SNOWMASS, COLO. – A patient who presents with symptomatic low-flow, low-gradient severe aortic stenosis, hypertension, and preserved left ventricular ejection fraction (LVEF) is often referred straightaway for consideration of aortic valve replacement. Not so fast – these patients actually constitute a special case for whom two essential questions must be answered before proceeding to that stage, Rick A. Nishimura, MD, said at the Annual Cardiovascular Conference at Snowmass sponsored by the American College of Cardiology.
The first question is, What happens to the patient’s symptoms upon control of the hypertension?
“Almost all of these patients with low-flow severe aortic stenosis with preserved ejection fraction are going to be hypertensive. Treat the hypertension first. If they become asymptomatic, you don’t need to intervene. The aortic stenosis wasn’t causing their symptoms. You can afford to continue to watch them,” according to Dr. Nishimura, professor of cardiovascular diseases and hypertension at the Mayo Clinic in Rochester, Minn.
An aortic valve area of less than 1.0 cm2 is a prerequisite for surgical or transcatheter aortic valve replacement. So the second key question is this, Does the patient have truly severe aortic stenosis (AS), or is it instead a case of pseudo-AS in which the small aortic valve area noted on echocardiography is caused by low flow secondary to a small left ventricle with a low stroke volume?
“If you increase the flow and remeasure the aortic valve area, you’ll find that a lot of these patients don’t have a really small aortic valve area of less than 1.0 cm2. You might find the aortic valve area pops up to 1.4-1.6 cm2,” he explained.
These patients with symptomatic low-flow, low-gradient severe AS with preserved LVEF are quite common.
“I don’t know why, but we’re seeing more and more of these patients. I think 10 years ago we just kind of ignored them. We thought we’d made a mistake in our calculations. But in fact if you’re very meticulous about your calculations, 30%-40% of your aortic stenosis patients fit into this category,” the cardiologist said.
Moreover, if these patients undergo aortic valve replacement when their symptoms stemmed from poorly controlled hypertension and/or pseudo-AS, they are not going to benefit from this major intervention, he added.
This issue was addressed, albeit briefly and obliquely, in the American Heart Association/ACC guidelines for management of patients with valvular heart disease, for which Dr. Nishimura served as first author and cochair of the writing committee (Circulation. 2014 Jun 10;129:e521-643) as well as for the 2017 focused update of the guidelines.
The guidelines give a IIa recommendation to aortic valve replacement as “reasonable” in “symptomatic patients with low-flow/low-gradient severe AS (stage D3) with an LVEF 50% or greater, a calcified aortic valve with significantly reduced leaflet motion, and a valve area 1.0 cm2 or less only if clinical, hemodynamic, and anatomic data support valve obstruction as the most likely cause of symptoms and data recorded when the patient is normotensive.”
Dr. Nishimura chose the 50th annual meeting of the storied ACC Snowmass conference to elaborate upon that brief guidance. He explained that these patients with low-flow, low-gradient symptomatic “severe” AS with preserved LVEF and hypertension have two resistors in a series.
“You have a resistor at the aortic valve area but probably a greater resistor in the systemic circulation. They have high resistance at the arterial level and diastolic dysfunction due to ventricular-vascular coupling,” the cardiologist continued.
Checking for pseudo-AS in these patients is a matter of boosting their low transvalvular flow. This can be accomplished by increasing their cardiac output via monitored exercise or by pharmacologic afterload reduction.
“We’re exercising these patients in the cath lab, but you could also do it in the echocardiographic laboratory. With exercise, if cardiac output increases and the aortic valve area increases without significant change in the aortic valve mean gradient, the patient probably doesn’t have truly severe AS,” according to Dr. Nishimura.
One reason referral centers are seeing a lot more of these patients during the last decade is an influential study by Canadian investigators entitled “Paradoxical low-flow, low-gradient severe aortic stenosis despite preserved ejection fraction is associated with higher afterload and reduced survival.” Those investigators warned “this condition may often be misdiagnosed, which leads to a neglect and/or underestimation of symptoms and an inappropriate delay of aortic valve replacement surgery” (Circulation. 2007 Jun 5;115(22):2856-64).
This report led to a great deal of interest in performing aortic valve replacement in such patients during a period when transcatheter replacement was really taking off.
When an audience member asked how commonly such patients have undergone inappropriate aortic valve replacement, Michael J. Mack, MD, took the question.
“I don’t think it’s a huge number,” said Dr. Mack, medical director of cardiovascular surgery at the Baylor Health Care System in Plano, Tex. “This is the patient group we wring our hands about most. We know they don’t do as well with aortic valve replacement as patients with high-gradient AS with a low or normal ejection fraction. We’re loathe to treat them. I think most centers are.”