CLIN SKILLS: ECG Interpretation Flashcards
1
Q
12 ECG leads
A
- unipolar: aVR, aVL, aVF (limb leads) and V1-6 (chest leads)
- bipolar: limb leads I, II, III
2
Q
3 bipolar limb leads used in an ECG
A
- lead I: R arm (-) to L arm (+)
- lead II: R arm (-) to L leg (+)
- lead III: L arm (-) to L leg (+)
3
Q
augmented limb leads:
- aV
- r
- l
- f
A
- aV: augmented voltage
- R: R arm (+)
- L: L arm (+)
- F: L foot (+)
4
Q
6 chest leads
A
- V1 → 4th R parasternal IC space
- V2 → 4th L parasternal IC space
- V3 → midway between V2 and V4
- V4 → 5th L midclavicular IC space
- V5 → 5th L anterior axillary IC space
- V6 → 5th L mid-axillary IC space
5
Q
describe the structure of the P wave and PR interval on ECG
A
- upward deflection = depolarisation of R atrium
- downward deflection = depolarisation of L atrium via Bachmann’s bundle
- PR segment = delay in AV nodal conduction to allow for ventricular diastole
6
Q
describe the structure of the QRS complex on ECG
A
- Q (small downward spike): depolarisation spreads from L>R side of septum = AWAY from lead 2 (+ve)
- R (big upwards deflection): depolarisation goes in the direction of the septum, towards the +ve terminal of lead II (bundle branches)
- R (big downward deflection): depolarisation in the OPPOSITE direction to the +ve terminal of lead II (purkinje fibres go up the ventricles)
- S (small further downwards deflection): ventricles fully depolarised
7
Q
what does the ST segment represent?
A
- ventricles fully depolarised
8
Q
normal height of T wave
A
- < 5mm in limb leads (I, II, III, avL, avR, avF)
- <10mm in chest leads (V1-V6)
9
Q
QT interval:
- what is it
- what does it represent
- how long should it be
A
- from beginning of Q to end of T
- represents total ventricular activity
- should be between 1-2 big squares
10
Q
U wave
A
- smaller +ve deflection occasionally seen after T wave
- thought to represent repolarisation of purkinje fibres
11
Q
describe the structure of the T wave
A
- ventricular repolarisation: REpolarisation makes the charge more NEGATIVE but we’re also moving AWAY from the +ve terminal of lead II - therefore we see a +ve delection
12
Q
systematic approach to ECG interpretation
A
- Pt name, date/time
- calibration signal + technical errors
- rate + rhythm
- electrical axis
- P, QRS, ST, T, U
- Dx
13
Q
how to check for technical errors
A
- check horizontal baseline is straight
- check that P and T waves are inverted for aVR
14
Q
how to check for calibration
A
- 2 big squares vertically and 1 small square horizontally
15
Q
how to assess rhythm
A
- regularly regular: each QRS complex is the same and equidistant (sinus, tachy, brady)
- irregularly regular: abnormal QRS complex but happens regularly
- regularly irregular: ectopic beats
- irregularly irregular: QRS complexes abnormal and not same distance apart (AF/VF)
16
Q
criteria for normal sinus rhythm
A
- regular
- every P wave followed by QRS and every QRS preceded by P
17
Q
how to assess rate
A
- if regular: 300/no. of big squares b/n 2 R waves or 1500/small squares
- if irregular: 1500/no. of BIG squares b/n 6 R waves
18
Q
how to calculate cardiac axis
A
- check if QRS complexes are positive in lead I and AVF
- (use lead II if need to differentiate for 1st quadrant - if +ve then normal, if -ve then LAD)
- if extreme axis deviation (no mans land): wrongly placed ECG or dextrocardia (entire thoracic region mirrored)
19
Q
- what is the normal size of a P wave?
- what happens if there’s a tall or notched/wide P wave?
A
- <3 small squares wide, <2.5 small squares high
- tall: R atrial hypertrophy
- bifid and wide: L atrial hypertrophy (mitral stenosis)
20
Q
how to distinguish b/n left and right ventricular hypertrophy on an ECG
A
- L: add height of deepest S wave in V1 or V2 and tallest R wave in V5 or V6, total will exceed 5 big squares (35mm)
- R: add tallest R wave in V1 or V2, and deepest S wave in V5 or V6, total will exceed 2 big squares (10mm)
21
Q
what is the normal PR interval size and what happens if it’s shortened or lengthened?
A
- normal: 3-5 small squares
- shortened: wolff-parkinson-white syndrome
- lengthened: AV block
22
Q
degrees of AV node block
A
- 1: prolonged PR (>1 large square) but regular
- 2 type 1 (wenckebach): PR gets progressively longer until there is a dropped QRS
- 2 type 2: normal PR interval but dropped QRS every 2-3 beats (2:1/3:1 etc)
- 3: atria beat normally but no association with ventricles = QRS complexes less frequent
23
Q
normal size of the QRS complex and what happens if there is an M-shaped R wave and longer QRS?
A
- <3 small squares
- V1, V2: R bundle branch block
- V5, V6: L bundle branch block
- also causes wide QRS
24
Q
atrial fibrillation vs flutter on ECG
A
- AF: quivering, irregularly irregular, no P waves
- atrial flutter: regularly irregular, sawtooth waves b/n R waves
25
ectopic beats
- when the atria/ventricles depolarise earlier than usual for one random beat
- QRS complex is very different on the ectopic beat
- ventricular: one big random QRS complex
- e.g. smoking, alcohol, caffeine, medication
26
which leads and regions of the heart do the coronary arteries correspond to?
- LAD: V1-V2 (septal) V3-V4 (anterior)
- RCA: II, III, aVF (inferior)
- circumflex: aVL, I, V5, V6 (left/lateral side)
27
STEMI vs NSTEMI on ECG
- NSTEMI: ST depression
- STEMI: ST elevation
28
stable vs unstable angina on ECG
- BOTH NORMAL ECG
29
how to tell an old AMI?
- deep Q waves
30
how to tell SVT
- narrow QRS
31
how to tell ventricular tachycardia on ECG
- wide QRS
- zigzags w/ no P or T waves
(could also be BBB)
32
what does an inverted T wave indicate
- ischaemia or hypokalaemia
33
what does a high T wave indicate
- hyperkalaemia
34
what could left axis deviation indicate
- L ventricular hypertrophy
35
indications for an ECG
- dizziness of unknown cause
- shortness of breath
