Cardiac cycle

Dr. shafali singh

Learning Objectives• Interpret in correct temporal relationship, the pressure,

volume, heart sound, and ECG changes in the cardiac cycle.

• Identify the intervals of isovolumic contraction, rapid ejection, reduced ejection, isovolumic relaxation, rapid ventricle filling, reduced ventricular filling and atrial contraction.

• Contrast the relationship between pressure and flow into and out of the left and right ventricles during each phase of the cardiac cycle.

• Interpret ventricular pressure-volume loop and on it label the phases and events of the cardiac cycle (ECG, valve movement).

CARDIAC CYCLE

1. ELECTRICAL CHANGE

2. MECHANICAL CHANGE

3. HEMODYNAMIC CHANGE

4. HEART SOUNDS

Cardiac cycleThe cardiac events that occur from beginning of one heart beat to the next are called the cardiac cycleAtria

Atrial systoleAtrial diastole

VentricleVentricular systoleVentricular diastole

Heart beat duration (rate is 75 beat/min)

Duration of cardiac cycle

• HEART RATE : 75/MIN• HENCE DURATION FOR ONE CYCLE IS: 60/75 =

0.8 Sec• ATRIAL CYCLE– ATRIAL SYSTOLE - 0.1 SEC– ATRIAL DIASTOLE- 0.7 SEC

• VENTRICULAR CYCLE– VENTRICULAR SYSTOLE – 0.3 SEC– VENTRICULAR DIASTOLE – 0.5 SEC

What happens to time spent and systole and diastole with tachycardia?

• Under Normal condition:n1/3rd time in systole and 2/3rd in diastole

• Tachycardia : time spent in diastole decreases dramatically whereas time spent in systole falls to lesser extent.

CARDIAC CYCLE

• IF HR ↑ - 150 / MIN• CARDIAC CYCLE – 0.4 Sec• SYSTOLE 0.25 Sec• DIASTOLE 0.15 Sec• HENCE LITTLE TIME FOR VENTRICULAR

FILLING

Mechanical Events of Cardiac cycle

1. Atrial systole 2. Isovolumic contraction phase3. Rapid ejection phase4. Reduced ejection phase5. Isovolumic relaxation phase6. Rapid filling phase7. Reduced filling phase (Diastasis)8. Last rapid filling phase

ATRIAL SYSTOLE

• Last phase of ventricular diastole

• Drives some more blood into the ventricles

• Increases the ventricular filling by 35%

• 0.1 Sec

• Coincides with ‘a‘ wave of JVP

• Contraction of atria-Fourth Heart sound

VENTRICULAR SYSTOLE

1.ISOVOLUMETRIC CONTRACTION

• Coincides with ‘c ‘wave in JVP• Semilunar valve : remain closed• AV valves close – First Heart sound• Closed chamber – Contracts • No change in the volume• BLOOD INCOMPRESSIBLE• Intraventricular pressure ↑

2.EJECTION PHASE

• ↑ Intraventricular pressure • > 80mm Hg- Diastolic pressure of

AortaOr > 10mmHg- Diastolic pressure of Pulmonary arteries• Semilunar valves forced to open• Blood flows into arteries from

ventricle

EJECTION PHASE

• MAXIMAL EJECTION – • Due to High Pressure gradient - Blood is ejected

into Aorta/Pul. Art.• REDUCED EJECTION – • Due to decreased Pressure gradient

• STROKE VOLUME – 70 ml• END SYSTOLIC VOLUME = 40-50 ml• EDV – SV = ESV [120 – 70 = 50]

Ventricular diastole

1.Protodiastolic period – 2.Isovolumetric relaxation – 3.Rapid filling phase – 4.Reduced filling phase (Diastasis)5.Last rapid filling phase/ Atrial systole follows

1.PROTODIASTOLIC PHASE

• Ventricle relaxes• Intraventricular pressure

< pressure in the aorta/Pul.Arteries• Blood flows back from aorta/pul art

into ventricle • SLV closes -Second heart sound

2.ISOVOLUMETRIC RELAXATION

• SLV and AV valves closed• Ventricle relaxes as closed

chamber• No volume change• Intraventricular pressure ↓

3.RAPID INFLOW PHASE

• ↓Intraventricular pressure< intra atrial pressure• Hence AV valves open• Blood flows from atria to ventricle• Third heart sound

4.DIASTASIS

• ↑ in intraventricular pressure due to ↑blood flow from atria• Blood flow from atria to ventricle at

low rate or static• Duration of diastasis variable

During diastole there is passive filling of the relaxed left ventricle. The ventricle does not suck blood into the lumen. Filling is by the venous pressure.

The first sign of activity in the heart is the atrial contraction. This weak structure pushes a small amount of blood into the ventricle (atrial kick)

Blood is also propelled back into the veins giving rise to the A-wave.

Not vital.

Isovolumetric contraction occurs as the ventricle starts to contract. The mitral valve closes The ventricular pressure rises toward aortic pressure .

The mitral valve bulges into the atrium causing the C wave in venous pressure

Ejection phase starts as the aortic valve opens. The ventricular contents are ejected during this time.

Isovolumetric relaxation begins as the aortic valve closes. Ventricular pressure falls from aortic to left atrial during this period.

Diastolic filling begins again as the mitral valve opens Accumulated blood in the atrium rushes into the ventricle

Movement of blood into the ventricle causes venous pressure to drop suddenly causing the V wave

EKG EVENT VALVULAR EVENT

SOUND

P wave Atrial depolarisation

Mitral valve open

(ventricle is filling)

S4(S3 prior to P

wave)

PR interval AV Node conduction

- -

QRS Ventricular depolarization

Mitral valve close

S1

QT interval Ejection phase Aortic valve is open

No sound

T wave Ventricular repolarization

Aortic valve closure

S2

HEMODYNAMIC CHANGES

• Pressure and volume changes in the atria & ventricle during cardiac cycle

• Intra atrial pressure curve• Intraventricular pressure curve• Aortic pressure curve• Ventricular volume curve

INTRA-ATRIAL PRESSURE CURVE

• Pressure changes in the atria is reflected in the veins near the heart, eg.jugular vein

• acv curve – Jugular Phlebogram - JVP

PHLEBOGRAM

• 3 Positive waves – a,c &v• 2 Negative waves x &y

a c v

x y

AS VS VD

1

2 3 4

Venous Pulse

a wave Highest deflection of the venous pulse and

produced by the contraction of the right atrium

Correlates with the PR intervalIs prominent in a stiff ventricle, pulmonic

stenosis and insufficiencyIs absent in atrial fibrillation and other

atrial arrhythmias

Venous Pulse

c waveMainly due to the bulging of the tricuspid

valve into the atrium (rise in right atrial pressure)

Occurs near the beginning of ventricular contraction (is coincident with right ventricular isovolumic contraction)

Venous Pulse

x descent Produced by a decreasing atrial pressure during atrial

relaxationSeparated into two segments when the c wave is

recordedv wave Produced by the filling of the atrium during ventricular

systole when the tricuspid valve is closed Corresponds to T wave of the EKG A prominent v wave would occur in tricuspid

insufficiency and right heart failure

Venous Pulse

y descentProduced by the rapid emptying of the right

atrium immediately after the opening of the tricuspid valve

A more prominent wave in tricuspid insufficiency and a blunted wave in tricuspid stenosis

• A common diagnostic technique is to place catheters at various points in the cardiovascular system and record their pressures.

AS VS VD

Isovolumetric contr

Ejection phase

Protodiastole

Isovolumetric Relax

12

3

4

5

6

Closure of AV Valve

SLV opens

Closure of SLV

AV valves open

7Atrial systole

INTRAVENTRICULAR PRESSURE CURVE

VD

AORTIC PRESSURE CURVE

80

100

120

Incisura

VS VD

1

2

3

4

5

1 – SLV open2 – Max. Ej. Phase2-3 – Reduced Ej. Phase3 – End of Vent. Diastole4 - SLV closes5 – Small positive wave

VENTRICULAR VOLUME CHANGES

VS VD

IVC

IVR A

S

120

60ml

A is atrial systole.

Causes the A wave in atrial pressure.

Helps fill the ventricle.

B is Isovolumic contraction.

It starts with mitral valve closure

Both the aortic and mitral valves are closed so the ventricle’s volume is constant.

C is rapid ejection period.

It starts with aortic valve opening.

Ventricular pressure leads aortic.

Flow out of the ventricle is accelerating.

D is the reduced ejection period.

Aortic pressure leads ventricular.

Flow out of the ventricle is decelerating.

E is the isovolumetric relaxation period.

Begins with aortic valve closure.

Ventricular volume is constant

Gives rise to the V wave as blood accumulate in the atrium

F is the rapid filling period.

Begins with opening of the mitral valve.

Gives rise to the y wave as blood accumulated in the atrium rushes into the ventricle.

y

G is the reduced filling period(diastasis).

Ventricular filling is now in equilibrium with venous return.

Events on the right side are the same except the pressure is lower.

Left ventricular end-diastolic volume (LVEDV)

Left ventricular end-systolic volume (LVESV)

stroke volume= LVEDV-LVESV

 cardiac output = stroke volume x heart rate

Notice the venous pressure trace with A, C and V waves

Since there are no valves between the atrium and veins atrial pressure is essentially equal to venous pressure.

Ventri

Q1. Ventricular filling begins at point?Q2. Closure of mitral valve begins at point?

• The volume and pressure tracings for the left ventricle of a 34 year old male are shown below. Which of the following points correspond to aortic valve opening?

A

B

C

D

E

PRESSURE-VOLUME LOOPS

Q.On the graph showing left ventricular volume and pressure, isovolumetric contraction occurs from point(A) 4 → 1(B) 1 → 2(C) 2 → 3(D) 3 → 4

Q The aortic valve closes at point(A) 1(B) 2(C) 3(D) 4

Q The first heart sound corresponds to point

(A) 1(B) 2(C) 3(D) 4

If the heart rate is 70 beats/min, then the cardiac output of this ventricle is closest to

(A) 3.45 L/min(B) 4.55 L/min(C) 5.25 L/min(D) 8.00 L/min(E) 9.85 L/min

70 140

The ejection fraction equalsa. 0.50b. 0.55c. 0.60d. 0.65e. 0.70

Mechanically Altered States

• Preload• Afterload• Increased contractility• Exercise• Heart failure• Aortic stenosis• Aortic insufficiency• Mitral stenosis • Mitral insufficiency