Author + information
- Mark C. Svendsen, PhD,
- Anjan K. Sinha, MD,
- James B. Hermiller, MD,
- Deepak L. Bhatt, MPH,
- Benjamin Jansen, BS,
- Zachary C. Berwick, PhD,
- Arika Kemp, BS,
- William Combs, MS and
- Ghassan Kassab, PhD∗ ()
- ↵∗California Medical Innovations Institute, 11107 Roselle Street, Room 211, San Diego, California 92121
Balloon underexpansion during percutaneous coronary intervention is a major reason for stent underdeployment, which occurs in part because the predicted relationship between balloon pressure and diameter is not always realized in vivo (1). We herein describe a new device that accurately measures balloon cross-sectional area (CSA) during inflation.
The CB catheter provides an accurate, real-time digital display of the balloon CSA based on continuous electrical conductance recordings made inside the balloon. Within each balloon, there are 4 radiopaque platinum-iridium electrodes mounted on the catheter body. The 2 outer electrodes inject a small and alternating electrical current (136 μApp, 10 kHz) during inflation/deflation, and the 2 inner electrodes make continuous voltage measurements related to the local balloon size across an approximate 3-mm cross-section at the center of the balloon (i.e., a focal measurement is made at the balloon center and is not averaged across the entire balloon). When the CB catheter is connected to a computer console, the local balloon CSA is calculated and displayed in real time (Figure 1A) based on Ohm’s law (CSA = I × L/[σ × V]), which states that the 3-mm focal central balloon CSA across the inner electrodes is equal to the known constant current (I) times the known length between the electrodes (L) divided by the known constant of the fluid conductivity (σ) and the continuously measured voltage (V).
Validation of the CB catheter was first completed on the bench using randomized, repeat measurements made in uniform plastic cylindrical phantoms of known dimensions. The average CSA difference between the CB catheter measurements and the true phantom dimension was −0.1 ± 0.2 mm2 with an error of 2.6%. The average CSA difference on the bench between the repeat CB catheter measurements was 0.0 ± 0.1 mm2 with an error of 1.6%.
Validation in vivo was completed in 5 domestic swine (approximately 70 kg each). The CB catheter studies were performed in 7 coronary vessels having previous mild fibrotic coronary injuries (CSA stenosis approximately 25%) and in 3 normal coronary vessels. Manual measurement of the vessel area by intravascular ultrasound (IVUS) (Eagle Eye coronary catheter, Volcano Corporation, San Diego, California) was used to determine the vessel size before stent deployment (8.2 ± 3.8 mm2). Bare-metal (Veriflex, Boston Scientific, Natick, Massachusetts) or drug-eluting stents (Xience, Abbott Vascular, Abbott Park, Illinois) were deployed at the manufacturer-specified pressure (4.0 to 16.0 atm; 9.1 atm average) and diameter (2.8 to 4.5 mm; 3.4 mm average), with an IVUS-measured CSA of 7.8 ± 2.9 mm2 versus an expected stent CSA of 9.4 ± 4.1 mm2. A high-pressure CB catheter (polyethylene terephthalate/nylon; fully inflated > 1 atm) larger than the deployed stent diameter determined by IVUS was selected and placed within the stent at the same location as the IVUS, and at least 4 repeat inflations/measurements (Figure 1B) were completed (no difference between the first and last CB measurements). As expected for these noncompliant balloons, the in vivo stent/vessel recoil (0.32 mm) was almost identical to what is described in published reports (0.28 mm) (1). The CB catheter had an average CSA of 10.9 ± 3.4 mm2 versus a predicted stent CSA of 9.4 ± 4.1 mm2 and a post-deployment IVUS CSA of 10.6 ± 3.4 mm2 when recoil was accounted for (1). The in vivo CSA measurement accuracy bias (difference) versus post-procedural IVUS when recoil was accounted for was 0.3 ± 0.9 mm2 with an error of 8.5%. There were no observed arrhythmias or deaths during any of the CB measurement procedures.
The overall excellent CB catheter accuracy and repeatability can be attributed to the fundamental electrophysical law governing the catheter design and the insulative nature of the balloon that gives accurate results regardless of the electrical properties of the surrounding environment. The CB catheter offers accurate, real-time sizing capabilities completely independent of subjective user input and allows the user to adjust the inflation instantaneously. The CB sizing electrodes easily integrate into existing standard coronary balloons and hence do not significantly alter clinical procedures. The CB catheter functionality is flexible and could easily be integrated into other devices, such as stent delivery balloons, drug-eluting balloons, and valvuloplasty balloons. Future work will include a first-in-man validation and the use of multiple sets of measurement electrodes inside the balloon to provide a balloon profile showing variation in the CSA dimension along the balloon length.
Please note: This study was supported by National Institutes of Health grant R43-HL120517. Drs. Svendsen and Berwick are employed by 3DT Holdings, LLC. Dr. Sinha has a speaking relationship with Boston Scientific; and has received a research grant from Edward Life Sciences. Dr. Bhatt has received research grants from Amarin Corporation, AstraZeneca, Bristol-Myers Squibb, Eisai, Ethicon, Medtronic, Roche, Sanofi-Aventis, and The Medicines Company; and has participated in unfunded research for FlowCo, PLx Pharma, and Takeda. Dr. Kassab is the founder of 3DT Holdings, LLC. All other authors have reported that they have no relationships relevant to the contents of this paper to disclose.
- 2015 American College of Cardiology Foundation