INTRODUCTION
Left ventricular outflow tract diameter (LVOTD) is a key measure in
echocardiographic practice because it allows the non-invasive estimation
of LV output and specifically of stroke volume and stroke volume index
(SVI). These measures are relevant in multiple clinical settings,
including risk-stratification in heart failure (1-4), decision to
operate atrial and ventricular septal defects (5) and for diagnosis,
risk-stratification and treatment of aortic stenosis (6-8). LVOTD is
routinely measured with transthoracic echocardiography (7). However, a
precise measurement of the LVOTD can be challenging in some patients and
measurement errors can lead to misevaluation of LV output and aortic
stenosis severity (9-13).
Previously, Leye et al. showed that a moderate linear correlation exists
between LVOTD and body surface area (BSA), thus they derived an equation
for estimating LVOTD from BSA (LVOTDBSA), which was
proposed as a safeguard when direct LVOTD measurement is difficult or
not possible (14). Due to the LVOTD correlation with BSA, some authors
have suggested the LVOT velocity-time integral (or stroke distance) to
be a SVI analog with simpler calculation and proposed it for prognostic
assessment (15). Analogously, a dimensionless index has been proposed in
addition to aortic valve area calculation to avoid LVOTD measurement for
aortic stenosis grading (7). However, we have recently observed a better
prognostic capability of SVI over stroke distance in heart failure (16),
suggesting a more active role of LVOTD in determining LV output. We
hypothesized that the variability of LVOTD over BSA was due to the size
of the anatomical structures close to the LVOT, such as the aortic root
and LV cavity, that have never been taken into account previously
(14,15).
In this study we decided to: 1) explore the relationship among LVOTD, LV
and aortic root dimension beyond BSA, in order to derive a more
comprehensive equation for predicting LVOTD size; and, 2) validate this
equation in a different cohort of patients, comparing its performance
with the previously published equation based on BSA only (14). We
preliminary compared LVOTD measurements obtained during transthoracic
echocardiography (TTE) with those performed during transesophageal
echocardiography (TEE) to verify the accuracy of the TTE LVOTD
measurements.