Valve gradient question

[rsgillmd]

I have a question that has been bugging me for a while and can't seem to get a satisfactory answer. I'm sure one of the cardiac guys here can probably help me. I'm also sure the answer will probably be obvious when explained, but that's the price of asking.

The question I wanted to ask is what is the clinical significance of a mean valve gradient? Other than to help define the degree of stenosis that is.

I know a peak gradient is useful in that if you have a gradient of 40 mmHg and your systolic BP is 100 mmHg then your LV pressure during systole has to be greater than 140 mmHg for ejection to occur.

I just don't know how to put a mean gradient into a practical clinical concept.

Any help you can give would be appreciated.

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[aredoubleyou]

I dont know the answer, but Ive got an oppinion 🙂. I do think that the significance of a gradient (or valve area) to me relates to the epidemiological factors (survival, hospitalizations, benefits from surgery, etc) and intraoperative managemnet as you alluded to. So a high gradient across the AoV means that I should pay particular attention to keeping the HR reasonable, BP high, and NSR, etc. Beyond that I dont know (outside of heart surgery - such as evaluating a new valve, etc).

 

[periopdoc]

The mean gradient is used because it correlates better with angiographically derived measurements than the peak gradient does.

Consider the peak gradient that you measure with echo. This is the maximum velocity (pressure difference) across the valve during the entire systolic ejection period.

Now consider the peak gradient that you measure with angio. You take a instantaneous peak pressure measurement proximal to the valve and a separate instantaneous peak pressure measurement distal to the valve, the peak to peak difference.

This sounds like semantics until you consider the time/pressure relationship between the chambers proximal and distal to the valve. (the graph on the left)

Here you can clearly see why the max delta-P, the peak velocity across the valve on echo, is quite different than the peak to peak delta-p, as measured by angio. They are both "peak gradients," but they can be quite different numbers.

Therefore, we use the mean gradient to make reliable comparisons between data derived from the two different techniques.

To avoid confusion, I personally prefer to refer to the peak velocity and mean gradient when discussing echo derived data and the peak to peak pressure gradient and mean gradient when discussing angio derived data.

Hope that helps

- pod

 

[rsgillmd]

Thanks periop. That makes a little more sense. Just so I know I'm understanding it: the mean gradient on an echo is generally comparable to a mean gradient on an angio?

If that's true then it definitely is useful because a person generally doesn't get repeated angios but they can repeated echos. So it would easier to say there has been a change. Also if they are comparable then you can document an improvement in the mean gradient after valve replacement/repair.

Is that correct or am I still confused/overreading this?

 

[periopdoc]

Correct with some reservation. The best correlation between the two modalities (angio and echo) is with the mean gradients. That doesn't guarantee that there is perfect correlation in every patient.

I would be cautious in interpreting that stenosis has improved or worsened based on two studies performed with different modalities. It is much better to either compare two echos or two caths than to mix modalities. You already knew that, I just want to be sure that I am not leading anyone astray.

Allowing for the pitfalls of measuring aortic regurgitant jets, a decrease in an echocardiographically measured mean gradient from a previous echocardiographically measured mean gradient is evidence of a decrease in stenosis.


- pod

 

[DScully]

Allowing for the pitfalls of measuring aortic regurgitant jets, a decrease in an echocardiographically measured mean gradient from a previous echocardiographically measured mean gradient is evidence of a decrease in stenosis.


- pod

So does this mean that the aortic insufficiency is getting worse with decreased mean gradient? i.e., increase in insufficiency (rather than decrease in stenosis)??

 

[periopdoc]

So does this mean that the aortic insufficiency is getting worse with decreased mean gradient? i.e., increase in insufficiency (rather than decrease in stenosis)??

No.

My last paragraph did not come out right (that is what I get for surfing SDN on my iPhone), so I modified it to hopefully be a little more clear. I was trying to say that there are pitfalls in measuring stenotic jets that should be considered. The most significant pitfall is in a patient with significant aortic regurgitation superimposed on his aortic stenosis.

In patients with both aortic stenosis and aortic regurgitation, the augmentation of the forward stroke volume with the regurgitant volume will increase the pressure gradient and can lead to overestimation of the degree of stenosis.

In patients with poor LV systolic function, the LV cannot generate enough force to develop a high gradient across the valve and stenosis severity can be underestimated.

In patients in a high output state, the gradient will increase and stenosis can be overestimated.

In the patient you mentioned (assuming a theoretically fixed, unchanged level of aortic stenosis and LV function/ volume status etc) a decrease in mean gradient would support the diagnosis of improvement of regurgitation and an increase in mean gradient would support the diagnosis of a worsening in regurgitation. Of course you are making the assumption that the only thing effecting the mean gradient is the regurgitant volume so this would be a poor way of temporally following aortic regurgitation.


- pod

 

[rsgillmd]

Thanks periop. I have a better understanding because of your explanations.

 

[DScully]

In patients with both aortic stenosis and aortic regurgitation, the augmentation of the forward stroke volume with the regurgitant volume will increase the pressure gradient and can lead to overestimation of the degree of stenosis.

In patients with poor LV systolic function, the LV cannot generate enough force to develop a high gradient across the valve and stenosis severity can be underestimated.

In patients in a high output state, the gradient will increase and stenosis can be overestimated.

I understand the above statements so far...but got a little bit confused with the following paragraph.

In the patient you mentioned (assuming a theoretically fixed, unchanged level of aortic stenosis and LV function/ volume status etc) a decrease in mean gradient would support the diagnosis of improvement of regurgitation and an increase in mean gradient would support the diagnosis of a worsening in regurgitation.

So in a patient with only aortic stenosis, I understand that a decrease in mean gradient would support the statement of improved valvular function (right?). Then, don't we typically say something like "improvement of the stenosis" (i.e. the valvular opening is bigger), instead of "improvement of regurgitation" (i.e., the valvular opening is smaller)?

Where is the regurgitation coming from?? Do we just use this term to describe any turbulent jet?? Or am I missing something super fundamental here??

This is probably just semantics and very likely not significant at all...anyway, thanks SO much for explaining this to me!!

 

[IN2B8R]

No.

My last paragraph did not come out right (that is what I get for surfing SDN on my iPhone), so I modified it to hopefully be a little more clear. I was trying to say that there are pitfalls in measuring stenotic jets that should be considered. The most significant pitfall is in a patient with significant aortic regurgitation superimposed on his aortic stenosis.

In patients with both aortic stenosis and aortic regurgitation, the augmentation of the forward stroke volume with the regurgitant volume will increase the pressure gradient and can lead to overestimation of the degree of stenosis.

In patients with poor LV systolic function, the LV cannot generate enough force to develop a high gradient across the valve and stenosis severity can be underestimated.

In patients in a high output state, the gradient will increase and stenosis can be overestimated.

In the patient you mentioned (assuming a theoretically fixed, unchanged level of aortic stenosis and LV function/ volume status etc) a decrease in mean gradient would support the diagnosis of improvement of regurgitation and an increase in mean gradient would support the diagnosis of a worsening in regurgitation. Of course you are making the assumption that the only thing effecting the mean gradient is the regurgitant volume so this would be a poor way of temporally following aortic regurgitation.


- pod

Could not be overstated....loading conditions on the heart, pre- and afterlaod, can both affect the gradient. One may even repair a valve completely, yet still have high gradient readings: why? Because a gradient is a DYNAMIC value that relates to DYNAMIC variables.

 

[sebsvenmdc]

Is this topic a major component of cardiac anesthesiology? It sounds VERY interesting! I may consider going into this field...the graphs and relationships being described are freaking awesome!

I had a question...I am a med student, so I'm definitely ignorant with respect to the rest of you, so forgive the simplicity of this in advance! It seems that the mean gradient can be increased by aortic stenosis, aortic regurgitation, or both since in the case of:
AS, there's an increased mean (and peak) LV systolic pressure required
AR, there's a decreased mean aortic systolic pressure (since some blood has regurgitated into the LV in the preceding diastole)
and in both, the increases are additive!