Definition
Events
- Electrical
- Mechanical
- Hemodynamic: Pressure & Volume changes
- Acoustic events: Heart sounds
Atrial Systole & Diastole
Ventricular Systole & Diastole
Heart
Acts as a double pump, i.e. it consists of 2 separate pumps
connected in series
- Right heart pumps blood through lungs
- Left heart pumps blood through peripheral organs
Right heart consists of
- Right atrium
- Right ventricle
Left heart consists of
- Left atrium
- Left ventricle
Atria are the primary pumps for ventricles
Ventricles pumps blood through pulmonary and systemic
circulation
Systole is the contraction phase and Diastole is the relaxation
phase
Heart has Autorhythmicity due to the pacemaker SA Node
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Wigger's diagram |
Cardiac Cycle
Definition
- The sequential cardiac events that occur from the beginning of one heart beat to the beginning of the next
- Duration – 0.8 sec (HR = 75)
Events during Cardiac Cycle
- Mechanical
- Electrical
- Hemodynamic
- Acoustic
Phases of Cardiac Cycle
Two cycles
1) Atrial Cycle
- Atrial contraction / systole (0.1 s)
- Atrial relaxation /diastole (0.7 s)
2) Ventricular Cycle
- Ventricular contraction / systole (0.3 s)
- Ventricular relaxation / diastole (0.5 s)
Pressure and Volume changes during Cardiac Cycle
Significant changes during events of cardiac cycle are
Pressure changes
- Atrial pressure changes
- Ventricular pressure changes
- Aortic pressure changes
Volume changes
- Ventricular volume changes
Atrial systole
Atrial depolarization
↓
Atrial contraction
↓
Atrial pressure rises
↓
Blood flows across AV valves
Coincides with last rapid filling phase of ventricular
diastole
Before beginning of atrial systole: Atria and ventricles
form a continuous cavity
- Ventricles are in relaxed state
- AV valves are opened
- Blood is flowing through great veins into atria and then to ventricles
75% of blood has already flown into ventricles
Rest 25% blood is pumped into ventricles when atria contracts
- Duration: 0.1 sec.
- Mechanical event: Atrial contraction
- Electrical event: Begins from the peak of P wave and ends with the peak of QRS complex
- Haemodynamics: Increase in intra atrial pressure leading to production of ‘a’ wave
- Acoustic event: S4 is recorded in phonocardiogram
Atrial diastole
Atrial repolarisation
↓
Atrial relaxation
↓
Gradual filling of atria from great veins
↓
Atria and ventricles becomes continuous cavity
- Duration: 0.7 sec.
- Mechanical event: Atrial relaxation
- Electrical event: Coincides with ventricular systole and most part of ventricular diastole Haemodynamics: Pressure gradually increases producing ‘v’ wave
- Acoustic event: S1, S2 & S3 is recorded in phonocardiogram
AV Nodal delay
A total delay of 0.16 sec.
This allows Atria to empty their blood into ventricles before its
contraction begins. This increases the pumping efficiency of the heart.
Ventricular Systole (0.3 sec.)
Ventricular depolarisation
↓
Ventricular contraction
Has 2 phases
1) Phase of isovolumic (isometric) contraction
2) Phase of ventricular ejection
- Rapid ejection phase
- Slow / Reduced ejection phase
Phase of isovolumic (isometric) contraction
Ventricles start to contract
↓
Ventricular pressure exceeds Atrial pressure
↓
Closure of AV Valves
↓
Production of First Heart Sound
AV valves closed and Semilunar valves not open
↓
Ventricles
contract as a closed chamber
↓
Pressure inside ventricles raise rapidly
- Duration: 0.05 sec.
- Mechanical event: Ventricular contraction
- Electrical event: Starts from peak of QRS complex
- Haemodynamics: Ventricular pressure rises abruptly from 0 to 80 mmHg, Volume does not change
- Acoustic event: S1 is recorded in phonocardiogram
Sharp rise in ventricular pressure → Bulge of AV valves →
Small sharp rise in intra atrial pressure → Production of ‘c’ wave
Ends with the opening
of semilunar valves
Phase of ventricular ejection
Has two 2 phases
- Rapid ejection phase: Blood ejected rapidly, duration - 0.1 s
- Slow/Reduced ejection phase: Rate of ejection and pressure starts declining, duration - 0.15 s
Rapid ejection phase
- Duration: 0.1 sec.
- Mechanical event: Starts with the opening of aortic valve & steep increase in aortic blood flow
- Electrical event: Corresponds to T wave
- Hemodynamics: Ventricular pressure increase, Aortic pr. also increases but remains below ventricular, Steep fall in ventricular volume
Slow ejection phase
- Duration: 0.15 sec..
- Mechanical event: Decrease in rate of ejection
- Electrical event: Corresponds with ST segment
- Haemodynamics: Ventricular and aortic pressure decreases, but aortic pressure exceeds ventricular pressure, Ventricular volume and aortic blood flow decreases
End diastolic volume
- Volume of blood present in the ventricles after the ventricular diastole = 130 ml
End systolic volume
- Volume of blood present in the ventricles after the ventricular systole = 50 ml
Stroke volume
Volume of blood ejected during from the ventricles during
one systole = 80 ml
Ventricular diastole (0.5 sec.)
Ventricular repolaristaion
↓
Ventricular relaxation
It has 5 phases
- Protodiastole (0.04 s)
- Isovolumic or isometric relaxation phase (0.06 s)
- Rapid passive filling phase (0.11 s)
- Reduced filling and diastasis (0.19 s)
- Last rapid filling phase (0.1 s)
Protodiastole
Ventricles starts relaxing
↓
Intraventricular pressure falls rapidly
↓
Elevated pressure in arteries pushed blood back toward
ventricles
↓
Snaps semilunar valves to close
↓
Production of Second Heart Sound
- Duration: 0.04 sec.
- Mechanical event: Ventricular
relaxation, Dicrotic notch
- Hemodynamics:
Ventricular pressure
decreases, Aortic pressure decreases, but exceeds ventricular pressure, No
significant change in ventricular volume
- Acoustic event: S2 is recorded in phonocardiogram
Isovolumic or isometric relaxation phase
Semilunar
valves closed and AV valves not open
↓
Ventricles
continue to relax as closed chamber
↓
Rapid
fall of pressure inside ventricles
↓
Opening
of AV Valves
- Duration: 0.06 s, begins after closure of semilunar valves
- Haemodynamics: Ventricular and Aortic pressured decreases further, No change in volume – hence Isovolumic relaxation phase
Rapid passive filling phase
AV valves opened
↓
Rapid initial (passive) flow of blood into ventricles
↓
Production of Third heart sound
- Duration: 0.11s
- Mechanical event: 3rd heart sound – not heard normally, may be heard in children
- Haemodynamics: Ventricular pressure starts to increase, Ventricular volume increases gradually
- Acoustic event: S3 recorded in phonocardiogram
Reduced filling and diastasis
- Reduction in blood flow from atria to ventricle
- Slow filling or virtually cessation of ventricular filling – Diastasis
- 75% of blood is already passed to ventricles
- Pressure change: Ventricular pressure increases slightly
- Volume changes: Ventricular volume almost remains same
Last rapid filling phase
- Coincides with Atrial systole
- Remaining 25% of blood is pushed from atria to ventricles
- Cardiac cycle is completed
- Pressure and volume changes in ventricles: Ventricular pressure and volume increases, with a steep increase in volume change
Cardiac cycle: Right vs Left Heart
Both ventricles pump the same volume of blood over any time,
but minor asynchronicity present between two sides
RV starts contracting after LV, but RV ejection begins
before LV ejection – Pulmonary Artery Pr. < Aortic Pr.
Pulmonary and Aortic valve close at same time during
expiration, whereas during inspiration, Aortic valve closes slightly before
Pulmonary valve because of negative intrathorasic pressure during inspiration
Variation in duration of Cardiac cycle
As heart rate increases, duration of cardiac cycle decreases
and vice versa
Change in duration of Cardiac cycle mainly involves change
in duration of diastole
Jugular venous pressure (JVP)
- S1 – Due to closure of AV valves
- S2 - Due to closure of semilunar valves
- S3 – Ventricular filling
- S4 – Atrial systole
