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Archive for the ‘Echocardiography-hemodynamics’ Category

*The post is not meant for those who understood GLS (Global longitudinal  strain) in a proper perspective. I am writing this, after a surprising answer from many students of Echocardiography, when I asked them what is GLS?  Most answered, GLS currently is the best global LV functional index available. What a misunderstanding? The fact is, EF % will always be the best global parameter*, while GLS remains a regional function index.(*The limitation of EF% is in the methods of measuring it and not in EF itself.)

                                   We are trying hard to ditch LV EF%  by Teichholz’s / even 2D Simpson method, as they are considered a crude way to measure global LV function. Unfortunately, we are doing this without a credible alternative. GLS is being promoted as the next best. The normal GLS is around(-20 ± 2) . Nothing is perfect. Best global LV function probably can be achieved by 3D Voxel Echo/MRI)

Normal GLS with various machines

Please note, the bullseye 17 segment model though brings an illusion of a radial perspective of cardiac contraction, its purely longitudinal stain represented in short axis format.

The much popular GLS (Global longitudinal stain ) is a poor surrogate for global function. The word global is apparently misguiding and conveys a false message. When we refer to GLS, it is an adjective for longitudinal function and nothing to do with overall global LV function. (Though we have many studies to show it has good correlation with global LV function).

The longitudinal function is presumed to contribute 60 % of LV function.  This means GLS is at best 60 % accurate in determining global LV function. Mind you, the heart doesn’t work in a longitudinal plane alone. The muscle fibers of heart are arranged in three distinct fashion (LOC) subendocardial- longitudinal,  Mid-oblique, & Sub epicardial -concentric (Remember LOC ) Each fiber either lengthens or shortens.

The left ventricle not only shortens longitudinally, It also contracts radially, shrinks circumferentially, rotates clockwise at the base (5-10º) , counter rotates at apex (Up to 60º) twist,  & un-twists.  It’s worth reminding ourselves, we are ignoring all these components and happy to fall for GLS.

What can be done to improve the accuracy of true global strain?

The simplest way is, to look LV in  short-axis by 2D and confirm everything is okay with radial contractile forces and deformation. Mind you, the most accurate tool to measure stain is the good old M mode with undisputed temporal (time) resolution ad frame rate the M mode thickening best deformation parameter to measure radial stain ( at a particular plane though).

Is the measurement of true global strain possible?  (GLS+ GRS)

Probably yes. What about GLS plus GRS (Global radial strain)  GLS measured by speckle + RS (Radial thickening by 2D/aided by M Mode)  We are working on a project where the radial strain component is added to GLS. Roughly, it should pull the negative GLS  beyond + 20  (If we assume GRS is + 30 to 60 ) This should be correlated with 3D voxel Echo  /MRI .

Final message

Beware,The “G in GLS” is a perfect miscommunicator. * GLS  can never reflect global LV function. If EF% by M-mode was criticized, for measuring only one aspect of cardiac function ie radial, the same would apply for GLS, in that it measures only longitudinal function. Never discard M mode/2D. It still, pours unadulterated ultrasonic data from myocardial contractile units in the highest resolution. We should continue to use it. In the name of modernity, we make it look outdated.

Reference

M S Amzulescu, M De Craene, H Langet, A Pasquet, D Vancraeynest, A C Pouleur, J L Vanoverschelde, B L Gerber, Myocardial strain imaging: review of general principles, validation, and sources of discrepancies, European Heart Journal – Cardiovascular Imaging, Volume 20, Issue 6, June 2019, Pages 605–619, https://doi.org/10.1093/ehjci/jez041

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A 45 year old man came with  recent onset breathlessness.His left ventricle was dilated along with left atrial enlargement.The LV EF was 42% (By current definition mid range preserved systolic function( Circ Heart Fail. 2016 Apr;9(4))

But, he was severely symptomatic because of combined  systolic and  diastolic dysfunction.Diagnosing and grading diastolic dysfunction has been extensively done in last decade.Now , we realise without significant diastolic dysfunction symptoms of pulmonary congestion can never occur in patients with DCM.

We don’t require complex tissue Doppler parameters to diagnose high-grade LV diastolic function.Just have a look at LA dimension,  concentrate the E to A ratio. A tall E that humbles the A by more than 2 to 3 times is clear evidence for  LA mean Pressure exceed  18 to 20 mmhg or so.

This , in combination with dilated LA is a marker of chronic severe diastolic dysfunction.The fact that A is diminutive in no way takes the Importance of Atrial contribution to LV filing at this critically compromised LV status.

Note E:A ratio is 3:1 .This simply means the early (and mid to a certain extent ) diastolic pressure in LA is high and most of the filling takes place before Atrial contraction .There is one more reason for diminutive A . Atrial contractility fails to prevail over E in late diastole as LV end diastolic pressure is significantly high in these patients with diastolic dysfunction.

A dilated left atrium is an Independent marker of significant LV diastolic dysfunction (In the absence of MR) .When does LA begin to enlarge in diastolic dysfunction ? There is uniform rule.Generally LA size more than 4.5cm indicate grade 3 or 4 LV diastolic dysfunction.

LA size and Pulmonary congestion 

It’s a paradox , a roomy  LA dampens the LA pressure curve and A reversal into lungs may not happen.

*AF irony on A reversal

Logic might suggest , loss of atrial contraction might attenuate A reversal and less blood flooding into pulmonary veins.No, It doesn’t happen that way.If  AF is precipitated for any reason its going to be “switch on”  for acute pulmonary edema.

What is the relation between systolic and diastolic dysfunction in DCM ?

We find about 30 % of DCM has documented resting diastolic dysfunction.This is actually a underestimation of true diastolic dysfunction as it can very well manifest only during exertion.

Though generally , there is good correlation of grade of diastolic and systolic dysfunction in terms of severity , some of the patients show severe diastolic dysfunction out of proportion with systolic dysfunction.

Note : In the above patient it’s actually a fairly preserved systolic function but still has advanced diastolic dysfunction.

Grading of diastolic dysfunction .Image courtesy MM Redfield et al: JAMA 289:194, 2003. Note E:A >1.5 is

Final message

Relying on E:A ratio to diagnose diastolic dysfunction  may appear  amateurish for some of us .The rampant reporting of E>A for grade 1 diastolic dysfunction has made this parameter a “Doppler cliché”. But , the fact of the matter is,  it does help us confirm severe (Grade 4) diastolic dysfunction when E stands  tall and towering over an almost dwarfed A.

Clinical Implication

Please realise ,In patients with DCM  when you find an  A that is too diminutive in combination with  a menacingly tall E , it may be prudent to raise diuretic dosage. It’s a sure signal for impending pulmonary edema.

Queued queries 

Can DT and IVRT normalise with progressive diastolic dysfunction ?

(more…)

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