Although much is known about the technical aspects of inferior vena cava visualization, it is much less about its counterpart: the superior vena cava (SVC). The aims of this study therefore, were to describe in detail the different possible transthoracic SVC visualization techniques in adults and to provide a series of normal values for its dimensions and Doppler signals.
The feasibility of SVC visualization by TTE was initially established in 40 patients with or without central venous catheters, or pacemaker wires. Subsequently, the newly found SVC visualization road maps were applied in 30 healthy adults to assess SVC dimensions, their respiratory variations and Doppler signal parameters. Dimensions were measured 3-5mm proximal (above) the RA-SVC junction at the end of both cardiac and respiratory cycles but the peak Doppler velocities were only measured at the end-held expiration. To clarify the SVC color flow, the Nyquist limit was set at 25-40 m/s.
The three new SVC visualization road maps included:
a) Modified apical 5-champber view (MA5CV),
b) Modified parasternal short axis view of great vessels (MSAVGV) and
c) Modified subcostal view (MSCV).
The 30 normal subjects included 17 males and 13females with an age range of 24-45 years, weight of 46-77 kg, height of 158-178cm and body mass index (BMI) of 15.73-27.24 kg/m2. The largest end systolic SVC dimensions at the end of the expiration and inspiration ranged from 7.7 to 14.0 mm (10.74 ± 1.7 mm) and 8.0 -14.0 mm (10.86 ± 1.53 mm) respectively, and the highest S wave velocity ranged from 0.49 - 0.65 m/s (0.57 ± 0.03 m/s).
The challenge of SVC visualization by TTE is over now and it is hoped that it could become a part of routine echocardiographic assessments by everybody and everywhere.