ECGs Flashcards
What is the DDx for tachycardia with narrow QRS complexes (<0.12)?
REGULAR:
- Sinus tachycardia
- SVTs (AVNRT, Orthodromic AVRT, AFlutter)
IRREGULAR:
- AFib
- AFlutter
What is the DDx for tachycardia with wide QRS complexes (>0.12)?
REGULAR:
- Hyperkalaemia
- VT (monomorphic)
- SVT + conduction abnormality
IRREGULAR:
- Hyperkalaemia
- AF + WPW
- Polymorphic VT (incl. torsades)
What are some causes of bradycardia?
- Sinus bradycardoa
- Second degree AV block
- Third degree AV block
- SA Block
How do you determine rate?
If irregular: # of QRS complexes x 6
Regular: Divide 300 by the # of boxes between the R waves
What features does an ECG need to be in sinus rhythm?
Every QRS is preceded by a p wave and this occurs in a regular rate
And the PR interval is less than 0.22s/some people say 200ms
How do you determine the axis of the ECG?
Trick: based on whether the QRS complexes in I, II and aVF are net positive or net negative
Normal= -30 to +90
I+, II+, aVF +
LAD= -30 to -90:
I+
II and aVF -
RAD: 90 to 180:
I-
II and aVF +
What is an extreme axis deviation?
-90 to 180
I-, II-, aVF-
What are some of the most common causes of RAD?
RVH
Acute cor pulmonale (PE)
Chronic cor pulmonale (COPD, pulmonary HTN)
LV infarction
What are some of the commonest causes of LAD?
LBBB
LVH
Inferior infarction
What does the p wave represent?
Depolarisation of the atria
What are the normal characteristics of p waves?
Duration <0.12 seconds
Amplitude <2.5mm (remember 1 lil square is 1 mm) in limb leads, <1.5mm in chest leads
What does a sawtooth p wave baseline indicate?
Atrial flutter
What does a chaotic p wave baseline indicate?
Atrial fibrillation
What does a flat line where the p wave should be indicate?
No atrial activity
What is p pulmonale?
P wave with an abnormally high amplitude in II
Caused by right atrial hypertrophy
What is p mitrale?
Biphasic p wave in II (second hump) and a deep negative deflection in V1
Caused by left atrial hypertrophy
What is the PR interval?
Time interval from the start of atrial depolarisation to start of ventricular depolarisation
Start of p wave to start of QRS
What is the PR segment?
From the end of the p wave to the start of the QRS
Reflects the slow impulse conduction through the AV node (baseline/isoelectric line of the ECG)
What is a normal PR interval?
0.12-0.22s (people kinda just say less than 200ms)
What does a PR interval of greater than 0.22s mean?
First degree AV block
What are some common causes of first degree AV block?
Degenerative fibrosis
Ischaemia
Beta blockers
What does a PR interval of less than 0.12 mean?
Pre-excitation –> WPW Syndrome
What is second degree AV block mobitz type 1?
Wenckebach
Gradually increasing PR interval until the atrial impulse (p wave) is blocked at the AV node and you don’t have a QRS
What is second degree AV block mobitz type 2?
The PR interval stays the same but you have intermittently blocked atrial impulses (a block infra-nodal, usually His bundle) so not every p wave causes a QRS
What is 3rd degree AV block?
Complete Heart Block
The p wave and the QRS have no relation BUT both the atrial and escape rhythm are typically regular (the atrial rhythm is just usually faster)
All atrial impulses/p waves are blocked by the AV node. The perfusing rhythm is maintained by a spontaneous escape rhythm
What are some common causes of 3rd degree AV block?
- Ischaemia heart disease (acute MI, ICM)
- Non-ischaemic heart disease: aortic stenosis, dilated cardiomyopathy, infiltrations (sarcoid, amyloidosis)
- Idiopathic fibrosis
- Infections: endocarditis, chagas, SLE, RA
- AV blocking drugs: CCBs, Bblocks, digoxin
What are the two types of escape rhythms?
Junctional (narrow QRS and 40-60bpm, originates in the His bundle) and Ventricular (wide QRS and 20-40bpm, originates below the His bundle)
What is the QRS complex?
The depolarisation of the ventricles
Q wave= first negative deflection (won’t be present in all leads). Represents the depolarisation of the septum (which travels in the opposite direction to the main conduction so it’s negative)
R wave= the positive deflection. Represents the depolarisation of the ventricles (but you don’t see the right ventricle because the LV produces too big of a vector)
S wave= the depolarisation in the purkinje fibres as they go back up through the walls of the ventricles (opposite to the main electrical vector so it’s negative)
What is a normal QRS complex duration?
<0.12s
What pathological thing should you check for when you look at the QRS complexes?
Pathological Q waves: >0.3s and/or an amplitude of >25% of the R wave in the same lead
What are some causes of broad QRS? >0.12s
It means slower than normal ventricular depolarisation
- Bundle branch block
- Hyperkalaemia
- Drugs (TCA, class 1 anti-arrhythmics)
- WPW syndrome
What are some causes of narrow QRS? <0.12s
Supra-ventricular complexes
What are the 3 main places that supraventricular complexes arise from?
SA node (normal p wave)
Atria (abnormal p wave- fibrillation or flutter)
AV node/junction= either no p wave or an abnormal p wave with an increased PR interval
What is the ST segment?
From the end of the QRS to the start of the T wave (relatively brief period)
Corresponds to the plateau phase in the cardiac conduction cycle. The membrane potential is relatively unchanged and most ventricular cells are in this phase simultaneously so nil electricular potential differences
What level of ST segment depression can you accept in the chest leads?
<0.5mm (half a lil square)
What are some causes of ST elevation?
STEMI!!!!!
Can be LBBB, LVH, Brugada syndrome, takotsubo, hyperkalaemia, PE
What are some causes of ST depression?
Ischaemia! NSTEMI!
Hypokalaemia, digoxin, LBBB/RBBB, LVH, RVH
What is the t wave?
Ventricular repolarization. Takes longer than depolarisation so typically longer
What are the characteristics of normal t waves?
Should be concordant with the QRS complex and positive in most leads
In what leads can an isolated t wave inversion be accepted?
V1 and III
What does t wave inversion with ST deviation indicate?
Acute myocardial ischaemia
What does t wave inversion in the absence of ST deviation indicate?
Not a sign of ongoing ischaemia but can occur post-ischaemia.
Cerebrovascular haemorrhage, PE, perimyocarditis
What can cause high t waves?
Hyperkalaemia
LVH
LBBB
What does the QT interval represent?
The total time for de and repolarisation. It is the time from beginning of the QRS to the end of the t wave
Why do we worry when someone has a prolonged QTc?
A high risk of ventricular arrhythmias- especially Torsades de Pointes
What is the normal QTc for men?
<0.45s
What is the normal QTc for women?
<0.46s
What are some causes of acquired QT prolongation?
Anti-arrhythmics
TCAs
SSRIs
Lithium
Hypokalaemia
Hypocalcaemia
Hypomagnesia
MI
Hypothyroidism
What causes congenital QT prolongation?
Genetic disease –> 15 variations
What is short QTc syndrome?
A QTc <0.32ms
Caused by hypercalcaemia and digoxin
What is a U wave?
The U wave sometimes occurs when the ECG picks up the repolarisation of the purkinje fibres. It isn’t very common.
What ECG changes happen in RBBB?
- QRS duration >0.12s (broad complex)
MaRRoW
- V1/V2: the QRS complex appears as an M
- V6: appears to have a W due to the broad S wave and S wave duration which is longer than the R wave duration
- ST changes that occur secondary to the other changes (because if depolarisation is whacky repolarisation will also be whacky): V1-V2 have down-sloping ST and TWI
What ECG changes happen in LBBB?
- QRS duration >0.12s (broad complex)
WiLLiaM
- V1/V2: the R wave is missing or smaller (R wave is normally the depolarisation of the LV wall as the electrical signals pass through the L+R bundle branches), so you have a broad and deep S wave which can be notched like a W
- V6: broad, clumsy, often notched R wave (looks like an M)
- ST changes: V1-3 = ST elevation and positive t waves. V5/6= TWI and ST depression
What are some overall characteristics of SVTs?
Narrow QRS complexes
Because the block is AV node or above, the conduction through the His-Bundle-Purkinje system is usually normal (unless an aberrant conduction issue like BB) so the QRS during the tachycardia is usually similar to that seen in the same patient at their baseline
What are the features of Slow-Fast AVNRT? (the most common)
Slow-Fast AVNRT =
- Slow AV nodal pathway for anterograde and fast AV nodal path retrograde
Rate is 140-280 bpm and it’s regular
P waves= either hidden behind the QRS complexes (because they’re retrograde) or appear as a pseudo R wave at the end of the QRS in V1
SO the typical SVT appearance of absent P waves and tachycardia!!
What are the features of Pre-Excitation on ECG?
Pre-excitation (e.g. WPW)
- Short PR interval <0.12s (because the QRS starts earlier than expected)
- Delta wave at the start of the QRS from the early depolarisation of the ventricles by the accessory path (broad QRS) which can cause a broad QRS
What is Torsades de Pointes?
A specific type of polymorphic ventricular tachycardia (PVT) that occurs in the context of QT prolongated
It has a characteristic morphology in which the QRS complexes twist around the isoelectric line
Can degenerate in VF but does usually self-terminate relatively quick
