Cardiac Cycle Flashcards
What is the ejection fraction
The percentage of blood leaving the heart each beat
Stroke volume/end diastolic volume(amount of blood left in ventricle after diastolic filling)
What is cardiac output
Amount of blood pumped out per minute
Stroke volume x heart rate
What is stroke volume
Amount of blood pumped out during systolic contraction
How to calculate cardiac cycle duration
60 seconds/heart rate (BPM)
E.g 60/75=0.8s per cycle
What is the path of electrical conduction in the heart
SAN - AVN - bundle of his - left/right bundle branch - purkinje fibres
Fibrous tissue which separates the atria and the ventricles prevents the electrical signal from passing directly into the ventricles. Instead the electrical activity depolarises the atrioventricular node cells, which in turn depolarises the Bundle of His and subsequently the Purkinje fibres, which spreads down the midline of the heart to the apex and back around to depolarise the walls of the ventricles
What are the steps of the cardiac cycle
- Atrial systole
- Isovolumetric contraction
- Rapid ejection
- Reduced ejection
- Isovolumetric relaxation
- Rapid passive filling
- Reduced passive filling
What occurs during atrial systole and why is there sometimes an abnormal 4th heart sound
The p wave on ECG shows start of atrial systole
Ventricles already almost full due to passive filling from pressure gradient, the atria contract to top up volume
The abnormal 4th heart sound is caused by ventricular hypertrophy leading to a ventricular vibration
What occurs in Isovolumetric contraction
QRS complex marks start of ventricular depolarisation
It is the interval between the tricuspid/mitral valves closing and the pulmonary and aortic valves opening
Contraction of ventricles with no change in volume
1st heard sound - lub - due to closure of AV valves
What are the complications of atrial fibrillation
The loss of coordinated atrial contraction does not often present with any significant clinical concern
However it can risk increase of thrombosis due to the turbulence of blood, this can travel to the brain and cause a stroke
What occurs during rapid ejection
Opening of aortic and pulmonary valves as pressure in the ventricles exceeds that of the pulmonary arteries and aorta
What occurs during reduced ejection
It is the end of systole
The pressure gradient in ventricles fall so aortic and pulmonary valves begin to close
What occurs during Isovolumetric relaxation
The aortic and pulmonary valves are closed - and the triscupid and mitral valves are also closed until ventricular pressure drops below atrial pressure
Atrial pressure increases, the dichrotic notch is caused by rebound pressure against the aortic valve as distended aortic wall relaxes
2nd heart sound - dub - due to closure of semilunar valves and associated vibration
Because of higher pressure, aortic valve opens last and closes first, Mainly seen during inspiration. Results in split S2
What occurs during rapid passive filling and why does the abnormal 3rd heart sound occur sometimes
Occurs during isoelectric T-P segment
AV valve open and blood rapidly rushes into ventricles
3rd heart sound – normal in children and pregnancy, otherwise abnormal. Caused by overfilling of ventricle resulting in recoil. Termed protodiastolic gallop or ventricular gallop
What occurs during reduced passive filling
Ventricular volume slowly considerably without the contraction of the atria.
How does the Jugular venous pressure differ during the cardiac cycle
Peak a – caused by contraction of the right atrium
AV trough – due to relaxation of the right atrium and closure of the tricuspid valve
C peak - early ventricular systole results in bulging of the tricuspid valve, reflecting this pressure change into the veins
X minimum – ventricle contracts and shortens during ejection phase of the cardiac cycle. The shortening of the heart, along with the closed tricuspid valve, pulls on the jugular vein leading to a pressure drop
V peak - right atrium fills against a closed tricuspid valve, causing right atrial pressure (and subsequently JVP) to rise. Opening of the tricuspid valve leads to the subsequent drop in pressure
Y minimum – fall in right atrial pressure during rapid ventricular filling. The increase in pressure following y occurs as ventricular filling slows.
