ecg Flashcards
what do the axis of an ecg show
- vertical is voltage
- horizontal is time
what is hypertrophy
when one side of the heart is larger than the other
what is on the vertical axis of an ecg
- voltage, in mV
- the higher the voltage the more that is drawn to this side of the heart
- suggest hypertrophy if big
what is shown on the horizontal axis of an ecg
- time, in milliseconds and seconds
- longer time shows a blockage in the normal electrical circuit
- increased time suggests heart damage
what are the different limb leads
aVL, Lead I, II, III, aVF, aVR
what are the different chest leads
V1, V2, V3, V4, V5, V6
what are the different views of limb leads
- lateral
- inferior
- right
what are the different views of the chest lead
- septal
- anterior
- lateral
which leads show a lateral view
aVL, lead I and lead II
which leads show an inferior view
lead II, lead III and aVF
which leads show the right view
aVR
which leads show a septal view
V1 and V2
which leads show an anterior view
V2, V3 and V4
which leads show a lateral view
V5 and V6
what does the septal ecg view show
the middle section of the heart
what does the anterior ecg view show
the main functioning wall of the heat
what is einthovens triangle
the net current of 2 limb leads
what view does aVL give
view of the heart from the left shoulder
what view does aVR give
view of the heart from the right shoulder
what view does aVF give
view of the heart from the foot looking up form the bottom
what view does lead I give
right arm to left arm
what view does lead II give
right arm to left leg
what view does lead III give
left arm to left leg
what is the path of conduction in the heart
- SA node fires to the AV node
- AV node then fires to bundle of his
- bundle of his signalling is sent down the heart septum and up the pirkinje fibres
what do the different ecg waves represent in conduction
- P wave in SAN to AVN firing
- Gap is the space between the AV and bundle of his firing
- QRS is the bundle branches down to the purkinje fibres
- T wave is relaxation
what are the 4 different cardiomyocytes
- intercalated discs
- desmosomes
- gap junctions
- contraction
what are desmones
scaffolding that holds everything together
what are gap junctions
water permeable junctions that allows sodium to leave through pours. when sodium leaves so does potassium
what are the contraction cardiomyocytes
the action potentials in the heart
what is the trigger for action potentials
a change in the voltage across membranes at -70mV
what do the pacemaker cardiomyocytes do
- they innate automatically without outside influence
- SAN - 60-90bpm
- AVN - 40-60bpm
what are the 2 phases of pacemaker cardiomyocytes
- phase 0, the climb phase
- phage 3, the plummet
what occurs in phase 0/ climb
- depolarisation
- calcium ion channels opens and calcium enters the cell making it more positive (upping the mV)
what occurs in phase 3/ plummet
- full repolarisation
- the potassium channels open and leave the cell causing full relaxation
what do the non-pacemaker cardiomyocytes do
- contractile muscle cells in the atria and ventricles
- do not generate spontaneous action potentials
what is the mV for resting membrane potential
-90mV
what is the mV for action potential trigger
-70mV
what are the stages of non-pacemaker cardiomyocytes
- summit/0
- plummet/1
- continue/2
- plummet/3
what happens in phase 0 of non pacemaker cardiomyocytes
- depolarisation
- sodium ion channels enter and sodium enters the cell making it more positive
what happens in phase 1 of non-pacemaker cardiomyocytes
- slight repolarisation
- potassium channels open and potassium leaves the cell making it more negative
what happens in phase 2 of non pacemaker cardiomyocytes
- slight repolarisation
- L type calcium channels open and calcium enters the cell and there is full contraction
what happens in phase 3 of non-pacemaker cardiomyocytes
- full repolarisation
- potassium ion channels open and potassium leaves the cells causing full relaxation
what is contraction-coupling
all cardiomyocytes are electrically couples and have gap junctions that link opposite cells to allow electrical activity to pass through
what are some accessory pathways in contraction couplin
- atriofascicular - RA to RBB
- atrio-Hisian - atrium to His
- nodofascicular - AV to RBB
- nodoventricular - AV to RV
- fasciculoventricular - His to ventricles
which axis show positive deflection in cardiac axis
lead II, I and aVF
which axis shows negative deflections in cardiac axis
aVR
which axis shows biphasic deflection
- lead III and aVL
- which one is more positive says the way the signal is travelling from
- if bigger it shows where the signal is being pulled from
what does a positive deflection show
signal towards the lead
what does negative deflection show
signal away from the lead
what does biphasic deflection show
signal perpendicular to the lead
what is right axis deviation
when depolarisation is being pulled to the right side of the heart
- increases positive deflection in lead III and negative deflection in aVL
what is left axis deviation
when depolarisation is pulled to the left side of the heart
- increases negative deflection of lead III and positive deflection of aVL
what are examples of a right axis deviation
- RV hypertrophy
- RV strain
- lateral stemi
- Wolff-parkinson-white
what are examples of left axis deviation
- LV hypertrophy
- LBBB
- inferior stemi
- Wolff-Parkinson-White
signs of situs inversus
- lead 1 net QRS negative and P negative
- lack of precordial R wave progression
- mirror-image dextrocardia
positioning of 12 lead ecg
- V1 = 4th intercostal space, right sternal edge
- V2 = 4th intercostal space, left sternal edge
- V3 = between V2 and V4
- V4 = 5th intercostal space, mid clavicular
- V5 = level of V4 at anterior axillary line
- V6 = level of V4/5 mix auxiliary line
lead grouping on ecgs
- Big LII (i,ii,iii)
- Little LI (aVL,iii)
- SAALL (V1,2,3,4,5,6)
what are the main blood vessels of the heart
- left anterior descending
- proximal left anterior descending
- left circumflex
- right coronary artery
- distal left anterior descending
which vessels are blocked in an anterior STEMI
left anterior descending
which vessels are blocked in a septal STEMI
proximal left anterior descending
which vessels are blocked in a lateral STEMI
left circumflex
which vessels are blocked in an inferior STEMI
right coronary artery and left circumflex
which vessels are blocked in an apical STEMI
distal left anterior descending, left circumflex or right coronary artery
which vessels are blocked in a posterior STEMI
right coronary artery or left circumflex
what does a normal p wave look like
- atrial depolarisation
- <3 small squares
- smooth hump, smaller than a t wave
- upright in L1 and L2 and inverted in aVR, biphasic in V1
what does a p wave look like in atrial enlargement
- left - looks m shaped
- right - looks peaked
what should a pr interval space be
3-5 squares
what does it mean when there is an change in pr interval length
- > 5 squares is an AV block
- <3 square is preexcitation/ junctional rhythm
how should a QRS look on an ecg
- normal = 3 small squares
- narrow = <3 supraventricular origin
- broad = >3 bundle branch block
what is the j point
the interval of ventricular depolarisation and repolarisation
what does a t wave show
- repolarisation phase
- is upright and asymmetric
what is the QT interval
the period of ventricular systole from contraction to relaxation
- measured in L2 or V5-6
changes to QT interval
- prolonged is >440ms (men) or >460 (women)
- shortened in fast HR and lengthened in slower HR
- > 500ms can lead to torsade de points
what causes changes in QT interval
either due to drug overdose or electrolyte imbalance
what is a U wave
- either: delayed purkinje fibre repolarisation, mid-myocardial repolarisation or ventricular wall after potentials
- proceeding T waves
what are the Chamberlin’s 10 rules
- PR interval 3-5 squares
- QRS complex <3 squares
- QRS upright in L1 and L2
- QRS and T waves in limb leads have same direction
- aVR all waves negative
- R waves grow V1-4 and S waves grow V1-3
- ST segment isoelectric in V1 and V2
- P waves upright in L1,2 and V2-6
- q waves absent or <1 square in L1,2 and V2-6
- T waves upright in L1,2 and V2-6
what are atrial ectopic waves
- electrical activity outside the SA node
- P wave present but not normal
what are ventricular ectopic waves
- electrical activity outside AV node
- broad QRS complex
- may have atrial pre-capture
what are Bi/Tri/Quad-rigeminy
- ectopic between beats, in any rhythm
- can trigger re-entrant tachycardia
what is the rhythm in a first degree AV block
regular rhythm with a prolonged PR interval
what is the rhythm in a second degree AV block type 2
irregular rhythm with a normal PR interval and a wide QRS. ratios of 2:1, 3:1, 4:1
what is the rhythm in a second degree AV block type 1
an increasingly prolonged rhythm with irregular PR intervals until a QRS is dropped
what is the rhythm in a 3rd degree AV block
a regular rhythm with no PR interval and P wave that are not related to the QRS complex
what is pre-excitation
an accessory pathway from atria to ventricles with earlier activation then in a normal circuit
what are different pacing spikes
- vertical spike <2ms
- atrial pace spike precedes p waves
- ventricular pace spike precedes QRS
- dual pace spike precedes both
what are common pacemakers
- atrial pace
- ventricle pace
- dual pace
what does ST elevation show
ST segment shit indicating MI, caused by a coronary artery occlusion
what does ST depression show
upside down ST elevation indicating ischaemia or reciprocal changes
what happens in a right bundle branch block
- delayed repolarisation of the right ventricle
- wide QRS >120ms
- RSR pattern in V1-3 (m shape)
- wide S wave in V5-6 (W shape)
what happens in a left bundle branch block
- delayed depolarisation of left ventricle
- QRS wide >120ms
- dominant S wave V1 (W shape)
- broad R wave V5-6 (M shape)
what are escape rhythms
-when the SAN is disabled and the AV node or ventricular cells take over
- junctional escape rhythm and idioventricular escape rhythm
what is torsades de pointes
- type of polymorphic VT
- self limits an can degenerate into VT or VF
- crescendo and diminuendo look
what can be seen in right ventricular hypertrophy
- R:S ration >1 or R wave is >7mm in V1
- ST depression and TWI in V1-3
what can be seen in left ventricular hypertrophy
- Sokolow Lyon criteria - s wave in V1 and R wave in V5 or V6 > 35mm
- Modified Cornell criteria - r wave in aVL >12mm
what are cerebral mimics
- QTS prolongation and giant T wave inversion
- caused by adrenaline surge
what are electrical alternans
- alternating beat variation
- QRS - big, small, big, small
- cardiac tamponade or pericardial effusion
what causes peaked T waves
- hyperkalaemia
- the action potential duration in shortened increasing K+ channel conduction, creating excess repolarisation
what causes prolonged PR and QT intervals
- hypermagnesemia
- AV ectopy, creating excess repolarisation
steps for ECG interpretation
- rate
- rhythm
- axis
- p waves
- intervals
- qrs morphology
- q waves
- st segments
- t waves
