Diagnostics Flashcards
What is the PR interval and what does it reflect?
- It’s the time imterval from the start of the p wave to the start of the QRS complex
- It reflects conduction through the AV node
What is the normal duration for the PR interval?
120-200ms
or 3-5 small squares
What ECG change is consistent with 1st degree heart block?
PR interval > 200ms
What does a PR interval or < 120ms suggest?
Pre-excitation (i.e. the presence of an accessory pathway between the atria and ventricles.
or AV nodal (junctional) rhythm
What is second degree heart block, mobitz type 1?
Successive prolongation of the PR interval until a QRS complex is dropped
Also called Wenckebach phenomenon
What are pre-excitation syndromes?
e.g. WPW and Lown-Ganong-Levine (LGL)
An accessory pathway connects the atria and ventricles
The accessory pathway conducts impulses faster than normal
It may also act an a re-entry circuit, predisposing the individual to re-entrant tachyarrhythmias
What are the characteristic ECG features of WPW syndrome?
Short PR interval
Widened QRS
Slurred upstroke to the QRS complex - the delta wave
What are the ECG features of Lown-Ganong-Levine syndrome?
Very short PR interval
Normal P waves and QRS waves and no delta waves
What are the ECG features of an AV nodal rhythm?
They are narrow complex regular rhythms arising from the AVN
P waves are either absent of abnormal (possibly inverted) with a short PR interval (=retrograde p waves)
What is a Q wave?
Any negative deflection that precedes an R wave
What does the Q wave represent?
The normal left to right depolarisation of the IV septum
Describe normal Q waves
- Small Q waves are typically seen in left sided leads (I, aVL, V5, V6)
- Small Q waves are normal in most leads
- Deeper Q waves (>2mm) may be seen in aVR and III
- Not normally seen in V1-3
When are Q waves considered pathological?
- > 40ms wide (1mm)
- > 2mm deep
- > 25% depth of the QRS complex
- Seen in leads V1-V3
What is the differential diagnosis of pathological Q waves?
Myocardial infarction
Cardiomyopathy
Extreme rotation of the heart
Lead placement errors
Is absence of Q waves in V5-6 considered normal?
- No
- Normally absent in LBBB
What is the R wave?
First upward deflection after the P wave
What does the R wave represent?
Early ventricular depolarisation
What are the 3 key R wave abnormalities?
Dominant R wave in V1
Dominant R wave in aVR
Poor R wave progression
What is the differential diagnosis of a dominant R wave in V1?
- Normal in children and young adults
- RVH - PE, persistant infantile patern, L-R shunt
- RBBB
- Post MI
- Incorrect lead placement (V1-3 switched)
- Dextrocardia
- Hypertrophic cardiomyopathy
- Dystrophy
What is the differential diagnosis of a dominant R wave in aVR?
- Sodium-channel blocking drugs poisoning e.g. TCA overdose
- Dextrocardia
- Incorrect lead placement
- VT
What is poor R wave progression?
R wave < 3mm in V3
What causes poor R waves progression?
Prior anteroseptal MI LVH Inaccurate lead placement May be normal Absent R wave progression is characteristically seen in dextrocardia
What is the normal QRS width?
70-100ms
Where do narrow QRS complexes originate from?
Supraventricular
- which could be sinus node (normal p wave)
- atria (abnormal p wave e.g. AF, flutter)
- AVN - absent or abnormal p wave with PR < 120ms
Where do broad QRS complexes originate from?
Either ventricular
or
Supraventricular with abberant conduction e.g. BBB, hyperkalaemia or sodium channel blockade
What causes aberrant conduction of QRS complexes?
BBB Hyperkalaemia Sodium channel blockade Ventricular pacing Hypothermia WPW
How wide does the QRS complex have to be to diagnose BBB?
> 120ms
What ECG changes are characteristic of RBBB?
RSR’ pattern in V1
Deep slurred S waves in the lateral leads
Widened QRS
What ECG changes are characteristic of LBBB?
Dominant S in V1
Broad notched R waves and absent Q waves in lateral leads
Widened QRS
What does high voltage QRS morphology mean?
Usually taken in infer LVH
May be normal in patients < 45 esp if slim and athletic
Describe the voltage criteria for LVH
Multiple voltage criteria exist
Most common are the Skolov-Lyon criteria
S wave in V1 and tallest R wave V5/6 > 35mm
Voltage criteria must be accompanied by non-voltage criteria to be diagnostic of LVH
What is the criteria for low-voltage QRS morphology?
< 5mm in all limb leads
< 10mm in all precordial leads
What is electrical alternans?
Alternating height of the QRS complex
Can be due to a massive pericardial effusion
What is Wellens syndrome?
Biphasic T wave changes in V2-3
Indicate reperfusion of LAD territory
What ECG changes are consistent with severe hypokalaemia?
Widespread ST depression/T wave inversion
Prominent Q waves
Long QU interval (> 500ms)
Which ECG leads does inferior ischaemia affect and which artery is implicated?
RCA
II, III, aVF
Which ECG leads does lateral ischaemia affect and which artery is implicated?
Circumflex or diagonal
I, aVL +/-V6
Which ECG leads does posterior ischaemia affect and which artery is implicated?
RCA or circumflex artery
R wave in V1-2 with ST depression
Which ECG leads does anterior ischaemia affect and which artery is implicated?
I, aVL, V2-5
Left anterior descending
Which ECG leads does anteroseptal ischaemia show up in?
V2-4
Which ECG leads does anterolater ischaemia show up in?
V3-5
Which ECG leads does apical ischaemia show up in and which artery is involved?
Left anterior descending artery
II, III, aVF, V5-6
