CARDIAC CYCLE

Define "systole" and "diastole."

Systole is the contraction phase, and diastole is the relaxation phase of the heart.

When does atrial systole occur in relation to the ECG?

Atrial systole begins after the P wave on the ECG.

When does ventricular systole begin and end on the ECG?

Ventricular systole starts near the end of the R wave and ends just after the T wave.

What is the role of the AV valves during mid-ventricular diastole?

The AV valves remain open, allowing passive blood flow from the atria to the ventricles.

What occurs during the late ventricular diastole phase?

The SA node fires, causing atrial contraction, which increases atrial pressure and adds more blood to the ventricles.

What is the end-diastolic volume (EDV), and what is its typical value?

EDV is the volume of blood in the ventricle at the end of diastole, typically around 135 mL.

Which ECG wave represents ventricular depolarization?

The QRS complex represents ventricular depolarization.

What causes the first heart sound (S1)?

The first heart sound (S1) is caused by the closure of the AV valves at the start of ventricular systole.

Describe isovolumetric ventricular contraction.

During this phase, all valves are closed, so ventricular pressure increases while volume remains constant.

What occurs during ventricular ejection?

Ventricular pressure exceeds aortic pressure, the aortic valve opens, and blood is ejected into the aorta.

Define stroke volume.

Stroke volume is the amount of blood ejected from the ventricle per beat, typically around 70 mL.

What remains in the ventricle at the end of systole, and what is it called?

• The blood remaining is called the end-systolic volume (ESV), typically around 65 mL.

Which ECG wave indicates ventricular repolarization?

The T wave indicates ventricular repolarization.

What causes the second heart sound (S2)?

The second heart sound (S2) is caused by the closure of the aortic and pulmonary valves at the beginning of ventricular diastole.

Describe isovolumetric ventricular relaxation.

During this phase, all valves are closed, so ventricular pressure drops without a change in blood volume.

When does ventricular filling begin, and what drives it?

Ventricular filling begins when atrial pressure exceeds ventricular pressure, allowing the AV valve to open.

How does atrial contraction aid ventricular filling?

Atrial contraction increases atrial pressure, pushing additional blood into the ventricle.

What does the TP interval on an ECG represent?

The TP interval represents the period after ventricular repolarization and before the next atrial depolarization.

How long is the typical cardiac cycle at rest, and how is it divided between systole and diastole?

The cardiac cycle lasts 0.8 seconds, with 0.3 seconds for systole and 0.5 seconds for diastole.

What happens to ventricular pressure during the isovolumetric contraction phase?

Ventricular pressure rapidly rises as the ventricle contracts with all valves closed.

During which phase does the AV valve open again, allowing blood to flow into the ventricle?

The AV valve opens during early ventricular filling, as ventricular pressure drops below atrial pressure.

How are heart sounds related to valve activity?

The first heart sound (S1) is due to AV valve closure, and the second heart sound (S2) is due to aortic and pulmonary valve closure.

What signals the beginning of a new cardiac cycle on the ECG?

The firing of the SA node, which produces the P wave, signals the start of a new cardiac cycle.