Cardiac+Cycle

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 * =Cardiac Contraction=
 * Muscle contraction initiated by AP originating from the SA node in RA
 * Action potentials depolarize cells which leads to contraction of muscle tissue
 * Depolarization sequence:
 * SA node --> AV node --> His bundle --> Purkinje fibers --> Ventricular myocardium
 * Sequence of contraction: Atria --> AV nodal delay --> Ventricles
 * =Phases of the Cardiac Cycle =


 * ==Systole==
 * Begins with ventricular contraction
 * Ends when ejection ceases
 * ==Diastole:==
 * Initiated with relaxation
 * Begins when ejection ceases as ventricles relax
 * Ventricular filling begins after sufficient relaxation occurs




 * ==Atrial Systole: ==
 * Initiated by depolarization (p wave of ECG)
 *  Occurs near end of diastole
 *  Transiently increased atrial pressure (a wave) --> forcing more blood in ventricles
 *  Accounts ~ 10% at rest, may rise up to 40% during exercise
 * ==Atrial Diastole: ==
 * Blood continuously enters atria, except during atrial systole (transient impedence)
 *  Occurs throughout ventricular systole & diastole, until p wave seen
 *  AV valves open suddenly once LVP < atrial pressure (creating the v wave)
 * Ventricular Systole:
 *  Filled volume is EDV, initiated by ventricular depolarization (QRS on ECG)
 *  LVP increases --> AV valves close --> isovolumetric contraction --> MV/TV closure (s1)
 *  AV/PV opens, repolarization (T wave) initiates relaxation causing ejection rate to rapidly decline
 * <span style="display: block; font-family: Arial,Helvetica,sans-serif; text-align: left;"> ESV: residual volume after ejection
 * <span style="display: block; font-family: Arial,Helvetica,sans-serif; text-align: left;"> LVP < AP --> closure of the AV and ejection ceases
 * ==<span style="display: block; font-family: Arial,Helvetica,sans-serif; text-align: left;">Ventricular Diastole: ==
 * Relaxation initiated by repolarization (T wave of ECG)
 * LVP decreases, outflow valves close, isovolumetric relaxation
 * AV valves open once LV pressure < atrial pressure
 * Most ventricular filling occurs before atrial contraction
 * EDV: maximal filled volume
 * Initially rapid filling phase then slow phase (atrial kick)
 * <span style="display: block; font-family: Arial,Helvetica,sans-serif; text-align: left;">Ventricular stroke volume (SV): EDV-ESV
 * <span style="display: block; font-family: Arial,Helvetica,sans-serif; text-align: left;">In a normal heart, EDV-ESV is the same volume (70ml) of blood as ejected into the aorta during each systolic event.

<span style="display: block; font-family: Arial,Helvetica,sans-serif; text-align: left;">Cardiac Cycle Animation <span style="display: block; font-family: Arial,Helvetica,sans-serif; text-align: left;">[|Anesthesia Labels]

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