The Steps of The Cardiac Cycle “The Rhythm is gonna get you”

The Steps of The The Steps of The Cardiac CycleCardiac Cycle

““The Rhythm is gonna get The Rhythm is gonna get you” you”

Atrial Systole Atrial Systole Lasts 0.1 secLasts 0.1 sec Atria contract, and the ventricles relaxAtria contract, and the ventricles relax SA node depolarizesSA node depolarizes This causes a P wave on an EKGThis causes a P wave on an EKG Forces blood through the open AV valves Forces blood through the open AV valves

into the ventriclesinto the ventricles Creates SystoleCreates Systole Atrial Systole contributes to the final Atrial Systole contributes to the final

forced push of about 25 mL of blood into forced push of about 25 mL of blood into the ventricles from the atriathe ventricles from the atria

Ventricular SystoleVentricular Systole Ventricles depolarize and the atria relaxVentricles depolarize and the atria relax Lasts 0.3-0.5 secondsLasts 0.3-0.5 seconds At the beginning of this phase the At the beginning of this phase the

pressure rises in the ventricle chambers pressure rises in the ventricle chambers and it pushes blood against the AV valves and it pushes blood against the AV valves forcing them shutforcing them shut

Myocardium begins to contract but does Myocardium begins to contract but does not exert force right awaynot exert force right away

As the ventricles begin to contract, As the ventricles begin to contract, pressure rises since the valves are closed pressure rises since the valves are closed offoff

Ventricular Systole ContVentricular Systole Cont Once left ventricular pressure rises above about Once left ventricular pressure rises above about

80 mmHg and right ventricular pressure rises 80 mmHg and right ventricular pressure rises above 20 mmHg, both semilunar valves open and above 20 mmHg, both semilunar valves open and blood is ejectedblood is ejected

Pressure continues to rise in the left ventricle to Pressure continues to rise in the left ventricle to about 120 mmHgabout 120 mmHg

Rises to about 25-30 mmHg in the right ventricleRises to about 25-30 mmHg in the right ventricle At the end of this phase the T wave of the EKG At the end of this phase the T wave of the EKG

marks the point of ventricular repolarization marks the point of ventricular repolarization This is the point where they cannot contract This is the point where they cannot contract

Relaxation PeriodRelaxation Period Lasts about 0.2-0.4 secondsLasts about 0.2-0.4 seconds Marks the time when the atria and ventricles both Marks the time when the atria and ventricles both

relaxrelax SL valves close off since blood begins to flow back SL valves close off since blood begins to flow back

due to the lack of pressure from the ventriclesdue to the lack of pressure from the ventricles As soon as the ventricular pressure falls below As soon as the ventricular pressure falls below

the atrial pressure the AV valves open up and the the atrial pressure the AV valves open up and the filling process begins over againfilling process begins over again

At the end of the relaxation period the ventricles At the end of the relaxation period the ventricles are about ¾ full and the next cycle beginsare about ¾ full and the next cycle begins

One cycle lasts 0.8 sec in an average heartOne cycle lasts 0.8 sec in an average heart

Cardiac Cycle

Process Diagrams Step-by-Step

Copyright © 2007 by John Wiley & Sons, Inc.

1

0

20

40

60

80

100

120

(d) Volume in ventricle (mL)

(c) Heart sounds

(b) Pressure (mmHg)

(a) ECG P

R

QS

Dicrotic wave

Left atrialpressure

Aorticpressure

Leftventricularpressure

T

130

60

0

Atrialcontraction

Atrialcontraction

Isovolumetriccontraction

Isovolumetricrelaxation

Ventricularejection

Ventricularfilling

(e) Phases of the cardiac cycle

0.3 sec0.1sec 0.4 sec

Ventricularsystole

Relaxationperiod

Atrialsystole

S1 S2 S3 S4

1 Atrial depolarization

1

0

20

40

60

80

100

120


(c) Heart sounds

(b) Pressure (mmHg)

(a) ECG P

R

QS

Dicrotic wave

Left atrialpressure

Aorticpressure


T

130

60

0

Atrialcontraction

Atrialcontraction



Ventricularejection

Ventricularfilling



Ventricularsystole

Relaxationperiod

Atrialsystole

S1 S2 S3 S4

2

1

2

Atrial depolarization

Begin atrial systole

1

0

20

40

60

80

100

120


(c) Heart sounds

(b) Pressure (mmHg)

(a) ECG P

R

QS

Dicrotic wave

Left atrialpressure

Aorticpressure


T

130

60

0

Atrialcontraction

Atrialcontraction



Ventricularejection

Ventricularfilling


End (ventricular) diastolic volume


Ventricularsystole

Relaxationperiod

Atrialsystole

S1 S2 S3 S4

2

3

1

2

3




0

20

40

60

80

100

120


(c) Heart sounds

(b) Pressure (mmHg)

(a) ECG P

R

QS

Dicrotic wave

Left atrialpressure

Aorticpressure


T

130

60

0

Atrialcontraction

Atrialcontraction



Ventricularejection

Ventricularfilling



Ventricularsystole

Relaxationperiod

Atrialsystole

S1 S2 S3 S4

41

2

3

4




Ventricular depolarization


0

20

40

60

80

100

120


(c) Heart sounds

(b) Pressure (mmHg)

(a) ECG P

R

QS

Dicrotic wave

Left atrialpressure

Aorticpressure


T

130

60

0

Atrialcontraction

Atrialcontraction



Ventricularejection

Ventricularfilling



Ventricularsystole

Relaxationperiod

Atrialsystole

S1 S2 S3 S4

4

5

1

2

3

4

5





Isovolumetric contraction


0

20

40

60

80

100

120


(c) Heart sounds

(b) Pressure (mmHg)

(a) ECG P

R

QS

Dicrotic wave

Left atrialpressure

Aorticpressure


T

130

60

0

Atrialcontraction

Atrialcontraction



Ventricularejection

Ventricularfilling



Ventricularsystole

Relaxationperiod

Atrialsystole

S1 S2 S3 S4

4

6

1

2

3

4

5

6






Begin ventricular ejection


5

0

20

40

60

80

100

120


(c) Heart sounds

(b) Pressure (mmHg)

(a) ECG P

R

QS

Dicrotic wave

Left atrialpressure

Aorticpressure


T

130

60

0

Atrialcontraction

Atrialcontraction



Ventricularejection

Ventricularfilling


Strokevolume


Ventricularsystole

Relaxationperiod

Atrialsystole

S1 S2 S3 S4

4

7

1

2

3

4

5

6

7







End (ventricular) systolic volume


6

5

0

20

40

60

80

100

120


(c) Heart sounds

(b) Pressure (mmHg)

(a) ECG P

R

QS

Dicrotic wave

Left atrialpressure

Aorticpressure


T

130

60

0

Atrialcontraction

Atrialcontraction



Ventricularejection

Ventricularfilling


Strokevolume


Ventricularsystole

Relaxationperiod

Atrialsystole

S1 S2 S3 S4

8 1

2

3

4

5

6

7

8








Begin ventricular repolarization


0

20

40

60

80

100

120


(c) Heart sounds

(b) Pressure (mmHg)

(a) ECG P

R

QS

Dicrotic wave

Left atrialpressure

Aorticpressure


T

130

60

0

Atrialcontraction

Atrialcontraction



Ventricularejection

Ventricularfilling


Strokevolume


Ventricularsystole

Relaxationperiod

Atrialsystole

S1 S2 S3 S4

8

9

1

2

3

4

5

6

7

8

9









Isovolumetric relaxation


0

20

40

60

80

100

120


(c) Heart sounds

(b) Pressure (mmHg)

(a) ECG P

R

QS

Dicrotic wave

Left atrialpressure

Aorticpressure


T

130

60

0

Atrialcontraction

Atrialcontraction



Ventricularejection

Ventricularfilling


Strokevolume


Ventricularsystole

Relaxationperiod

Atrialsystole

S1 S2 S3 S4

10

1

2

3

4

5

6

7

8

9

10









Isovolumetric relaxation

Ventricular fillingEnd (ventricular) diastolic volume

8

9

1

0

20

40

60

80

100

120


(c) Heart sounds

(b) Pressure (mmHg)

(a) ECG P

R

QS

Dicrotic wave

Left atrialpressure

Aorticpressure


T

130

60

0

Atrialcontraction

Atrialcontraction



Ventricularejection

Ventricularfilling



Ventricularsystole

Relaxationperiod

Atrialsystole

S1 S2 S3 S4

1 Atrial depolarization

The Steps of The Cardiac Cycle “The Rhythm is gonna get you”

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