ECGs Flashcards
What is the mechanism of atrial flutter?
a re-entry circuit within right atrium
List some causes of AF
ischaemic heart disease
thyrotoxicosis (hyperthyroidosis)
sepsis
valvular heart disease
alcohol excess
PE
hypokalaemia/hpomagnesaemia
What is the mechanism of atrial tachycardia?
A single ectopic focus, outside the SAN that’s triggering rapid depolarisation of the atria
List causes of atrial tachycardia
digoxin toxicity
atrial scarring
catecholamine excess
congenital abnormatlities
What is the mechanism of junctional tachycardia?
AV junctional pacemaker rhythm exceeds that of SAN. There is increased automaticity in AVN coupled with decreased automaticity in SAN.
Describe the ECG changes seen in right bundle branch block
broad QRS >120ms
RSR pattern in V1-3 (‘m’ shaped complex)
wide, slurred S waves in lateral leads (I, aVL, V5-6) giving a ‘W’ shaped complex in V6
(MarroW - M in V1, W in V6, rr = right)
possible ST depression in precordial leads (V1-3)
What is the mechanism in RBBB?
activation of R ventricle is delayed as depolarisation has to spread across septum from left ventricle due to blockage of R bundle of Purkinje fibres
left ventricle is activated normally, so early part of QRS is unchanged, but delayed R ventricle activation produces a secondary R wave in V1-3 and a slurred S wave in lateral leads
List causes of RBBB
RVH / cor pulmonale
PE
IHD
rheumatic heart disease
myocarditis or cardiomyopathy
degenerative disease of conduction system
congenital heart disease
Describe the ECG changes seen in left bundle branch block
broad QRS >120ms
dominant S wave in V1 - W
broad, notched R wave in V6 - M
(WilliaM - W in V1, M in V6, ll = left)
no Q waves in lateral leads (I, V5-6, small Q waves in aVL)
prolonged R wave peak time >60ms in V5-6
List causes of LBBB
aortic stenosis
ischaemic heart disease
dilated cardiomyopathy
anterior MI
primary degnerative disease (fibrosis) of the conducting system
hyperkalaemia
digoxin toxicity
Describe the mechanisms in LBBB?
septum is activated R to L instead of L to R
spreads via right bundle branch, and then via septum to left bundle branch
this extends the QRS duration and removes Q waves in lateral leads
as the venrticles are activated sequentially, broad R waves are produced
Describe the ECG changes seen in junctional escape rhythms
no p waves, or p waves completely unrelated to QRS
normal QRS, maybe slightly narrow
slow HR
What is the mechanism of junctional escape rhythms?
there are pacemaker cells at various points in the conduction system
junctional escape rhythm occurs when the rate of AV node depolarisation is less than the intrinsic rate of an ectopic pacemaker
list causes of junctional escape rhythms
severe sinus bradycardia
sinus arrest
sino-atrial exit block
high-grade second degree heart block (4:1, 5:1 etc)
complete heart block
hyperkalaemia
drugs:
beta blockers
CCBs
digoxin poisoning
Describe the ECG changes seen in a ventricular escape rhythm
ventricular rhythm of 20-40bpm
broad QRS complexes, possibly with a LBBB or RBBB morphology
what arteries are likely to be blocked in a lateral STEMI
LAD and LCx
Describe the ECG changes seen in a lateral STEMI
ST elevation in the lateral leads
(I, aVL, V5-6)
reciprocal ST depression in inferior leads (III and aVF)
Describe the ECG changes seen in an inferior MI
ST elevation in II, III and aVF
progressive development of Q waves in II, III and aVF
reciprocal depression in aVL (±lead I)
Which artery most commonly causes an inferior STEMI?
right coronary artery
(more ST elevation in lead III than II)
LCx can cause it less commonly
(ST elevation in lead II = lead III)
Describe the ECG changes seen in posterior MI
In V1-V3:
horizontal ST depression
tall, broad R waves
upright T waves
dominant R wave in V2
Occlusion of what artery causes an anterior STEMI?
LAD
Describe the ECG changes seen in anterior STEMI
ST elevation with Q wave formation in the precordial leads (V1-6) ± the high lateral leads (I and aVL)
reciprocal ST depression in the inferior leads (mainly III and aVF)
In what leads would ST elevation be maximal in a septal STEMI?
V1-2
In what leads would ST elevation be maximal in an anterior STEMI?
V2-5
In what leads would ST elevation be maximal in an anteroseptal STEMI?
V1-4
In what leads would ST elevation be maximal in an anterolateral STEMI?
V3-6, I + aVL
What is seen in an NSTEMI?
pathological Q waves only
Describe the ECG changes that may be seen in a ventricular tachycardia
very broad QRS (>160ms)
no p waves
T waves difficult to identify
rate > 200bpm
Describe the ECG changes seen in ventricular fibrillation
chaotic irregular deflections of varying amplitude
no identifiable P waves, QRS complexes or T waves
rate 150-500bpm
Causes of VF
myocardial iscahemia/infarction
electrolyte abnormalities
cardiomyopathy (dilated, hypertrophic, restrictive)
Long QT
Brugada syndrome
Drugs
environmental - electrical shock, drowing, hypothermia
PE
cardiac tampnoade
blunt trauma
Describe the ECG changes seen in Wolff-Parkinson-White syndrome
sinus rhythm
right axis deviation
short PR interval
sluured upstroke of the QRS complex, best seen in V3 and V4 - wide QRS due to this delta wave
dominant R wave in V1
what is the mechanism in Wolff-Parkinson-White?
accessory pathway, usually from left atria, allows direct transmission of signal, bypassing AVN (hence short PR)
Describe the “digoxin effect”
downsloping ST depression with “sagging” appearance
flattened, inverted or biphasic T waves - hockey stick
shortened QT
What is the mechanism behind the digoxin effect?
shortening of atrial and ventricular refractory periods - producing short QT
increased vagal effects at AVN - prolonged PR interval
Describe the ECG changes seen in pericarditis
widespread concave ST elevation and PR depression
Reciprocal ST depression and PR elevation in aVR
What is P Pulmonale?
peaked P waves
What is seen in p mitrale?
bifid p waves
list causes of p pulmonale
anything that cause right atrial enlargement
e.g. tricuspid stenosis, pulomnary hypertension
