Lecture on Cardiac Cycle by Dr Roomi

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CARDIAC CYCLE

BY

DR. MUDASSAR ALI ROOMI (MBBS, M. PHIL)

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DEFINITION OF

CARDIAC CYCLE:

Period between start of

one beat to start of

next. It consists of one

complete heart beat.

It consists of one systole& one diastole.

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INITIATION OF CARDIAC CYCLE:

Initiated by Cardiac

Impulse, which

originates from SA

node.

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EVENTS THAT OCCUR IN THE

CARDIAC CHAMBERS DURING CARDIAC CYCLE

Pressure Changes.

In ventricles

In atria

Volume Changes. Production of Heart

Sounds.

Closure & Opening of

Cardiac Valves. Electric Changes (ECG

recording).

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VENTRICULAR SYSTOLE 0.31 sec

(Peak of R wave of QRS

complex to the end of T wave)

ISO-VOLUMETRIC CONTRACTION 0.06 secMAXIMUM EJECTION (2/3) 0.11 secREDUCED EJECTION (1/3) 0.14 secVENTRICULAR DIASTOLE 0.52 sec

(End of T wave to the peak

of R wave of QRS complex)PROTODIASTOLE 0.04 secISO-VOLUMETRIC RELAXATION 0.06 secRAPID INFLOW 0.11 secSLOW INFLOW / DIASTASIS 0.2 secATRIAL SYSTOLE (after P wave) 0.11 sec

8 Phases of CARDIAC CYCLE 0.8 sec

8 Phases of CARDIAC CYCLE

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PRESSURE CHANGES:

A) Pressure changes in left

ventricle during cardiac

cycle.B) Pressure changes in right

ventricle during cardiac

cycle.

C) Pressure changes in atria.

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Pressure changes in

Left Ventricle (L.V) during cardiac cycle:

Phase 1 of cardiac cycle / Iso-volumetric contraction ofventricle:

At the start of ventricular systole L.V is full of blood which isequal to EDV.

All the valves are closed. Nochange in blood volume.

Pressure in L.V at the start = 1-3mm Hg.

Then pressure increases to justbelow 80 mmHg.

Duration of I.V.C of Ventricle =0.06 sec.

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Pressure changes in

Left Ventricle (L.V) during cardiac cycle:

Phase 2 of cardiac cycle / MaximalEjection Phase (M.E.P) / RapidEjection Phase (R.E.P):

Ventricle muscle is contractingpowerfully with opening of Aortic

valve.

Blood is ejected from ventricle (2/3of stroke volume) Aorta (atmaximum rate). 70% EMPTYINGoccurs in first 1/3 of ejection phase.

In this phase: I.V.Pmaximum = 120mm Hg.

Duration of M.E.P = 0.11 sec.

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Pressure changes in

Left Ventricle (L.V) during cardiac cycle:

Phase 3 of cardiac cycle / ReducedEjection Phase (R.E.P):

Blood ejection (remaining 1/3 ofstroke volume, 30% EMPTYINGoccurs in last 2/3 time of ejectionphase) from L.V Aorta, continues

but at a reduced rate.

I.V.P falls from maximum.

This phase ends when I.V.P becomesequal to OR

slightly less than AORTIC PRESSURE.

Duration of R.E.P = 0.14 sec.

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Duration of ventricular systole (3 phases):

1. Isovolumetric contraction = 0.06 sec

2. Maximum Ejection Phase = 0.11 sec

3. Reduced Ejection Phase = 0.14 sec

So, Ventricular Systole = 0.31 sec

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Pressure changes in

Left Ventricle (L.V) during cardiac cycle:

Phase 4 of cardiac cycle /Protodiastole:

duration = 0.04 sec.

At the junction of systole & diastole,but included in diastole.

At this stage, I.V.P = Aortic Pressure orI.V.P is slightly less than Aortic pressure,

BUT SMALL AMOUNT OF BLOODCONTINUES TO OOZE, because ofmomentum.

In protodiastole: THIS MOMENTUM ISOVERCOME due to further fall in I.V.P &there is some retrograde flow of Aorticblood in 1st part of Aorta closure ofAortic valve end of Protodiastole.

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Pressure changes in

Left Ventricle (L.V) during cardiac cycle:

Phase 5 of cardiac cycle /

Isovolumetric Relaxation Phase

(I.V.R):

Starts with closure of Aortic

valve. All the valves are closed.

Opening of left AV valve /mitral valve end of I.V.R

phase. Durationof I.V.R = 0.06 sec.

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Pressure changes in

Left Ventricle (L.V) during cardiac cycle

Phase 6 of cardiac cycle / RapidInflow Phase (R.I.P) / Rapidfilling phase (R.F.P):

Starts with opening of mitralvalve.

Blood from Left Atrium rapidlyflows into Left Ventricle.

2/3 of ventricular filling occurs inthis phase (during first 1/3 ofejection phase)

Duration of R.I.P = 0.11 sec.

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Pressure changes in

Left Ventricle (L.V) during cardiac cycle:

Phase 7 of cardiac cycle / Slow InflowPhase / Diastasis:

It appears that: No blood is flowing from Lt.Atrium Lt. Ventricle because:

Only slight filling of Lt. Ventricle in thisphase.

Duration of diastasis / Slow Inflow Phase =0.20 sec.

THE LONGEST PHASE OF CARDIAC CYCLE.

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Pressure changes in

Left Ventricle (L.V) during cardiac cycle:

Phase 8 of cardiac cycle / AtrialSystole:

Last phase of cardiac cycle

Lt. Atrium contracts 20% ventricular

filling by atrial contraction.

Atria contract towards the end ofventricular diastole.

With atrial contraction, ventricularfilling is complete.

Duration: 0.11 sec.

.

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Duration of ventricular diastole (5 phases):

Protodiastole = 0.04 sec

Isovolumetric Relaxation = 0.06 sec

Rapid Inflow Phase = 0.11 sec

Slow Inflow Phase = 0.20 sec

Atrial Systole = 0.11 sec

Ventricular Diastole = 0.52 sec

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Duration of Cardiac Cycle (8 phases):

= Duration ofsystole + diastole =

(0.31) + (0.52) = [0.8 sec]

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Pressure Changes in

Right Ventricle:

Same phases as for Lt. ventricle.

Same duration as for Lt. ventricle.

Only change in pressure levels & in names of valves.

Aortic valve is replaced by pulmonary valve.

Mitral valve is replaced by Tricuspid valve.

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Pressure Changes in

Right Ventricle:

At the beginning of Rt. Vent. Systole:

Pressure = 0-1 mm Hg.

During I.V.C just exceeds 8 mmHg opening ofpulmonary valve

Maximum increase in pressure in Rt. Vent systole =

25 mmHg

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Duration of cardiac cycle &

heart rate:

Duration of cardiac cycle = 0.8 sec at heartrate = 70 beats / min.

When heart rate increases duration of

cardiac cycle decreases. Diastole is more affected as compared to

systole with rapid heart rate.

At heart rate = 180 / min, cardiac cycleduration = 0.33 sec: (systole = 0.18 sec,diastole = 0.15 sec).

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Cardiac output:

Output of heart per unit time = 5 L / min at rest.

Cardiac output = stroke volume x heart rate

= 70 ml x 72 beats / minnearly equal to 5 L / min

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Stroke volume (S.V):

Difference between End Diastolic Volume (EDV) &End Systolic Volume (ESV).

S.V = EDV - ESV

S.V = 120 50

S.V = 70 ml

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EJECTION FRACTION:

Fraction of EDV that is

ejected in one systole or

one stroke = Ejection

Fraction.

Value of Ejection Fraction =

60-65% (usually).

heart failure Ejection

Fraction decreases.

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Volume changes in Ventricles during

Cardiac Cycle:

Beginning of ventricular systole: 130ml (EDV)

Ejection Phases: Maximum Ejection Phase:

2/3 of Stroke Volume (total = 70 ml)

is ejected out.

Reduced Ejection Phase:

Remaining 1/3 is ejected out.

Iso-volumic Relaxation Phase: 50 ml =(ESV)

Rapid Inflow Phase: 2/3 of ventricularfilling.

Diastasis / Slow Inflow Phase: Onlyslight filling occurs.

Atrial Systole: last1/3 filling (30%).

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Pressure changes in Atria during the Cardiac Cycle:

Atrial systole duration =0.11 sec

Atrial diastole duration =0.70 sec

Atrial systole + Atrialdiastole = 0.8 sec = cardiaccycle.

Atrial diastole > Atrialsystole, because basicfunction of atria is toreceive blood from largeveins & it can receive bloodonly when it is relaxed.

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Right atrial pressure =

Central Venous Pressure (CVP).

During most of cardiac cycle, this pressure remains almost

zero.

During wave a, c & v pressure rises. Otherwise remains

almost zero.

4-6 mm Hg Rt. Atrium (during a, c, v)

7-8 mm Hg Lt. Atrium (during a, c, v)

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Pressure changes in Atria during the Cardiac Cycle:

3 waves can be recordedfrom atria whichrepresent atrialpressure changes:

a-wave, c-wave & v-wave (Seen as JugularVenous Pulse, not atrue pulse, but areflection of pressure

changes in right atrium. Two descents: x and y

descent.

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PRESSURE CHANGES IN ATRIA DURING THE CARDIAC

CYCLE:

a-wave: Due to increase

in atrial pressure during

atrial systole.

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PRESSURE CHANGES IN ATRIA DURING THE CARDIAC

CYCLE:

c-wave: Recorded at

beginning ofcontraction of

ventricle. During

isovolumetric contraction,ventricular pressure

increases Cusps of AV

valves are pushed into atrial

cavity pressure rises in

atria ascent of c-wave.

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PRESSURE CHANGES IN ATRIA DURING THE CARDIAC

CYCLE:

The top of c-wavecoincides with openingof semi-lunar valves(Aortic & Pulmonary).

With opening of semi-lunar valves, ejectionphase starts. AV valve ispulled to ventricular

cavity pressure fallsin the atriax-descent

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PRESSURE CHANGES IN ATRIA DURING THE CARDIAC CYCLE:

v-wave: Due to gradualincrease in atrial pressure,resulting from venous fillingof blood (from the venaecavae) into the atria, withclosed AV valves ascentof v-wave.

Top of v-wave coincideswith opening of AV valves

rapid inflow phasedecrease pressure in atriay-descent

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JUGULAR VENOUS PULSE:

(a, c, v waves)

Normally arteriolar pulseends in arterioles & in veins no pulsation.

But we can record pulsationin jugular vein, which is nota true pulse.

It is just backward

transmission of pressurechanges in Rt. Atrium (a, c. vwaves) transmitted in neckveins.

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Significance of J.V.P:

ac interval coincides with PR interval of ECG.

ac interval increases in delayed AV conduction(AV nodal blocks).

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Significance of J.V.P:

a waves are absent in: ATRIAL

FIBRILLATION.

Cannon a WAVES: (a wave) > (c

wave) in COMPLETE AV BLOCK(3rd degree AV block).

Giant a waves in TRICUSPID &

PULMONARY STENOSIS.

Pulsating Neck Veins in CCF

(Congestive Cardiac Failure).

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Closure & Opening of

Heart Valves:

AV VALVES: Are closed at the beginning of

Isovolumic contraction Phase.

Are open at the beginning ofRapid Inflow phase.

AV valve closure is slow & soft &does not require backward flowof blood.

Cusps of AV valves are soft & thinbecause they are not subjected toincrease in pressure & rapidblood flow.

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Closure & Opening of Heart Valves:

SEMILUNAR VALVES:

Are closed at the beginning ofIsovolumic relaxation phase.

Cusps of these valves are thick &

heavier (as they are subjected toincreased pressure & rapid bloodflow).

Their closure is rapid & requires

backward flow of blood (incisurain case of Aortic valve).

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Closure & Opening of both AV & Semilunar

Heart Valves:

Forward pressure gradientopening.

Backward pressure gradientclosure.

AV valves prevent, leakage ofblood from ventricle atria,during ventricular systole (whenpressure rises in ventricle).

Semilunar valves prevent leakageof blood from large arteriesventricles, during ventriculardiastole (when pressure falls inventricle)

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