THE CARDIAC THE CARDIAC CYCLECYCLE

A period from the beginning of one heart beat to the beginning of the next one. It consists of two parts:

1. Contraction called systole.2. Relaxation called diastole

RELATING: Mechanical events in the heart Pressure and volume changes Electrical activity of the heart (ECG) Heart sounds

CARDIAC CYCLE

PHASES OF CARDIAC CYCLE (0.8 PHASES OF CARDIAC CYCLE (0.8 sec)sec) * Phase 1 - Atrial Contraction * Phase 2 - Isovolumetric Contraction * Phase 3 - Rapid Ejection * Phase 4 - Reduced Ejection * Phase 5 - Isovolumetric Relaxation * Phase 6 - Rapid Filling * Phase 7 - Reduced Filling

EVENTS IN CARDIAC CYCLE Atrial systoleVentricular systole (Atrial Diastole)

Isovolumetric contraction Rapid ejectionReduced ejection

Isovolumetric relaxation Rapid ventricular filling Reduced ventricular filling

Next cycle

ATRIAL SYSTOLEATRIAL SYSTOLE

The end of The end of diastolediastole

ATRIAL SYSTOLE - HeartATRIAL SYSTOLE - HeartPrior to atrial systole, blood has

been flowing passively from the atrium into the ventricle through the open AV valve.

During atrial systole the atrium contracts and tops off the volume in the ventricle with only a small amount of blood. Atrial contraction is complete before the ventricle begins to contract.

Duration: 0.1 sec

ATRIAL SYSTOLEATRIAL SYSTOLEECGECG

An impulse arising from the SA node results in depolarization and contraction of the atria (the right atrium contracts slightly before the left atrium).

The P wave is due to this atrial depolarization. The PR segment is electrically quiet as the

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

ventricles to fill completely with blood.

Ventricular Systole (Ventricular Systole (0.3 0.3 sec)sec)

ISOVOLUMETRIC ISOVOLUMETRIC CONTRACTIONCONTRACTIONThe Beginning of systole.......The Beginning of systole.......

ISOVOLUMETRIC CONTRACTION: HeartISOVOLUMETRIC CONTRACTION: Heart

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

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

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).

Duration : 0.03 sec

ISOVOLUMETRIC CONTRACTION: ECG

The electrical impulse propagates from the AV node through the His bundle and Purkinje system to allow the ventricles to contract from the apex of the heart towards the base.

The QRS complex is due to ventricular depolarization, and it marks the beginning of ventricular systole. It is so large that it masks the underlying atrial repolarization signal. the ventricles to fill completely with blood.

RAPID EJECTIONRAPID EJECTION

RAPID EJECTION: HeartRAPID EJECTION: HeartThe SL valves open at the

beginning of this phase.But AV Valves Remain ClosedThis phase represents initial,

rapid ejection of blood into the aorta and pulmonary arteries from the left and right ventricles, respectively

when the intra-ventricular pressures exceed the pressures within the aorta and pulmonary artery, which causes the aortic and pulmonic valves to open

RAPID EJECTIONRAPID EJECTIONECGECG

No Deflections

REDUCED EJECTIONREDUCED EJECTION

The end of The end of systolesystole

REDUCED EJECTION: Heart & ECG REDUCED EJECTION: Heart & ECG Ventricular pressure falls slightly

below outflow tract pressure At the end of this phase the

semilunar (aortic and pulmonary) valves close.

But outward flow still occurs due to kinetic (or inertial) energy of the blood

Repolarization leads to a decline in ventricular active tension and pressure generation;

therefore, the rate of ejection (ventricular emptying) falls

The T wave is due to ventricular repolarization. The end of the T wave marks the end of ventricular systole electrically.

ISOVOLUMETRIC ISOVOLUMETRIC RELAXATIONRELAXATION

The The beginning of Diastolebeginning of Diastole

ISOVOLUMETRIC RELAXATION: HeartISOVOLUMETRIC RELAXATION: Heart Phase starts with closure of the AV

valves When the IV pressures fall sufficiently

at the end of phase 4, the SL valves abruptly close

The aortic and pulmonary artery pressures rise slightly

Valve closure is associated with a small backflow of blood into the ventricles

Although ventricular pressures decrease during this phase, volumes do not change

Left atrial pressure rises because of venous return from the lungs.

ISOVOLUMETRIC RELAXATIONISOVOLUMETRIC RELAXATIONECGECG

No Deflections

RAPID VENTRICULAR RAPID VENTRICULAR FILLINGFILLING

RAPID VENTRICULAR FILLINGRAPID VENTRICULAR FILLINGHeartHeart

Once the AV valves open, blood that has accumulated in the atria flows rapidly into the ventricles.

REDUCED VENTRICULAR REDUCED VENTRICULAR FILLINGFILLING (Diastasis) (Diastasis)

REDUCED VENTRICULAR REDUCED VENTRICULAR FILLING FILLING ECGECG

No Deflections

Pressure Changes in Cardiac CyclePressure Changes in Cardiac Cycle

Heart SoundsHeart Sounds

Primary sounds:S1 & S2

Secondary SoundsS3 & S4

Heart sounds are associated with heart valves closing, causing changes in blood flow.

S1 Closure of AV Valves sudden block of reverse blood flow due to closure of the

BI and TRI cuspid valves. Begins ventricular contraction The papillary muscles are attached to the tricuspid and

mitral valves via chordae tendineae, which bring the cusps or leaflets of the valve closed

– Causes of a loud S1» mitral stenosis» left to right shunts» short PR interval, atrial premature beats» hyperdynamic states

S2 Sudden block of reversing blood flow due to closure of

the semilunar valves (the aortic valve and pulmonary valve)

End of ventricular systole and the beginning of ventricular diastole

Pressure fall in Ventricles after emptying, blood flow quickly reverses back toward the ventricle makes the SL valve cups to be closed

– Causes of a widely split S2» • deep inspiration» • RBBB» • pulmonary stenosis» • severe mitral regurgitation

Gallop RhythmS3

– caused by diastolic filling of the ventricle– youth, some trained athletes, and sometimes

in pregnancyS4

produced by the sound of blood being forced into a stiff or hypertrophic ventricle.

MURMURSHeart murmurs are produced as a result of turbulent flow of blood strong enough to produce audible noise