Aortic Valvular Stenosis: Management of Low Flow / Low Gradient / Normal EF / Low EF

Educational Objectives

After completing the activity, the clinician will be better able to assess low-flow, low-gradient aortic stenosis.

Summary

Interviewer: Deepak Bhatt, MD, MPH, FACC, Boston, MA

Take-home Messages:

• Low-flow, low-gradient (LF-LG) aortic stenosis (AS) may occur with depressed or preserved left ventricular ejection fraction (LVEF). In either case, these are among the most challenging situations encountered in patients with valvular heart disease.
• In the case of LF-LG with depressed LVEF, the main challenge is to distinguish between true severe AS, which generally benefits from aortic valve replacement (AVR), and pseudo-severe AS, which should be managed conservatively.
• Aside from updated guidelines for managing patients with valvular heart disease, 2017 saw the publication of appropriate use criteria for the treatment of patients with severe aortic stenosis.

Medical and interventional approaches to the management of patients with valvular AS depend on accurate diagnosis of the cause and on precise disease staging. According to current guidelines¹ (including the 2017 update²), stages of AS range from being at risk of AS (stage A) to progressive hemodynamic obstruction (stage B) to severe asymptomatic AS (stage C) to symptomatic AS (stage D).

Hemodynamic severity is best characterized by transaortic maximum velocity (or mean pressure gradient) — at least when transaortic volume flow rate is normal. The challenge is that some patients with AS have a low transaortic volume flow rate, because of either LV systolic dysfunction with a low LVEF or a small hypertrophied LV with low stroke volume.

Patients with low-flow AS are designated as D2 if they have low LVEF (5%–10% of the AS population) and as D3 if they have with normal LVEF. In both cases, the decrease in gradient relative to AS severity is caused by a reduction in transvalvular flow, i.e., low-flow, low-gradient AS (Table). These categories of severe AS pose a diagnostic and management challenge that is distinctly different from that of most cases of AS, which are characterized by a high gradient and high velocity when AS is severe (stage D1).

Valve Hemodynamics Defining Low-flow/Low-gradient Aortic Stenosis

Symptomatic severe low-flow/low-gradient AS with reduced LVEF
Low flow	Stroke volume index <35 ml/m2
Low gradient	Mean gradient <40 mm Hg (or Vmax <4 m/sec)
Aortic valve area	1.0 cm2
Reduced LVEF	<50%
Symptomatic severe low-gradient AS with normal LVEF or ­paradoxical low-flow severe AS
Aortic valve area*	1.0 cm2 with aortic Vmax <4 m/s or mean pressure gradient <40 mm Hg
Indexed aortic valve area*	6 cm2/m2
Stroke volume index*	<35 ml/m2

*Measured when patient is normotensive (systolic blood pressure <140 mm Hg)
AS = aortic stenosis; LVEF = left ventricular ejection fraction.

The main challenge in patients with depressed LVEF is distinguishing between true severe AS, which generally benefits from aortic valve replacement, and pseudo-severe AS, which should be managed conservatively. There is also a need to accurately assess the severity of myocardial impairment.³ Paradoxical LF-LG severe AS despite a normal LVEF (10%–25% of the AS population) is characterized by pronounced LV concentric remodeling, small LV cavity size, and restrictive physiology. This restrictive physiology often leads to impaired LV filling, altered myocardial function, and poorer prognosis. Until recently, this entity was often misdiagnosed, resulting in underestimation of AS severity and inappropriate delays of surgery.

A low-dose dobutamine stress echo may be used for this purpose in patients with classic LF-LG AS and reduced ejection fraction. Aortic valve calcium scoring by multidetector computed tomography is the preferred modality in those with paradoxical LF-LG or normal flow-LG AS, especially in those with no LV flow reserve (in whom dobutamine stress echo is often inconclusive).⁴

Although patients with LF-LG severe AS have poorer outcomes than those with high-gradient AS following AVR, they nonetheless display an important survival benefit. Given that operative risk for open heart surgery is generally extremely high in absence of flow reserve, some studies suggest that transcatheter AVR could provide a valuable alternative in these patients.

Guidelines from the American Heart Association/American College of Cardiology also note that AVR is reasonable in patients with LF-LG severe AS (stage D3) who are normotensive and have LVEF ≥50% — if clinical, hemodynamic, and anatomic data support valve obstruction as the most likely cause of symptoms.

It should be noted that, aside from updated guidelines, 2017 saw the publication of appropriate use criteria for the treatment of patients with severe AS.⁵

Readings

1. Nishimura RA, Otto CM, Bonow RO, et al. 2014 AHA/ACC guideline for the management of patients with valvular heart disease: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines. J Am Coll Cardiol 2014;63:e57-185. www.onlinejacc.org/content/63/22/e57

2. Nishimura RA, Otto CM, Bonow RO, et al. 2017 AHA/ACC Focused Update of the 2014 AHA/ACC Guideline for the Management of Patients with Valvular Heart Disease: A Report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines. J Am Coll Cardiol 2017;70:252-89. www.onlinejacc.org/content/70/2/252

3. Pibarot P, Dumesnil JG. Low-flow, low-gradient aortic stenosis with normal and depressed left ventricular ejection fraction. J Am Coll Cardiol 2012;60:1845-53. www.onlinejacc.org/content/60/19/1845

4. Clavel MA, Magne J, Pibarot P. Low-gradient aortic stenosis. Eur Heart J 2016;37:2645-57.

5. Bonow RO, Brown AS, Gillam LD, et al. ACC/AATS/AHA/ASE/EACTS/HVS/SCA/SCAI/SCCT/SCMR/STS 2017 Appropriate Use Criteria for the Treatment of Patients with Severe Aortic Stenosis. J Am Coll Cardiol 2017 Nov 14;70(20):2566-98. www.onlinejacc.org/content/70/20/2566

Disclosures

Patrick T. O'Gara, MD, MACC
Edwards Scientific Corp (O); Medtronic (O)

Interviewer: Deepak Bhatt, MD, MPH, FACC
Takeda Pharmaceutical Co Ltd (C); The Medicines Company (G); Johnson and Johnson Services Inc (G); Medscape (G); Bristol-Myers Squibb Co (G); AstraZeneca (G); Sanofi (G); Eisai Co Ltd (G); Medtronic (G); PLx Pharma (G); Amarin Corp (G); FlowCo Inc (G)

Acknowledgements

CME/CE INFO

Accreditation:

The Audio- Digest Foundation is accredited by the Accreditation Council for Continuing Medical Education to provide continuing medical education for physicians.

The Audio- Digest Foundation designates this enduring material for a maximum of 0 AMA PRA Category 1 Credits™. Physicians should claim only the credit commensurate with the extent of their participation in the activity.

Audio Digest Foundation is accredited as a provider of continuing nursing education by the American Nurses Credentialing Center's (ANCC's) Commission on Accreditation. Audio Digest Foundation designates this activity for 0 CE contact hours.

Lecture ID:

AC500706

Expiration:

This CME course qualifies for AMA PRA Category 1 Credits™ for 3 years from the date of publication.

Instructions:

To earn CME/CE credit for this course, you must complete all the following components in the order recommended: (1) Review introductory course content, including Educational Objectives and Faculty/Planner Disclosures; (2) Listen to the audio program and review accompanying learning materials; (3) Complete posttest (only after completing Step 2) and earn a passing score of at least 80%. Taking the course Pretest and completing the Evaluation Survey are strongly recommended (but not mandatory) components of completing this CME/CE course.

Estimated time to complete this CME/CE course:

Approximately 2x the length of the recorded lecture to account for time spent studying accompanying learning materials and completing tests.

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