Non-Invasive Intra-cardiac Pressure Measurements Using Subharmonic-Aided Pressure Estimation: Proof of Concept in Humans

Abstract

This study evaluated the feasibility of employing non-invasive intra-cardiac pressure estimation using subharmonic signals from ultrasound contrast agents in humans. This institutional review board-approved proof-of-concept study included 15 consenting patients scheduled for left and right heart catheterization. During the catheterization procedure, Definity was infused intra-venously at 4-10 mL/min. Ultrasound scanning was performed with a Sonix RP using pulse inversion, three incident acoustic output levels and 2.5-MHz transmit frequency. Radiofrequency data were processed and subharmonic amplitudes were compared with the pressure catheter data. The correlation coefficient between subharmonic signals and pressure catheter data ranged from -0.3 to -0.9. For acquisitions with optimum acoustic output, pressure errors between the subharmonic technique and catheter were as low as 2.6 mmHg. However, automatically determining optimum acoustic output during scanning for each patient remains to be addressed before clinical applicability can be decided.

Keywords: Cardiac catheterization; Intra-cardiac pressures; Non-invasive pressure estimation; Subharmonic-aided pressure estimation; Ultrasound contrast agents.

Figure 1

A snap-shot of ultrasound data-acquisition for SHAPE. In this case, a 4.5 mm pulsed-Doppler gate (arrow) was placed in the right ventricle of a patient for data acquisition.

Figure 2

Sample results from right ventricle of 2 patients where SHAPE data were acquired not at (a; r = −0.3) and at (b; r = −0.9) optimum incident acoustic output. Solid line indicates SHAPE output whereas dotted line indicates the pressure catheter data.

Figure 2

Sample results from right ventricle of 2 patients where SHAPE data were acquired not at (a; r = −0.3) and at (b; r = −0.9) optimum incident acoustic output. Solid line indicates SHAPE output whereas dotted line indicates the pressure catheter data.