The Cardiac Cycle Flashcards
What are the phases of the cardiac cycle?
- atrial contraction
- systolic isovolumetric contraction
- systolic rapid ejection
- reduced ejection phase
- diastolic isovolumetric relaxation
- diastolic ventricular rapid filling
- diastolic ventricular reduced filling
What is the electrical event of atrial contraction?
firing of the SA node (P wave)
What is the mechanical event of atrial contraction?
contraction of atria
What is happening anatomically during atrial contraction?
- av valves open, semilunar valves closed
- 20-40% of ventricular filling
- atrial systole produces “A” wave
What is the electrical event of systolic isovolumetric contraction?
peak of the “R” wave
What is the mechanical event of systolic isovolumetric contraction?
ventricles contract and atria relax
What is happening anatomically during systolic isovolumetric contraction?
- all valves are closed (produces S1 sound)
- no change in volume
- amount of blood in left vent at end of diastole is called EDV (end diastolic volume)
What is the electrical event of systolic rapid ejection?
none
What is the mechanical event of systolic rapid ejection?
- ventricular pressure > arterial pressure
- rapid ejection of blood into arteries occurs
What is happening anatomically during systolic rapid ejection?
- semilunar valves open
- as ventricles contact, av valves bulge back into atria to produce “C” wave
What is the electrical event of reduced ejection?
“T” wave on the ECG
What is the mechanical event of reduced ejection?
ventricular volume decreases then ventricle pressure plateaus and decreases
What is happening anatomically during reduced ejection?
- atrial pressure continues to rise during ejection period because of continued flow of blood into the atria
- produces the “V” in the arterial pressure waveform
What is the electrical event of diastolic isovolumetric relaxation?
as blood impacts the semilunar valves, they snap shut. closure produces the S2 sound
What is the mechanical event of diastolic isovolumetric relaxation?
ventricles relax
What is happening anatomically during diastolic isovolumetric relaxation?
- all valves are closed
- no change in volume
- abrupt shift in aortic pressure and produces the dicrotic notch
What is the electrical event of diastolic ventricular filling?
none
What is the mechanical event of diastolic ventricular filling?
atria have continued to fill and atria pressure exceed ventricular pressure
What is happening anatomically during diastolic ventricular filling?
- av valves open, semilunar valves closed
- lasts 0.1 second and accounts for 60-80% of filling
What must precede mechanical events?
electrical events
What are the keys to the direction of blood flow?
- pressure events
- pressure gradients
What does blood volume rely on?
- chamber filling
- filling pressures
- chamber emptying
What are heart sounds normally associated with?
valve closure
How do you calculate stroke volume?
EDV - ESV = SV
How do you calculate ejection fraction?
EF = (SV/EDV) x 100%
