Catheter steering in interventional cardiology: Mechanical analysis and novel solution

Abstract

In recent years, steerable catheters have been developed to combat the effects of the dynamic cardiac environment. Mechanically actuated steerable catheters appear the most in the clinical setting; however, they are bound to a number of mechanical limitations. The aim of this research is to gain insight in these limitations and use this information to develop a new prototype of a catheter with increased steerability. The main limitations in mechanically steerable catheters are identified and analysed, after which requirements and solutions are defined to design a multi-steerable catheter. Finally, a prototype is built and a proof-of-concept test is carried out to analyse the steering functions. The mechanical analysis results in the identification of five limitations: (1) low torsion, (2) shaft shortening, (3) high unpredictable friction, (4) coupled tip-shaft movements, and (5) complex cardiac environment. Solutions are found to each of the limitations and result in the design of a novel multi-steerable catheter with four degrees of freedom. A prototype is developed which allows the dual-segmented tip to be steered over multiple planes and in multiple directions, allowing a range of complex motions including S-shaped curves and circular movements. A detailed analysis of limitations underlying mechanically steerable catheters has led to a new design for a multi-steerable catheter for complex cardiac interventions. The four integrated degrees of freedom provide a high variability of tip directions, and repetition of the bending angle is relatively simple and reliable. The ability to steer inside the heart with a variety of complex shaped curves may potentially change conventional approaches in interventional cardiology towards more patient-specific and lower complexity procedures. Future directions are headed towards further design optimizations and the experimental validation of the prototype.

Keywords: Biomedical devices; biomechanical testing/analysis; biomedical instrumentation; cardiovascular implants; cardiovascular system mechanics.

Figure 1.

Mechanical analysis scheme.

Figure 2.

Three steering possibilities of mechanically steerable catheters with (a) 1-DOF steering with one steerable segment, (b) 2-DOF steering with one steerable segment, and (c) 4-DOF steering with two steerable segments.

Figure 3.

The effect of the cardiac environment on catheter movement including tight curves, tortuous vessels, blood flow, beating and breathing motion, weak or calcified structures, and complex three-dimensional shapes. The blood flow and movements in different directions are represented by arrows.

Figure 4.

Segments and parts of the catheter tip, all manufactured from Stainless Steel 316. Segment one consists of steering elements 2–8 and Segment two consists of steering elements 10–16.

Figure 5.

Joystick design: (a) exploded view of joystick components, (b) joystick in assembled configuration, and (c) joystick cross-section including steering cables enclosed by springs. From left to right, Figure a shows: diamond-shaped controller, cylindrical cover, ball joint, first baseplate, compression spring, second baseplate, adjustment bolt.

Figure 6.

Final catheter prototype.