Relation of Velocity-Time Integral of the Left Ventricular Outflow Tract to that of the Descending Thoracic Aorta and Usefulness of a Fixed Ratio for Internal Validation

Measurement of left ventricular outflow tract velocity-time integral (LVOT VTI) is technician-, instrument-, and reader-dependent; variability is more common for pulsed-wave Doppler than continuous-wave Doppler. We hypothesize that in a population with normal cardiac structure and function, LVOT VTI is higher than VTI of the descending thoracic aorta (DTA) and this relation may be used clinically to validate the former. Furthermore, the DTA VTI could also be used to estimate LVOT. We retrospectively compared the LVOT VTI against VTI measured from DTA, abdominal aorta, and pulmonary artery among 108 healthy subjects. The ratio of LVOT VTI (n = 108) to DTA VTI (n = 108) was 1.27. There was a difference of 19.6% between LVOT VTI and DTA VTI with the former being higher. This percentage decrease in VTI from LVOT VTI to abdominal aortic (AA) VTI was directly proportional to the LVOT VTI. Similarly, there was a difference of 23.4% in the VTI values obtained from DTA and abdominal aorta. Moreover, there was a decrease of 40.4% when LVOT VTI was compared against AA VTI. The ratio of LVOT VTI to pulmonary VTI was 1.19. VTI values decrease in a linear fashion from the LVOT to abdominal aorta likely because of progressive decrease in circulating volume, and this change is not obscured by diminishing aortic diameter. Any deviation from this relation should be treated as abnormal and should prompt further investigation. Our findings support routine measurement of DTA VTI in clinical practice.