Exam 3: Heart Part 2: Arrhythmias Flashcards
what sets the normal sinus rhythm
SA node
arrhythmia or dysrhythmia
disruption in normal rhythm
P wave
atrial depolarization
SA node firing, start to get waves across atria
PR interval
depolarization of atria completed, now delay bc reached the AV node, ventricles filling
QRS complex
ventricular contraction - down bundle branches to the purkinje fibers
ST interval
completion of contraction of ventricles
T wav
ventricular repolarization
bradycardia
below 60bpm
tachycardia
above 100bpm
when does a heart block occur
when conductive tissue has been impaired
when communication between SA node and AV node is “blocked”
first degree heart block
still communicating from SA to AV node
lengthened PR interval - so a delay but still getting overdrive suppression
second degree heart block
each P wave does not result in a QRS can be 2:1 or 3:1
drop a QRS - indicative of at least 2nd degree heart block
third degree heart block
complete block
no communication between SA and AV node
AV node set its own pacemaker (ectopic pacemaker)
distance between p waves regular and QRS but would not coordinate with eachother and heart would not fill and pump properly
atrial flutter
SA node gets irritable, atria going very fast in contractions
sawtooth pattern
problem with filling
up to 350 bpm
ventricular flutter
ventricles cannot contract
up to 450 bpm
atrial fibrillation
can lead to ventricular fibrillation
irritability in the muscle: many ectopic sites working at once - get no pattern
see QRS but cannot respond to activity in atria
ventricular fibrillation
no pattern at all
need to look into defibrillation to reset heart so SA node can resume overdrive suppression
things that can cause irritability
inc epinephrine
inc sympathetic stimulation
drugs: caffeine, cocaine, amphetamines, excess digitalis
some toxins
hyperthyroidism
inc stretch of heart muscle
hypoxia - if blood flow impaired to heart get irritable
cardiac output
amount of blood ejected from heart per minute
CO = SV x HR
stroke volume
volume of blood ejected from ventricle per contraction
SV = EDV-ESV
heart rate
contractions per minute
EDV
end diastolic volume
amount of blood in ventricle at end of filling
ESV
end systolic volume
amount of blood left in ventricle after contracting
ejection fraction
EF = SV/EDV
normal range = 55-75%
preload
how much venous return comes back into heart , how it fills and stretches
afterload
ability of heart to contract, force it gives, resistance needed by heart
if lots of resistance, higher afterload - ex: hardening of arteries
frank-starling law
the contraction force of the heart increases as EDV increases
the inc force is due to inc stretching during filling
this allows blood flow to keep up with needs of tissues and organs
bigger preload, stronger the contraction should be
factors affecting venous return
muscle contraction - activity
body position - gravity
venous compliance
the SV will only increase if the afterload…
remains constant
