electrocardiomyography 2 Flashcards
where does a supraventricular arrhythmia start
abvove the SAN
where does a junctional arrhythmia start
in the AVN or bundle branches
where does a ventricular arrhythmia start
in the ventricle muscle itself
what 3 things can a ECG detect
conduction abnormalities
structural abnormalities
perfusion abnormalities
how can you see electrical abnormalities
measuring electrical conduction
how can we see the structural abnormality left ventricular hypotrophy
increase in muscle in L wall - reduce vol
left ventricle to base
L axis deviation
(can tell it is L axis deviation because the axis is deviate clockwise)
what is cardiac axis
the net direction of cardiac depolarisation
how can you tell if there are perfusion abnormalities, ie a blockage in the coronary artery
the tissue is ischemic so cannot contract,
endocardium
inside of the heart
myocardium
muscle
epicardium
outside of the heart
what are the 4 things you do before reading the ECG
check it is the correct recording ie the name
review the signal quality (can be changed by muscular movement, controlled by signals from the brain) and the leads - ie 12 leads, check not noisy
verify the voltage and the paper speeds (paper speed = 25ml/s, V= 10ml/mvol
review the patient and background info - will help to explain things
steps when looking at an ECG
- rate and rhythm - gap between r waves regular, or is rate irregular on rhythm strip, 60-100bpm normal rate
- check the p wave and PR interval - how long takes for wave of depolarisation to go through the atrial myocardium and AVN (meant to impede)
- QRS duration - 160, broad/narrow
- QRS axis
- ST segment - isoelectric, look at height
- QT interval
- T wave - tall and tented/small aand narrow- can see electrolyte disturbance and repolarisation of the heart beat.
characteristics of a sinus rhythm
1:1 ratio of P:QRS - P always followed by QRS
rate regular and normal
otherwise unremarkable
how do you calculate a rate from an ECG
calculate the average number of little squares * 0.04
ANS/60 = rate
what is bradycardia
slow heart
characteristics of sinus bradycardia
1:1 ratio
rate regular
rate slow
can be healthy - just have bigger heart, mediatation, extra vagal (ie PNS stimulation)
quick way to calculate the rate
300/number of big squares
what is tachycardia
fast heart
characteristics of tachycardia
1:1 rate regular rate fast not healthy but it is physiological eg response to overactive adrenal gland/SNS, or SV lower than it should be because of a smaller venous return
why is resting heart rate difficult to measure
always going to be some excitation
in sleep - underestimate
how can you tell axis deviation from an ECG
L axis deviation = L1 +ve, L3 -ve both leaving the paper
R axis deviation = L1 -ve and L3 +ve - both entering the paper
characteristics of sinus arrhythmia
1:1
irregular rate - variable R-R intervals
reading depends on where it is taken
varies with breathing cycle
characteristics of atrial fibrillation
oscillating baseline - atria contract asynchronously
rhythm irregular
rate may be slow
turbulent flow = blood sitting and not circulating = increased clot risk
atria not essential for the cardiac cycle - passive filling does most of it, only important in terms of contraction
QRS normal
T wave present - less obvious because smaller and baseline oscillates
characteristics of atrial flutter
regular sawtooth pattern in baseline in leads 2, 3 and aVF
2:1 or 3:1 or higher
not always visible in all leads
T wave can be obscured or have similar morphology to the P waves
has a vector because regular pattern
duration of the P wave is the same
characteristics of the 1st degree block
prolonged PR segment - slower AV conduction regular rhythm 1:1 benign but progressive disease of aging QRST fine AV valve healthy so no backflow V still contract normally
characteristics of a 2nd degree heart block - Mobitz 1
gradual prolonged PR, until beat is skipped
most P waves followed by QRS, some not
regularly irregular - caused by diseased AVN
also called Wencebach
each part is independently regular
characteristics of a 2nbd degree heart block - Mobitz 2
p wave regular - only some followd by QRS
no P-R prolongation
regularly irregular eg successes: failures 2:1
can rapidly deteriorate into 3rd degree heart block
detected by patient as palpitations
characteristics of 3rd degree heart block
complete
P waves regular, QRS regular - no relationship
P waves can be hidden in bigger vectors
non-sinus ie no pacemaker
pacemaker intrinsic setting at 75bpm
AVN 50bpm
ventricular myocardium- 30bpm
normally because SAN is the highest rate it controls everything
here ventricles act independently
looks like P waves are moving L because they are less frequent than QRS
characteristics of ventricular tachycardia
P waves hidden, dissociated atrial rhythm
V fast and coordinated
need it to be coordinated - other wise it contracts faster than it can fill
rate regular and fast
high risk of deteriorating into fibrillation
shockable rhythm
regular vectors
characteristics of ventricular fibrillation
unable to talk - brain getting no oxygen HR .250bpm heart unable to generate an output shockable rhythm no filling irregular
characterisitics of ST elevation
any deviation- blood flow problem regular rhythm and normal rate P wave visible 1:1 ST segment elevated >2mm above isoelectric line caused by infarction
characteristics of ST depression
regular rhythm and normal rate
P wave visible
1:1
ST segment depressed >2mm below isometric line
caused by myocardial ischemia - coronary arties cannot supply the myocardium with enough O2
