Session 6- Interpreting ECGs Flashcards
deflection
deviation from straight line- in ECG either an upward or downward wave/peak from the baseline
how many views does a ECG provide
12
what is excitation-contarction coupling
depolarisation wave causes coordinated contraction of atria and ventricles
sinoatrial node
- fastest rate of depolarisation in the heart - suppresses other pacemakers
- intrinsic firing rate 50-100 times/minute
- sets heart rate and rhythm- sinus rhythm
atrioventricular node
slows conduction
gives them to atria to contract before ventricles
intrinsic firing rate without stimulation (such as from the SA node) 40-60 times/minute
what are the - LBB RBB
ventricular electrical conducting system cells also have am intrinsic firing rate although this is NOT typically manifested
intrinsic firing rate 20-40 times/minute so slow
how does electrical activity spread throughout the heart
initiated at SA node
depolarisation right atrium and left atrium
hits AV
from AV to bundle of His- wide conducting muscle fibres that travel through Annulus Fibrosus
bundle of his to interventricular septum then dividides into LBB and RBB
RBB and LBB terminate in extensive network of fast conducting fibres- pukinje fibres
annulus fibrosus
separates atria from ventricles
what does an ecg do
electrocardiogram
measures changes in electrical potential (in mVolts) produced in successive areas of myocardium during cardiac cycle via a series of LEADS
what does a ECG lead
1) cable used to connect electrode to ECG recorder
2) electrical view of the heart obtained from any one combination of electrodes
what is an electrode
is conductive pad is attached to skin and enables recording of electrical currents
what is the grounding electrode
right leg electrode
what are the chest leads
v1 v2 v3 v4 v5 v6
which leads are bipolar
Limb Leads I, II, III
negative and positive electrode
limb lead 1
voltage difference between electrode RA and LA; LA (+) electrode
limb lead II
voltage difference between electrode RA and LL; LL (+) electrode
limb lead III
voltage difference between electrode LA and LL; LL (+) electrode
what are the augmented limb leads
aVR, aVL and aVF unipolar
only have a positive electrode
aVR
right arm
LL1
aVL
left arm
LL2
aVF
left leg- f for foot
LL3
septal leads
v1 and v2
anterior leads
v2 v3 and v4
lateral precordial leads
v4 v5 and v6
what determines the height of deflection
how directly depolarisation wave is coming towards from the positive electrode and the number of cells generating the signal
what is the p wave
atrial depolarisation- spreads along atrial muscle fibres and internodal (SA-AV) pathways
-direction- downwards and to the left towards AV
what is the isoelectric flat line segment
conduction slowed at AV to allow atrial contraction to fill ventricle
signal very small
R wave
a large upward deflection
upward because depolarisation moving directly towards electrode
large because large muscle mass- more electrical activity
if left ventricle is hypertrophied- R wave will be correspondingly taller
s wave
Downward because moving away
small because not moving directly away
depolarisation finally spreads upwards to the base of the ventricles
ventricular repolarisation
begins on the epicardial surface of the heart
spreads in the opposite direction to depolarisation
produces a medium upward deflection- T wave
why is the t wave upwards
it is a wave of repolarisation moving away from electrode- when repolarisation moves AWAY from lead produces upward deflection- in comparison with when depolarisation moves away from lead produces a negative deflection
QRS
depolarisation of ventricles not contraction of ventricles
what limb leads look at the left side of the heart
Leads I and aVL
what causes a lateral wall MI
occlusion branch left coronary artery-circumflex
what leads look at the inferior surface of the heart
Lead II III AVF
what causes a inferior myocardial wall infarction
muscle necrosis due occlusion right coronary artery
V1 -V4
ANTERO-SEPTAL
V1 AND V2
FACE RV & SEPTUM ‘septal leads’
V3 AND V4
FACE APEX AND ANTERIOR WALL OF RV AND LV
V5 AND V6
face the LV - lateral leads
calculating HR
1 small square- 40ms
1 large square- 200ms
5 Large squares- 1 second
300 large squares = 1 minute
regular- R-R one heart beat
300 divided by number of large boxes
calculating irregular heart beat
count number of QRS complexes in 6 seconds- 30 large boxes- then multiply by 10
how long should the PR interval be
0.12 - 0.2 3-5 small boxes
prolonged if > 1 large box
what does a prolonged PR interval indicate
delayed conduction through AV node and bundle of His
how long should the QRS interval be
< 0.12 seconds
< 3 small boxes
what does a widened QRS indicate
usually a depolarisation arising in ventricle; not spreading via the rapid conducting His-Purkinje system; hence takes more time
electrode placement- limb lead
RIDE YOUR GREEN BIKE Right arm- red left arm- yellow left leg- green right leg-black
c1
fourth intercostal space at the right border of the sternum
c2
fourth intercostal space at the left border of the sternum
c2
midway between location c3 and c4
c4
at the mid-clavicular line in the 5th intercostal space
c5
at the anterior axillary line on the same horizontal plane at c4
c6
at the mid axillary line same horizontal plane as c4 and c5
