Summary
The management of asymptomatic patients with severe aortic stenosis is challenging. Unfortunately, evaluation of symptoms such as dyspnoea remains subjective. The use of exercise echocardiography may help to predict major events in patients with asymptomatic severe aortic stenosis. This article explains how to perform the test and discusses which echocardiographic measurements should be obtained, focusing on the diagnostic and prognostic value of these measurements. An increase in mean transaortic pressure gradient ≥ 18 mmHg predicts a worse prognosis in patients with severe aortic stenosis. The absence of left ventricular contractile reserve also has an important prognostic impact. Evaluation of filling pressures and looking for a worsening or a new mitral regurgitation are also part of the exam. Further studies are required to determine whether surgery should be recommended in the presence of an abnormal exercise echocardiogram in severe asymptomatic aortic stenosis.
Résumé
La prise en charge des patients présentant un rétrécissement aortique (RA) sévère asymptomatique reste difficile. L’évaluation des symptômes tels que la dyspnée est souvent subjective. L’utilisation de l’échocardiographie à l’effort permet de mieux stratifier le risque de survenue d’évènements majeurs. Cet article détaille les différentes mesures utiles lors de l’échocardiographie à l’effort ainsi que la valeur diagnostique ou pronostique de ces mesures. Une augmentation du gradient transaortique moyen de supérieure ou égale à 18 mmHg prédit un moins bon pronostic chez les patients avec RA sévère. L’absence de réserve contractile du ventricule gauche à l’effort est également un facteur pronostique important. Enfin, l’évaluation des pressions de remplissage et la recherche d’insuffisance mitrale à l’effort font partie intégrante de l’échocardiographie à l’effort dans cette population. D’autres études sont requises pour valider l’indication de procéder à un remplacement valvulaire aortique précoce suite à une échocardiographie d’effort anormale chez le sujet avec RA sévère asymptomatique.
Introduction
Valvular aortic stenosis (AS) is the most prevalent valvular heart disease in Europe . The European Society of Cardiology guidelines recommend prompt aortic valve replacement when patients with severe AS are symptomatic or develop left ventricular (LV) dysfunction (ejection fraction < 50%) . However, the management of asymptomatic patients with severe AS remains challenging. Although symptoms of angina and syncope are relatively easy to identify, dyspnoea, fatigue or dizziness are more difficult to elicit in sedentary and elderly patients, and remain substantially subjective. In addition, the operative risk of asymptomatic patients with severe AS is probably equivalent to or even higher than the risk of sudden death. Indeed, the risk of sudden death in these patients is around 1% per year and is a rare phenomenon in patients without preceding symptoms . To help to guide clinician decisions, exercise stress testing is advocated strongly by the European Society of Cardiology guidelines, and is a Class IIb recommendation by the American College of Cardiology/American Heart Association . Nevertheless, exercise stress testing does not discriminate accurately between the signs and symptoms of masked symptomatic severe AS and severe coronary artery disease. In this situation, stress echocardiography may help to make a diagnosis of ischaemic heart disease in patients with severe asymptomatic AS. One of the most important roles of stress echocardiography in patients with AS is to discriminate the haemodynamic effects on the valve itself and on the left ventricle, and to assess the mechanisms behind a positive exercise stress test in asymptomatic severe AS . This article describes how to perform exercise echocardiography in asymptomatic severe AS, which echocardiographic measurements should be obtained and how to interpret exercise-induced changes.
How to perform stress echocardiography in asymptomatic severe aortic stenosis
Before performing this test, it is mandatory to ensure that the patient is truly asymptomatic. Some patients may reduce their level of daily activities as an adaptation to the disease. Table 1 summarizes the contraindications to perform an exercise stress test in patients with severe AS. An exercise echocardiogram should be performed under the strict supervision of an experienced physician, with close monitoring of heart rate and blood pressure. A symptom-limited exercise with a stepwise protocol is used. Dobutamine echocardiography has been analysed in the assessment of valve compliance but it is less physiological and the clinical value of valve compliance requires further study . A post-exercise echocardiogram, after treadmill or upright bicycle ergometry, can be obtained but a supine or a semi-supine bicycle exercise test is probably preferable. First, there is a reduced risk of haemodynamic collapse in this position and second, it allows continuous two-dimensional and Doppler echocardiographic examination. The sensitivity and specificity of having an abnormal test may be influenced by the position. The treadmill test may induce dizziness and angina more frequently, and may provide higher rate-pressure product at peak exercise; it has demonstrated a higher sensitivity than cycling for the diagnosis of ischaemic heart disease . However, exercise in the supine position may enhance ST-segment depression, increasing the sensitivity of the test . It should also be emphasized that abnormal stress testing was described initially in the context of coronary heart disease and fewer data are available for valvular heart disease. In particular, the evolution of systolic blood pressure differs according to the patient’s position. A decrease in blood pressure – a classical criterion of positivity – is indeed observed less frequently in the supine position. Special attention should be given to patients with confounding factors like chronic obstructive pulmonary disease or obesity. In the first case, breathlessness may be the result of pulmonary disease or the valve disease, or both. In this setting, a cardiopulmonary exercise test with gas exchange may be useful to distinguish whether the symptoms are related to cardiac, pulmonary or peripheral limitations.
| Contraindications |
|---|
| Symptoms (angina, heart failure symptoms, syncope) |
| Low left ventricular ejection fraction (< 50%) |
| High blood pressure (systolic > 200 mmHg or diastolic >110 mmHg) |
| Uncontrolled or symptomatic arrhythmias |
| Systemic illness |
| Physically or mentally incapable of performing an exercise stress test adequately |
A stepwise protocol of 25 watts every 2 min is used. Electrocardiography is monitored continuously and blood pressure is measured every 2 min. Evaluation of symptoms such as angina, syncope or dizziness is mandatory during exercise. At the end, maximum workload, total exercise time, peak heart rate and blood pressure, and the reason for stopping the examination are recorded. The exercise test is considered abnormal in the presence of at least one of the following criteria: symptoms; fall in systolic blood pressure or a rise < 20 mmHg during the exercise; < 80% of normal level of exercise tolerance; > 2 mm ST-segment depression compared with resting electrocardiography; and occurrence of ventricular arrhythmias ( Table 2 ).
| Criteria |
|---|
| Symptoms during exercise: angina, syncope or near syncope |
| Fall in systolic blood pressure or < 20 mmHg rise during exercise |
| < 80% of normal level of exercise tolerance |
| > 2 mm ST-segment depression during exercise (horizontal or down-sloping, compared with baseline, not attributable to other causes) |
| Ventricular arrhythmias |
Which echocardiographic measurements?
Performing exercise stress echocardiography in valve disease requires in-depth training with a learning curve. In the case of AS, obtaining the maximal gradients is sometimes limited by the supine position of the patient. The right parasternal position is not suitable on a left tilting table. The duration of exercise should be long enough to record different variables. This part of the article will focus on the echocardiographic measurements that are important to obtain in patients with asymptomatic severe AS. A complete echocardiographic examination should be performed before the exercise stress test in all patients. Moreover, at the time of echo, the measurement of systolic blood pressure is mandatory, as it could affect the assessment of AS severity. New measurements, such as energy loss index and global LV afterload (valvulo-arterial impedance) are of growing interest and may allow the identification of patients with paradoxical low-flow AS and preserved LV function . Echocardiographic measurements may be separated into valvular components, LV components and other components, such as mitral regurgitation (MR) and pulmonary pressures ( Table 3 ). Of course, exploring for concomitant coronary artery disease is part of the examination. The occurrence of new wall motion abnormalities during stress echocardiography in patients with AS should be interpreted with caution because it not only reflects the presence of exhausted coronary flow reserve but could also be a sign of significant coronary artery disease. In this situation, a coronary angiography should be scheduled in cases of low ischaemic threshold and extensive exercise-induced ischaemia.
| Component | Findings |
|---|---|
| Valvular components | |
| Aortic valve area | Increased: compliant valve |
| Stable: fixed and non-compliant valve | |
| Mean gradient | Increased: fixed and non-compliant valve or presence of contractile reserve (should be correlated to ejection fraction) |
| Decreased: no contractile reserve | |
| Left ventricular components | |
| Systolic function | |
| Ejection fraction | Increased: presence of contractile reserve |
| Stable or decreased: absence of contractile reserve | |
| Strain imaging by TDI or speckle tracking | Decreased: absence of contractile reserve |
| Diastolic function | |
| E / E ′ | Increased: elevated filling pressure |
| Other components | |
| Mitral regurgitation | Worsening or occurrence: elevated global afterload |
| Transtricuspid gradient | Increased > 50 mmHg: elevated pulmonary pressure |
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