We read with interest the article by Studer Bruengger et al . and the related scientific editorial. The study confirmed previous reports of normal exercise E/e′ ratios, considered an index of left ventricular filling pressure (LVFP), in healthy subjects. The article encourages the use of diastolic stress echocardiography in clinical practice, especially to investigate patients with exercise dyspnea.
We agree that despite normal investigations at rest, latent heart failure can be observed in a number of patients upon effort. In addition, the value of the E/e′ ratio to estimate invasively measured LVFP was reported. However, the validation study of exercise E/e′ included a selected population with a high prevalence of coronary stenosis (75%); of the 37 patients in whom E/e′ results were compared with invasive measures of mean left ventricular diastolic pressure, six (16%) had left ventricular ejection fractions < 45%. Moreover, conflicting results have been reported in other studies assessing E/e′ to evaluate exercise LVFP in various populations with preserved left ventricular ejection fractions, including healthy subjects.
For noninvasive estimation of LVFP at rest, current guidelines encourage the use of pulsed-wave tissue Doppler for calculating the ratio between the preload-dependent transmitral E velocity and the annular e′ velocity, which has been described as relatively load independent. However, although e′ was minimally preload dependent in patients with impaired relaxation, it was strongly preload dependent in those with preserved relaxation. Consistently in the guidelines, it is clearly stated that E/e′ ratio should not be used to assess LVFP in “normal subjects” (no history of heart disease along with normal cardiac structure and function). Moreover, “normal” cardiac structure and function do not exclude the diagnosis of heart failure in patients with exercise dyspnea.
There is no doubt that diastolic stress echocardiography is a step forward and will probably enhance in the future the contribution of ultrasound in the management of patients. However, to date we think that exercise E/e′ ratio should be used with caution in clinical practice to assess exercise LVFP at the individual level. The diagnostic approach probably should be adjusted to the patient profile. In particular, further studies are warranted to define the best noninvasive strategy to use in patients with dyspnea and normal cardiac structure and left ventricular ejection fractions.