The Cardiac Cycle and Hemodynamics

Flashcards covering the physiology of the cardiac cycle, Klabunde's seven-phase model, Wiggers diagram landmarks, ECG electrical correlations, pressure-volume relationships, and heart sounds.

Cardiac cycle

lasts approximately $0.8\,\text{seconds}$ at a resting rate of $75\,\text{beats per minute}$.

Systole

encompasses isovolumetric contraction, rapid ejection, and reduced ejection.

Diastole

encompasses isovolumetric relaxation, rapid filling, reduced filling (diastasis), and atrial contraction.

End-diastolic volume (EDV)

The volume of blood in a ventricle at the end of filling

End-systolic volume (ESV)

The volume of blood remaining in a ventricle after ejection

Stroke volume (SV)

The volume of blood pumped out of the heart per beat, defined mathematically as $SV = EDV - ESV$.

Ejection fraction (EF)

The fraction of end-diastolic volume expelled during systole, calculated as $EF = \left(\frac{SV}{EDV}\right) \times 100\%$.

Phase 1: Atrial contraction (atrial systole)

The first phase of the cardiac cycle where the atria contract, forcing blood into the ventricle.

a wave

ventricle at edv

Phase 2: Isovolumetric contraction

the first heart sound ($S1$) occurs as av valve closes

ventricle still at edv with no blood flow

c wave

Phase 3: Rapid ejection

pressure reaches peak and then flows to outflow tracts and then ventricle volume falls

Phase 4: Reduced ejection

during which forward flow diminishes, ventricular pressure falls, and volume reaches the end-systolic volume.

atria start refilling

Phase 5: Isovolumetric relaxation

semilunar valves close producing s2

aortic closure produces dicrotic notch

ventricle volume stays at esv

Phase 6: Rapid filling

av valves open and blood flows passively into ventricles

Phase 7: Reduced filling

slowed filling and atrial and ventricle pressure are starting to even out

ends with diastasis

diastasis

longest phase of the cardiac cycle before atrial contraction and ventricles are 90% full atp

c wave

An atrial pressure elevation caused by the retrograde bulging of the closed atrioventricular valves into the atria during early isovolumetric contraction (phase 2).

v wave

An atrial pressure elevation reflecting passive venous filling against closed atrioventricular valves throughout ventricular systole, peaking immediately prior to AV valve opening.

First heart sound (S1)

The auditory event signaling the beginning of isovolumetric contraction (phase 2), produced by the closure of the atrioventricular valves and surrounding tissue vibrations.

Second heart sound (S2)

The auditory event signaling the onset of isovolumetric relaxation (phase 5), produced by the closure of the semilunar valves.

Third heart sound (S3)

A low-frequency heart sound occurring during phase 6 that is associated with rapid passive ventricular filling.

Fourth heart sound (S4)

An abnormal heart sound occurring during phase 1 immediately before $S1$, generated by active atrial contraction into a stiff or non-compliant ventricle.