Aortic valve stenosis is a burgeoning, degenerative disease, for which transcatheter aortic valve replacement (TAVR) has entered U.S. clinical practice for some clinically indicated patients. While planning for the treatment is a multifaceted process including physicians and caregivers from varied specialties, the imaging work-up from diagnosis to post-procedure relies heavily on echocardiography. However, CT and fluoroscopy also play a routine role in pre- and intra-TAVR planning.
Aortic stenosis (AS) is the most common valvular heart disease in the elderly, for which the numbers are growing due to the aging population in developed nations. In older adults, mild thickening, calcification or both of a trileaflet aortic valve without restricted leaflet motion (i.e., aortic sclerosis) affects approximately 25 percent of the population older than 65 years, while calcific aortic stenosis affects approximately 2 percent to 3 percent of those older than 75 years (J Am Coll Cardiol 2006;48:e1-e148).
Over the past decade, Doppler echocardiogram has replaced cardiac catheterization as the gold standard diagnostic technique for identifying AS. This was solidified by the 2012 multi-societal expert consensus document. "Although invasive cardiac catheterization has historically been the standard for quantification of AS, this function has been largely replaced by echocardiography," partly due to the "convenience and wide-spread applicability TTE [transthoracic echocardiogram]" (J Am Coll Cardiol 2012;59;1200-1254).
The real-time, 3D images produced by contemporary TTE systems provide a unique perspective of heart valves. "Most physicians today would start with a TTE to help define the severity of the aortic stenosis and its effects on the heart," says William J. Stewart, MD, of the section of cardiovascular imaging at the Heart and Vascular Institute at the Cleveland Clinic.
Using echocardiography in their initial assessment, Linda D. Gillam, MD, MPH, medical director of the cardiac valve program at Columbia University Medical Center in New York City, says that physicians are able to assess three things:
- The anatomy of the valve and the anatomic basis for the stenosis, which is "critically important";
- A quantitative assessment of the severity of the stenosis to measure the gradients across the valve and calculate the size of the opening, called the aortic valve area; and
- Any associated leakage of the valve.
Also, the 2009 American Society of Echocardiography/European Association of Echocardiography consensus document stated that TTE "usually is adequate" for anatomic evaluation of the aortic valve because the combination of imaging and Doppler allows for the determination of the level of obstruction (whether subvalvular, valvular or supravalvular)—although transesophageal echocardiography (TEE) also may be helpful when image quality is "suboptimal" (J Am Soc Echocardiogr 2009;22:1-23).
While TTE has an external probe that is placed on the surface of the patient's chest, TEE contains an ultrasound transducer at its tip that is passed into the patient's esophagus, allowing the image and Doppler evaluation to be registered and recorded.
In clinical practice, at least 30 percent of patients with severe AS do not undergo surgery for replacement of the aortic valve, due to advanced age, left ventricular dysfunction or the presence of multiple coexisting conditions, according to the PARTNER researchers (N Engl J Med 2010;363:1597-1607). Due to the elderly nature and comorbidities of this population, providers need to meticulously assess which patients are appropriate for TAVR. Once a patient is diagnosed with AS, there is a complete diagnostic work-up of these typically elderly patients to determine whether or not he or she is a candidate for TAVR, which includes echo screening.
"We need to precisely plan everything about a TAVR procedure with echo, including the size of the patient's aortic annulus, which is where the valve will be implanted, and the leakiness of the valve, which could present a problem during the valve implantation," says Stewart.
"The [preoperative] aortic valve morphology is assessed; bicuspid valves may or may not be less amenable to percutaneous valve replacement," wrote Stewart in a 2008 editorial (J Am Coll Cardiol Img 2008;1:25-28). "Both TTE and TEE visualize the distribution of calcium on and adjacent to the valve, the distance from the valve to