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CARDIAC CYCLECARDIAC CYCLE

Cardiac CycleCardiac Cycle

 The cardiac events that occur from beginningThe cardiac events that occur from beginning

of one heart beat to the beginning of the nextof one heart beat to the beginning of the next

are called the cardiac cycle.are called the cardiac cycle.

 Initiated by spontaneous generation of AP inInitiated by spontaneous generation of AP in

SA node.SA node.

 Atria act as PRIMER PUMPS for ventricles &Atria act as PRIMER PUMPS for ventricles &

ventricles provide major source of power forventricles provide major source of power for

moving the blood through the vascularmoving the blood through the vascular

system.system.

Atrial SystoleAtrial Systole

 (^) Blood normally flowsBlood normally flows

continually from greatcontinually from great veins into atria :veins into atria :  (^) 75% flows directly thr75% flows directly thr

atria into ventricleatria into ventricle before the atriabefore the atria contracts.contracts.  (^) 25% of filling of25% of filling of

ventricles – atrialventricles – atrial contractioncontraction  (^) Atrial contraction isAtrial contraction is

complete before thecomplete before the ventricle begins toventricle begins to contract.contract.

Atrial SystoleAtrial Systole

Pressures & Volumes Pressures & Volumes

 ‘ a ‘ wave – atrial contraction,‘ a ‘ wave – atrial contraction,

when atrial pressure rises.when atrial pressure rises.

 Blood arriving at the heartBlood arriving at the heart

cannot enter the atrium so itcannot enter the atrium so it

flows back up the jugularflows back up the jugular

vein, causing the firstvein, causing the first

discernible wave in thediscernible wave in the

jugular venous pulse.jugular venous pulse.

 Atrial pressure drops whenAtrial pressure drops when

the atria stop contracting.the atria stop contracting.

Atrial SystoleAtrial Systole

Heart Sounds Heart Sounds

 S4 - end of atrial emptying after atrialS4 - end of atrial emptying after atrial

contraction.contraction.

 rapid emptying of atrium into non compliantrapid emptying of atrium into non compliant

ventricleventricle

 physiological : children , young adults – onlyphysiological : children , young adults – only

recordablerecordable

 pathological : HOCM, sys.htn, CAD – angina, MI,pathological : HOCM, sys.htn, CAD – angina, MI,

ven.aneurysmven.aneurysm

Beginning of Ven.SystoleBeginning of Ven.Systole

Isovolumetric Contraction Isovolumetric Contraction

 (^) The atrioventricular (AV)The atrioventricular (AV) valves close at thevalves close at the beginning of this phasebeginning of this phase

 (^) Mechanically, ventricularMechanically, ventricular systole is defined as thesystole is defined as the interval between the closinginterval between the closing of the AV valves and theof the AV valves and the opening of the semilunaropening of the semilunar valves (aortic andvalves (aortic and pulmonary valves).pulmonary valves).  (^) Electrically, ventricularElectrically, ventricular systole is defined as thesystole is defined as the interval between the QRSinterval between the QRS complex and the end of thecomplex and the end of the T wave (the Q-T interval).T wave (the Q-T interval).

Isovolumetric ContractionIsovolumetric Contraction

ECG ECG

 (^) The QRS complex is due to ventricularThe QRS complex is due to ventricular

depolarization, and it marks the beginningdepolarization, and it marks the beginning of ventricular systole.of ventricular systole.

Isovolumetric ContractionIsovolumetric Contraction

Heart Sounds Heart Sounds

 (^) S1 is d/t closure ofS1 is d/t closure of

AV Valves .AV Valves.

Pressure & Volume ChangesPressure & Volume Changes

 (^) When ventriclesWhen ventricles

continue to contract ,continue to contract , pressure in ventriclespressure in ventricles exceed that of in aortaexceed that of in aorta & pul arteries & then& pul arteries & then semilunar valves open,semilunar valves open, blood is pumped out ofblood is pumped out of ventricles & volventricles & vol decreases rapidly.decreases rapidly.  (^) JVP: c wave- RightJVP: c wave- Right

ventricular contractionventricular contraction pushes the tricuspidpushes the tricuspid valve into the atriumvalve into the atrium and increases atrialand increases atrial pressure, creating apressure, creating a small wave into thesmall wave into the jugular vein. It isjugular vein. It is normally simultaneousnormally simultaneous with the carotid pulse.with the carotid pulse.

ECG & Heart SoundsECG & Heart Sounds

 (^) In rapid ejectionIn rapid ejection

part of the ejectionpart of the ejection phase there nophase there no specific ecgspecific ecg changes /changes / heartsounds heard.heartsounds heard.

Slow EjectionSlow Ejection

 (^) After the peak in ventricularAfter the peak in ventricular

and arterial pressures , bloodand arterial pressures , blood flow out of the ventriclesflow out of the ventricles decreases and ventriculardecreases and ventricular volume decreases more slowly.volume decreases more slowly.  (^) When the pressure in theWhen the pressure in the

ventricles falls below theventricles falls below the pressure in the arteries, bloodpressure in the arteries, blood in the arteries begins to flowin the arteries begins to flow back toward the ventricles andback toward the ventricles and causes the semilunar valves tocauses the semilunar valves to close. This marks the end ofclose. This marks the end of ventricular systoleventricular systole mechanically.mechanically.

ECG & Heart SoundsECG & Heart Sounds

 (^) T wave –T wave – slightlyslightly

before the end ofbefore the end of ventricularventricular contractioncontraction

 (^) it is d/t ventricularit is d/t ventricular

repolarizationrepolarization

 (^) heart sounds :heart sounds :

nonenone

Isovolumetric relaxationIsovolumetric relaxation

ECG & Heart Sounds ECG & Heart Sounds

 (^) ECG : no deflectionsECG : no deflections

 (^) Heart Sounds : S2 isHeart Sounds : S2 is

heard when theheard when the semilunar vlavessemilunar vlaves close.close.

 (^) A2 is heard prior toA2 is heard prior to

P2 as Aortic valveP2 as Aortic valve closes prior tocloses prior to pulmonary valve.pulmonary valve.

Rapid Inflow ( Rapid Ven.Rapid Inflow ( Rapid Ven.

Filling) Filling)

 (^) Once AV valves are openOnce AV valves are open

the blood that has the blood that has accumulated in atria flows accumulated in atria flows into the ventricle into the ventricle