Excitations of heart rhythms and ECG.ppt

The Electric development with in the heart

1. Physiology
Theme. Cardiovascular system
Lecture: Excitatory –conductive system.
Electrocardiogram

2. Summary
•Specialized excitatory and conductive
system of the heart, its components.
•The normal electrocardiogram, its features.
•ECG and cardiac cycle.
•Leads of the ECG.

3. Objectives
•To describe the characteristics of the structures of the Specialized
excitatory system
•To identify the events in normal electrocardiogram establishing
the relation with the maechanical events during one cardiac cycle
•To identify the Leads of the electrocardiogram

4. Conduction System of Heart

5. Conductive system
•Sinus (Sinoatrial) Node
•Internodal Pathways
•Atrioventricular Node
•A-V Bundle
-Left bundle branch
-Right bundle branch
•Purkinje Fibers

6. Rhythm of Conduction System
•SA node fires spontaneously 70-90 times per minute
•AV node fires at 40-60 times per minute
•If both nodes are suppressed fibers in ventricles by
themselves fire only 20-40 times per minute
•Artificial pacemaker needed if pace is too slow
•Extra beats forming at other sites are called ectopic
pacemakers
–caffeine & nicotine increase activity

7. Cardiac Action Potential
Phases: Depolarization, plateau, repolarization

8. SINOATRIAL
NODE
•Superior posterolateral
wallrightatrium
•Fibersconnectwith
atrial fibers
•RMP –55 to-60milivolts
•Natural leakof Sodiumand Calciumions
•Selfexcitationand fastestrythm-pacemaker

9. Internodal Pathways
•Allowtheactionpotentialto
travelfromsinusnodetoA-V
node
•Rapid conduction
•Presenceof specialized
conductionfiberssimilar to
Purkinjefibers

10. Atrioventricular
Node(AV)
•Behind the tricuspid valve
•The impulse comes 0.03 sec. later
•Impulse delay of 0.09 sec. in AV Node
•Final delay of 0.04 second in penetrating portion of the A-
V bundle
•Total delay in this node is about 0.13 second caused by
diminished numbers of gap junctions
•Time from excitation of SA node to ventricles excitation –
0.16 second
•Discharge rate-40 to 60 times/minute

11. Purkinje
System
•Very large fibers
•High permeability-gap junctions
•High velocity to transmit AP
•Almost intastaneous transmission of the impulse
throughout the remainder of the ventricular muscle
•Time spent to cover the whole ventricular mass about 0.03
second
•Discharge rate-15 to 40 times per minute

12. Electrocardiogram
•Impulse conduction through the heart generates
electrical currents that can be detected at the
surface of the body. A recording of the electrical
changes that accompany each cardiac cycle is called
an electrocardiogram(ECGor EKG).
•The ECG helps to determine if the conduction
pathway is abnormal, if the heart is enlarged, and if
certain regions are damaged.

13. Electrocardiogram
•The recording of electrical potentials generated in
the excitatory or conductive system of the heart
•Electrical current spreads from the heart into the
adjacent tissues
•Electrodes are placed on the skin
•Depolarization and repolarization waves can be
recorded

14. Einthovenassignedthe
lettersP,Q,R,SandTto
thevariousdeflections,
andhedescribedthe
electrocardiographic
featuresofanumberof
cardiovasculardisorders.
In1924,hewasawarded
theNobelPrizeinMedicine
forhisdiscovery

15. Electrocardiogram---ECG or EKG
•P wave
–atrial depolarization
•P-Q or P-R interval
–conduction time from atrial
to ventricular excitation
•QRS complex
–ventricular depolarization
•T wave
–ventricular repolarization

16. Intervals and segments
•Q-T interval
•P-R Interval
•S-T segment
•P-R segment

17. Where is the atrial repolarization? Does it occur?

18. 18

19. ECG and Cardiac cycle events
•As atrial fibers depolarize, the P wave appears.
•After the P wave begins, the atria contract (atrial systole). Action
potential slows at the AV node giving the atria time to contract
and complete the filling of the ventricles.
•The action potential moves rapidly through the bundle branches,
Purkinje fibers, and the ventricular myocardium producing the
QRS complex.
•Ventricular contraction after the QRS complex and continues
through the ST segment.
•Repolarization of the ventricles produces the T wave.
•Atrial repolarization occurs when ventricles are being
depolarized. (QRS hides it)

20. ECG and Cardiac Cycle
•P wave is followed by atrial contraction
•QRS complex is recorded before ventricular systole
•T wave represents ventricular repolarization and occurs by
the end of its contraction.

21. ElectrocardiogramLeads

22. Electrocardiogram Leads
•Three Bipolar Limb Leads
LI LII LIII
•Augmented Unipolar Limb Leads
aVR aVL aVF
•Chest Leads ( Precordial )
V1 V2 V3 V4 V5 V6
To record the first two, the electrodes are placed in
the four limbs (wrists and ankles) according to their
colours (yellow-green-red-black)

24. Precordial Leads: places to record

25. Electrocardiograph

26. Bibliography
•Guyton-Hall. Medical Physiology. Chapter 10 & 11.
Page 117,123
•Wiliam F. Ganong. Medical Physiology.
Chapter 28. Page 523