Heart Flashcards
1st degree AV block
slow AV conduction (long P-R interval)
depolarization gets to ventricles ALWAYS but @ diff. times
AV block
inhibition of conduction through AV node
2nd Degree AV Block
some impulses aren’t conducted through AV node
P not always followed by QRS
Can you hide 2nd degree AV block?
yes by sympathetic stimulation
3rd degree AV block
no impulses conducted across AV node
P & QRS occur but are NOT related in time. P by SA node, QRS by another node
fibrillation
arrhythmia characterized by rapid, repetitive, uncoordinated excitation of myocardium
atrial fibrillation
affects rhythm (irregularly-irregular rhythm) -doesn't lead to ventricular fibrillation because of AV node's refractory period
ventricular fibrillation
rapidly lethal
doesn’t push blood out correctly b/c muscle fibers twitch around the walls and not in a systemic fashion
Premature Ventricular Complex
QRS occurs early
ventricular depolarization does NOT start in SA node
PVC depolarization comes from:
near or above AV node (supraventricular)
septum or ventricular free wall (ventricular)
Supraventricular PVC
QRS has normal shape but not preceded by P wave
specialized conduction system used normally!
Ventricular PVC
QRS is wide & bizarre.
slow depolarization
specialized conduction system not used normally!
PVC stands for
premature ventricular complex
suppression of electrical stimulation for early QRS could be
good
suppression of electrical stimulation for late QRS could be
bad
ECG readings of PVC in lead 2 of LEFT Ventricular PVC
QRS has negative deflection
ECG readings of Right Ventricular PVC in lead 2
QRS has positive deflection
effect of PVC on QRS and T waves
they blend together because with PVC, repolarization is more organized.
normal repolarization is…
less organized than normal depolarization
Normal heart sounds caused by
sudden slowing of a moving column of blood.
normal heart sounds occur when
energy of blood is transferred to valves causing vibrations
normal heart sounds are
s1, s2, s3, s4
S1
closure of AV valves
beginning of systole
in ALL species
S2
closure of aortic & pulmonic valves
end of systole/beginning of diastole
in ALL species
S3
rapid ventricular filling
may occur w/ gallop rhythm
not normally auscultable in dogs/cats
can hear in pregnant mares due to ^ venous return
S4
atrial contraction
immediately before S1
not auscultable in dogs/cats
present but hard to hear in horses
Laminar blood flow
smooth
murmurs
NOT heart sounds
Murmurs def.
abnormal vibrations caused by turbulent blood flow
Murmurs created by
pressure gradients across relatively small holes
murmur lengths
longer than heart sounds
Origins of Murmurs
- Stenosis
- Incompetent (Insufficient) Valves
- Anemia
- Septal Defects/patent ductus arteriosus
Stenosis def
abnormally narrow opening
Stenosis could be
valve or ventricle related.
Example of stenosis
subaortic stenosis = smaller ventricular area
Incompetent (Insufficient) Valve murmurs
valve doesn’t close right & blood regurgitates through “closed” valve
Anemia murmurs
viscosity of blood is lower, making turbulent flow more likely
Septal Defects/Patent Ductus Arteriosus
blood jets through these abnormal openings causing turbulence
Systolic Murmurs
incompetent AV valves
stenosis of pulmonic or aortic valves
ex: sub-aortic stenosis
Diastolic Murmurs
incompetent pulmonic or aortic valves
AV valve stenosis
Point of Maximal Intensity (PMI)
where you can hear each valve sound the best
Pulmonic PMI
low left 3rd
Aortic PMI
High Left 4th
Left AV valve PMI
low left 5th
Right AV Valve PMI
Low Right 3rd-5th
Sinus Rhythm
normal heart rhythm
Sinus Rhythm mechanism
Depolarization starts in SA node
Atria depolarize & contract Right to Left
AV node, AV bundles, L & R AV bundles,
Sinus Rhythm ECG Lead 2
upright P
normal P-R interval
normal upright narrow QRS
T wave
Tachycardia
faster heart rate
Tachyarhythmia
fast abnormal pattern on ECG
bradycardia
slow heart rate
bradyarhythmia
slow abnormal pattern on ECG
Sinus Arhythmia
sinus beat with irregular R-R interval
Sinus Arrhythmia originates
in SA node => upright P wave
Sinus Arrhythmia related to
changes in vagal and sympathetic tone during respiration.
Common in relaxed dogs
Sympathetic stimulation of the heart
- increases contractility strength
- Increases rate of relaxation
- increases heart rate
Sympathetic stimulation of SA node
increases heart rate
how does sympathetic stimulation of the SA node increase heart rate?
increases conductance of Na & Ca leading to hypopolarization of plasma membrane which increases rate of spontaneous depolarization
Sympathetic stimulation of AV node
decreases AV nodal delay
How does sympathetic stimulation of AV node decrease AV nodal delay?
It increases conductance of Na & Ca which increases conduction velocity (^ excitability) and AV node gets better conduction.
Sympathetic stimulation of atrial and ventricular contractile cells
increases contractile strength and increases rate of relaxation
How does sympathetic stimulation increase contraction strength?
It Ca loads the cell.
Plasma mem. Ca channels phosphorylated & open which ^ Ca permeability of cell mem. Phosphorylation of phospholamban stimulates SR Ca pump which increases Ca uptake into SR => more Ca available for release on depolarization
How does sympathetic stimulation increase the rate of relaxation of contractile cells?
^ Ca uptake into Sr & phosphorylation of troponin I via cAMP => decrease in Ca sensitivity of troponin complex => decreased myosin binding
Increasing contraction strength is
positive inotropic
increasing rate of relaxation is
positive lusitropic
Parasympathetic stimulation effects on heart
- slows heart rate
2. increases AV nodal delay
Parasympathetic stimulation of SA node
decreases heart rate
How does parasympathetic stimulation of SA node decrease heart rate?
^ K conducance => SA node hyperpolarization => decrease in If and Ica currents => slower spontaneous depolarization
Parasympathetic stimulation of AV node
increases AV nodal delay (induces 3rd degree AV block)
How does parasympathetic stimulation of AV node increases AV ndoal delay?
^ K permeability => decreased cell excitability => slower/stopped impulse transmission => AV block
Parasympathetic stimulation of SA & AV nodes caused by…
increased vagal stimulation/tone
Type of receptors used in the parasympathetic stimulation of the heart
muscharinic cholinergic receptors
P wave
atrial depolarization
QRS complex
ventricular depolarization
T wave
ventricular repolarization
R wave has
positive deflection ALWAYS
QRS complex doesn’t have
to have all 3 waves
T wave must be
consistent and present. deflection isn’t important
R-R interval
time b/n ventricular depolarization
ventricular rate
measures heart rate
PR interval
AV nodal delay time
ST interval
complete depolarization of ventricle
What about atrial repolarization?
ECG doesn’t show it.
ECG baseline
when heart is at RMP
Why does Lead 2 give us the most info about a heart’s activity?
it cross RV to LV in body & RA to LA
ECG
measure of heart’s ELECTRICAL ACTIVITY
ECGs do not:
detect specialized conduction system activation or give info about mechanical activity (contraction strength)
