Stress Testing: AS

ECHONOMY
Tools for Echocardiographic Calculations
Muhamed Saric, MD, PhD
New York University

Stress Testing: AS

Exercise Stress Testing for Aortic Stenosis

Target patient group: Stage C severe AS

Indication: Exercise testing is reasonable to assess physiological changes with exercise and to confirm the absence of symptoms in asymptomatic patients with a calcified aortic valve and an aortic velocity 4.0 m per second or greater or mean pressure gradient 40 mm Hg or higher (stage C)

Contraindication: Exercise testing should NOT be performed in symptomatic patients with AS when the aortic velocity is 4.0 m per second or greater or mean pressure gradient is 40 mm Hg or higher (stage D).

Evidence Class IIA; level of evidence B

Brief overview: Only stage C patients (severe asymptomatic or vaguely symptomatic patients with severe AS) should be considered for exercise stress testing. Do NOT perform stress testing in stage D patients (severe symptomatic patients) with severe AS) having typical symptoms.

Monitoring: Direct supervision in the exercise room by a physician or physician asstantis mandatory.

When to stop exercise (Positive exercise echo end-points in AS):

Symptoms:

	Syncopal or pre-syncopal episode, including severe dizziness
	Angina
	Limiting dyspnea or decreased exercise tolerance, defined as inability to reach 60% of age and sex adjusted metabolic equivalents of task (METs)

Abnormal BP response:

	Lack of increase or a drop in systolic blood pressure
	Exercise-induced hypotension is defined in some studies as failure to increase SBP by at least 20 mm Hg)

Ventricular arrhythmia

Significant ventricular arrhythmias (≥4 consecutive ventricular premature beats)

AS gradients at peak stress: Data on prognostic value of exercise-induced AS gradient are equivocal. Some suggest that a mean pressure gradient increase >20 mm Hg with exercise is prognostic of future cardiac events.

Interpretation: A patient with a positive stress echo using above criteria becomes a stage D patient and should be considered for AV replacement.

Dobutamine Stress Echo for Aortic Stenosis

Target patient group: Stage D2 (severe AS with low LVEF)

Indications: Low-dose dobutamine stress testing using echocardiographic or invasive hemodynamic measurements is reasonable in patients with stage D2 AS with all of the following:

	Calcified aortic valve with reduced systolic opening
	LVEF less than 50%;
	Calculated valve area 1.0 cm² or less; and
	Aortic velocity less than 4.0 m per second or mean pressure gradient less than 40 mm Hg

Contraindications: DSE should not be performed in patients who are not in stage D2.

Evidence Class IIA; level of evidence B

Brief overview: Stage D2 patients are typically characterized by severe AS by AVA (< 1.0 cm2) and only moderately elevated AS gradients. Only stage D2 patient should undergo dobutamine stress testing; dobutamine stress testing is NOT indicated in patients with stage D1 (severe, high-gradient AS) or stage D3 (low-flow, log-gradient AS with normal LVEF).

Monitoring: Direct supervision in the exercise room by a physician is mandatory.

Dobutamine stages: Baseline, 5 ug/kg/min; 10 ug/kg/min; 20 ug/kg/min. Please note that 20 ug/kg/min is the MAXIMUM dose to be given to these AS patients.

Parameters to be obtained at each stage: LVOT VTI, LVOT Vmax; LVOT stroke volume; AV Vmax; AV VTI; peak/mean AS gradient; AVA

When to stop dobutamine infusion (Positive dobutamine stress echo end-point in AS):

	Vmax > 4.0 m/sec AND valve area < 1.0 cm2 at any point during the test protocol.
	Do not increase dobutamine dose further if the goal is already achieved at a lower dose; stop the test.

Interpretation: There are 3 possible outcomes of DSE in stage D2 patients

	Stoke volume increases by >20%; significant increase in AS gradient (> 4.0 m/sec) with no significant change in AVA (AVA < 1.0 cm2) >>> Fixed AS; consider AV surgery
	Stroke volume increases by >20%; modest increase in AS gradient accompanied by an increase in AVA >>> Pseudo-AS; no AV surgery
	Stroke volume increases by <20% >>> No flow reserve; outcomes bad with or without AV surgery.

References

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 Jun 10;63(22):e57-185.