Assessment of systolic function in small animal cardiology: is it acceptable to eyeball it?
Conventional teaching in veterinary cardiology tends to put the emphasis on objective, technical methods of assessing systolic function requiring considerable skill: primarily left ventricular ejection fraction by Simpson method of discs (SMOD) and fractional shortening. However, intra- and inter-observer variation is considerable and I worry that even quite experienced sonographers place reliance on numbers which, firstly, may not always be technically accurate and, secondly, may not be mean what people think they mean.
We live in a world with a growing resource of reference ranges. This is undeniably welcome; but tends to imply a cut off between ‘normal’ and ‘pathological’ which isn’t always helpful.
One could be slightly cynical and suggest that for veterinary cardiologists it’s nice to have exclusive access to a technically-demanding tool which confers special powers. How frustrating it would be to train for years and then find that eyeballing systolic function is just as good…or better!
Int J Cardiol 2005 May 25;101(2):209-1
Visually estimated left ventricular ejection fraction by echocardiography is closely correlated with formal quantitative methods
Petri Gudmundsson, Erik Rydberg, Reidar Winter, Ronnie Willenheimer
https://pubmed.ncbi.nlm.nih.gov/15882665/
Yes, this is a human study.
‘This finding is in concordance with prior studies, indicating that eyeballing ejection fraction may be the most accurate echocardiographic method for the assessment of left ventricular systolic function. Since it is readily and quickly performed, eyeballing ejection fraction could be used for routine echocardiography instead of formal methods.‘
Estimated values, inter-observer and intra-observer variability were all very similar to quantitative measures.
It’s good to challenge conventions and this paper is worth considering with respect to veterinary small animal cardiology.
‘Compared to visual quantification, formal quantitative measurements of left ventricular ejection fraction, such as single- or biplane Simpson ejection fraction, may be considered superior echocardiographic methods for clinical and scientific use, because these methods may appear to be little
influenced by subjectivity. But these methods are influenced by subjectivity, since the decision about were to mark the endocardial borders is subjective.‘
Not only are formal quantitative measures non-superior they also take longer to perform. Admittedly, we’re not talking hours. On the other hand, if you’re going to rely on EF by SMOD then I think it’s good practice to take several sets of measurements and average them. In veterinary medicine it’s more than just a matter of efficiency, time and money: a lot of canine and especially feline patients will tolerate a brief echocardiogram but become progressively more difficult to restrain and to assess accurately. A longer examination increases the chances of needing sedation. More fundamentally, there’s a risk of ending up obsessing over measurements while missing the wider picture. Veterinary sonographers are likely to be responsible for a significant part of patient management and decision-making. We’re not generally just echocardiography technicians. If you’ve done the basic echocardiogram quickly then there’s more time to do a better physical exam or to scan, for example, thyroids, abdomen or vessels which may have an important bearing on case management.
It’s important to say that the sonographers in this study were experienced and qualified human echocardiographers. These guys obviously have considerable background in conventional quantitative methods which must inform their judgement when visually estimating systolic function. That’s a big qualification on the central premise of the study: it doesn’t mean that novice sonographers can just pick up a probe and accurately guess systolic function.
So, what level of experience is required? This issue has also been examined in the human field:
Clin Cardiol 1995;18:726 – 9
Visual estimation of ejection fraction by two-dimensional echocardiography: the learning curve.
Akinboboye O, Sumner J, Gopal A, et al.
https://onlinelibrary.wiley.com/doi/abs/10.1002/clc.4960181208?sid=nlm%3Apubmed
In summary, these authors found that if a person with no previous experience of echocardiography, after each evaluation is given instant feedback from a gold standard, only about 60 evaluations are required to achieve the same accuracy as an experienced echocardiographer.
OK, so if you’re an inexperienced vet sonographer (for the sake of argument, fewer than 60 echocardiograms with feedback) then I would argue that quantitative measurements are likely to be unreliable. If I were advising such a practitioner remotely, due to geographical or financial constraints, then I’d much prefer to have their subjective assessment of whether ventricular function looks strong or not: rather than a number of debatable value. Or to subjectively assess it myself by remote video.
For experienced echocardiographers, it’s quite likely (extrapolating from the human data) that a subjective assessment is as good as objective measures in many circumstances. The fact that this might be the case when advising remotely becomes daily more significant. There’s always going to be a balance between wanting as much information as possible in difficult cases vs needing to be quick in urgent scenarios. A hypothetical case where I would want a quantitative measure is a Cocker Spaniel with poor systolic function…where a 5% improvement over a few months with taurine is useful information.
Personally, I find that doing a lot of measurements and taking longer to scan usually just detracts from my overall case management. Or I’m just lazy!
