1Department of Radiology, San Carlo Borromeo Hospital, Milan; 2Department of Interventional Radiology, EMO GVM Centro Cuore Columbus, Milan; 3Department of Radiology, Pesenti Fenaroli Hospital, Alzano Lombardo, Italy. The authors can be contacted via Dr. Bruno Damascelli at email@example.com. This article received a double-blind review from members of the CLD editorial board. Disclosures: Dr. Bruno Damascelli reports he is named as joint applicant in the patent application relating to the steerable medical device described in the article. The remaining authors have no conflict of interest to declare.
The choice and availability of vascular catheterization equipment are two essential aspects of interventional and vascular radiology.1-3 Over the past decade, these procedures have been offered to patients with highly variable clinical anatomy and vascular pathology, and at the extremes of age ranges. If we consider, for example, placement of a stent for renal artery stenosis, a series of sheath shapes are offered: RDC-RDC1 Renal Double Curve, LIMA Left Internal Mammary Artery, C1-C2 Cobra, RE-S Renal Short, RESS Renal Short Standard, Bates 1-2-3-4 (Boston Scientific). Likewise, for other vascular accesses, a variety of catheters and sheaths are available to address the need for engagement of various veins and arteries. The performance of these devices varies considerably, depending upon the materials used, and the best performances often come with higher costs. Further increasing costs, it is not unusual for more than one catheter or sheath to be used during a single procedure, because of the difficulty both in achieving access and in maintaining it during the interventional procedure. A catheter of a certain shape may allow access, but not maintain it upon insertion of interventional devices such as angioplasty or occlusion catheters, and ablation electrodes, which have different physical characteristics.
Catheter sheaths for abdominal vascular catheterization are usually shaped according to the anatomical district where they are to be used. One of the drawbacks of these sheaths is their stiffness and poor navigability through tortuous vessels. When a device is introduced coaxially, arterial or venous engagement is easily lost. The market offers introducers that can be deflected in two opposite directions (Destino Twist, Oscor Inc., and Agilis NxT Steerable Introducer, St. Jude Medical). These are normally used for cardiac ablation via femoral vein catheterization, but their large diameter of 10 to 12 French (Fr) makes them unsuitable for use in percutaneous arterial catheterization. Deflection of the distal end of these introducers is achieved by means of pull wires, which run in the thickness of the wall and are connected to a handle attached to the base of the catheter.
It is difficult to combine the various desirable features of a product for abdominal vascular catheterization, namely an acceptable outside diameter, the largest possible inside diameter, effective torque control, low friction coefficient, kink resistance, and easy endovascular navigation, in catheters and sheaths that are made as a fixed structure. We therefore thought it useful to design a steerable pre-shaped sheath that meets all these requirements and thus is able to cover a wide range of vascular interventional applications in the abdomen.
Description of the Oscor Destino Twist TD*
The Oscor Destino Twist TD is a steerable sheath for arterial or venous use, with special pre-shaping suitable for abdominal vascular catheterization or for catheterization of the vena cava and its branches. The pre-shaping consists of a combination of a distal curve similar to that used to catheterize the left internal mammary artery (LIMA) and a wide-radius proximal curve, generally known as a Cobra (Figure 1).
We decided to allow the curve to be modified in only one direction by manipulating the rotating collar on the handle (Figure 1). This means that the number of pull wires that run within the wall of the sheath can be reduced and the wires can have a smaller section, thus reducing the outside diameter of the sheath. Thanks to the LIMA-Cobra pre-shaping, less deflection is required. The catheter returns to the initial shape when the handle control is released, facilitated by passage of a device inside the sheath. During this maneuver, which easily leads to a loss of vessel engagement when non-steerable sheaths are used, the handle can be used to recover the desired curve radius and maintain the position of the sheath in the selectively catheterized artery or vein.
The handle has an entry port protected by a hemostatic valve and a two-way side port for fluid infusion or connection to the endovascular pressure monitor. The Destino Twist TD has an outer diameter of 2.85 mm (8.5 Fr) and the lumen can accommodate catheters or instruments with an outer diameter up to 6 Fr, while a larger version has an inside diameter of 7 Fr. This steerable sheath is placed percutaneously by means of a tapered coaxial dilator over a .038-inch angiographic guide wire. The inner lumen of the sheath effectively allows high quality angiography by simple manual injection, with enough space for injection of flushes, pharmacological solutions, and contrast media, even when the sheath is occupied by a coaxially inserted interventional device or catheter.
In clinical tests carried out to date, the Destino Twist TD has proved easy to use in a number of procedures presenting critical aspects that are difficult to overcome with the equipment currently available on the market. The Destino Twist TD is, to all intents and purposes, a sheath, thus avoiding preliminary insertion of a vascular introducer. The outside diameter of little more that 8 Fr allows percutaneous transfemoral arterial and venous catheterization while maintaining the possibility of arterial hemostasis with the most widely used, dedicated systems (Angio-Seal 8 Fr, St. Jude Medical). The inside diameter coaxially accepts devices from 6 to 7 Fr, depending upon the version. The usable lengths available are 45 cm, 55 cm and 65 cm, and the sheath can be used for crossover procedures for contralateral peripheral endovascular treatment in lower limb pathology. For many applications, the inside diameter is large enough to maintain effective radiological monitoring of progress of the procedure through injection of contrast media. A side port on the handle allows for measurement of endoarterial pressure or alternatively for injection of fluids.
The LIMA-type distal curve is continuously modified by turning the rotating collar on the handle. The Cobra-type proximal curve maintains contact of the sheath with the opposite wall of the abdominal aorta. The radius of both curves is adjusted by turning the rotating collar in the two directions according to the behavior of the various devices that are inserted into the sheath. An important intraprocedural aspect we have observed is the stable engagement achieved through better adaptation of the Destino Twist TD to the actual shape of the vessel.
The usefulness of the new sheath is most evident when an interventional procedure promises to be relatively complex and requires switching between various devices. The steerable sheath carries the required device directly from the vascular access point to the distant point of use.
We initially used the device for endovascular renal sympathetic denervation4 (Figure 2), in which stable engagement of the renal arteries is critical. When using a fixed-shape catheter from a femoral approach, the initial position in the selectively catheterized renal artery is easily lost on passage of the electrode, which has a relatively stiff shaft. The Destino Twist TD allows stable engagement of the artery to be maintained by turning the rotating collar on the handle to adapt the curve of the sheath as the electrode is passed. The renal arteries could also be accessed from a radial approach using a multipurpose catheter, but there are currently no radiofrequency electrodes or ultrasound transducers approved for use in Europe that can be introduced through the radial arteries. Although this situation is likely to change in the near future, in our experience, the femoral approach also tends to be preferred by interventional radiologists, unlike interventional cardiologists, who might prefer the radial approach. The difficulty of the femoral approach for renal sympathetic denervation is not so much in engaging the renal arteries as it is in maintaining the position within the artery when the electrode is passed. This difficulty can be overcome with the new steerable sheath.
The new device is proving valuable in various abdominal interventional procedures, from crossover to treatment of pelvic bleeding and abdominal aneurysms, to transcatheter embolization. In venous applications, the sheath can readily be used in the vena cava for stable catheterization of the suprahepatic veins for venous sampling during provocative tests to detect pancreatic insulinomas. In the renal veins, it can be used for super-selective cannulation of specific branches such as the spermatic and adrenal veins, while allowing the possibility of fluoroscopic control with injection of contrast media (Figure 3).
The Destino Twist TD is aimed predominantly at interventional radiologists, who carry out a variety of abdominal vascular procedures, but it is also used by interventional cardiologists for renal artery stenting and renal sympathetic denervation.
- Trost DW, Kandarpa K. Needles, guidewires, catheters and stents. In: Kandarpa K, Machan L, editors. Handbook of Interventional Radiologic Procedures, 4th ed. Philadephia: Lippincott Williams and Wilkins, 2011.
- Martin LG. Endovascular therapies: renal. In: Geschwind J-FH, Dake MD, editors. Abrams’ Angiography, Interventional Radiology, 3rd ed. Philadelphia: Lippincott Williams & Wilkins, 2014.
- Angle JF. Closure devices. In: Mauro MA et al, eds. Image-Guided Interventions: Expert Radiology Series, Vol. 1, Section 3, Instruments of Intervention. Philadelphia: Saunders Elsevier, 2008.
- Damascelli B, Patelli GL, Tichà V, et al. Catheter-based radiofrequency renal sympathetic denervation for resistant hypertension. J Vasc Interv Radiol. 2013 May; 24(5): 632-639.