Cardiac Cycle

CARDIAC CYCLE

• Cardiac Cycle=All events that occur from one heartbeat to the next
• Diastole, filling stage. 2/3 of cardiac cycle. All about pressure changes so as blood fills in atria, pressure increases, currently pressure is 0 in ventricles, so blood starts to flow.
• Systole, pumping stage. 1/3 of cardiac cycle. Ventricular muscles contract and forces blood through the semi lunar valves into the aorta and pulmonary artery. Chordae Tendinae holds the AV valves in place.
• Ejection phase starts when AV valves SHUT to prevent back flow
• Some Key Formulas
• Cardiac Output= STROKE VOLUME X HEART RATE
• Ejection Fraction= EDV - ESV / EDV
• Mean Blood Pressure= DBP + 1/3 (SBP-DBP)
• EDV: Volume of blood in VENTRICLE after diastole
• ESV: Volume of blood in ventricle after end of systole

How the cardiac cycle is maintained

• SAN sends wave of electrical
• activity across atria causing atrial contraction. It begins at the right atrium as thats where SAN is but then the impulse travels across Bachmann's bundle to left atrium.
• Non-conducting tissue prevents
• immediate contraction of
• ventricles/prevents impulses
• reaching the ventricles
• AVN delays (impulse) whilst blood
• leaves atria/ventricles fill
• (AVN) sends wave of electrical
• activity / impulses down Bundle of
• His;
• Causing ventricles to contract from
• base up
• Remember the pressure changes, pressure forces valves open, as blood fills, pressure increases. Blood always moves from an area of high pressure to area of low pressure