ECG Basics and Cardiac Cycle Flashcards
P wave
SA node causes atria to depolarize from right to left.
QRS complex
Ventricular depolarization from right to left, apex to base and interior to exterior.
ST segment
Action potential phase 2 delays repolarization of ventricles.
T wave
Ventriclar repolarization from left to right.
PR interval
Beginning of P wave until beginning of QR.
QT interval
From beginning of QR to the end of T wave.
PR segment
End of P wave to the beginning of QRS.
ST segment
End of QRS to the beginning of T wave.
Aortic pressures
120/80
Ventricular pressures
120/0
Ventricular volumes
120 mL to 50 mL
Atrial pressures
15/4
Atrial systole
Arial pressure increases as the atria contract. Ventricular pressure mildly increases as blood is pushed from atria to the ventricles.
Ventricular systole
After the atria contract and begin to relax, the ventricles start to contract. The ventricular pressure increases rapidly. Once the ventricular pressure exceeds atrial pressure, the AV valves close and prevent back flow. There is mild increase in atrial pressure as venous blood returns.
What causes the ejection of blood from the ventricles?
When the pressure in the ventricles exceeds the pressure in the pulmonary artery and the aorta.
Isovolumetric contraction
Occurs in ventricular systole.
Ventricular volume remains constant while the pressure increases rapidly.
What pressure does the L and R ventricles have to reach before the AV valves open?
Must exceed the diastolic pressure on each side to open the valve.
Once the pressure in the aorta exceeds ventricular pressure, what happens to volume?
Valves open and volume decreases.
Ventricular diastole
Pressure in the ventricle drops below arterial pressure and the valves close. Aortic and ventricular pressures diverge rapidly.
When the atrial pressure exceeds ventricular pressure, the AV valves will open and blood will passively move into the ventricles.
Dicrotic notch is produced by:
Closing of the aortic valve.
Isovolumetric relaxation
Occurs in ventricular diastole.
No blood enters or leaves the ventricle while it is relaxing because the AV and aortic valves are closed.
Why does blood flow rapidly into ventricles?
Because the ventricular pressure and volume are both very low.
Peripheral runoff
Blood leaving the aorta and flowing into the smaller vessels in the periphery during ventricular diastole.
a wave
Venous pressure created by atrial contraction.
The pressure is reflected backwards.
c wave
Venous pressure wave created by the period of isovolumetric contraction of the ventricles.
v wave
Venous pressure wave created as blood returns back to the heart but cannot enter the ventricle.
