ECG - Cardiac chamber enlargement Flashcards
Why does the voltage of the QRS complexes in chest leads increase in LVH?
LV muscle mass causes greater depolarisation currents
What are the sokolow-lyon criteria?
S(V1) + R (V5 or V6) > 35mm = LVH
What is the LV strain pattern in LVH?
ST elevation in leads V1-3 and ST depression in V4-6
Why does the LV strain pattern occur in LVH?
Due to thickened wall myocardial cells beginning to repolarise before entire wall has depolarised, due to them reaching their intrinsic depolarisation time. This means the overall direction of repolarisation ends up being in the same direction as depolarisation, causing inversion of T waves and ST depression
What do you need to be careful of in someone with suspected LV strain pattern in LVH?
Check these changes are chronic - easy to confuse with ACS changes
What criteria are used to diagnose RVH on ECG?
- V1 - R wave >/= 7ss or R wave V1:Swave V6 ratio > 1
- Can also have positive QRS in V2 and V3
- Can have right axis deviation
Why can you get T-wave inversion in RVH?
Secondary to T-wave inversion - not necessarily due to acute ischaemia
What proportion of RVH can be diagnosed from ECG analysis alone?
1/5th
How does atrial depolarisation cause the P-wave deflection on ECG?
Atrial depolarisation moves towards leads I, II and III. If axis is normal, p-wave will be tallest in lead II. The p-wave axis can be determined based on how positive/negative p-waves are in the limb leads and augmented leads
If atrial depolarisation axis was normal, would p-wave deflection be positive, isoelectric or negative in lead aVR?
Negative
Why can normal p-wave be considered as two overlapping components?
Due to location of SA node, RA depolarises slightly before LA. The overal p-wave produced is an amalgam of the depolarisation of each together
What changes occur in RA enlargement on ECG?
Increased amplitude due to dilatation, leading to increased depolarisation vector down through RA. This causes taller peaked p-waves in inferior leads, but p-wave duration remains normal. The p-wave axis may also shift
What criteria are used to diagnose RA enlargement on ECG?
P-wave > 2.5 ss in leads II, III and aVF
What changes occur on the ECG in LA enlargement?
LA enlarges away from SA node. This prolongs the LA component of the p-wave, leading to overall prolongation of p-wave. In some cases, increased asynchrony can occur, leading to 2 identifiable peaks in the p-wave.
What criteria are used to determine if someone has LA enlargement if they have 2 peaks in the p-wave?
> 1 ss bewtween the peaks = p mitrale
Why can V1 have a negative deflection in the p-wave, and why can this be regarded as normal?
Due to orientation of the heart. LA depolarisation moves in opposite direction to V1, causing negative deflection following initial positive deflection
How can LA enlargement affect the negative deflection of the p-wave in lead V1?
Can increase negative deflection. >1 mm depth and width of negative p-wave deflection in V1 is highly suggestive of LA enlargement
What do you need to be aware of when interpreting signs of LA enlargement on ECG?
Signs may not necessarily indicate enlargement - may be due to other pathology which slows conduction in a normal sized atrium. Therefore, changes should be interpreted as “left atrial abnormality” until underlying cause is determined on ECHO
