Echo assessment of LV diastolic function

Assessing left ventricular diastolic function can get complicated. However, things were made a bit easier recently with the publication of some new joint ASE/EACVI guidelines on the echo evaluation of LV diastolic function. The guidelines are detailed (they're almost 40 pages long), but the principal take home message can be summarized as follows:

Echo diagnosis of LV diastolic dysfunction

The guidelines recommend measuring four key parameters to assess LV diastolic function:

Annular e' velocity

An abnormal e' velocity is indicated by a septal e' <7 cm/s, or a lateral e' <10 cm/s.

Average E/e' ratio

The authors recommend that an average E/e' ratio is used (rather than separate septal and lateral E/e' ratios), and that the average E/e' ratio is considered to be abnormal if it is >14. If an average can't be calculated, then a lateral E/e' >13, or a septal E/e' >15, is considered to be abnormal.

Left atrial volume index

The left atrial maximum volume index is abnormal if it is >34 mL/m2.

Peak tricuspid regurgitation velocity

This is abnormal if peak TR velocity is >2.8 m/s.

Judging whether LV diastolic function is normal or abnormal depends upon how many of the measured parameters are abnormal:

• If more than 50% of the measured variables are abnormal, then LV diastolic function is abnormal
• If less than 50% of the measured variables are abnormal, then LV diastolic function is normal
• If 50% of the measured variables are abnormal, then LV diastolic function is indeterminate

This method of using the majority of available parameters to make an overall judgement about LV diastolic function is useful, as it allows a conclusion to be made about diastolic function even if all four parameters aren't available.

The guidelines can be found by clicking here, and are well worth reading. As well as giving overall advice about the echo assessment of LV diastolic function, they also contain guidance on assessing diastolic function in specific situations (such as atrial fibrillation and hypertrophic cardiomyopathy).

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Understanding LVH: Concentric versus eccentric hypertrophy

When we talk about left ventricular hypertrophy (LVH) in cardiac imaging, the terms concentric LVH and eccentric LVH are often used. However the word 'eccentric' sometimes causes confusion - it's important to realise that the word 'eccentric' does not mean 'asymmetric' in the context of LVH. So what is eccentric LVH, and how does it differ from concentric LVH?

Cardiac MRI showing severe concentric LVH

Concentric LVH is seen in situations where there is pressure overload of the left ventricle. Examples include hypertension and aortic stenosis. The heart adapts to pressure overload by adding new sarcomeres in parallel to existing sarcomeres. This leads to an increase in left ventricular wall thickness and left ventricular mass, but the cavity size remains normal.

Eccentric LVH, in contrast, occurs when there is volume overload of the left ventricle. This is seen with valvular regurgitation (aortic or mitral), or can occur as a result of cardiac remodelling in endurance athletes. In this situation, the heart adapts to volume overload by adding new sarcomeres in series with existing sarcomeres. The end result is an increase in left ventricular cavity size and an increase in left ventricular mass, but the wall thickness remains normal.

Concentric versus eccentric LVH

If you'd like to read more on this topic, check out these links:

Mihl C, et al. Cardiac remodelling: concentric versus eccentric hypertrophy in strength and endurance athletes. Neth Heart J 2008; 16: 129–133.

Marwick TH, et al. Recommendations on the use of echocardiography in adult hypertension: a report from the European Association of Cardiovascular Imaging (EACVI) and the American Society of Echocardiography (ASE). European Heart Journal – Cardiovascular Imaging 2015; 16: 577-605.

Surrogate markers of LV systolic function: dP/dt

In a recent blog post we looked at the use of E-point septal separation (EPSS) as a surrogate marker of left ventricular systolic function. In this blog, we're going to look at another surrogate marker, namely dP/dt.

When left ventricular systolic function is normal, there is a rapid rise in left ventricular systolic pressure during systole. The rate at which the ventricular pressure rises is expressed by the term dP/dt, which is the rate of change in pressure (dP) with time (dt). If left ventricular systolic function becomes impaired, the rate of rise in pressure is slower and therefore dP/dt starts to fall.

Measurement of dP/dt using CW Doppler of mitral regurgitation

It's possible to measure dP/dt using echocardiography, but only if mitral regurgitation is present. To make the measurement, we need to obtain a continuous wave (CW) Doppler trace of the mitral regurgitation (MR) from the apical 4-chamber view. It's helpful to set the sweep speed as high as possible, to 'spread out' the trace (this makes it easier to take the measurements).

Freeze the CW Doppler trace, and using the calipers mark the points where the mitral regurgitation jet velocity is 1 m/s and 3 m/s. You need to measure the time interval between these two points, i.e. the time taken for the MR jet velocity to rise from 1 m/s to 3 m/s. The illustration above shows how this measurement is made.

We know from the Bernoulli equation that when the MR jet velocity is 1 m/s, the pressure gradient 'driving' the jet is 4 mmHg (pressure gradient = 4 x velocity squared). Similarly, when the MR jet velocity is 3 m/s, the pressure gradient driving it is 36 mmHg. From this, we can deduce that the change in pressure between the two time points is 32 mmHg (36 mmg minus 4 mmHg).

It's now possible for us to calculate dP/dt, by dividing 32 (the 'dP') by the measured time interval (the 'dt'). The longer it takes for the pressure in the left ventricle to rise during systole, the longer the duration of dt, and therefore the smaller the value of dP/dt.

When left ventricular systolic function is normal, dP/dt is usually >1200 mmHg/s. As left ventricular function deteriorates, dP/dt falls. A severely impaired left ventricle usually has a dP/dt <800 mmHg/s.

So, if your patient has measurable mitral regurgitation, you can use the dP/dt method to assess their left ventricular systolic function. However, there are a couple of pitfalls - the dP/dt method isn't reliable if the mitral regurgitation is acute, or if there is significantly increased afterload (aortic stenosis or systemic hypertension).

You can read more about dP/dt in my textbook, Making Sense of Echocardiography (2nd edition), or in the following paper:

Chung N, et al. Measurement of left ventricular dP/dt by simultaneous Doppler echocardiography and cardiac catheterization. J Am Soc Echocardiogr 1992; 5: 147-152.

Is a left ventricular ejection fraction of 50% 'normal'?

What is a normal left ventricular ejection fraction? A seemingly straightforward question and, if you work in cardiology, you'll probably already have a specific number in mind. But this number probably depends upon which guidelines you use.

There's a surprising variation between guidelines in what is deemed a 'normal' LVEF, and this confusion of reference values has been added to this month with the publication of the ESC's 2016 Heart Failure Guidelines.

Calculating left ventricular end-diastolic volume

If you work in the US, then you probably use the ASE recommendations for cardiac chamber quantification, published in 2015. For 2D echo, there are separate normal ranges for males and females. For males, a normal LVEF is 52-72%, and for females it's 54-74%.

If you work in the UK, then you'll most likely use the BSE guidelines for chamber quantification. According to these, for males and females a normal LVEF is 55% or above. Anything less than 55% is 'impaired'.

So in the US, an LVEF of 54% would be labelled 'normal', whereas in the UK it would be labelled as 'impaired'. A difference of just a few percent might seem like splitting hairs, but the diagnostic labels we give our patients matter - just ask someone who's trying to buy life insurance how much difference a label of 'impaired LV function' can make.

Things have become even more confusing this month with the publication of the European Society of Cardiology's new guidelines on heart failure. These take a new approach to diagnostic labels in heart failure, differentiating between 'reduced' LVEF (<40%) and 'mid-range' LVEF (40-49%). However they clearly identify a 'preserved' LVEF as being 50% or above.

So now we have three different cut-off values for what constitutes a 'normal' LVEF: 50% (ESC), 52%/54% (ASE), and 55% (BSE). Oh, and for one added layer of confusion, the ASE guidelines are endorsed by the European Association of Cardiovascular Imaging, a community of the ESC - so one organisation effectively promotes two different 'normal' values.

One thing that is clear is that there's a grey area around those with 'borderline' LVEF measurements, and a lot of work remains to be done to define which treatments are appropriate within this group. By highlighting those with 'mid-range' LVEFs with their new diagnostic category of HFmrEF, the new ESC guidelines have made a start in encouraging work on this group.

But for those whose LVEFs are somewhere in the low 50's, I suspect it's going to be some time before we can agree upon a clear definition for those all-important diagnostic labels.

Surrogate markers of LV systolic function: EPSS

When we assess left ventricular systolic function with echocardiography, we usually think in terms of left ventricular ejection fraction. But there are many other indicators of left ventricular function, some of which are rarely used. One of these is E-point septal separation, or EPSS.

Increased EPSS in severe dilated cardiomyopathy

EPSS refers to the distance between the anterior leaflet of the mitral valve and the interventricular septum during early diastole. This is easiest to measure using M-mode echo, and the measurement is taken when the anterior mitral leaflet is at its closest to the septum (see image).

Normally, the EPSS is no more than 6mm. The distance gets bigger with worsening left ventricular systolic function, and an EPSS >7mm is a sensitive measure for severely impaired systolic function.

What is the mechanism underlying the EPSS method? The increase in EPSS in left ventricular systolic dysfunction is partly because of ventricular dilatation causing the separation between the anterior mitral leaflet and the septum to increase, but also because of a reduced transmitral flow volume causing the mitral leaflets to open less widely during diastole.

So an increased EPSS is a surrogate marker of impaired left ventricular systolic function. However, you can't use EPSS in mitral stenosis or aortic regurgitation (both of which will falsely increase the EPSS because the anterior leaflet opens less fully), nor should it be used in the presence of septal hypertrophy (which tends to falsely reduce the EPSS).

To read about the value of EPSS in bedside echo, check out the following paper:

McKaigney CJ, Krantz MJ, La Rocque CL, et al. E-point septal separation: a bedside tool for emergency physician assessment of left ventricular ejection fraction. Am J Emerg Med 2014; 32: 493-497.