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Right ventricular volume measurement by conductance catheter
Mark H D Danton1, Gerald F Greil, John G Byrne
1Department of Cardiac Surgery, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA. markdanton@yahoo.com
Summary
The conductance method can accurately measure right ventricular (RV) volume under steady-state conditions when calibrated. However, complex RV geometry can introduce non-linearity, impacting accuracy across wider volume ranges.
Area of Science:
- Cardiovascular Physiology
- Medical Imaging
- Biomedical Engineering
Background:
- Continuous ventricular volume measurement relies on assumptions of homogeneous electrical fields.
- Dense trabeculation and complex geometry in the right ventricle (RV) may compromise conductance-based volume measurements.
- Magnetic Resonance Imaging (MRI) offers a reference standard for volumetric assessment.
Purpose of the Study:
- To evaluate the accuracy and limitations of RV volume measurement using the conductance method.
- To compare conductance measurements against MRI-derived volumes in a porcine model.
- To assess the impact of single-field (SF) versus dual-field (DF) excitation on RV volume accuracy.
Main Methods:
- ECG-gated MRI was used to acquire transverse images for RV volume calculation via Simpson's technique.
- An RV conductance catheter was inserted, and signals were recorded using SF and DF excitation.
- Saline-dilution corrected for parallel conductance, and the gain factor (alpha) was calculated.
- Alpha variation during the cardiac cycle (alpha(t)) was analyzed against MRI volumes and pulmonary flow.
Main Results:
- After calibration, conductance and MRI volumes showed good linear correlation (r=0.96 SF, r=0.94 DF).
- Individual plots revealed slight curvilinearity, indicating alpha(t) variation during the cardiac cycle (significant with SF, P=0.011).
- Dual-field (DF) excitation improved volume measurement accuracy (alpha SV=0.96) and reduced alpha(t) variation (P=0.66).
Conclusions:
- The calibrated conductance method can provide absolute RV volume measurements under steady-state conditions.
- Dual-field excitation enhances the accuracy and reliability of RV conductance volumetry.
- Potential non-linearity exists when RV volumes fluctuate over a wide range due to geometric complexities.