5.2 - Structural heart diseases 1/2 Flashcards
What are the two main phases of a heartbeat?
- diastole - ventricular relaxation (ventricles fill with blood), lasts approx 2/3 of each beat, split into 4 distinct phases
- systole - ventricular contraction (ventricles generate pressure + eject blood into arteries), lasts approx 1/3 of each beat, split into 3 distinct phases
What are the steps of the cardiac cycle?
- atrial systole (d)
- isovolumetric contraction (s)
- rapid ejection (s)
- slow ejection (s)
- isovolumetric relaxation (d)
- rapid passive filling (d)
- slow passive filling (d)
What shows atrial systole on an ECG?
P-wave
What happens in atrial systole?
- electrical activity of P-wave stimulates atrial muscle contraction
- atria already almost full from passive filling driven by pressure gradient
- atria contract to ‘top-up’ volume of blood in ventricle
Are there any heart sounds in atrial systole?
Usually no heart sounds - might hear S4 (atrial contraction against high ventricular pressure) - abnormal and occurs with congestive heart failure, PE or tricuspid incompetence
What shows isovolumetric contraction on an ECG?
QRS complex marks the start of ventricular depolarisation
What happens in isovolumetric contraction?
- interval between AV valves closing and semilunar valves opening (both are closed)
- contraction of ventricles with no change in volume as closed valves (AV closed as ventricular Pa > atrial Pa)
- ventricular pressure increases to aortic pressure
Are there any heart sounds heard during isovolumetric contraction?
S1 (‘lub’) due to closure of AV valves and associated vibrations
What happens in rapid ejection?
- opening of aortic and pulmonary valves marks start of this phase
- as ventricles contract, pressure within them exceeds pressure in aorta –> SL valves open –> blood pumped out due to pressure gradient and ventricular volume decreases
- rise in aortic pressure and ventricular pressure
Are there any heart sounds during rapid ejection?
No heart sounds as valves opening not closing
What shows slow ejection in an ECG?
T wave (repolarisation phase)
What happens in slow ejection?
- marks end of systole
- reduced pressure gradient means aortic and pulmonary valves begin to close (ventricular Pa < aortic Pa)
- blood flow from ventricles decreases and ventricular volume decreases more slowly
- ventricular muscle cells repolarise
What happens in isovolumetric relaxation?
- SL valves shut (as ventricular < aortic), AV valves remain closed until ventricular pressure drops below atrial pressure
- atrial pressure continues to rise
What is lusitropy?
Rate that ventricular pressure drops due to relaxation
What is the dichrotic notch caused by?
Rebound pressure against aortic valve as distended aortic wall relaxes = due to elasticity of aorta
Are there any heart sounds in isovolumetric relaxation?
S2 (‘dub’) due to closure of SL valves and associated vibrations
What shows rapid passive filling on an ECG?
Occurs during isoelectric (flat) ECG between cardiac cycles
What happens during rapid passive filling?
Once AV valves open (ventricular Pa drops below atrial Pa), blood in atria flows rapidly into the ventricles
Are there any heart sounds heard during rapid passive filling?
S3 - usually abnormal and may signify turbulent ventricular filling, can be due to severe hypertension or mitral incompetence (MS/MR) or congestive heart failure
What happens in reduced passive filling (diastasis)?
- ventricular volume fills more slowly
- ventricles able to fill considerably without contraction of the atria
- aortic pressure decreases, ventricular and atrial pressure fairly stable
What is end-diastolic volume?
Maximum volume of blood in the left ventricle just before the ventricles start to contract (at max relaxation of heart, at isovolumetric contraction)
What is end-systolic volume?
Volume of blood that is left in the left ventricle after contraction has completed (residual blood left in heart)
How do you calculate cardiac output?
CO = HR x SV
How do you calculate stroke volume?
SV = EDV - ESV
