L8 - electrical & mechanical events of cardiac cycle Flashcards
what is the order an impulse travels through the heart
SA node through atrial wall to AV node (pause) bundle of His purkinje fibres apex
what does slower diastolic depolarisation of the SA node lead to
slower HR
what determines the rate of depolarisation of the SA node
funny current (pacemaker current ) If
carried through HCN channels
increased size of funny current =
faster depolarisation - faster HR
what is the purpose of the pause at the AV node
allows ventricle filling
prevents transmission of many impulses (Atrial fibrillation)
what is P wave
atrial depolarisation
what is QRS wave
ventricular systole
what is Q point
depolarisation of septum towards atria
what is R point
depolarisation of ventricles towards apex
what is S point
depolarisation of ventricles towards atria
what is T wave
ventricular repolarisation
why cant atrial repolarisation be seen?
obscured by ventricular systole
what does the P-S interval represent
atrial AP
what does the Q-T interval represent
ventricular AP
how are intervals measured eg Q-T
from the start of Q to the start of T (not including T)
what is the P-Q interval duration a measure of
atrial conduction + AV node delay
what is QRS duration a measure of
speed of ventricular conduction from top to bottom
what is S-T interval
segment where entire ventricle is depolarised
what can a change in a patients S-T segment show?
part of the ventricles are not depolarising as they should - could be a sign of myocardial infarction
what is isovolumetric contraction
when ventricle is full of blood and contracts but SL valves aren’t yet open so pressure increases but volume stays the same
when do SL valves open?
when the pressure inside ventricle is higher than either aorta or pulmonary artery
what is the dichroitic notch
the point at which ventricle is emptying and its pressure falls below the aortic pressure so aortic AL valve shuts
what is isovolumetric relaxation
the period after SL valve has shut so volume inside ventricle stays the same but the ventricle is relaxing so pressure decreases
how is stroke vol calculated from pressure volume loop
width of loop
distance from the left line (lowest vol) to right line (highest vol)
how is stroke work measured from pressure volume loop
area of loop
if heart working harder - bigger area
what is ejection fraction
fraction of blood in heart at the end of diastole (when ventricle is full), that is ejected with each beat
what is ejection fraction formula
SV/ EDV x 100
what nerves innervate SA node
SNS - accelerator nerve
PSNS - vagus
is conduction quicker through atria or ventricles
ventricles
