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