General

Are thick LV walls the same as LV hypertrophy??

Measuring left ventricular size and wall thickness is a standard part of the routine echo examination. There are normative values for LV wall thickness, and the trainee sonographer is taught basic pattern-recognition in the early phases of training to identify patients with left ventricular hypertrophy.  It is often assumed that Thick walls = hypertrophy. However the influence of left ventricular volume to wall thickness is completely overlooked in that equation. Today’s post looks at the relationship (or interaction) between wall thickness, LV volume and LV hypertrophy.

The 2015 ASE guidelines for chamber quantification describe a normal LV wall thickness (IVS or PW) as 0.6-1.0 cm (male) and 0.6-0.9 cm (female). This is measured at the blood tissue interface using either 2D or m-mode, typically from the PLAX view. An increased wall thickness may be suggestive of LV hypertrophy, however as an isolated number we have no indication about LV modelling, or left ventricular mass. During a recent heart dissection tutorial, one of my students made the observation that the cow’s heart they had cut open had very thick LV walls. This was a true statement, but the blood had been emptied from the heart and the remaining cavity size was much less than the usual diastolic chamber size. It is a bit like a helium balloon…when the balloon is empty, the balloon is very small and the wall of the balloon is quite thick (too thick to see through). When we inflate the balloon, the cavity increases in size, but the wall thickness is stretched to be quite thin and translucent. The wall is remodelled to accommodate the increase in chamber size. This is exactly what is happening in the heart.

But who cares? I never look at empty hearts…

True statement, but we do look at a lot of underfilled hearts, particularly in a post operative setting. In this example, we see a septal and posterior wall thickness measuring 11mm.

Original PLAX view. Upper normal wall thickness. LV mass - 214g.

Original PLAX view. LV mass – 214g.

The following echo was then performed 6 months later in the setting of marked hypotension post septic knee washout. Note the drastic increase in wall thickness, now measuring 14 mm. The wall muscle has not hypertrophied in this time. It has not had an increase in the number of fibres in the myocardium. The ventricle has remodelled due to the drastically reduced blood volume in the LV. The walls are like that of a deflated balloon. The right ventricle has become severely hypokinetic and the left ventricle is underfilled as a result (was 51mm – now 40 mm).

PLAX view in ICU.

PLAX view 6 months later in ICU. Note the increase in wall thickness, but no significant change in LV mass – 209g.

A4C view - note the severely hypokinetic right ventricle and underfilled left ventricle.

A4C view – note the severely hypokinetic right ventricle and underfilled left ventricle.

Looking solely at the wall thickness we may draw the wrong conclusion…but let’s look at the LV mass in this patient. The left ventricular mass looks at the total heart volume (epicardial volume) and subtracts the volume of blood that is in the cavity (endocardial volume) to be left with a myocardial volume. The volume is multiplied by the specific gravity of tissue (a standard factor of 1.05) to estimate a left ventricular mass.

mass form

There are several techniques for measuring mass by echo, but for simplicity of this case, I will use the linear method (cubed equation). I don’t want to get bogged down in pros/cons of the various techniques… I just want to focus on the big picture and this is the easiest way to make the point. Read the 2015 ASE guidelines for chamber quantification (table 5) for more information on the different techniques… and remember, if you are going to report a mass, it should ALWAYS be indexed to patient size.

LV Mass=0.8(1.04((LVEDD+IVSd+PWd)³−LVEDD³))+0.6

Using the cubed formula in this case, we can see that the mass is within 5g of each other between the 2 studies, despite a marked increase in absolute numbers of wall thickness. Yes, the wall thickness has increased, but this is not due to hypertrophy or an increase in mass. It is just that the LV is underfilled. More than likely (based on the mass calculation) if we inflated the LV to 51mm, the walls would stretch out to be closer to 11mm, rather than 14mm.

mass graph_mm

 

The take home point is to consider the serial data carefully. An increase in wall thickness, must always be taken in the context of changes to LV cavity size.

Not the point of this post, but still an important point…  I always suggest the use of contrast enhancement (Definity) if you are going to report increased wall thickness. There are too many examples of inadequate border delineation with standard 2D imaging which can be easily resolved with contrast.

Enjoy!

Echo.Guru

A special thankyou to Tony Call and Hearts 1st for supplying the case for today’s post.

UPDATE: A couple of readers have emailed me highlighting other processes which can cause an increase in wall thickness which is not due to hypertrophy of the myocardium. This includes infiltrative processes such as amyloidosis and tumor invading the myocardium. This was a deliberate omission from Echo.Guru as I wanted to focus on the concept of LV volume loading and how this influences LV wall thickness. The processes can be differentiated by looking at the calculated mass (hypovolumia will result in an increase in wall thickness without an increase in mass, whereas any of the other processes will typically increase mass as well).

Subscribe to be updated on new Echo.Guru posts

Enter your email address to subscribe to this blog and receive notifications of new posts by email.


Title image courtesy of Hyena Reality at FreeDigitalPhotos.net

Previous Post Next Post

You Might Also Like

10 Comments

  • Reply LITFL Review 167 - LITFL February 1, 2015 at 11:01 pm

    […] a great post from the Echo Guru on why LV wall thickness is not the same as LV hypertrophy. Useful for critical care echo practitioners. […]

  • Reply Ken Spencer February 3, 2015 at 3:50 pm

    Such a great technique using beautiful case images and short written notes to focus the reader.

  • Reply Kristen Billick October 9, 2015 at 9:12 pm

    I think it is also important to inform people of using relative wall thickness combined with LV mass to divide into concentric LVH, concentric remodeling, eccentric hypertrophy, and normal. This is also in the guidelines and it is how we grade hypertrophy/wall thickness in our lab.

    • Reply echoguru October 9, 2015 at 10:18 pm

      I agree Kristen. The type of hypertrophy is absolutely important. I will cover that in a different post…just really wanted to focus on the concept that not all increases in thickness is due to hypertrophy. We often think of this with infiltrative processes, but hypovolemia is a much more common scenario that rarely gets a mention.

      • Reply Margaret May 13, 2016 at 10:58 am

        I have an IVSd of 1.29 LV Mass of 129.1. Could this increase be cause of dehydration? Or weight gain?

        • Reply Margaret May 13, 2016 at 10:59 am

          My report states all is normal??

          • echoguru May 18, 2016 at 11:27 pm

            Hi Margaret
            I am unable to comment on the findings of a report. This site is an educational site for sonographers to discuss techniques and practice to improve their skills. I acknowledge the importance of clinical correlation. We may debate findings from time to time, but this is largely in isolation from the clinical background. The clinician takes the findings from the testing and uses that as a tool in forming a clinical diagnosis. I suggest that if you have questions related specifically to your echo findings, that you discuss this with your physician, or obtain a second opinion from another physician. Best of luck.

        • Reply echoguru May 13, 2016 at 11:00 am

          Hi Margaret, without seeing the pictures or additional data, it is impossible to say. Rarely is an echo diagnosis made from limited data points.

  • Reply Kiara Kimona-Smith May 18, 2016 at 3:40 pm

    I am glad I stumbled upon this sight very informative. I have found in echo patients who are diagnosed with POTS that their wall thickness is slightly abnormal when they are having symptoms and normal when they are hydrated although their LV Mass still is in normal range. Have any of you had any POTS patients that you have performed an echo on that had an abnormal thickness that was not hypertrophy

  • Reply theophilus September 9, 2017 at 11:45 am

    what is your take when you have normal wall thickness values, normal LV mass index , but the Relative Wall Thickness (RWT) is higher than normal (>0.42). Will you consider this as concentric LV remodeling. I usually feel uncomfortable labelling otherwise normal patients with this assessment simply because the RWT is slightly increased.

  • Leave a Reply

    %d bloggers like this: