Electrocardiography

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Electrocardiography

• Method of measuring the electrical activity of
  the heart from electrodes placed on the body
  surface.

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The heart becomes electrically polarized during
the cardiac cycle.

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Atria Depolarized Ventricles not Depolarized
Atria Repolarized, Ventricles Depolarized
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aVL
aVR
I
II
III
Electrocardiograph- instrument for measuring ECG
aVF
Electrocardiogram graphic recording of
electrical events of the heart.
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Polarized
Heart Muscle Fiber
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Depolarized

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Repolarized
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R
P
T
Q
S
P-R
Q-T
P-Wave Depolarization of Atria
QRS Depolarization of Ventricles
T-Wave Repolarization of Ventricles
P-R Interval Time for A.P. to pass from atria
to ventricles through A-V node.
Q-T Interval Time of ventricular contraction
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12 Lead ECG
I
aVR aVL aVF
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V1 V2 V3 V4 V5 V6
III
Guyton, p122, 1991
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Tachycardia gt100 beats/min at rest
Normal
Tachycardia
Fever, Sympathetic Nerve Stimulation, weak heart
Guyton, p 139, 1991
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Bradycardia lt 60 beats/min at rest
Normal
Bradycardia
Physical Training, Increased parasympathetic
stimulation
Guyton, p 139, 1991
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Sinus Arrythmia
Small increases and decreases in heart rate
during the respiratory cycle.
Cardiotachometer records heart rate
Normal Breathing
Deep Breathing
Guyton, p139, 1991
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Atrial Flutter
Atria contract 200-350/min
Normal
2-3 atrial/ventricular contraction
A.P.
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Atrial Fibrillation
Uncoordinated contractions of atria
Normal
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Ventricular Fibrillation
Uncoordinated contractions of ventricles
Normal
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Electrical Defibrillation
Apply strong electrical shock across chest -
depolarize all fibers simultaneously - all in
refractory period same time. S-A node resumes
pacemaker role.
Normal
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Premature Ventricular Contractions
PVCs
Impulse arises from hyperexcitable area (ectopic
focus) instead of S-A node.
Ectopic Focus
Sherwood Fig 7-8, 1995
Ischemia, caffeine, nicotine, anxiety
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First Degree Heart Block
Delay in conduction from atria to ventricles -
increase in P-R interval.
Slow conduction across A-V node
Normal
Sherwood Fig 7-8, 1995
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Second Degree Heart Block
Two or three P waves for every QRS
Impaired conduction
Normal
Sherwood Fig 7-8, 1995
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Third Degree Heart Block
No relationship between P waves and QRS Atria
beat at one rate and ventricles at another
Blocked conduction
Normal
Sherwood Fig 7-8, 1995
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Bundle Branch Block
Impairment of conduction of the impulse along one
of the bundle branches.
Blocked conduction
Sherwood Fig 7-8, 1995
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Bundle Branch Block
Impairment of conduction of the impulse along one
of the bundle branches, causing prolonged
depolarization of the ventricle on that side.
Normal
LBB
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Myocardial Infarction
Death of a region of heart tissue due to
inadequate supply of oxygen Heart Attack
Ischemia Insufficient blood supply to a region
of the heart.
Normal
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Heart Sounds
1st Heart Sound Closure of A-V Valves
2nd Heart Sound Closure of Aortic and Pulmonary
Semilunar Valves
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Heart Murmurs
Caused by leaky or stenotic heart valves.
Stenotic stiff and narrow - higher resistance
to flow causes swishing sound as blood is
forced through the smaller opening.
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Echocardiography
Visualization of the heart using ultrasound.
Non-invasive technique for seeing the heart
beating in the thoracic cavity. Function of
valves can be seen nicely by this technique.
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Left A-V Valve
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Diastole
Systole