At a recent American Society of Echocardiography (ASE) event, James Thomas, MD, director of the Center for Heart Valve Disease at Northwestern’s Bluhm Cardiovascular Institute, asked the large group of cardiologist attendees if they had ever used speckle-tracking strain echocardiography. About one-third of the audience raised a hand. Thomas found the response encouraging because the same question posed to a similar group a few years earlier had yielded only “one, maybe two, hands in the air.” This signals progress, Thomas says, but he and other cardiologists told CVB that strain echo still is underused despite its diagnostic and prognostic value with conditions where Doppler imaging falls short.
Doing what Doppler doesn’t
Proponents of speckle-tracking strain echo consider it a viable alternative to Doppler-based modalities, which have been accepted as the staple for measuring myocardial strain. The modality uses image-processing algorithms to identify and track small, stable myocardial footprints, or “ speckles,” generated by ultrasound-myocardial tissue interactions, explains Theodore Abraham, MD, clinical chief of cardiology, director of echocardiography and co-director of the hypertrophic cardiomyopathy program at the University of California, San Francisco (UCSF). Frame by frame through the cardiac cycle, the software both tracks the distances between speckles in a user-defined region of interest and converts the segmental values into global longitudinal strain (GLS) values. These values provide information about the presence and extent of global and segmental myocardial deformation that can’t be determined from Doppler imaging.
“In general, strain echocardiography is more sensitive than ejection fraction and is an early warning that something is happening with the heart,” Thomas says. “As such, it’s the canary in the coal mine.”
Unlike standard ejection fraction, strain echo isn’t limited when it comes to measuring contractility, which means it can use GLS to reliably assess global systolic function in conditions such as undifferentiated left ventricular hypertrophy, cardiac amyloidosis, pericardial disease, ischemic heart disease and aortic stenosis.
Strain echo also is gaining recognition as a means to identify systolic dysfunction in the context of normal ejection fraction. This capability can be helpful for diagnosing hypertrophic cardiomyopathy and cardiac amyloidosis and in assessing the prognosis of patients with these conditions, says Allan Klein, MD, director of the Center for Diagnosis and Treatment of Pericardial Diseases at the Cleveland Clinic.
Klein also likes strain echo for its prognostic value, particularly in patients who have diabetes or cancer. These patient populations are increasingly on physicians’ radar for cardiovascular risk, but predicting which of them will actually develop heart disease is still a challenge.
Strain echo’s value as a prognosticator is especially helpful in the cardio-oncology space. When assessing heart disease risk in his cardio-oncology patients, Klein is on the lookout for lower strain values; the lower the strain values in these patients, he explains, the greater the likelihood they will develop cardiovascular complications. At least one study found it could detect subclinical effects of chemotherapy on the heart before there were changes in ejection fraction (Eur Heart J Cardiovasc Imaging 2017;18:930-6).
Abraham, of UCSF, believes strain echo could be leveraged for a still larger role, such as in screening for cardiomyopathy in individuals with a family history of cardiac disease.
Beyond diagnosis and prognosis, strain echo might earn a place in cardiologists’ treatment-planning toolbox. “Suppose, in cardio-oncology, that a breast cancer patient being treated with Adriamycin [doxorubicin] or trastuzumab is evaluated using strain echocardiography every three months and is found to have abnormal GLS values,” Thomas suggests. “We can consider this a call to action and start the patient on beta-blockers or pause the trastuzumab cycle.”
Strain echo results also might point the way to testing for cardiac amyloidosis not just by revealing apical sparing but also by leading “to other confirmatory testing, including workup for amyloid light-chain amyloidosis vs. transthyretin amyloidosis,” Klein says.
Another possible benefit, says Thomas, is that strain echo could help cardiologists decide whether to recommend transcatheter aortic valve replacement (TAVR) to patients with amyloidosis. “[Strain echocardiography] shows a distinct pattern of apical strain that is very common” in patients in whom TAVR may be warranted.
Dollars & other drawbacks
With so many opportunities for value, why does strain echo remain outside what Thomas describes as “the norm” of cardiovascular assessment? Part of the reason for slow adoption comes down to cost. While most echocardiography equipment vendors offer strain modules specific to their machines, the price tags can be prohibitive. As an example, Abraham points to the $45,000 cost of an “advanced software bundle [with] a strain package” along with other modules, such as stress and auto ejection fraction. An “unbundled” strain module is usually priced at approximately $25,000, according to both Abraham and Thomas.
Some degree of financial relief may have arrived, however. Based on RVS Update Committee recommendations for work relative value units and practice expense inputs for strain echo, the Centers for Medicare & Medicaid Services published a new Category 1 CPT code for myocardial strain imaging, effective Jan. 1, 2020.
“With Medicare reimbursement [afforded by the new CPT code], breaking even on a strain echo investment should be easier,” Abraham observes. The return from investing in the technology also will come from more referrals, he adds. “Increasingly, referring physicians, particularly those with cardiomyopathy and cancer patients, are asking for strain echo for their patients,” he notes. “[Cardiologists who] can fulfill the requests stand to gain.”
Another obstacle to increased adoption of strain echo lies in the training that teams need to perform strain studies and analyze the data they generate. While vendors offer training, a significant learning curve has been associated with left ventricle strain analysis in particular because of the user intervention needed to place the sample volume, Thomas says. Other contributors to the steep learning curve include mastering how to make manual adjustments to the region of interest and timing when to begin and end speckle tracking. One study found it takes training on at least 50 studies for a physician to achieve competency in interpreting strain echo studies (J Am Soc Echocardiogr 2017;11:1081-90).
Still, the technology is getting easier to master as “contemporary” equipment becomes available, Thomas says. He notes various features that “automatically” place sample volumes, allowing strain to be calculated with minimal user intervention; “tweak” regions of interest; and handle tracking timing.
Bigger than cost and educational hurdles are clinical and technical drawbacks that even the technology's proponents acknowledge are true obstacles to adoption. On the clinical side, a multitude of factors could impact GLS values, according to Klein. Various studies have indicated that patient age, sex, race, ethnicity, and nationality rank among these factors, he says. Other variables may include hemodynamics; cardiovascular risk factors, such as hypertension, obesity and diabetes; pregnancy; and, in children, dyslipidemia.
Further, sources told CVB, there’s too much variation in how the modules from different vendors perform, particularly with tracking the myocardium through the cardiac cycle. In some cases, poor image quality can make the tracking difficult, if not impossible. Artifacts also can make it a challenge to track speckle patterns, and foreshortened images may reveal inaccurate strain values.
Reinforcing the idea that not all technology is created equal are vendor-specific variations in how GLS values are calculated from segmental values. Cross-platform values aren’t necessarily interchangeable, Klein says. Consequently, physicians may struggle to draw conclusions if a patient isn’t always tested on the same equipment or with the same software. The European Association of Cardiovascular Imaging (EACVI)/ASE Inter-vendor Comparison Study illustrated this point. When 62 volunteers had strain echo performed under optimized conditions using machines provided by seven different vendors, absolute GLS values varied from -18 percent to -21.5 percent with absolute differences among vendors of up to 3.7 percent strain units (J Am Soc Echocardiogr 2015;26:185-91).
Overcoming the obstacles
The Strain Standardization Task Force, an entity created by the EACVI and ASE in 2010 that now also has vendor members, is developing standards aimed at resolving the variation among strain modules. “The more uniformity we see, the greater the clinical appeal of strain echocardiography will be because we can be more certain that assessments from one module are consistent with assessments from another,” Thomas says.
As for clinical variables, Klein expects these issues will be smoothed out as researchers dig into how to account for such unavoidable factors and professional groups like ASE and the American College of Cardiology (ACC) publish practice guidelines. In the meantime, he says, ASE is recommending patients have strain echocardiography prior to chemotherapy and, depending on the agent, at three- and six-month intervals during their treatment. The current chamber quantification guidelines don’t specifically recommend strain echo but rather identify it as an important adjunct to ejection fraction.
“It will be a matter of time that ACC will incorporate strain into its guidelines,” predicts Klein, who is a member of the college’s imaging council. He also expects the Intersocietal Accreditation Commission—which currently deems strain echo an optional best practice—eventually will make the modality standard “as more sonographers are trained to utilize strain and more physicians are able to interpret it.”
Thomas also anticipates wider acceptance. He expects the modality will continue to attract more attention and adoption will follow. “There may be glitches along the way,” he says, “but strain echocardiography is here to stay.”