With an increasing prevalence of patients with valvular heart disease, a dedicated management approach is needed[14]. The evaluation of valve defect only under resting conditions might underestimate the full impact of the lesion and its clinical effects[15]. Orthostatic-induced alterations in Doppler echocardiographic measures of ventricular function have not been well-defined and in very recent study[16] echocardiographic changes from the supine to the sitting position were measured in a small group. However, the sitting position causes less hemodynamic stress (but is more comfortable) than the standing position. Standing is a fundamental activity of daily life[1] and may induce a fall in cardiac patients predisposed to syncope due to (sub) valvular obstruction. The Orthostatic test is a provocative maneuver that is definitely physiologically based and most relevant to conditions under which patients predisposed to (pre)syncope incur symptoms. In HCM patients standing is recommended as a physiologic provocative maneuver[6–8] and in some patients standing may guide therapy. Measuring subvalvular gradients by echocardiography in the supine position, as is routine practice for assessing patients, does not reflect the pathophysiology of this pathology during daily activities, which trigger the symptoms that patients report to their cardiologists.
In the current study among AS patients, the mean value of maximum aortic gradient significantly decreases after orthostatic stress. In minority patients peak aortic gradient slightly increases during the stress test (mainly by a few percent) in contrast there is a decrease in the majority of AS patients (sometimes more than one-third). All patients were symptomatic. In previous studies with different patients i.e. asymptomatic[12, 17] exercise as stress was preferred and the provocation of the gradient was measured in the (semi) supine position. This methodology facilitates the measurement of the gradient. Additionally in the supine position, the left ventricular preload is greater than in the upright position. From a methodological point of view, the standing position is more natural and reflects a more physiological condition during everyday activity than the supine position[6]. In every-day life, AS patients have experienced syncope mostly in the upright position. Using the orthostatic test, we tried to reproduce the physiological conditions occurring during daily life.
We postulate that future Guidelines of Scientific Societies should recommend the orthostatic stress test (isolated or combined with exercise) to be employed in groups of patients with predisposition/presence of subvalvular or valvular gradients.
We did not calculate LV diastolic and systolic volumes in the standing position. In the standing position, we concentrated on the gradient measurements from the apical window. However, we did not perform short and long parasternal axis imaging. Additionally, we cannot simultaneously measure both gradient and LV dimensions, and we chose to focus on gradient recording as the main aim of this study. The measurement of LV dimensions in the standing position is difficult to obtain, and the alternative stress test, i.e. lower body negative pressure (LBNP), may provide an opportunity to measure LV unloading in the supine position (the most suitable for echocardiography). However LBNP is not a natural stress test in contrast to the natural standing position which is common everyday activity. The orthostatic stress test has additional advantages. It is fast, simple, without any cost and any devices.
Limitation of study and further direction of studies
The exclusion criteria (methodological) in the study significantly constrained patient recruitment. In the upright position, only the apical window was used for aortic gradient measurement. The preload may be the most important for gradient changes. According to our experience and data for others publications, comprehensive echocardiographic examination is hard to perform in upright position. Practically only apical view is imaginable. In previous studies in aortic stenosis the echocardiography was performed in semi-supine position. New approach (novel position) have been proposed by Rowland T, et al.[16]. Authors have performed examination in young healthy males in sitting position, however, not in upright (erect) position. In our study not only position (erect) during echo recordings was more difficult but also study group was more demanded for echo imaging. Our unselected patients were elderly (mean age 75 years), frequently obese or with pulmonary emphysema. The group consisted of many women with breast responsible for additional difficulties in imaging. The group represent “natural AS patients”. Rowland et al. studied only very young, male, non-obese patients.
In comparison to our previous study in hypertrophic cardiomyopathy[5], the LVOT gradient is easier to measure than the transvalvular gradient via the stenosed aortic valve. Consequently, we did not extend our pilot study to the upright exercise test. In the standing position, the low-exercise fixed load may be the more advantageous test[11]. However, it should also be considered that the transvalvular gradients measured by the Doppler echocardiography are highly dependent on the angle between the ultrasound beam and the flow jet direction through the narrowed valve, which may vary during exercise. Importantly, the assessment of AS by exercise-stress echocardiography is technically challenging even in experienced hands and time consuming, which may limit its application in clinical practice. It should be added that exercise Doppler echocardiography can only be performed in patients with adequate echocardiographic windows[11].
Probably in a substantial portion of patients, transvalvular thin blood jet should be hard to measure during patient movement and breathing motion. However, such measurements at peak exercise may be particularly informative for patients with presyncopal episodes during exercise. In our AS group, a minority of patients experienced increased gradients. The number of ‘non-dippers’ was too small for statistical comparison but we expect that this subgroup may have more preserved LV contractility and may be candidates for valve repair later than the decreasing responders group. Further studies with a larger group of patients is needed to verify the hypothesis about the role of contractility force and depressed load.
We preferred the simple upright test than the tilt table test. We simply achieved “true stress”, i.e. 90 degree position (identical to every day activity). The stress was truly natural without any cost and devices (tilt-table). It is proposed that this test is fully standardized by life conditions.
Clinical implication
The potential role of the orthostatic test should be used in patients with borderline SA for valve replacement therapy and for monitoring procedure in post-operative patients with abnormal gradient across valvular prosthesis (borderline mismatch).
