ECG Tips
21/2/11
FANZCA Notes
Life in the Fast Lane
Crit-IQ
PY Mindmaps
Stuart Lane Tutorial – Nepean Written Course (2011)
The 12 Lead ECG
- 10 physical leads
- 12 electrical leads
CALIBRATION
- normal = 25mm/s
- calibration = 5mm wide, 10mm high = 1mV
- 1 small square = 1mm = 0.04s = 40ms
- 1 large square = 5mm = 0.2s = 200ms
RATE
- QRS complexes on rhythm strip x 6 = rate/min
- number of large squares between R waves: 300-150-100-75-60-50
Tachycardia
- narrow complex vs wide complex?
- narrow:
-> AV node independent (ST, unifocal, mutlifocal, AF, Aflu)
-> AV node dependent (AVN re-entry, AV re-entry, junctional)
- wide:
-> VF
-> supra-ventricular tachycardia with BBB
-> VT
-> accelerated idioventricular rhythm
- regular or irregular?
- irregular:
-> multiple ventricular ectopics
-> AF with aberrancy
-> AF with BBB
-> AF with pre-excitation pathway
- regular:
-> sinus
-> junctional
Bradycardia
- sinus:
-> arrest
-> pauses
-> inappropriate bradycardia (vagal overactivity, myxoedema)
-> physical fitness
-> beta blockade
- AV node dysfunction:
-> 1st degree – prolongation of PR interval (>0.2s)
-> 2nd degree (Mobitz type I) – progressive lengthening of PR interval with eventual dropped ventricular conduction
-> 2nd degree (Mobitz type II) – intermittent dropping of ventricular conduction
-> 2nd degree (2:1 type) – alternate p-wave not conducted to ventricles
-> 3rd degree – complete dissociation between atria and ventricular
RHYTHM
- SR or not?
AXIS
- QRS positive in I and aVL = normal
- I positive and aVF negative = LAD
- I negative and aVF positive = RAD
- I and aVF negative = extreme RAD or LAD
RAD
- RVH
- Left posterior hemiblock
- Lateral myocardial infarction
- Acute right heart strain (PE)
- Normal in infants and children
LAD
- AS
- Dilated cardiomyopathy
- AMI
- IHD
- HT -> aortic root dilation -> AR
- Left anterior hemiblock
Extreme Axis Deviation
- situs inversus
- limb lead on backwards
- VT
P WAVE
= atrial depolarisation
- look for in V1 and II (best seen)
- must be negative in aVR (otherwise leads misplaced)
- normal duration: 0.12s
- normal eight: < 2mm
- dual: heart transplant
- bifid: LA enlargement (mitral stenosis)
- peaked: RA enlargement (pulmonary hypertension) or LA enlargement
- inversion: atrial ectopic, junctional rhythms, dextrocardia
- variable morphology: multifocal atrial rhythms
PR INTERVAL AND PR SEGMENT
- normal duration 0.12-0.2s (3 to 5mm)
- long: 1st, 2nd (type I and II) and 3rd degree HB
- short: WPW, LGL
- depression: pericarditis, atrial ischaemia
Q WAVES
- normal: < 25% of R wave in I, aVL, aVF, V4,5,6.
- pathological: if long (>0.04s) and deep (>2mm)
QRS COMPLEX
- normal duration < 0.12s (3 small squares)
- normal transition point of R wave: V3-V4
- amplitude: normal, large, low voltage, alternans
- morphology: notched, RBBB, LBBB
Positive QRS in V1
- RVH
- posterior infarction
- WPW type 1
- RBBB
- Duchenne’s muscular dystrophy
- dextrocardia
- incorrect lead placement
- rare causes: LV ectopics, acute right heart strain, hypertrophic cardiomyopathy, normal variant, Brugada syndrome
J WAVE
= positive deflection @ QRS and ST junction (J point)
1. Hypothermia (increases with severity)
2. Severe hypercalcaemia
ST SEGMENT
ST Elevation
1. AMI
2. Pericarditis (with PR interval depression)
3. Tako-tsuba cardiomyopathy
4. LBBB
5. Brugada syndrome
6. Benign early repolarisation (isn’t so benign -> higher risk of cardiac death)
7. LV aneurysm
Contour
- horizontal
- upsloping
- downsloping
T WAVE
- normal amplitude: < 2/3rds R wave
- peaked
- inverted
- alternans
U WAVE
= small positive deflection following T wave
1. Hypokalaemic Periodic Paralysis
2. Bradycardia
3. Hypothermia
4. Drug OD – digoxin, phenothiazines, anti-arrhythmics (sotalol, amiodarone, quinidine, procainamide)
5. Hypomagnaesaemia
6. Hypocalcaemia
7. Increased ICP
QT INTERVAL
- rate dependent
- should be less than 50% of R-R interval
- measure in II or V5-6 (include large u wave that is fused with T wave)
- QTc > 440ms (11 small squares) in men or > 460ms in women (11.5 small squares)
Causes of Prolonged QT
- drugs: anti-arrhythmics, anti-histamines, macrolide, anti-depressants, methadone…)
- electrolytes: hypokalaemia, hypoMg2+, hypocalcaemia
- stroke: SAH
- ACS
- bradyarrhythmia
- congenital
-> complication = Torsade de Ponte
OTHER CONDUCTION DISTURBANCES
RBBB
- activation of the right ventricle is delayed
- QRS > 120ms
- RSR in V1 (‘M’), and ‘W’ in V6 (MARROW)
- broad S wave in LV leads (I and V6)
- normal axis
1. Can be normal
2. Massive PE
3. RVH
4. IHD
5. Congenital heart disease
LBBB
- septal depolarisation reversed (right to left)-> change in initial direction of QRS
- QRS > 120ms
- Q waves seen in left ventricular leads
- WILLIAM (W in V1, M in V6)
- normal axis
- always pathological
1. IHD
2. Cardiomyopathy
3. LVH
Left anterior hemiblock – LAD, Q waves in I and aVL, small R in III (and absence of LVH)
Left posterior hemiblock – RAD, small R in I, small Q in III (and absence of RVH)
Bifascicular block
- RBBB + block of either left anterior or posterior fascicle.
- RBBB + left anterior fascicle block -> LAD
- RBBB + left posterior fascicle block -> RAD
Trifascicular block – 8 types:
(1) Prolonged PR interval + LAD+ RBBB
(2) LBBB + RAD
(3) AF + LAD+ RBBB
(4) Junctional rhythm + RAD + RBBB
(5) Alternating BBB
(6) RBBB + alternating fascicular block
(7) BBB + second degree HB type II
(8) Any bifascicular block + 1st or 2nd degree AV block
TRICKS AND TRAPS
Artifacts – tremor
Dextrocardia
- RAD
- P in I
- QRS complexes decrease in amplitude across the chest leads
HypoMg2+
- wide QRS
- peak T waves
- R prolongation
- TWI
- U waves
- VT -> Torsades
Lown-Ganong-Levine
- short PR interval < 0.12s
- no delta wave
- may have normal QRS (unless IVCD present)
Overdose -> Na+ channel blockade
1. Positive QRS in II
2. Dominant R wave in aVR
3. QRS duration > 100ms
Packing Spikes – failure to sense/capture/output
WPW
- PR interval < 0.12s
- QRS duration > 0.12s
- Delta wave
Cardiac Arrest in a Young Person
- ARVD: RV strain and epsilom wave
- Long QT: TW after 50% of R-R distance
- Brugada: V1 and V2 have funny ST elevation
- HOCM: LVH
- WPW: see above
V5R – most sensitive lead for RV infarction (ST segment will be elevated)
Pericardial tamponade
- electrical alternans -> heart swinging in massive pericardial effusion (c/o change in impedance)
ELECTROLYTE ECG CHANGES
Hyperkalaemia
- tall T waves
- flat P waves
- prolonged PR
- wide QRS
Hypokalaemia
- ST depression
- T wave flattening
- U waves
- SVT
- VT
- Torsades de Pointes
Hypermagnasaemia
- bradyarrhythmias
- cardiac arrest
Hypomagnasaemia
- prolonged PR
- wide QRS
- ventricular arrhythmias
- Torsades
Hypercalcaemia
- shortened QTc
- Osborn or J wave
Hypocalcaemia
- prolongation of ST segment and QT interval
- VT
Jeremy Fernando (2011)