Breaking Down Obstructive Gradients

Indroduction

Hypertrophic cardiomyopathy (HCM) refers to the left ventricular walls becoming abnormally thick, which can restrict the amount of blood that is pumped out of the body. In most cases of HCM, there is an obstruction gradient created within the heart which can be referred to as hypertrophic obstructive cardiomyopathy (HOCM) or left ventricular outflow tract obstruction (LVOTO). Understanding and accurately assessing LV obstructive gradients are crucial in diagnosing and managing these conditions effectively. Through appropriate diagnostic techniques like echocardiography or cardiac catheterization, healthcare professionals can evaluate the severity and location of the gradients, aiding in treatment decision-making. Having an understanding of the hemodynamics of obstructions as well as analyzing the structures and measurements will help to provide accurate testing. In this course, we will be looking at how to properly assess LV obstructive gradients during an echocardiogram.

What is Left Ventricular Obstruction?

Left Ventricular (LV) obstruction is defined as when the blood flow is being limited out of the LV
Echocardiography evaluation is the imaging modality of choice to assess HCM
Some patients will not have symptoms, however if they do, the following symptoms could occur:
- Unexplained syncope
- Sudden cardiac death
- Non-sustained SVT
- Murmur
  - It will be a crescendo-decrescendo heard best in the left lower sternal border with stethoscope
- Dizziness or lightheadedness
- Dyspnea on exertion
- Chest pain
When there is an obstruction in the LV, it creates a decreased forward flow, which will increase the afterload
- This can result in LVH, LV dilation or heart failure over time
- The severity of the obstruction can vary based on loading conditions and contractility of the LV

What to Look for on Echocardiogram

Increased wall thickness of the myocardium >1.5 cm
- Measure at end diastole
  - Careful when measuring the septum to not include RV trabeculation
  - For posterior wall, careful to not measure the papillary muscle
- If there is apical hypertrophy, make sure the apical images are not foreshortened, which can limit the views of the true apex

Figure 2.2 Example of types of HCM

When you see a late peaking or “dagger-shaped” systolic flow on CW Doppler (obstruction flow as shown in figure 2.3), it is important to exclude other pathology
- Being able to pinpoint the location and severity will help physicians determine the treatment plan for the patient

Figure 2.3 example of late systolic peaking CW Doppler obstruction signal

Assess the location of obstruction by using pulse wave (PW) Doppler:
- Location possibilities within the LV are:
  - LVOT (most common)
  - Mid LV Cavity
  - LV Apex
Assess severity of obstruction
- Obtain continuous wave (CW) Doppler with and without Valsalva through the LV and calculate the peak velocity and peak gradient
  - You should not trace the signal, it is measured by a caliper placed at the peak of the signal
  - Peak gradient should be at least 30 mmHg at rest to diagnose as obstructive HCM
    - If there is a late peaking gradient below 30 mmHg it is labeled as non-obstructive HCM but these patients should be monitored as they can develop obstruction
  - Depending on the lab policy, some labs recommend not performing Valsalva on a resting peak velocity of over 5 m/s
Assess with color Doppler
- This helps view the area of increased flow (aliasing) in the LV and can also assess if there is mitral regurgitation (MR) being caused from a LVOT obstruction

Figure 2.4 Example of obstruction through LVOT shown with color

Assessment of LV systolic function
- If there is hyperdynamic systolic function, CW Doppler can demonstrate a similar late-peaking signal. This is different pathology than HCM, so it is important to do careful assessment to differentiate between them when initially diagnosing the patient as treatment plan may differ however:
  - It is also important to recognize that hyperdynamic function can be present with HCM and can create an even higher peak gradient

Assess diastolic function
- Diastolic dysfunction is common in HCM due to increasing wall stiffness, leading to impaired LV relaxation
Assess the amount of MR
- If there is systolic anterior motion (SAM) of the anterior MV leaflet, it can cause more regurgitation as the leaflet is being pulled towards the septum during systole keeping the valve from closing properly
  - SAM is not always specific to just to HCM and can occur in other conditions provoked by a reduced afterload, reduced preload and hyperdynamic function
- The MR jet can be very eccentric, typically a posterior direction, so you might have to pan through the valve in order to insure accuracy

Other types of assessment that can be used:
- Strain rate imaging can help identify regional heterogeneity of contractile function
  - In long term HCM, myocardial fibrosis may result in decreased systolic function
    - A decrease of the EF has been associated with increased mortality (up to 11% per year) and sudden cardiac death

Figure 2.5 Example of strain image analysis showing decreased area in the apex

Assessment of LV filling pressures is helpful in the correlation of symptoms and disease stage
- Elevated pressures can indicate that the thickened walls are becoming stiff
Contrast echo images can help verify and define wall thickness as well as enhance the CW Doppler signal
- Especially on technically difficult studies where color and 2D are difficult to evaluate
Assess for interventricular dyssynchrony
- HCM patients have a higher rate of dyssynchrony than hypertension LVH
Measure tissue Doppler (TDI)
- Will typically be decreased in true HCM vs LVH from HTN

Types and Examples of Obstruction

HOCM (hypertrophic obstructive cardiomyopathy) or LVOTO (left ventricular outflow tract obstruction)
- Occurs when the LV outflow tract is narrowed from basal septal hypertrophy (also referred to as sigmoid septum), causing an increase gradient

Getting a PW LVOT signal for the AVA calculation can be difficult as the obstruction signal can merge into the signal, however these are separate signals

Mid cavity obstruction
- Occurs when the LV wall thickness in the middle of the ventricle is increased and/or if there is hyperdynamic function

Figure 2.6 In this CW example, you can see there are 2 signals. The late systolic signal is the obstruction. Measure the peak velocity. The other signal is MR.

Apical obstruction
- Occurs when the LV apex has increased wall thickness and/or hyperdynamic function

Figure 2.7 Apical Hypertrophic Cardiomyopathy 2D Image Example with apical obstruction

Obtaining Accurate Measurements During the Echocardiogram

Start by assessing the location of the obstruction by imaging with PW Doppler signal at all 3 locations to find where the main area of obstruction (accelerated flow) is within the LV
- Start by placing the PW sample volume at the apex, take a clip of the Doppler signal, then move to mid cavity, and then LVOT making sure to acquire an image at each location

Figure 2.8 Example of PW Doppler at the apex. You can see that the late peaking signal is minimal.

Figure 2.9 Example of PW Doppler at mid cavity

Figure 2.10 Example of PW Doppler at the LVOT.

Since we were able to say based on the PW signals, that the flow acceleration was in the LVOT, meaning that is where the obstruction was at.
- There can be multiple locations of obstruction, especially when there is concentric hypertrophy
Next, use CW Doppler to get the peak gradient and velocity by placing the CW cursor through the LV

Figure 2.11 Example of CW Doppler to obtain the highest velocity. Do at least 2 different signals by placing the cursor through the middle of the LV and one through the outflow tract

Figure 2.12 Example of obstruction that is originating from mid LV cavity

Figure 2.13 example of proper CW Doppler cursor alignment

Valsalva

Gradients can dramatically change with Valsalva so it is important to include this as part of the evaluation of the obstruction
- The “strain phase” of Valsalva creates an increased intrathoracic pressure and a decrease in venous return

Figure 2.14 Example of heart at rest and what happens during Valsalva. You can see from the area within the circle why syncope can happen due to total obstructing the flow out of the heart

Figure 2.15 Example of Valsalva with CW Doppler that shows the gradient increasing

Peak gradient at rest of >30 mmHg can indicate significant obstruction
It is also important to acquire a clip of the MR during Valsalva with color as the higher the obstruction, the more likely it is to “pull” the MV leaflet and/or chordae tendineae towards the septum, creating more backward moving flow (MR). When this happens, it is called SAM (systolic anterior motion). If the amount of MR is not evaluated during Valsalva, you could be underestimating the significance of the obstruction and delay proper treatment.

Figure 2.16 This image with color shows the increased flow through the LVOT and eccentric MR from SAM

If there is MR, the signals can overlap in the Doppler CW signal. To differentiate, look for the late systolic signal (MV prolapse is also late systole so r/o MVP from PLAX first)
You can also try to re-align the cursor through the AV, instead of MV to try to separate out the signals. In figure 2.17 you can see that even though the signals overlap, you can still determine correct measurement placement

Figure 2.17 This image shows both MR and HCM on the CW Doppler

Similar to the MV and HCM CW signals combining, the AV CW signal can overlay the HCM
- It is very important to understand that an obstruction gradient is a separate signal, both for PW and CW than the AV signal

Figure 2.18 Example of CW signal with both AV and obstructive signal overlapping with a correct trace and an incorrect trace of the AV

Getting a LVOT PW AV Doppler signal can be difficult on patients with LVOT obstruction as there is not always a way to separate out the signals
- Try to place the sample volume right above the AV. The LVOT PW signal is most likely going to be increased as the pressures are higher than normal going through the valve
- You can also try placing the sample volume into the sinus of Valsalva so it is not aligned to the HCM area
- The LVOT gradient can be calculated using the modified Bernoulli equation
  - LVOT gradient = 4 X (LVOT vel)2
If there is aortic stenosis (AS) in addition to an obstruction, it is important to evaluate the severity of each condition separately, as these are different pathology abnormalities. On the Doppler signal, use the timing (late systole for obstruction vs early to mid systole for AS) to help accurately differentiate between the signals

Figure 2.19 example of both AS and HOCM on the CW Doppler signal

Figure 2.20 example of AS and HOCM CW signal

Figure 2.21 Even on TDS, you can still see with color aliasing that indicates there is a increase in velocity through the LVOT

Figure 2.22 Severe basal septal hypertrophy

Contrast

Contrast can help you see the obstruction area, especially on difficult images
Contrast can help bring in the Doppler as well on those hard to get signals

Figure 2.23 Contrast example of mid cavity gradient with hypokinetic apex

Treatment of HOCM

Cardioversion if the patient is in A-fib
Medications
- Goals of meds:
  - Increase LV compliance
  - Improve diastolic function
  - Increase LV volume
  - Decrease ventricular contractility
  - Decrease systolic gradient (decrease obstruction)
- Recommended medications that can be used:
  - Beta blockers (metoprolol, propranolol or atenolol)
  - Calcium Blockers (Verapamil or diltiazem) )
  - Antiarrhythmic (Amiodarone or disopyramide)
Antibiotic prophylaxis for help prevent endocarditis

Dual chamber pacemaker
- Goal of pacemaker is to reduce LVOT gradient
- Long term effects however are unknown
- Should be considered if the EF is <50% to decrease risk of sudden cardiac death
Surgery
- Myotomy/myectomy
  - Myotomy = cutting a muscle
  - Myectomy = surgical removal
- Alcohol Septal ablation
  - For basal septal hypertrophy that creates an obstruction
- Mitral valve replacement or repair
Patient restrictions:
- Avoid strenuous exercise
- Competitive sports is not allowed if any of following are present:
  - Marked LV hypertrophy
  - Evidence of significant outflow obstruction
  - Important supraventricular or ventricular arrhythmias
  - History of sudden death in relatives with HOCM
- Low-intensity competitive sports allowed if none of the above conditions are present

Conclusion and Final Tips

On an echocardiogram exam, PW Doppler helps determine the location of the obstruction within the LV, and CW Doppler helps determine the severity by measuring the peak velocity and peak gradient at rest and with Valsalva
Getting the LVOT TVI and CW AV trace is more difficult in these studies as you need to make sure the cursor is out of the obstruction as much as possible so it is accurate and not overestimated. Do not include the obstructive Doppler signal in the trace

What if you cannot get a clear AV signal because the signals from both the AV and HOCM are merged together?
- This is a situation where the “corrected” mean gradient can be used
- Calculate this by subtracting the AV mean gradient from the LVOT mean gradient and the result is the new accurate mean gradient
Even if the CW gradient isn’t very high at rest, you should still try to have the patient Valsalva, especially on patients with thickened walls and/or aliasing color flow noted in the LV to ensure nothing is being missed
Hyperdynamic function can also make an obstruction worse so make sure the EF calculations are accurate

Breaking Down Obstructive Gradients

Chapter 1