cardiac cycle Flashcards
cardiac cycle is defined as
the cardiac events initiated by the P wave in the ecg and continuing until the next P wave.
Phase 1
Atrial systole, ventricular diastole
is atrial contraction essential for ventricular filling
no, only accounts for about 10% of LV filling when HR is low but is important during exercise
during phase 1 atrial systole, is the AV valve open or closed
open
during phase 1 atrial systole, are the aortic and pulmonic valves open or closed?
closed
what does the p wave represent
depolarization of the atria.
what does the a wave represent
atrial contraction, pressures within atrial chambers increase.
at the end of phase 1, ventricular volumes are
maximal. (end diastolic volume) ~120ml
Phase 2
isovolumetric contraction. systole.
what is special about the valves in phase 2
all are closed
what causes the x-descent on the atrial tracing
when atrial contraction is complete, atrial pressure begins to fall. this causes a slight pressure gradient reversal across the AV valves. as the pressure falls within the atria, the AV valves float upward before closure.
Phase 3
(systole)rapid ejection
phase 3 aortic and pulmonic valves are
open
phase 3 AV valves are
closed
why does ejection occur?
total energy of the blood in the ventricles exceeds the total energy of the blood in the aorta and PA. an aery gradient is present.
maximal outflow velocity is reached
early in the ejection phase
what heart sounds are typically heart during ejection?
none. the opening of healthy heart valves is silent
x’ descent
occurs as the base of the atria are pulled downward, expanding the atrial chambers (decreasing initial atrial pressure)
what do atria do in phase 3
fill with blood from respective venous inflow tracts. volume is increasing
phase 4
(systole) reduced ejection
during phase 4, aortic and pulmonic valves are
open
during phase 4, AV valves are
closed
what does the T wave represent
ventricular repolarization
phase 5
isovolumic relaxation. (diastole)
phase 5 valves are?
all closed
what causes the second heart sound
closure of aortic and pulmonic valves (a before p)
incisura (dicrotic notch) represents
aortic / pulmonic valve closure
pressure rapidly falls in the ventricle, but aortic and PA pressure..
is not abrupt bc of potential energy in their elastic walls and because systemic and pulmonic vascular resistances impede the flow of blood into distributing arteries of the systemic and pulmonary circulations.
why do ventricular volumes remain constant in phase 5?
because all valves are closed
End-Systolic volume (ESV)
the residual volume of blood that remains in the ventricle.
what is the ESV in the LV?
50ml
stroke volume
the difference between end diastolic volume and end systolic volume.
what is the approx stroke volume in the ventricle
70ml
phase 6
rapid ventricular filling. diastole
which valves are open in phase 6
AV valves
which valves are closed in phase 6
aortic and pulmonic
what contributes to rapid, passive filling of the ventricles?
the ventricles are still relaxing, causing pressures to still fall within them. atrial volumes are maximal just prior to AV valve opening.
what does the v-wave represent
peak of the atrial pressure just before the AV valve opens
what is y descent
opening of the AV valve that causes a rapid fall in atrial pressure
what sounds do AV valves make as they open
none
s3
may occur during rapid filling. tensing of the chord tendinae and AV ring. pathological in adults and often associated with ventricular dilation.
phase 7
reduced ventricular filling (diastole)
phase 7 which valves are open
AV valves
phase 7 which valves are closed
aortic and pulmonic
during what phase is ventricular filling nearing completion
7
as the ventricles fill with blood they become
less compliant (stiff) and pressures rise
without compensatory mechanisms, the cycle length reduction in higher heart rates would cause
less ventricular filling
what phases are part of ventricular systole
2 3 4
what phases are part of ventricular diastole
1 5 6 7
what causes heart sounds
closing of valves
what causes the first heart sound
closure of AV valves
during which phase is the majority of blood ejected from the LV
phase 3 rapid ejection
during which phase does most of the filling of the LV occur
6 rapid ventricular filling
how much does atrial kick usually contribute to ventricular filling
10%
if a person is tachycardia,how much does atrial kick contribute
up to 40%of ventricular filling
during A-fib, what happens to the contribution of atrial contraction to ventricular filling
it is lost, leading to inadequate filling.
