Evolutionary design of magnetic soft continuum robots

Worldwide cardiovascular diseases such as stroke and heart disease are the leading cause of mortality. While guidewire/catheter-based minimally invasive surgery is used to treat a variety of cardiovascular disorders, existing passive guidewires and catheters suffer from several limitations such as low steerability and vessel access through complex geometry of vasculatures and imaging-related accumulation of radiation to both patients and operating surgeons. To address these limitations, magnetic soft continuum robots (MSCRs) in the form of magnetic field–controllable elastomeric fibers have recently demonstrated enhanced steerability under remotely applied magnetic fields. While the steerability of an MSCR largely relies on its workspace—the set of attainable points by its end effector—existing MSCRs based on embedding permanent magnets or uniformly dispersing magnetic particles in polymer matrices still cannot give optimal workspaces. The design and optimization of MSCRs have been challenging because of the lack of efficient tools. Here, we report a systematic set of model-based evolutionary design, fabrication, and experimental validation of an MSCR with a counterintuitive nonuniform distribution of magnetic particles to achieve an unprecedented workspace. The proposed MSCR design is enabled by integrating a theoretical model and the genetic algorithm. The current work not only achieves the optimal workspace for MSCRs but also provides a powerful tool for the efficient design and optimization of future magnetic soft robots and actuators.

Cardiovascular diseases such as stroke and heart disease are the leading cause of long-term disability and death worldwide, with an annual cost of over $300 billion in the United States alone (1, 2). Diverse cardiovascular diseases are treated with minimally invasive surgery (Fig. 1A), which is less traumatic and more effective than open surgery (3–6). The conventional minimally invasive treatments of cardiovascular diseases typically employ a passive guidewire and catheter with a preshaped tip that is manually operated under radioscopic imaging. For example, in mechanical thrombectomy, a surgeon usually inserts a guidewire/catheter combination from the patient’s femoral artery over the leg and navigates this combination using fluoroscopic imaging through the aorta into the target occluded artery (usually in the brain or lungs) for mechanical clot removal (7). As another example, in atrial fibrillation ablation, a surgeon usually threads a catheter into the patient’s heart, where the catheter’s tip applies high or low temperature to disrupt heart conduction that generates faulty electrical signals (8). This manual operation of passive guidewires and catheters, however, is often limited by low steerability through complex vasculatures, difficulty in accessing small branches, long operation times, and/or increased accumulated imaging-related radiation to both patients and operating surgeons (9). To overcome these challenges, immense efforts have been committed to exploring robotic-assisted minimally invasive treatments in a remotely operated manner. In particular, because of the untethered and biocompatible nature of magnetic fields, a promising robotic-assisted minimally invasive platform has recently emerged based on magnetic field–controllable elastomeric fibers—magnetic soft continuum robots (MSCRs) (10–13).Open in a separate windowFig. 1.MSCRs for minimally invasive treatments. (A) Cardiovascular diseases in hard-to-reach areas across the human body where MSCRs can find utility. (B) Schematic illustration of the active bending of the MSCR navigating in a complex blood vessel. The workspace is defined as the area of attainable locations by the MSCR’s end effector via tuning the actuation magnetic field. (C) Schematic illustration of operating the MSCR at lesion tissues in atrial fibrillation ablation. (D) Schematic illustration of the distal portion of an MSCR in which hard-magnetic particles (e.g., NdFeB) are dispersed in the polymer matrix (e.g., silicone).An MSCR typically consists of a magneto-active distal portion that can be actively bent by tuning the actuation magnetic field and a nonmagnetized body that can be advanced or retracted by controlling the motor connected to the MSCR’s proximal end. In a typical minimally invasive treatment, a surgeon remotely controls the motor to advance the MSCR up to locations that require active steering, such as in front of branches of blood vessels (Fig. 1B) or lesion tissues (Fig. 1C) (14, 15). At these locations, the surgeon needs to remotely apply a magnetic field to bend the distal portion of the MSCR so that the MSCR’s end effector reaches the desired location. Thereafter, the surgeon further advances or operates the MSCR actively steered by the actuation magnetic field. Evidently, the steerability of an MSCR is largely determined by the set of attainable locations by its end effector via tuning the actuation magnetic field named the workspace of the MSCR (16, 17). A larger workspace gives a higher steerability of the MSCR in minimally invasive treatments.Existing MSCRs are mostly fabricated by embedding one or more permanent magnets in the distal portion of the MSCR (18–25). More recently, a new type of MSCR has been developed by uniformly dispersing hard-magnetic particles in elastomeric fibers (16) (Fig. 1D). However, the workspaces of MSCRs with both embedded magnets and uniformly distributed hard-magnetic particles are still limited, mainly because of the lack of efficient design and optimization tools for MSCRs. Indeed, existing designs of MSCRs heavily rely on experimental trial and error or numerical simulations (26, 27) that are not ideal for design or optimization with a large number of design parameters. Hence, an efficient design strategy capable of maximizing the workspaces of MSCRs remains an important, yet unresolved, challenge in the field.Here, we report an evolutionary design strategy to maximize the workspaces of MSCRs by integrating theoretical modeling (17, 28) and the genetic algorithm (29) to identify the optimal magnetization and rigidity patterns within the MSCRs (Fig. 2A). We first develop a hard-magnetic elastica theory to calculate the deflections of an MSCR with a specific magnetization and rigidity pattern under uniform magnetic fields up to 40 mT applied along various directions in one plane (17) (SI Appendix, Fig. S1). Notably, 40 mT is a typical magnetic-field strength for operating MSCRs (16, 30). We then calculate the area of the workspace for this MSCR and repeat the calculations for MSCRs with various random magnetization and rigidity patterns. Thereafter, we only select the MSCRs with relatively large workspaces, mutate and cross over their magnetization and rigidity patterns to give a new generation of MSCRs, and then calculate the workspaces of the new generation of MSCRs (29). By repeating this evolutionary process over a few generations, we can achieve an optimal design of the MSCR with an unprecedented workspace. We further validate this evolutionary design of the MSCR by both finite element simulations and experiments.Open in a separate windowFig. 2.Designing MSCRs by programming their magnetization and rigidity pattern in the distal portion. (A) Each voxel is encoded with a specific remanent magnetization M by tuning its magnetic particle volume fraction ϕ. The direction of the remanent magnetization of all voxels is along the axial direction pointing to the distal tip. (B) The normalized magnetization strength M(ϕ)/M0 (Left, black) and shear modulus G(ϕ)/G0 (Right, red) of the MSCR as a function of particle volume fraction ϕ.     

Detection of inadvertent catheter movement into a pulmonary vein during radiofrequency catheter ablation by real-time impedance monitoring

Introduction: During radiofrequency ablation to encircle or isolate the pulmonary veins (PVs), applications of radiofrequency energy within a PV may result in stenosis. The aim of this study was to determine whether monitoring of real-time impedance facilitates detection of inadvertent catheter movement into a PV.
Methods and Results: In 30 consecutive patients (mean age 53 ± 11 years) who underwent a left atrial ablation procedure, the three-dimensional geometry of the left atrium, the PVs, and their ostia were reconstructed using an electroanatomic mapping system. The PV ostia were identified based on venography, changes in electrogram morphology, and manual and fluoroscopic feedback as the catheter was withdrawn from the PV into the left atrium. Real-time impedance was measured at the ostium, inside the PV at approximately 1 and 3 cm from the ostium, in the left atrial appendage, and at the posterior left atrial wall. There was an impedance gradient from the distal PV (127 ± 30 Ω) to the proximal PV (108 ± 15 Ω) to the ostium (98 ± 11 Ω) in each PV (P < 0.01). There was no significant impedance difference between the ostial and left atrial sites. During applications of radiofrequency energy, movement of the ablation catheter into a PV was accurately detected in 80% of the cases (20) when there was an abrupt increase of ≥4 Ω in real-time impedance.
Conclusion: There is a significant impedance gradient from the distal PV to the left atrium. Continuous monitoring of the real-time impedance facilitates detection of inadvertent catheter movement into a PV during applications of radiofrequency energy. (J Cardiovasc Electrophysiol, Vol. 15, pp. 1-5, June 2004)     

Adenosine myocardial perfusion single-photon emission computed tomography in women compared with men. Impact of diabetes mellitus on incremental prognostic value and effect on patient management

OBJECTIVES: This study was designed to assess the incremental prognostic value of adenosine stress myocardial perfusion single-photon emission computed tomography (MPS) in women versus men, and to explore the prognostic impact of diabetes mellitus. BACKGROUND: Limited data are available regarding the incremental value of adenosine stress MPS for the prediction of cardiac death in women versus men and the impact of diabetes mellitus on post-adenosine MPS outcomes.Of 6,173 consecutive patients who underwent rest thallium-201/adenosine technetium-99m sestamibi MPS, 254 (4.1%) were lost to follow-up, and 586 with early revascularization < or = 60 days after MPS were censored, leaving 2,656 women and 2,677 men. RESULTS: Women had significantly smaller adenosine stress, rest, and reversible defects than men. During 27.0 +/- 8.8 month follow-up, cardiac death rates were lower in women than men (2.0%/year vs. 2.7%/year, respectively, p < 0.05). Before and after risk adjustment, cardiac death risk increased significantly in both men and women as a function of MPS results. Multivariable models revealed that MPS results provided incremental prognostic value over pre-scan data for the prediction of cardiac death in both genders. Also, while comparative unadjusted rates of early (< or =60 days post-test) coronary angiography (17% vs. 23%) and revascularization (8% vs. 12%) were significantly lower in women (p < 0.05), after adjusting for MPS, these rates were similar in men and women. Importantly, diabetic women had a significantly greater risk of cardiac death compared with other patients. Also, after risk adjustment, patients with insulin-dependent diabetes mellitus (IDDM) had higher risk of cardiac death for any MPS result than patients with non-insulin-dependent diabetes mellitus. CONCLUSION: The findings suggest that adenosine MPS has comparable incremental value for prediction of cardiac death in women and men and that MPS is appropriately influencing subsequent invasive management decisions in both genders. Diabetic women and patients with IDDM appear to have greater risk of cardiac death than other patients for any MPS result.     

Pulmonary vein isolation as an end point for left atrial circumferential ablation of atrial fibrillation.

OBJECTIVES: We sought to determine whether elimination of pulmonary vein (PV) arrhythmogenicity is necessary for the efficacy of left atrial circumferential ablation (LACA) for atrial fibrillation (AF). BACKGROUND: The PVs often provide triggers or drivers of AF. It has been shown that LACA is more effective than PV isolation in eliminating paroxysmal AF. However, it is not clear whether complete PV isolation is necessary for the efficacy of LACA. METHODS: In 60 consecutive patients with paroxysmal (n = 39) or chronic (n = 21) AF (mean age 53 +/- 12 years), LACA to encircle the left- and right-sided PVs, with additional lines in the posterior left atrium and along the mitral isthmus, was performed under the guidance of an electroanatomic navigation system. The PVs were mapped with a decapolar ring catheter before and after LACA. If PV isolation was incomplete, no attempts at complete isolation were made. RESULTS: After LACA, there was incomplete electrical isolation of one or more PVs in 48 (80%) of the 60 patients. The prevalence of PV tachycardias was 82% before and 8% after LACA (p < 0.001). At 11 +/- 1 months of follow-up, 10 (83%) of the 12 patients with complete and 39 (81%) of 48 patients with incomplete PV isolation were free from recurrent AF without antiarrhythmic drug therapy (p = 1.0). A successful outcome was not related to the number of completely isolated PVs per patient (p = 0.6). CONCLUSIONS: Left atrial circumferential ablation modifies the arrhythmogenic substrate within the PVs. Complete electrical isolation of the PVs is not a requirement for a successful outcome after LACA.     

Mechanism of recurrence after radiofrequency catheter ablation of atrial fibrillation guided by complex fractionated atrial electrograms

Background A better understanding of the mechanisms of recurrent atrial fibrillation (AF) after radiofrequency ablation of complex, fractionated atrial electrograms (CFAEs) may be helpful for refining AF ablation strategies. Methods and results Electrogram-guided ablation (EGA) was repeated in 30 consecutive patients (mean age = 59 ± 8 years) for recurrent paroxysmal AF, 10 ± 4 months after the first ablation. During the first procedure, CFAEs were targeted without isolating all pulmonary veins (PVs). During repeat ablation, all PVs and the superior vena cava (SVC) were mapped with a circular catheter and the left atrium was mapped for CFAEs. EGA was performed until AF was rendered noninducible or all identified CFAEs were eliminated. During repeat ablation, ≥1 PV tachycardia was found in 83 PVs in 29 of the 30 patients (97%). Among these 83 PVs, 63 (76%) had not been completely isolated previously. During repeat ablation, drivers originating in a PV or PV antrum were identified only after infusion of isoproterenol (20 μg/min) in 12 patients (40%). At 9 ± 4 months of follow-up after the repeat ablation procedure, 21 of the 30 patients (70%) were free from recurrent AF and flutter without antiarrhythmic drugs. Conclusions Recurrence of AF after EGA is usually due to PV tachycardias. Therefore, it may be preferable to systematically map and isolate all PVs during the first procedure. High-dose isoproterenol may be helpful to identify AF drivers.     

Assessing rheumatologists’ attitudes and utilization of classification criteria for ankylosing spondylitis and axial spondyloarthritis: a global effort

Clinical Rheumatology - This study aims to assess rheumatologists’ perceptions, utilization patterns, and attitudes towards the modified New York (mNY) criteria for ankylosing spondylitis...     

Experience with similar biologic rituximab in 77 patients of granulomatosis with polyangiitis—a real-life experience

Clinical Rheumatology - To present single centre experience on the efficacy and safety of similar biologic of rituximab in patients with granulomatosis with polyangiitis (GPA). This was a...     

Incidence and predictors of de novo late-onset persistent atrial fibrillation in postoperative rheumatic heart disease patients (LOAF-RHD study)

Journal of Interventional Cardiac Electrophysiology - Late-onset atrial fibrillation (LOAF) after valve surgery for degenerative mitral valve disease often with underlying mitral valve prolapse is...