Cardiac Cycle Flashcards
What fraction of time does the heart spend in diastole? Systole?
Diastole = 2/3 Systole = 1/3
True or false: the cardiac cycle reduces in time in equal proportion to the increase in heart rate
False–not exactly proportional, although they are inversely related
Where are the precordial leads positive (toward the outside of the body, or on the inside near the heart)?
Outside, on the body wall
What is R wave progression?
The fact that the R wave increases in amplitude as your move through the precordial leads
What is corresponding event in the cardiac cycle to depolarization of the SA node?
Blood is returning to the right atrium
What is corresponding event in the cardiac cycle to atrial depolarization?
Atrial contraction
What is corresponding event in the cardiac cycle to depolarization of the AV node (specifically, the delay here)?
Ventricular filling
What is corresponding event in the cardiac cycle to depolarization of the bundle of His and the Purkinje fibers?
Ventricular contraction
What is corresponding event in the cardiac cycle to ventricular depolarization?
Blood expulsion to lungs or periphery
What are the units for cardiac cycle?
time/beat (inverse of HR, but not proportional)
True or false: diastolic periods reduce less proportionally than systole when you increase the heart rate
False–more than proportionally (i.e. as the heart rate goes up, the heart spends a larger amount of time in systole than would be expected if it were a linear relationship)
When is the heart perfused, during diastole or systole?
Diastole
When does isovolumic contraction occur, in ventricular systole or diastole?
Ventricular systole
When does isovolumic relaxation occur, in ventricular systole or diastole?
Ventricular Diastole
When does rapid ejection occur, in ventricular systole or diastole?
Ventricular systole
When does rapid filling occur, in ventricular systole or diastole?
Ventricular Diastole
When does atrial systole occur, in ventricular systole or diastole?
Ventricular Diastole and systole (bridges the two)
When does reduced ejection occur, in systole or diastole?
Ventricular systole
What are the seven periods of the cardiac cycle?
- Atrial systole
- Isovolumic contraction
- Rapid ejection
- Reduced ejection
- Isovolumic relaxation
- Rapid filling
- Reduced filling
What accounts for the increase in atrial pressure in the isovolumic ventricular contraction phase?
AV valve will bulge back into atrium
What accounts for the steady increase in atrial pressure in the rapid and reduced ventricular ejection phases?
Refilling of the atria from the venous system
What accounts for the drop in the atrial pressure in the rapid filling phase of the ventricle?
Blood flowing from atria and into the ventricles
What is the “a” wave in the atrial pressure curve?
The contraction of the atria
What causes the AV valves to close?
Atrial pressure dropping below the ventricular
What is the purpose of the chordae tendiae?
Ensure that the AV valves do not fold back into the atria (do NOT pull the valves open as is commonly believed)
What is the event that corresponds to the “c” wave of the atrial pressure curve?
The bulging of the AV valves back into the atria
What is occurring in the atria as the ventricles contract?
They fill
When in the cardiac cycle do the AV valves open (what is the corresponding event in the ventricles)?
Ventricular isometric relaxation
What does the “v” point on the atrial pressure curve correspond to?
Opening of the AV valves
Pathologic increases in right atrial pressure leads to what physical exam finding?
JVD
What relieves the increase in the atrial pressure that is caused by the AV valves bulging back?
Overall contraction of the heart
In what phase does the ventricular pressure increase dramatically?
Isovolumic contraction
What causes the increase in ventricular pressure during atrial systole?
Movement of blood into the ventricles from the atria
What is the “atrial kick”? What effect does this have on ventricular filling?
An expulsion of blood into the ventricle from the atria
Fills about another 15-20%
True or false: in a normal, healthy individual, the atrial kick does not do much. It utilized more if the heart is under stress
True
What causes the isovolumic stage of ventricular contraction to end? What is the next stage?
Opening of the semilunar valves
Next stage = repid ejection
What does the aorta do to accomodate the rapid rise in pressure?
Balloons out
For what fraction of time does the rapid ejection phase last compared to total systolic time?
1/3
For what fraction of time does the reduced ejection phase last compared to total systolic time?
2/3
What does the end of the ejection phase/ start of the isovolumic relaxation phase correspond to on an EKG?
T wave
What causes the reduced ejection phase to end?
Closure of the semilunar valve
What causes the end of the isovolumic relaxation phase?
Opening of the AV valve
What happens to both the ventricular and atrial pressure in the rapid fillig phase? Why?
Falls, because there is passive distention of the walls
What causes the reduced filling phase / increase in pressure in the atria and ventricles?
Active expansion of the walls of the heart
What is the only factor that determines valve opening/closure?
Pressure differentials
When does the abrupt rise in the aortic pressure curve end (which ventricular phase)?
Start of the rapid ejection phase
What is the effect on systolic pressure of the aorta expanding to accommodate the blood its receiving?
Lowers the pressure
What is the effect on the the aorta expanding to accommodate the blood its receiving on the flow of blood (once the valves are shut, that is)?
Increases the flow
Why don’t the semilunar valves close after the ventricular pressure has fallen below aortic pressure?
Momentum of blood
What accounts for the dicrotic notch (incisura) of the aortic pressure curve?
Due to the backward pressure wave returning from the periphery
What causes the backward pressure wave (P aug on her graph) in the aorta?
The reflection of the pressure wave when it hits the bifurcation
What is the first upstroke in pressure in the aorta caused by?
Blood flow from venticle to aorta
What is the second upstroke in the pressure in the aorta caused by? (the “first shoulder”)
Due to the backward pressure wave returning from the periphery
What is the third upstroke in the pressure in the aorta caused by? (the “secondshoulder”)
Systolic ejection
What are the two major effects of a calcified aorta on aortic pressure? Why? (hint: one answer is obvious, the other has to do with the reflected pressure wave from the bifucation)
Increases greatly, because it cannot accommodate the rapid increase in pressure from the heart, AND the fact the blood flows faster through the calcified aorta down the artery, causing a larger reflected wave
What determines the slope (rate) of the aortic pressure drop after systole?
The pressure in the periphery of the body
What would happen to the slope of the aortic pressure line if peripheral resistance increased?
Become flatter
What are the three events (in order) that occur when the AV valve opens?
Rapid ventricular filling
Decreased filling (diastasis)
Atrial contraction
What happens once the AV valve closes?
isometric contraction
What are the two events that occur when the semilunar valves open?
Rapid ventricular ejection
Decreased ventricular ejection
What occurs when the semilunar valve closes?
Isometric relaxation
When does the opening of the AV valves occur (systole or diastole)?
diastole
When does the closing of the AV valves occur (systole or diastole)?
Systole
When does the opening of the semilunar valves occur (systole or diastole)?
Systole
When does the closing of the semilunar valves occur (systole or diastole)?
Diastole
Through which period(s) of the cardiac cycle are the AV valves open?
(atrial systole, iso contract, rapid ejec, reduced ejec, iso relax, rapid filling, or reduced filling)
Atrial systole, then rapid and reduced filling
Through which period(s) of the cardiac cycle are the semilunar valves open?
(atrial systole, iso contract, rapid ejec, reduced ejec, iso relax, rapid filling, or reduced filling)
Rapid ejection and reduced ejection
When, in the cardiac cycle, are no valves open?
atrial systole, iso contract, rapid ejec, reduced ejec, iso relax, rapid filling, or reduced filling
Iso contraction and iso relaxation
Review all of the things, including the ventricular volume changes during the cardiac cycle.
Don’t you dare click 5 yet
What is the stroke volume?
The LVEDV - LVESV
left ventricular end diastolic volume - end systolic volume
What cardiac event does S1 correspond to?
Closure of the mitral and tricuspid valves
What cardiac event does S2 correspond to?
The closure of aortic and pulmonary valves
What causes the physiological splitting of S2?
Delayed closure of the pulmonic valve OR
Early closure of the aortic valve
Why would the pulmonary valve close late with inspiration (in terms of physiological splitting of S2)?
Greater venous return to the right heart increases the time it takes to expel all of the blood
Why would the aortic valve close early with inspiration (in terms of physiological splitting of S2)?
Less blood returns to the left heart, so less time to change the pressure and close the valve
If physiological splitting occurs, which event always comes first: closing of the aortic valve, or pulmonary valve?
Aortic before pulmonic
When is an “opening snap” heard? What does this correspond to physiologically?
may be heard if the mitral or tricuspid is hard to open (e.g. in mitral stenosis d/t very fibrous, calcified mitral valve)
What causes S3?
When the ventricular myocytes reach their maximum passive stretch length, and the chordae tendinae and AV ring are pulled taut by the stretched ventricle.
What causes S4?
Pathological increase in ventricular pressure at the end of atrial systole (a stiffer ventricle)
What causes a diastolic murmur?
Mitral valve stenosis
What can cause a systolic murmur?
Leaflets not closing completely, causing turbulent blood flow through a partially closed valve
What could be the causes of paradoxical splitting?
Any pathology that causes an increase in conduction through one ventricle more than another
In a LBB, will a split be heard with inspiration or expiration? Why?
Expiration, since LV ia already delayed, and since the split will manifest itself as the pulmonic valve closing before the aorta
