ECG interpretation Flashcards
normal dimensions of the calibration trace
1 big square wide, 2 tall. 1mV
normal measurement of squares
1 large = 5mm 1 small = 1mm
normal rate of ECG trace
25mm/s
1 large square = 0.2sec
how do you calculate HR
300/number of big squares between R
normal PR
120-220ms = 3-5 small squares
normal QRS
less than 120ms = 3 small squares.
when does contraction occur
between the s and the T. the ECG is just the electrical activity
prolonged QT
if over 450 sec
what counts as left and right axis deviation
left is between aVL and straight up
right is between aVF and straight up
what is progression
QRS change between V1 and V6. inflection point = inter ventricular septum
overview of good ECG reporting/presenting
- Report the name and age of the patient
- Date of the ECG
- Note whether or not the patient was experiencing any chest pain when the ECG was performed.
- Record the rate of the ECG. This can be done by dividing 300 by the number of large squares between two QRS complexes, if the rhythm is irregular divide 900 by the number of large squares between 4 successive QRS complexes
- Rhythm – check there is a P wave in front of every QRS complex. Is the rate regular, irregular or
irregularly irregular? - Look for prolongation of the PR interval
- Look for extra beats or deflections e.g. that may occur with a paced rhythm
- Axis – if the S wave is greater than the R wave in lead I, there is right Axis deviation. If the S wave
is greater than the R wave in lead II there is left axis deviation - Look at the configuration of the QRS complexes
- Look at the ST intervals to see if they are raised or depressed.
- Look at the T wave to see if it is normal, inverted or peaked
- Give a summary and diagnosis
direction of septum depol
from left to right
define 1st degree heart block
P:QRS = 1:1
PR over 220msec
often a normal variant. poss MI. no treatment .
define 2nd degree heart block
when sometime a P wave is not followed by a QRS. 3 subtypes
1 - mobitz type 1 (wenckebach phenomenon). benign. PR gets progressively longer then drops a beat and resets
2 - mobitz type 2 = constant PR but occasionally a QRS is dropped.
3 - fixed ratio eg 2:1 or 3:1 etc
often causes by an MI. no treatment for mobitz 1 and 2. if fixed ratio results in bradycardia then can have artificial pacing.
define 3rd degree heart block
no association between P and QRS. results in an escape rhythm with a ventricular focus.
MI or fibrosis of the bundle of his or both bundle branches.
often caused by MI or fibrosis. needs a pacemaker.
what happens when you see LBBB
cannot interpret further
can be caused often by aortic stenosis or MI
no symptoms means no action treatment.
name of the left sided fascicles
left anterior and posterior.
LAF damage = LA hemlock with left axis deviation
LPF damage is rare and causes right axis deviation.
RBBB + LAF damage results in RBBB and left axis deviation = bifascicular block.
what is sinus rhythm
when deploy starts in the SAN.
possible supraventricular rhythms
sinus, junctional (AVN) and atrial (anywhere).
what are escape rhythms
those initiated by a ventricular focus. often slow. can get atrial/ junctional escape rhythms too. atrial escape just has a weird looking p wave but normal QRS. junctional escape = no p wave but normal QRS.
ventricular is wide and abnormal QRS , no p wave. often big gap in rhythm before.
extrasystole vs escape beat
same appearance but an extrasystole comes early and an escape beat comes late.
r on t phenomenon
a ventricular extrasystole that occurs at the peak of the preceding T wave. can precipitate VF.
different effect on p wave cycle of supra ventricular extrasystole and ventricular
the supra’s reset the p wave cycle
atrial flutter
no flat baseline. sawtooth. can have second degree block to cause narrow complex tachycardia.
carotid massage does what
causes reflex vagal activity which slows SAN activity and reduces AVN conduction.
atrial fibrillation
no p waves just an irregular baseline. sometimes flutter waves for a few seconds. QRS complexes come at irregular intervals but are a normal shape.
peaked pointy p waves
RA hypertrophy eg tricuspid stenosis or pulmonary HT.
broad and bifid p waves
LA hypertrophy
right ventricular hypertrophy
V1 height of R wave exceeds that of the S wave and a deep S wave in V6. also sometimes right axis deviation, peaked p waves and T wave inversion in V1 to V4.
signs of a PE
peaked p waves
right axis deviation
tall r waves in V1
RBBB
inverted T waves in V1 (normal) spreading to V2 and 3.
a shift of the inflection point to the left.
left ventricular hypertrophy
r wave over 25mm in V5/6 and deep s wave in V1/2
inverted t waves in I, aVL, V5 and 6.
ECG not sensitive to small amounts of hypertrophy
what are pathological q waves.
bigger than 2 mm deep and 1 mm wide. suggests infarcted tissues with full thickness window.
st segment elevation, depression and slope
should be isoelectric
elevation = acute injury e.g. MI or pericarditis
depression with an upright t wave is usually ischaemia
downward slope = digoxin
t wave
normal inversion in WR and W1 and sometimes 3 and v2.
in a semi the st segments will resolve in 24-48 hrs but t wave inversion will often be permenent.
leads adjacent to those with inverted t waves sometimes show biphasic t waves.
hypokalaemia
flattened t wave and u waves lump
hyperkalaemia
peaked t waves and st segment disappears. QRS can be widened. magnesium can cause similar changes
hypocalcaemia
long qt
hypercalcaemia
short qt
causes of RBBB
normal, ASD/congenital/ PE
causes of LBBB
ischaemia, AS, HTN, cardiomyopathy.
how do you calculate corrected QT
start of Q to end of T
QTc drops as HR rises
massive rise in QTc proportional to risk of ventricular arrhythmia inc torsade de pointes.
maximum slope intercept method to define end of t wave.
QTc = QT/ square root RR, where RR = 60/ HR
can get iPhone apps for this.
when QTc is over 440 sec it is pathological .
lead positioning
chest =
v1 = 4th intercostal, right sternal edge
v2 = 4th intercostal left sternal edge
v3 between 2 and 4
v4 = 5th intercostal , midclavicular line
v5 = same level as 4 but anterior axillary line
v6 = same level as 4 but mid axillary line.
ra = avr la = avl ll = avf rl = neutral
