There are two aspects to this – when to echo and what to look for.
When to Echo
With established KD, its relatively easy, and most will follow guidance such as the comprehensive protocol detailed in McCrindle et al.‘s 2017 AHA consensus document published in Circulation. The description of what to do starts on page e940 and the timings are on e943.
Briefly, echo should be done at these times in suspected or confirmed KD:
- when the diagnosis is first considered
- between 1 and 2 weeks after the initial images
- between 4 and 6 weeks after treatment
If all normal, that’s it. However if there are abnormalities – bright coronaries, dilated coronaries (Z>2.5) then twice weekly imaging until dilatation has stopped. Thereafter, guidance from a centre is needed to plan further imaging.
Much is made of the Z score. This is a measure of the distance away from the mean, in relation to the standard deviation. So mean is 0, one SD above the mean is +1, two SD’s about the mean is +2. This is super useful at monitoring bits of anatomy in children.
There are several Z score apps around. The excellent Cardio Z app https://apps.apple.com/gb/app/cardio-z/id494844989 does this and so much more super efficiently.
What to Echo
KD causes a vasculitis of medium sized arteries, a myocarditis, pericarditis and valvulitis. It can also lead to vasoplegia (ie abnormal and inappropriate vasodilation). Patients presenting with a low BP or low output state may have preload issues due to third space losses, poor pump function, valve dysfunction or cardiac ischaemia. The echo in this situation should look for all of these issues and be combined with an ECG. Subsequent scans, if the first was normal and the patient clinically stable, can be more focussed on the coronaries.
Essential views for initial echo:
- SC Longditudinal – to assess right heart filling.
- IVC dimensions
- emptying during respiration
- Apical 4 chamber – to assess ventricular function and performance
- comparison of RV and LV size
- review RV and especially LV filling and emptying pattern
- MV e/a ratio or…
- TAPSE can also be useful
- VTi to estimate cardiac output (not essential)
- Parasternal Long Axis – to assess LV performance and regional wall motion
- view of LV contraction
- M-Mode measurement of Fractional Shortening (NR >30%)
- Parasternal Short Axis (ventricles) – to assess LV performance and regional wall motion
- view of LV contraction at several levels looking for non-circumferential wall motion
- Parasternal Short Axis (coronaries) – self-explanatory
First up, this is a normal view – see how the IVC is basically fairly full all the time, but does vary in time with breathing. To accentuate this, you can get the patient to sniff, so long as they are not ventilated.
The IVC may be empty with third space losses in acute KD, or already be full. The second loop shows this. This patient is not going to be fluid responsive if they are hypotensive.
Apical 4 chamber
Here is what it should look like – normal and abnormal (look at the poor apical contraction in the second clip).
Parasternal Long Axis
Here is a normal view of a LA, and then one with globally impaired function:
Parasternal Short Axis (ventricles)
Ideally view at level at the papillary muscles of the LV. This is a good place to look for regional wall movement abnormalities. Here is a schematic of the difference sections of the LV at this level and a still from a short axis view.
Here is what it should look like – normal and abnormal, with oedema and poor movement of the mid anterior and lateral segments:
Parasternal Short Axis (coronaries)
The way to get the coronaries seen is by first getting a really nice round aortic ring with the valve leaflets opening clearly. Then look a tiny bit higher. This should bring in the coronaries.
The RCA is usually at between 10 and 12 o’clock, the LCA between 3 and 5 o’clock.
Here’s what it looks like on a loop:
More pictures, more reading…check out this excellent book chapter on echo in KD with some great images of dilated arteries.