Combowire for Intravascular Surgery
BME 240: Applications in Clinical Medicine
Combowire System
1. Complete Combowire System -Simultaneous Pressure and Flow Measurement

The system is very portable and user-friendly with convenient touch-screen navigation for easy operative toggling and pre-operative calibration. The 15” LCD monitor displays charts and values in real-time and is able to calculate physiological parameters instantaneously.

2. ComboWire Guide Wire Design – Specifications

While ComboWire guide wire had an earlier version with the pressure sensor positioned 1.5 cm from the tip flow sensor, the newer version, shown in the box above, has both sensors located at the tip. This was motivated by the clinical need to obtain dual modality data from the same location as well as a reduction in procedural complexity and error. This is the first guide wire that obtains intravascular flow and pressure information simultaneously which enable the calculation of a new hemodynamic index (HSR) discussed below.

3. Discordance in Current Hemodynamic Parameters – FFR and CFR


While both FFR and CFR are highly utilized to ascertain the physiological effect of a stenotic lesion, the best cutoff value of 0.75 and 2.0 for FFR and CFR respectively, does not always correspond in intermediate lesions (40% to 70% diameter stenosis).  Figure A shows a scatter plot of data from 150 patients with intermediate lesions. While upper right and lower left quadrants correspond in terms of diagnostic significance of the lesion, the other two quadrants are discordant values. Similarly, the graph B illustrates the uncertain nature of the 4 possible diagnostic outcomes as well as the variability in the pressure drop at increased flow rates (hyperemia) compared to resting flow.

4. Patients with Discordant Assessment – Table

Out of 150 patients with intermediate stenosis, 41 had discordant values leading to uncertainties in treatment options.

5.  New Index – HSR Motivation

The curvilinear relationship between pressure drop across the stenotic region and flow velocity illustrates the possible confounding effects of measuring FFR and CFR alone. Ratios of pressure measurements (FFR) and flow reserves (CFR) are subject not only to initial resting conditions (baseline), but also to the ability to pharmacologically induce maximum flow in the patient. A new index called HSR (= ∆P/v) was proposed to offset this dependence on flow variation within patient groups. The HSR index is less sensitive to variation flow conditions since an increase in the denominator (v) corresponds to an increase in the numerator (∆P) thereby minimizing variability.

6. HSR Validation

A panel of nuclear medicine physicians conducted an SPECT emission scan and evaluated the group of 151 patients post FFR, CFR, and HSR measurements. The table on the right shows the number of patients in each of the misclassified categories with HSR having almost half the number of FFR and CFR alone. An ROC curve on the left, further shows a higher area under curve (AUC) for HSR with values of 0.90, 0.82, and 0.80 for HSR, FFR, and CFR respectively.