Challenging the Holy Grail of Echo
Left ventricular ejection fraction (LVEF) is the “Holy Grail of cardiology”. When you enter the keyword “ejection fraction” into the search engine of pubmed you will get close to 40,000 hits. If you use the term in Google you get over 1,2 Million. Ejection fraction is everywhere. It is used to define disease, determine its severity, establish the prognosis and most of all to guide therapy. Ejection fraction is part of many guidelines. Based on cut off values for LVEF we recommend valve operation, ICD implantation or even which medication patients should receive. We are literally “forced” to obey to the Holy Grail of ejection fraction in our daily practice. But should we really follow blindly? Sure, it is cool to have a number available that gives you guidance, something to cling to in the world of uncertainty.
There is one problem: The ejection fraction we get does not tell us the entire story. In some situations it is even misleading. And I am not talking about false measurements due to technical limitations or poor image quality. (This itself is another story). Let me give you some examples to show you what I mean:
Dyssynchrony and LVEF
Look at the left ventricle in this patient: LVF is reduced right? When we calculated EF we got a value of 48%.
Does the patient truly have a cardiomyopathy? No he does not. His problem is simply dyssynchrony caused by a left bundle branch block. This does not allow us to define end-diastole and end-systole when we calculate ejection fraction. The septum and the lateral wall show their maximum inward- or outward motion at different times. This young patient (35a) is otherwise completely healthy and rides his mountain bike up and down the steepest trails.
Myocardial infarction and LVEF
Imagine you have a patient who just had a myocardial infarction and you read the echo report, which tells you that his LVEF is 59%? Your conclusion: the infarct was not so large just a little “graze” shot. But take a closer look at the echo of just such a patient:
This woman had an acute anterior infarct. Is the infarcted area really so small? No – several segments are involved (distal septum, part of the medial anterior septum and apex). His LVEF turns out to be normal because the remaining segments are hypercontractile. They compensate for the areas that are ischemic / necrotic. Again the LVEF does not tell the entire story.
The small ventricle and EF
And what about the following case? Here we calculated an EF of 63%. Is left ventricular function really as good as the value indicates?
The answer is again no; the patient has severe left ventricular hypertrophy and a rather small ventricle. In the setting of a small ventricle there simply must be exaggerated motion of the myocardium so that an adequate stroke volume can be maintained. What will happen when the patient exercises’? He will rapidly come to a point were a further increase in the ejection fraction is not possible. His exercise capacity is limited. What does this tell us? LVEF overestimated the function of the heart in small ventricles. Are you ready for more?
Afterload and EF
What about left ventricular function in this patient with very severe mitral regurgitation?
better than it actually is.
Afterload is the resistance against which the left ventricle must contract. If there is a hole in the mitral valve (regurgitation) resistance to contraction is reduced. Left ventricular function will look better than it actually is. To help you understand this principle. Imagine you are in the fitness center and you are on one of these training machines. If you load up only a few pounds the others in the fitness center will be impressed if they see how easy you can lift the wait (You only have to keep the weight you are lifting hidden). We can only determine your muscle strength if we also consider how much pounds you are lifting. Can we really predict how good contractility is by using EF in the setting of mitral regurgitation? My honest feeling is no: Even if we try to account for the presence of reduced afterload and set a higher limit for normal (i.e. 60%) we can still misjudge LV function. I have seen patients with severe MR and an EF of over 70% in whom MV repair was performed and in where the EF dropped far below 55% after operation.
Regional Wall motion abnormalities and EF
The following patient had a postero-lateral myocardial infarction. Still we calculated a normal EF using the biplane Simpson (65%). Does this value really represent left ventricular function? Certainly not. With biplane Simpson we use a four- and a two-chamber view. The segments visualized in these views were normal. This is why we overestimate EF in this patient:
This view is not used to calculate biplane Simpson EF.
Despite this limitation of the Biplane Simpson it is still used in many studies of patients with coronary artery disease regardless of the issue if the postero-lateral wall is scarred or not. Let me ask you: Does it make sense to use a strict cut off value of 35% (determined by Biplane Simpson) in a patient with segmental wall motion abnormalities to determine if he should get an ICD? I honestly have my doubts (please leave your thoughts in the comments, I am a curious to read your opinion). Is there a solution to the problem? Is there a way to really understand ventricular function?
Light in the distance:
I think there is. First, we have to understand the limitations of EF calculations. Ejection fraction is NOT the Holy Grail. Second we should also use other modalities that provide additional information. One of the most promising techniques that can help us is deformation imaging. Deformation Imaging looks at function at the myocardial level. This can be done with a methodology called speckle tracking. Here is just one example to illustrate the potential benefits of this method; A patient with severe aortic stenosis:
How good is LVF really?
Again we see a small ventricle where LVF seems normal, his EF is 69% but if we look at longitudinal function of the ventricle using Speckle Tracking Echocardiography (STE) we see that not all segments contract normally.
Bulls –Eye display of regional longitudinal function
in the same patient as above (aortic stenosis).
Function is already reduced in the basal segment (pink and blue opposed to red). This is an early sign that LVF is starting to deteriorate. Speckle Tracking Echocardiography is evolving quickly as a very important tool to detect early left ventricular dysfunction, there are even patterns of dysfunction that are indicative of specific disease entities. In some conditions STE might even be superior to LVEF in describing left ventricular function.
My prediction: STE will sooner or later become a standard procedure in many patients. It will change our understanding of left ventricular dysfunction and be used in guidelines and recommendations. While LVEF measurements will certainly not vanish STE will at least cast a shadow on LVEF as the “holy grail” in cardiology.
PS: More Interesting cases can be found on our Blog!