.
 Robergs and Keteyian. 2003.
Fundamentals of Exercise Physiology, 2nd
ed. McGraw-Hill.