ECGs Flashcards
What HR is considered sinus tachycardia?
>100bpm
Name some causes of sinus tachycardia
Anxiety, dehydration, recent exercise, sepsis, pneumonia etc etc
What lead(s) would you look in to assess sinus bradycardia/tachycardia?
any - rhythm strip is best
What HR is considered sinus bradycardia?
<60bpm
List some causes of left axis deviation
left anterior hemiblock
WPW syndrome
inferior MI
ventricular tachycardia
LVH
What is the most likely cause of right axis deviation? List any alternative causes
RVH is most likely
normal variant - tall thin people
lateral MI
WPW syndrome
dextrocardia or R/L arm lead switch
left posterior fascicular block
How would you detect left axis deviation?
Look for lead I and II “Leaving” each other - small lead I, negative lead II and III
What is a more likely cause of left axis deviation, conduction issues or LVH?
conduction issues
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.
List causes of first degree heart block
increased vagal tone
athletic training
inferior MI
mitral valve surgery
Myocarditis (Lyme disease)
electrolyte disturbances (e.g. hyperkalaemia)
AV nodal blocking drugs:
beta blockers
CCBs
digoxin
amiodarone
Describe the ECG trace in Mobitz type I 2nd degree heart block (Wenckebach phenomenon)
progressive lengthening of PR interval, followed by absent QRS (a non-conducted P wave), then cycle repeats
PR interval is longest just before dropped beat, and shortest just after
What is the mechanism of Mobitz I 2nd degree heart block?
usually due to reversible conduction block at AVN - malfunctioning AVN cells progressively fatigue until they fail to conduct an impulse (dropped beat)
List causes of Mobitz I 2nd degree heart block
Drugs: beta blockers CCBs digoxin amiodarone
Increased vagal tone (e.g. athletes)
inferior MI
myocarditis
cardiac surgery
Describe the ECG trace in Mobitz type II 2nd degree heart block
intermittent non-conducted P waves without progressive prolongation of PR interval
P waves ‘march through’ at constant rate
What is the mechanism of Mobitz II 2nd degree heartblock?
usually due to failure of conduction at His-Purkinje system
generally due to structural damage to conducting system “all-or-nothing”
- no progressive fatigue like in Mobitz I, instead His-Purkinje cells suddenly and unexpectedly fail to conduct
List causes of Mobitz II 2nd degree heart block
Anterior MI (septal infarction wiht necrosis of bundle branches)
Idiopathic fibrosis of conducting system
cardiac surgery
inflammatory conditions (rheumatic fever, myocarditis, Lyme disease)
autoimmune (SLE, systemic sclerosis)
infiltrative myocardial disease (amyloidosis, haemochromatosis, sarcoidosis)
hyperkalaemia
Drugs: beta blockers CCBs digoxin amiodarone
List causes of complete heart block
inferior MI
AVN blocking drugs - CCBs, beta blockers, digoxin
Idiopathic degeneration of conducting system
In what lead(s) is complete heart block best seen?
II and V1
What is the mechanism of complete heart block?
there is complete absence of AV conduction - end point of second degree heart block.
Either progressive fatigue of AVN cells (mobitz I) or due to sudden onset of complete conduction throughout His-Purkinje system (mobitz II)
What is the clinical significance of complete heart block? How would it be treated?
high risk of sudden cardiac death - urgent admission for cardiac monitoring, backup temporary pacing followed by permanent pacemaker insertion
Describe what is seen:
Complete heart block.
atrial rate is 60bpm
ventricular rate is 27bpm
slow ventricular escape rhythm
Describe what is seen:
2:1 heart block
Describe what is seen:
3:1 heart block
Describe what is seen:
Mobitz II second degree heart block
Intermittent P waves without progressive lengthening of PR interval
Describe what is seen:
Mobitz I second degree heart block
aka Weckebach phenomenon
progressive lengthening of PR interval until a QRS fails to conduct (dropped beat)
Describe what is seen:
First degree heart block
PR >0.2s (5 small squares)
Describe what is seen:
Right axis deviation
leads I and II reaching towards each other
Describe what is seen:
Left axis deviation
Leads I and II are leaving each other
Describe what is seen:
atrial fibrillation
irregularly irregular, absent P waves