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