Cardiology - Cardiac Cycle

What does the term 'cardiac cycle' refer to in physiology?

The cardiac events that occur from the beginning of one heartbeat to the beginning of the next.

Which structure initiates each cardiac cycle via an action potential?

The SA node.

In a human cardiac cycle, what is the typical duration of atrial (auricular) systole?

0.1ms

In a human cardiac cycle, what is the typical duration of ventricular systole?

0.3ms

In a human cardiac cycle, what is the typical duration of complete cardiac diastole?

0.4ms

What are the two basic functional stages of the heart as a pump?

Diastole (relaxing and filling) and systole (contracting and ejecting).

During which phase of the cardiac cycle is blood ejected into the ventricles following the P-wave?

Atrial systole.

Which electrical event on an ECG initiates ventricular systole?

Ventricular depolarization (QRS complex).

What occurs during ventricular diastole in terms of blood flow and ECG timing?

The ventricles relax and refill between the T-wave and the next QRS complex.

True or False: The ventricles empty completely during ventricular systole.

False, they do not empty completely.

What is the mathematical relationship between the total duration of the cardiac cycle and the heart rate?

The duration of the cardiac cycle is the reciprocal of the heart rate.

If a patient's heart rate is 72bpm, what is the duration of one cardiac cycle in seconds?

0.833 seconds/beat

End-diastolic volume (EDV)

The volume of blood in the ventricles at the end of each diastole.

End-systolic volume (ESV)

The volume of blood remaining in each ventricle after each systole.

What is the typical end-diastolic volume in a single ventricle of a large dog?

~60mL

What is the typical end-systolic volume in a single ventricle of a large dog?

~30mL

What is the formula for calculating stroke volume?

Stroke volume = End-diastolic volume - End-systolic volume

What is the formula for calculating the ejection fraction?

Ejection fraction = Stroke volume / End-diastolic volume

Which anatomical structure serves as the 'Input' system of the heart?

Veins

Which anatomical structure serves as the 'Output' system of the heart?

Arteries

Which anatomical structure is responsible for the 'Pumping' action of the heart?

Myocardium

Seven distinct phases of the cardiac cycle.,

1. Atrial systole,

2. Isovolumic contraction,

3. Rapid ejection,

4. Reduced ejection,

5. Isovolumic relaxation,

6. Rapid filling, and

7. Reduced filling.

How do the rapid filling and slow filling phases differ during ventricular diastole?

Rapid filling occurs first upon AV valve opening, followed by slow filling (diastasis) as pressures equalize.

What are the two sub-phases of ventricular ejection?

Rapid ejection and slow (reduced) ejection.

What physiological event is represented by the P wave of an ECG?

The spread of depolarization through the atria.

What physiological event is represented by the T wave of an ECG?,

Ventricular repolarization, marking the beginning of ventricular muscle relaxation.

How does the timing of the QRS complex relate to the onset of ventricular systole?

The QRS complex begins slightly before the onset of ventricular systole.

How does the timing of the T wave relate to the end of ventricular contraction?

The T wave occurs slightly before the end of ventricular contraction.

What are the seven specific recordings typically included in a Wiggers diagram?,

ECG, ventricular pressure, atrial pressure, aortic pressure, ventricular blood volume, aortic blood flow, and heart sounds.

Which mechanical event marks the beginning of ventricular systole on a pressure graph?

Closure of the mitral valve.

Which mechanical event marks the beginning of ventricular diastole on a pressure graph?

Closure of the aortic valve.

What does each counterclockwise revolution of a pressure-volume (PV) loop represent?

One cardiac cycle.

In a PV loop, what characterizes 'Phase I: Period of filling'?

Ventricular volume increases from the end-systolic volume to the end-diastolic volume at low pressure.

In a PV loop, what characterizes 'Phase II: Period of isovolumic contraction'?

Ventricular pressure increases to meet aortic pressure while all valves remain closed and volume is constant.

"In a PV loop, what characterizes 'Phase III: Period of ejection'?"

Ventricular volume decreases as blood flows into the aorta while systolic pressure continues to rise and then fall.

In a PV loop, what characterizes 'Phase IV: Period of isovolumic relaxation'?

Ventricular pressure falls back to the diastolic level while all valves are closed and volume is constant.

How do the ventricular blood flow rates compare between the left and right sides of the heart?

The blood flow rates are similar for both sides.

How does the systolic pressure in the right ventricle compare to that of the left ventricle?

Right ventricular systolic pressure is much lower (~20 mmHg) compared to the left (~120 mmHg).

What causes the 'a wave' in an atrial pressure recording?

Atrial contraction.

What causes the 'c wave' in an atrial pressure recording?

The ventricles beginning to contract, causing backward bulging of the AV valves.

What causes the 'v wave' in an atrial pressure recording?

Slow flow of blood into the atria from the veins while the AV valves are closed.

What happens to atrial pressure when the AV valves open following the 'v wave'?

Stored atrial blood flows rapidly into the ventricles and pressure falls.

Why does left ventricular pressure (LVP) rise rapidly during isovolumic contraction?

The ventricle is contracting against closed AV and aortic valves.

What is the 'incisura' (or dicrotic notch) in an aortic pressure curve?

A short period of backward blood flow followed by sudden cessation when the aortic valve closes.

What characterizes the 'Diastasis Period' during the cardiac cycle?

A phase of slow ventricular filling where atrial and ventricular pressures rise slowly together.

At what approximate pressure level is the aorta maintained during diastole?

~80mmHg

Which mechanical event is associated with the first heart sound (S1, 'lub')?

Closure of the AV valves (mitral and tricuspid).

What physical phenomenon actually creates the S1 heart sound?

Momentary vibrations created when the backflow of blood is brought to a sudden stop by closing valves.

Which mechanical event is associated with the second heart sound (S2, 'dub')?

Closure of the aortic and pulmonic (semilunar) valves.

How do the pitch and duration of S2 compare to S1?

S2 is briefer, sharper, and higher pitched than S1.

In the cardiac cycle, which phase occurs between heart sounds S1 and S2?

Ventricular systole.

In which animals are the S3 and S4 heart sounds considered normal findings?

Horses and cows.

What physiological event causes the S3 heart sound?

Recoil of the ventricles during rapid ventricular filling (often due to overfilling).

What is the alternative clinical name for the S3 heart sound?

Protodiastolic gallop or ventricular gallop.

With which event does the S4 heart sound coincide?

Atrial contraction.

What is the alternative clinical name for the S4 heart sound?

Presystolic gallop or atrial gallop.

What does a 'split' first heart sound represent on a phonocardiogram?

The separate mitral (M1) and tricuspid (T1) components of AV valve closure.

What does a 'split' second heart sound represent on a phonocardiogram?

The separate aortic (A2) and pulmonary (P2) components of semilunar valve closure.

Which abnormal heart sound is associated with the opening of a stenotic mitral valve?

Opening snap (OS).

What is the general term for heart sounds of brief duration like S1, S2, S3, and S4?

Transients

What is the primary cause of heart murmurs?

Turbulent blood flow through cardiac defects.

What five criteria are used to classify a heart murmur?

Location (PMI), Timing, Quality, Radiation, and Intensity (Grade).

How is a Grade 1 heart murmur described in terms of audibility?

Barely audible; requires careful auscultation in a quiet environment.

Which grade is assigned to a loud murmur that is audible with a stethoscope not flushed with the body wall?

Grade 6

What clinical finding distinguishes a Grade 5 murmur from a Grade 4 murmur?,

A Grade 5 murmur has a palpable thrill, whereas a Grade 4 does not.

Thrill

A physical vibration felt on the surface of the body caused by a loud heart murmur.

What is the difference between a holosystolic and a merosystolic murmur?

A holosystolic murmur fills the entire systolic period, while a merosystolic murmur occupies only a part of systole.

What is a 'pansystolic' murmur?

A murmur that begins before the end of S1 and ends after the onset of S2.

How is a 'continuous' murmur defined in relation to the cardiac cycle?

It lasts throughout the cardiac cycle from one heartbeat to the next.

Three timing sub-divisions for systolic or diastolic murmurs.

Proto- (first third), Meso- (middle third), and Tele-/Pre- (last third).

A 'presystolic gallop' is another name for which heart sound?

S4

A 'ventricular gallop' is another name for which heart sound?

S3

What does the abbreviation 'PMI' stand for in murmur classification?

Point of maximum intensity.

True or False: Heart murmurs in puppies are always indicative of pathophysiological consequences.

False, some murmurs in puppies are normal.