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.