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Cardiovascular system- L3
Faisal I. Mohammed, MD, PhD
University of Jordan
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Electrocardiogram
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ECG or EKG
Composite record of
action potentials
produced by all the
heart muscle fibers
Compare tracings
from different leads
with one another and
with normal records
3 recognizable waves
 P, QRS, and T
University of Jordan
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The Electrocardiogram
The major deflections and intervals
in a normal ECG include:
 P wave - atrial depolarization
 P-Q interval - time it takes for
the atrial kick to fill the
ventricles
 QRS wave - ventricular depolarization
and atrial repolarization
 S-T segment - time it takes to empty the ventricles
before they repolarize (the T wave)
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Correlation of ECG Waves and Systole
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1.
2.
3.
4.
5.
6.
Systole – contraction/ diastole – relaxation
Cardiac action potential arises in SA node
 P wave appears
Atrial contraction/ atrial systole
Action potential enters AV bundle and out over ventricles
 QRS complex
 Masks atrial repolarization
Contraction of ventricles/ ventricular systole
 Begins shortly after QRS complex appears and
continues during S-T segment
Repolarization of ventricular fibers
 T wave
Ventricular relaxation/ diastole
University of Jordan
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Cardiac Cycle
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All events associated with one heartbeat
Systole and diastole of atria and ventricles
In each cycle, atria and ventricles alternately contract and relax
 During atrial systole, ventricles are relaxed
 During ventricle systole, atria are relaxed
Forces blood from higher pressure to lower pressure
During relaxation period, both atria and ventricles are relaxed
 The faster the heart beats, the shorter the relaxation period
 Systole and diastole lengths shorten slightly
University of Jordan
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Cardiac Cycle
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Cardiac cycle refers to all events associated with
blood flow through the heart
 Systole – contraction of heart muscle
 Diastole – relaxation of heart muscle
Cardiac Cycle
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Atrial systole 0.1 second
Atrial diastole 0.7 second
Ventricular systole 0.3 second
 Rapid ejection period
 Slow ejection period
Ventricular diastole 0.5 seconds
 Rapid filling
 Slow filling (Diastasis)
 Atrial contraction
Phases of the Cardiac Cycle
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R
T
P
(a) ECG
1
4
8
Q
Atrial depolarization
2
Begin atrial systole
3
End (ventricular) diastolic volume
4
Ventricular depolarization
5
Isovolumetric contraction
6
Begin ventricular ejection
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End (ventricular) systolic volume
8
Begin ventricular repolarization
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Isovolumetric relaxation
S
0.1
sec
Atrial
systole
0.3 sec
Ventricular
systole
120
0.4 sec
Relaxation
period
9
Dicrotic wave
100
Aortic
pressure
5
80
6
(b) Pressure
(mmHg)
1
Left
ventricular
pressure
60
40
Left atrial
pressure
10
20
2
0
(c) Heart sounds
S1
S2
S3
S4
3 End (ventricular) diastolic volume
130
10 Ventricular filling
Stroke
volume
(d) Volume in
ventricle (mL)
60
7
0
(e) Phases of the
cardiac cycle
Atrial
contraction
Isovolumetric
contraction
UniversityIsovolumetric
of Jordan
Ventricular
ejection
relaxation
Ventricular
filling
Atrial
contraction
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Stroke Volume
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SV = end diastolic volume (EDV) minus end systolic
volume (ESV)
EDV = amount of blood collected in a ventricle
during diastole
ESV = amount of blood remaining in a ventricle after
contraction
Cardiac cycle …cont
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End diastolic volume (EDV) – End systolic
volume (ESV) = Stroke volume (SV)
SV X heart rate (HR) = cardiac output (CO)
Ejection fraction = SV/EDV
Autonomic control of cardiac cycle (pump)
Cardiac Output
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CO = volume of blood ejected from left (or right)
ventricle into aorta (or pulmonary trunk) each minute
CO = stroke volume (SV) x heart rate (HR)
In typical resting male
 5.25L/min = 70mL/beat x 75 beats/min
Entire blood volume flows through pulmonary and
systemic circuits each minute
University of Jordan
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Thank You
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