ECGs Flashcards
ECG square dimension (time)
small square: 1mm, 0.04 sec
big square: 5mm, 0.20 sec
what does the p wave represent
atrial depolarisation, conduction from SAN throughout atria
PR interval represents
time for electrical activity to go from atria to ventricles through the AVN
what does QRS complex represent
ventricular depolarisation
what does ST segment represent
time taken after depolarisation finishes for repolarisation to begin
what does t wave represent
ventricular repolarisation
what does qt interval represent
time for ventricles to depolarise then repolarise
what does rr interval represent
time between two QRS complexes, time for one complete heart cycle
normal pulse
60-100 bpm
what is sinus rhythm
p wave starting each qrs complex
how to calculate rate if regular
1500/number of small squares
300/number of large squares
which leads are used to assess cardiac axis
I, II, aVF
how to assess cardiac axis
if II is +ve and I is +ve then cardiac axis normal
if II is -ve and I is +ve then left axis deviation
If II is +ve and I is -ve then right axis deviation
if aVF is -ve and I is -ve then there is extreme axis deviation
is axis deviation always pathological
no. LAD seen in short fat ppl and RAD in tall thin ppl
how should p waves look
+ve in leads I, II
inverted in aVR
biphasic in V1
how can p waves be abnormal
absent
sawtooth
p pulmonale (right atrial enlargement)
p mitrale (left atrial enlargement)
p wave inversion
what does a wide QRS indicate
ventricles not correctly depolarised
how does calcium affect qt interval
hypercalcaemia shortens it
hypocalcaemia prolongs it
atrial fibrillation ECG
irregularly irregular rhythm
absent p waves
narrow QRS
rule of thumb for if activity is from atria or ventricles
if the activity is starting at or above AVN then narrow QRS
broad QRS implies ventricular origin or aberrant conduction
atrial flutter ECG
regularly irregular rhythm
absent p waves with sawtooth baseline
narrow QRS
Supraventricular tachycardias ECG
any tachyarrythmia above bundle of His
retrograde p waves (after QRS)
p wave could be in T waves or look like double t waves
1st degree heart block ECG
prolonged PR interval
can be seen in healthy ppl
Mobitz type 1 heart block ECG
also 2nd degree heart block type 1 or Wenckeback phenomenom
usually benign
starts with shorter PR interval
gets longer each cycle
eventually p wave without QRS
then cycle begins again
represents increased delay at AVN
Mobitz type 2 heart block ECG
aka 2nd degree heart block type 2
PR interval constant when QRS present
some p waves not followed by QRS
represents damage to conduction tissue below AVN - always pathological
could be broad or narrow QRS
3rd degree heart block ECG
complete cessation of AV conduction
p waves and qrs independent
can be broad or narrow qrs
patient usually bradycardic
Wolff-Parkinson-White ECG
accessory pathway from atria to ventricles typically connecting left atria to left ventricle
short pr interval
broad QRS with slurring of start
ventricular fibrillation ECG
incompatible with life
rapid, broad, irregular, chaotic ventricular depolarisation
no discernible waves
monomorphic VT ECG
most common VT
fast HR
broad, consistent ventricular complexes
loss of other features
sometimes occasional normal cycles
left bundle branch block ECG
damage to left bundle branch, usually pathological
broad QRS
deep S wave in V1
notched R wave in V6
can also see notched top in other lateral leads
new LBBB consistent with STEMI
right bundle branch block ECG
damage to right bundle branch usually pathological
broad QRS
RSR in V1 and adjacent leads
wide slurred S wave in V6
ST depression and t wave inversion v1-3
Torsades de Pointes (TdP)
type of polymorphic VT
broad QRS
changing amplitude beat to beat
twisting appearance
NSTEMI ECG
subendocardial ischaemia (sub-total occlusion)
widespread ST depression
T wave inversion
pericarditis ECG
widespread concave ST elevation (often saddle shaped)
widespread PR depression
may be tachycardic
hyperkalaemia ECG
potassium >5.5
tented T waves
hypokalaemia ECG
potassium <3.5
ST depression
T wave inversion and U waves
