Cardiac Cycle

Cardiac Cycle

• The cardiac events that occur from beginning of one heart beat to the beginning of the next are called the cardiac cycle.

• Initiated by spontaneous generation of AP in SA node.

• Atria act as PRIMER PUMPS for ventricles & ventricles provide major source of power for moving the blood through the vascular system.

CARDIAC CYCLECalculation

For 72 beats time is 60 secFor 1 beat=60/72=0.8 sec

Total duration of each cardiac cycle=0.8sec In Tachycardia /Bradycardia what happen to CC

duration.

Duration

• Cardiac cycle has• a period of relaxation - • Diastole , during which heart fills with blood a period of contraction- Systole during which blood is ejected. Systolic Duration=0.3 sec Diastolic duration=0.5sec

CARDIAC CYCLE

Phases

Phases of Systole Isovolumetric contractionRapid ejectionSlow ejection Phases of DiastoleIsovolumetric relaxationRapid fillingSlow fillingAtrial systole

1-Low pr. System

2.High pr system

3.Heart sound

4.Ventricular volume 5.Jugular VP

6.ECG

Relation

EVENTS INSIDE HEART

PRESSURE & VOLUME CHANGES DURING CARDIAC CYCLE

Atrial Systole

Blood normally flows continually from great veins into atria :

75% flows directly from atria into ventricle before the atria contracts.

25% of filling of ventricles – atrial contraction

Atrial contraction is complete before the ventricle begins to contract.

Atrial SystolePressures & Volumes

• ‘ a ‘ wave – atrial contraction, when atrial pressure rises.

• Blood arriving at the heart cannot enter the atrium so it flows back up the jugular vein, causing the first discernible wave in the jugular venous pulse.

• Atrial pressure drops when the atria stop contracting.

Atrial SystoleECG

• p wave – atrial depolarization• impulse from SA node results in depolarization &

contraction of atria ( Rt before Lt )• PR segment – isoelectric line as depolarization

proceeds to AV node.• This brief pause before contraction allows the

ventricles to fill completely with blood.

Atrial SystoleHeart Sounds

• S4 - end of atrial emptying after atrial contraction. • rapid emptying of atrium into non compliant ventricle• physiological : children , young adults – only recordable • pathological : HOCM, sys.htn, CAD – angina, MI,

ven.aneurysm

Beginning of Ven.SystoleIsovolumetric Contraction

• The atrioventricular (AV) valves close at the beginning of this phase

• Mechanically, ventricular systole is defined as the interval between the closing of the AV valves and the opening of the semilunar valves (aortic and pulmonary valves).

• Electrically, ventricular systole is defined as the interval between the QRS complex and the end of the T wave (the Q-T interval).

Isovolumetric ContractionPressure & Volume Changes

• The AV valves close when the pressure in the ventricles (red) exceeds the pressure in the atria (yellow).

• As the ventricles contract isovolumetrically -- their volume does not change (white) -- the pressure inside increases, approaching the pressure in the aorta and pulmonary arteries (green).

Isovolumetric ContractionECG

• The QRS complex is due to ventricular depolarization, and it marks the beginning of ventricular systole.

Isovolumetric ContractionHeart Sounds

• S1 is d/t closure of AV Valves .

Ejection

• The Semilunar valves ( aortic , pulmonary ) open at the beginning of this phase.

• This at first 1/3 rapid ejection (70%) & remaining 2/3 slow ejection.(30%)

Pressure & Volume Changes• When ventricles continue to

contract , pressure in ventricles exceed that of in aorta & pul arteries & then semilunar valves open, blood is pumped out of ventricles & vol decreases rapidly.

• JVP: c wave- Right ventricular contraction pushes the tricuspid valve into the atrium and increases atrial pressure, creating a small wave into the jugular vein. It is normally simultaneous with the carotid pulse.

ECG & Heart Sounds

• In rapid ejection part of the ejection phase there no specific ecg changes / heartsounds heard.

Slow Ejection

• At the end of ejection, the semilunar valves close.

Slow Ejection

• After the peak in ventricular and arterial pressures , blood flow out of the ventricles decreases and ventricular volume decreases more slowly.

• When the pressure in the ventricles falls below the pressure in the arteries, blood in the arteries begins to flow back toward the ventricles and causes the semilunar valves to close. This marks the end of ventricular systole mechanically.

ECG & Heart Sounds

• T wave – slightly before the end of ventricular contraction

• it is d/t ventricular repolarization

• heart sounds : none

Beginning of DiastoleIsovolumetric relaxation

• Throughout this and the previous two phases, the atrium in diastole has been filling with blood on top of the closed AV valve, causing atrial pressure to rise grad

• JVP - "v" wave occurs toward end of ventricular contraction – results from slow flow of blood into atria from veins while AV valves are closed .

• pressure & volume of ventricle are low in this phase .

Isovolumetric relaxationECG & Heart Sounds

• ECG : no deflections• Heart Sounds : S2 is

heard when the semilunar vlaves close.

• A2 is heard prior to P2 as Aortic valve closes prior to pulmonary valve.

Rapid Inflow ( Rapid Ven. Filling)

• Once AV valves are open the blood that has accumulated in atria flows into the ventricle

Volume changes

• Ventricular volume increases rapidly as blood flows from the atria into the ventricles.

Rapid Inflow ( Rapid Ven. Filling)

ECG & Heart Sounds• ECG : no deflections• Heart sounds : S3 is heard –

Initial passive filling of ventricles

• physiological : children, atheletes, pregnancy

• pathological : HOCM, High output states, MR , AR , ASD,VSD,PDA, sys.htn

Diastasis

• remaining blood which has accumulated in atria slowly flows into the ventricle.

DiastasisVolume changes

• Ventricular volume increases more slowly now. The ventricles continue to fill with blood until they are nearly full.

ECG & Heart Sounds

• ECG : no deflections• Heart Sounds : none

DifferentVolume

• End diastolic vol :During diastole, filling of ventricle increases vol of each ventricle to 110 -120 ml

• Stroke Vol : amount of blood pumped out of ventricle during systole - 70 ml

• End systolic vol : the remaining amount of blood in ventricle after the systole , 40 -50 ml

• Ejection Fraction-