Wk 3 Flashcards
(20 cards)
what do these components of the ecg indicate
p wave
qrs complez
st segment
twave
qt interval
tp interval
p wave; atrial depolarisation
qrs complex; ventricular depolarisation
st segment; ventricular contraction
twave; ventricular repolarisation
qt interval; complete de/repolaisation of ventricles
tp interval; ventricular filling
where does the P wave start in the heart
in the right atrium and spreads to inferior atrium- there is upwards deflection and moves to postive lead
where does the qrs complex begin in the heart
from the upper right ventricle to the lower left ventricle- there is upwards deflection to the positive lead
where does the t wave move
upwards to the right- it moves to the upwards lead and produces positive deflection
what is the action potential
when cardiac muscle cells are connected by intercalated discs to form a link
cell is activated and AP spreads to adjacent cells by gap junctions- chain effect occurs and the myocardium is activated
myocardial cells act as a unifed mass
The roles of the conducting systems in the heart;
sinoatrial node (SA)
internodal pathways
atrioventricular node (AV)
purkinje fibres, av bundles…
SA: initiates activation of heart
internodal pathways; propagates AP across AV nodes
AV: AP propagates slowly
purkinje; goes fast throughout ventricles
What is the direction of depolarisation of the heart, how long does it take
SA node - atrial depolarisation
Atria + AV node- slow propagation intro av node
AV bundle
R+L bundle branches
Purkinje Fibres
Myocardium
about 250 msec
what is atrial fibrillation (AF)
is a cardiac rhythm disorder; fast irregular heart beart
- activation of SA Is disrupted by rogue electrical signals in pulmonary vein
- risks of blood clot forming
what is ventricular tachycardia
form of arrhythimia due to abnormal electrical activity-irregular heartbeat
what is ventricular hypertrophy and common causes for each side of the heart
LVH: hypertension, aortic sternosis
RVH: pulmonary hypertension. chronic lung disease
Cardiac ischaemia; what does it show
ST depression- early sign of cardiac ischaemia- heart cannot pump as much blood
ST elevation; myocardial infection or blockage of coronary artery
What is the refractory period
- the time after cell fires AP and cannot fire again to heart contraction to continue in skeletal muscle
What are the channels in cardiac muscle cells
Na+, K+, Ca+
What are the 3 stages during contractile cell action
- rapid depolarisation; Na+ entry and closes voltaged gate and opens K+ channels, decrease in positive charge outside cell
- plateau: Ca+ entry, K+ decrease, calcium channels close and opens slow K+ channels
- repolarisation; K+ loss, potassium channels close, restoring resting membrane potental
Membrane potential of SA node; what are the two parts and their purpose
action potential; activation of the cell
pacemarker potential; rise in membrane potential towards threshold- AP initiates here
What is sympathetic stimulation
activation of cardiac sympathetic nerves or hormone; increases slope of pacemaker potential, rate of repolarisation and heart rate
increase in Na+
what is parasympathetic stimulation
activation of cardiac parasympathetic nerves, decrease in the slope of pacemaker potential, rate of depolarisation, heart rate
increase in K+, decrease in Na+
mechanical event following the P wave
Atrial contraction occurs between the P and R waves (following the start of atrial depolarization)
mechanical event following QRS complex
Ventricular contraction occurs between the end of the Q wave and the end of the T wave (following the start of ventricular depolarization).
mechanical event following T wave
ventricles relax
