On Acquiring Intra-Cardiac Pressures Noninvasively in Real-Time Using Subharmonic Aided Pressure Estimation (SHAPE)

Subharmonic aided pressure estimation (SHAPE) measures ambient pressure dependent subharmonic signals from contrast microbubbles. This study evaluated if Definity® (Lantheus Medical Imaging, N Billerica, MA, USA) or Sonazoid (GE Healthcare, Oslo, Norway) microbubbles are useful for real-time noninvasive intra-cardiac pressure estimation using SHAPE. Patients scheduled for a right and/or left heart catheterization procedure were approached to participate in this IRB approved study and provided written consent. During the standard-of-care catheterization procedure, a pressure catheter was advanced into the cardiac chambers or the aorta to obtain clinically relevant systolic and diastolic pressures. After catheter placement, the patients received either an infusion of Definity (40 patients; 2 vials in 50 mL of saline; infusion rate: 4-10 mL/min) or Sonazoid (41 patients; rate (mL/hour) = 0.18 x weight in kg co-infused with saline at 120 mL/hour). A customized interface on a SonixTablet scanner (Analogic Corporation, Peabody, MA, USA) was used to acquire SHAPE data synchronously with the pressure catheter data. Previously determined optimal transmit parameters were used for data acquisition with Definity (f
_transmit
: 3.0 MHz; chirp down pulse) and Sonazoid (f
_transmit
: 2.5 MHz; square wave pulse) microbubbles. An algorithm to determine optimum incident acoustic output was initiated for each patient (to account for attenuation differences). Then, SHAPE data were acquired at the optimum incident acoustic output. Linear correlation between the SHAPE and pressure catheter data were computed using MATLAB (Mathworks, Natick, MA, USA). The correlation coefficient between SHAPE and pressure catheter data obtained using Definity was -0.86 ± 0.06 (n=15) and -0.87 ± 0.06 (n=18) for data obtained from the left and right ventricles, respectively. In two cases, adverse events were observed post Definity infusion. Both events were resolved with return to baseline conditions. Using Sonazoid, the correlation coefficient between the SHAPE and pressure catheter data was -0.83± 0.05 (n=10) and -0.82 ± 0.06 (n=7) for data obtained from left and right ventricles, respectively. These results indicate that SHAPE is a useful technique to noninvasively obtain intra-cardiac pressures in real-time.