I can even remember one day when I had seven patients in a row with moderate to severe aortic stenosis. It can certainly be frustrating and time consuming for inexperienced sonographers to have to take additional images and to add on to our study time. Even experienced sonographers must sometimes take a step back and to remember that these patients need that extra time and attention to further the clinical decision making process for the treating physician and to bring answers and solutions to our patients. We are all human and it is easy to look at our schedules and our busy lives and get frustrated when something throws off our plans. However, treating every patient as though they are our own mothers, our fathers and our friends, will help to put our scanning protocols and requirements in the right perspective. This is the reason we do what we do.... patient care. Above all else, our imaging techniques, protocols and scanning skills should be sharpened and enhanced to further benefit the patients we serve.
Aortic stenosis is very common in populations over 65 years old and progression of the disease from sclerosis to critical stenosis can take less than 5 years. If you scan in an accredited lab, there may be many more additional protocol images to add when assessing aortic stenosis. However, with a few tips and tricks even a very new sonographer can master the art of imaging aortic stenosis and save the frustration of this very common pathology. This is the core of what we do, which is why this is included as a case study requirement for adult echocardiography accreditation through the Intersocietal Accreditation Commission.
So let's start with the basics... knowing the anatomy of the valve is important when using descriptions of aortic disease. The valve is comprised of three leaflets:
• right coronary cusp
• left coronary cusp
• non-coronary cusp
Another core basic item in evaluation aortic stenosis is the Continuity Equation. Having an understanding of the hemodynamics is really the basis for an understanding of the disease process and echo evaluation of aortic stenosis. The Continuity Equation in it's most basic explanation is conservation of mass.... what goes in MUST come out.
Also, due to the fact that the continuity equation squares the LVOT diameter, this can significantly introduce errors into the equation if that value is only slightly off or mis-measured. It is critical that the sonographer measure the LVOT very carefully and with attention to detail. According to the American Society of Echocardiography the LVOT (aortic annulus) should be measured with the following parameters and considerations:
•Inner edge to inner edge convention
•Mid-Systole with aortic valve leaflets open
•At the aortic valve leaflet hinges (typical placement)
•Perpendicular to the axis of flow
Doppler angle and sample placement. What more can I say? This is critical to the mathematics. It is important to place the LVOT Doppler sample at approximately the same location as the LVOT diameter is measured from. The LVOT Doppler waveform should also not show significant valve clicks, otherwise Doppler sample placement is too far into the aortic valve.
It's important to ensure correct angle THROUGH the aortic valve orifice. In reviewing countless numbers of echo cases through the years for accreditation and quality review, I've seen many aortic valves evaluated incorrectly.
It is important to place your continuous wave Doppler sample THROUGH the valve orifice and NOT across the valve leaflets. Simple hand maneuvers and tilting the transducer can open up the LVOT and allow for correct Doppler angle through the valve.
Now that you have the basics down, there are few extra steps we can do to evaluate aortic stenosis. Protocols should always include evaluation from the suprasternal notch view, and also evaluation with the Pedoff/dedicated continuous wave transducer. Additional Doppler attempts can also be performed in the subcostal view and the high right parasternal view (always ensuring that true valve clicks are obtained on continuous wave Doppler as this ensures the angle is positioned through the valve orifice).
While the pedoff transducer might be scary for some newer sonographers, once you get the hang of it, you'll realize it's really very simple. For the apical approach, start by beginning where you were able to obtain the best apical window of the aortic valve and LVOT. While observing the CW spectral display, listen to the blood flow and isolate one of the typical valve waveform patterns of either the mitral, aortic or tricuspid valves. Remember the aortic valve is in between the two atrioventricular valves so, keep that in mind when adjusting the probe. Also, SLOW DOWN - use very slow adjustments when optimizing the transducer waveforms and trying to bring in the aortic valve.
When using the suprasternal notch approach, have the patient extend their neck and try to visualize the position of the ascending aorta and direct the face of the probe at a steep downward angle. One important thing to remember is that because there are no images, you must annotate the location on your images. This is required for accreditation and also just a good practice.
Let's not forget that high right parasternal view! The best patient positioning for this is right lateral decubitus. The patients' arm should be positioned up and out of the way.
Often it is helpful to find this view with 2D imaging and assess the valve both with the imaging and non-imaging transducers. I suggest that you practice the Pedoff transducer and additional windows on normal patients and practice often when first beginning your echo career...
practice makes perfect! Before you know it, you'll be an AS pro!
2D Echocardiography sTRAIN IMAGING
To STRAIN or not to STRAIN!?! That is the question.....
2D Strain imaging has been around for quite some time now, but it seems as though many echo labs still don't use it in day to day echo protocols. This leaves us wondering why?!
Strain is useful for so many reasons and has been proven to be more accurate than traditional method of disks ejection fraction measurements when evaluating patients at risk for heart failure. Strain can be highly effective for the detection of cardiotoxicity, with strain abnormalities often showing on echo before there are any measurable declines in ejection fraction or any onset of clinical symptoms. Strain can be a valuable resource to evaluate decreased cardiac function and cardiotoxicity in patients with compromised left ventricular function, such as chemo patients.
Many sonographers simply don't understand the benefits of strain and how to best utilize it within the day to day echo routine. The negative values with strain can be a little confusing, but in reality strain is simple and once you have a good understanding of how it works, you will see that it is easy to incorporate this into your lab protocols and is extremely beneficial to your patients.
Left ventricular ejection fraction is the most commonly used parameter of systolic function. It is essential for the management of heart failure patients. The assessment of ejection fraction by Simpson’s biplane, measures changes in volume. It is often limited in sensitivity and reproducibility. Due to geometric modeling and inadequate visualization of the left ventricular apex, as well as measurement variability, this often limits the ability to detect small changes in left ventricular contractility and can often lead to decreased sensitivity and inaccurate EF measurements. Utilization of strain imaging can reduce many of these errors and provide a more reliable assessment.
So what is strain? There are three fundamental types of strain or deformation: Longitudinal, Radial and Circumferential. During systole, the left ventricle shortens along the longitudinal and circumferential axis, and it thickens in the radial dimension. Of the three, longitudinal strain has been proven to be the most reproducible. It has also been documented to correlate well with clinical outcomes.
Global Longitudinal Strain assesses the twist of the left ventricle as it shortens along the longitudinal axis. Imagine a rubber band... when the 2 end points move away from each other as in diastole, strain is increased or positive. When the two points move closer together as in systole, strain is decreased or negative. Because of it's negative normal values, many sonographers aren't quite sure of how to assess strain and it can be confusing when you think in positive terms regarding ejection fraction.
So what is normal and what do we do with it?
Normal global longitudinal strain has a value of -20%. Some literature suggests that values higher than -17% predict severe heart failure or cardiotoxicity. Imaging with strain is pretty simple, if you can get your apical views, you can do strain imaging! Here are a few tips and tricks:
In summary, strain imaging is a simple tool that can be put to everyday use within your echo lab. Protocols for establishing baseline global longitudinal strain are extremely valuable when evaluating chemo patients for left ventricular function. Strain imaging can be easily incorporated into your daily routine.