Author + information
- Naoko Sawada, MD,
- Hirotsugu Yamada, MD, PhD∗ (, )
- Kenya Kusunose, MD, PhD,
- Shuji Hayashi, MD, PhD,
- Takashi Iwase, MD, PhD and
- Masataka Sata, MD, PhD
- ↵∗Department of Cardiovascular Medicine, Tokushima University Hospital, 2-50-1 Kuramoto, Tokushima 770-8503, Japan
Measurement of the cross-sectional area (CSA) of the right ventricular outflow tract (RVOT) has been required to calculate stroke volume, especially for estimation of the pulmonary blood flow/systemic blood flow ratio. Current guidelines of the American Society of Echocardiography state that the CSA should be calculated using the RVOT diameter measured in either the parasternal long-axis view or parasternal short-axis view. Recently, the shape of the RVOT has been reported to be oval when using 3-dimensional (3D) transesophageal echocardiography (1); however, the dynamic change of RVOT geometry in a cardiac cycle has not been well validated with any modality. The aim of this study was to assess morphological and dynamic features of the RVOT using multidetector computed tomography (MDCT) and to compare the CSA of the RVOT obtained by MDCT and by 3D or 2-dimensional (2D) transthoracic echocardiography (TTE).
A total of 20 patients with clinically indicated contrast MDCT were prospectively enrolled between May and September 2014 at Tokushima University Hospital. This study was conducted in accordance with the Declaration of Helsinki, was approved by the Institutional Review Board of the University of Tokushima, and each subject gave written informed consent. The MDCT examination was performed using a 320-MDCT scanner (Aquilion ONE, Toshiba Medical Systems, Tokyo, Japan). Retrospective electrocardiography-gated MDCT was performed; 10 phases of images were reconstructed at a 10% R-R interval. The RVOT was manually traced in the double-oblique transverse view, and the CSA (RVOT-CT) was measured at just below the pulmonary annulus in all 10 phases (0% to 90% R-R interval). Echocardiographic studies were performed using the iE33 ultrasound imaging system (Philips Medical Systems, Andover, Massachusetts). We measured the long- and short-axis diameters of the RVOT in early systole by a 2D probe and calculated the CSA using each diameter, assuming that the RVOT is circular (RVOTsax, RVOTlax) and using both diameters, assuming that the RVOT is oval (RVOToval). The RVOT CSA in the same cardiac phase was also measured offline from the 3D dataset obtained by a 3D probe (RVOT3D). Three patients were excluded from this analysis because of poor image quality.
The RVOT CSA changed dynamically in a cardiac cycle. The pulmonary valve opened from 10% to 30% phases, and the maximum CSA was defined in the 10% phase. Figure 1 shows comparisons among various CSAs obtained by multimodalities (MDCT, 3D-TTE, and 2D-TTE). The RVOTsax underestimated the RVOT-CT (bias: −105.3 mm2), and there was no significant correlation between them (r = 0.08, p = 0.75). The RVOTlax overestimated the RVOT-CT (bias: +111.3 mm2), and there was a modest correlation between them (r = 0.59, p = 0.01). The RVOToval had a small bias (bias: −13.5 mm2) compared with the RVOT-CT, but there was no significant correlation between them (r = 0.41, p = 0.11). The correlation between the RVOT3D and the RVOT-CT was excellent (r = 0.92, p < 0.001) with less bias (bias: +24.9 mm2).
The present study is the first to demonstrate the morphological and dynamic features of RVOT CSA by MDCT. The CSA of the RVOT calculated by the diameters in either view of 2D-TTE may be inaccurate in some cases; the 3D-TTE provides more accurate measurement of the parameter.
Please note: The study protocol was approved by our institutional clinical research ethics committee. The authors have reported that they have no relationships relevant to the contents of this paper to disclose.
- American College of Cardiology Foundation