Kent R. Nilsson

Reduced skeletal muscle oxidative capacity and impaired training adaptations in heart failure

Systolic heart failure (HF) is associated with exercise intolerance that has been attributed, in part, to skeletal muscle dysfunction. The purpose of this study was to compare skeletal muscle oxidative capacity and training‐induced changes in oxidative capacity in participants with and without HF. Participants with HF (n = 16, 65 ± 6.6 years) were compared with control participants without HF (n = 23, 61 ± 5.0 years). A subset of participants (HF: n = 7, controls: n = 5) performed 4 weeks of wrist‐flexor exercise training. Skeletal muscle oxidative capacity was determined from the recovery kinetics of muscle oxygen consumption measured by near‐infrared spectroscopy (NIRS) following a brief bout of wrist‐flexor exercise. Oxidative capacity, prior to exercise training, was significantly lower in the HF participants in both the dominant (1.31 ± 0.30 min−1 vs. 1.59 ± 0.25 min−1, P = 0.002; HF and control groups, respectively) and nondominant arms (1.29 ± 0.24 min−1 vs. 1.46 ± 0.23 min−1, P = 0.04; HF and control groups, respectively). Following 4 weeks of endurance training, there was a significant difference in the training response between HF and controls, as the difference in oxidative training adaptations was 0.69 ± 0.12 min−1 (P < 0.001, 95% CI 0.43, 0.96). The wrist‐flexor training induced a ~50% improvement in oxidative capacity in participants without HF (mean difference from baseline = 0.66 ± 0.09 min−1, P < 0.001, 95% CI 0.33, 0.98), whereas participants with HF showed no improvement in oxidative capacity (mean difference from baseline = −0.04 ± 0.08 min−1, P = 0.66, 95% CI −0.24, 0.31), suggesting impairments in mitochondrial biogenesis. In conclusion, participants with HF had reduced oxidative capacity and impaired oxidative adaptations to endurance exercise compared to controls.

MRI-based visual and haptic catheter feedback: simulating a novel system's contribution to efficient and safe MRI-guided cardiac electrophysiology procedures

Background MRI-guided Electrophysiology (EP) procedures integrate real-time MRI images with catheter position during Radiofrequency Ablation (RFA) of arrhythmias [1]. Using simultaneous MR catheter tracking and imaging [2], this technology can both guide catheter manipulation and provide dynamic assessment of lesion efficacy [3]. Despite advances in MRI-guided EP, maneuvering catheters to the desired location and ensuring appropriate tissue contact is still challenging inside an MRI due to two issues: (1) inconsistent catheter-tissue contact force (CTCF); and (2) visual-motor disorientation arising from differences between manipulation of the catheter’s proximal controlling handle and visualization of the catheter-tissue interface. Both issues can increase the risk of cardiac perforation during catheter manipulation. We hypothesized that a technique based on MR imaging to generate force and vibrotactile alarms, as well as the presentation of a reproducible endoscopic view to the catheter operator, could facilitate precise application of RF energy, thereby increasing efficacy and reducing complications.

MRI-conditional catheter sensor for contact force and temperature monitoring during cardiac electrophysiological procedures

Background MR-guided cardiac electrophysiological (EP) ablations has drawn increasing attention from both the MRI and EP communities, as high-contrast MR images provide images that couple anatomical information with lesion efficacy [1]. Catheter manipulation can be challenging for cardiac electrophysiologists as conventional electroanatomical maps, frequently include false space. Perforation of heart vessels and chambers by catheters is an uncommon, but devastating, complication during EP procedures arising from either excessive force or vaporization of tissue. Ultimately, these complications arise from an inability to adequately determine catheter-tissue Contact Force (CF) at the catheter tip [2]. Accurate catheter temperature control is of importance during EP Radiofrequency Ablation (RFA) for determining lesion efficacy. We hypothesized that a novel optical sensor design, attachable to a conventional ablation catheter, could allow simultaneous CF and temperature monitoring, providing useful information to the EP physician during the procedure. Methods

Temperature-Insensitive Fiber-Optic Contact Force Sensor for Steerable Catheters

A steerable catheter with a compact fiber optic sensor for temperature-insensitive contact force measurement is demonstrated. A fiber Bragg grating (FBG) is used as the sensor, which is very small and can be fixed on the outer arc of a steerable catheter, such that it does not occupy any space inside the catheter. Contact force sensing performance under various curve diameters during steering is studied and the results show high repeatability. Since the curve diameter during steering is predetermined, accurate contact force measurement can be performed through calibrating the measurement with various steered catheter positions. Different from most conventional FBG contact force sensors, this approach does not require the analysis of FBG reflection spectra. Instead, contact force applied on the catheter tip is determined by the direct measurement of total FBG reflection power, enabling real time, low cost, and compact sensing. Furthermore, the proposed catheter is tested under different temperatures, and temperature-insensitive performance is also obtained.

Intracardiac Magnetic Resonance Imaging Catheter With Origami Deployable Mechanisms

Atrial fibrillation (AF) contributes to an estimated 750,000 hospitalizations and 130,000 deaths per year in the US [1]. Radiofrequency Ablation (RFA) therapy is a catheter-based minimally invasive treatment for AF. RFA electrodes embedded in the tip of a catheter are inserted from the femoral artery and maneuvered into the atrium (Fig. 1a & 1b). The abnormal tissue in the pulmonary veins of the atrium is ablated to electrically inactivate the sites causing irregular heart rhythm (Fig. 1c). Multi-parametric Magnetic Resonance Imaging (MRI) (e.g. T2-weighted, delayed contrast enhancement imaging) provides excellent soft tissue contrast and lesion visualization, which could serve as a roadmap for preoperative planning and intraoperative catheter navigation. With the use of an intra-cardiac (IC) MR imaging coil for real time visualization of the operation, electrophysiologists can monitor the ablated lesions, gaining greater control over the outcome of the procedure. In this study, we hypothesize that a specially designed catheter mechanism, which integrates a unique origami deployable mechanism for MR imaging, could enhance the safety and reliability of MRI guided RFA procedures. 2 Methods

Near infrared spectroscopy-guided exercise training for claudication in peripheral arterial disease

Rationale Supervised treadmill exercise for claudication in peripheral arterial disease is effective but poorly tolerated because of ischemic leg pain. Near infrared spectroscopy allows non-invasive detection of muscle ischemia during exercise, allowing for characterization of tissue perfusion and oxygen utilization during training. Objective We evaluated walking time, muscle blood flow, and muscle mitochondrial capacity in patients with peripheral artery disease after a traditional pain-based walking program and after a muscle oxygen-guided walking program. Method and results Patients with peripheral artery disease trained thrice weekly in 40-minute-long sessions for 12 weeks, randomized to oxygen-guided training (n = 8, age 72 ± 9.7 years, 25% female) versus traditional pain-based training (n = 10, age 71.6 ± 8.8 years, 20% female). Oxygen-guided training intensity was determined by maintaining a 15% reduction in skeletal muscle oxygenation by near infrared spectroscopy rather than relying on symptoms of pain to determine exercise effort. Pain free and maximal walking times were measured with a 12-minute Gardner treadmill test. Gastrocnemius mitochondrial capacity and blood flow were measured using near infrared spectroscopy. Baseline pain-free walking time was similar on a Gardner treadmill test (2.5 ± 0.9 vs. 3.6 ± 1.0 min, p = 0.5). After training, oxygen-guided cohorts improved similar to pain-guided cohorts (pain-free walking time 6.7 ± 0.9 vs. 6.9 ± 1.1 min, p < 0.01 for change from baseline and p = 0.97 between cohorts). Mitochondrial capacity improved in both groups but more so in the pain-guided cohort than in the oxygen-guided cohort (38.8 ± 8.3 vs. 14.0 ± 9.3, p = 0.018). Resting muscle blood flow did not improve significantly in either group with training. Conclusions Oxygen-guided exercise training improves claudication comparable to pain-based training regimens. Adaptations in mitochondrial function rather than increases in limb perfusion may account for functional improvement. Increases in mitochondrial oxidative capacity may be proportional to the degree of tissue hypoxia during exercise.

Cardiovascular Catheter With an Expandable Origami Structure

Interventional catheter ablation treatment is a noninvasive approach for normalizing heart rhythm in patients with arrhythmia. Catheter ablation can be assisted with magnetic resonance imaging (MRI) to provide high-contrast images of the heart vasculature for diagnostic and intraprocedural purposes. Typical MRI images are captured using surface imaging coils that are external to the tissue being imaged. The image quality and the scanning time required for producing an image are directly correlated to the distance between the tissue being imaged and the imaging coil. The objective of this work is to minimize the spatial distance between the target tissue and the imaging coil by placing the imaging coil directly inside the heart using an expandable origami catheter structure. In this study, geometrical analysis is utilized to optimize the size and shape of the origami structure and MRI scans are taken to confirm the MRI compatibility of the structure. The origami expandable mechanism could also be applied to other medical device designs that require expandable structures. [DOI: 10.1115/1.4036581]

Temperature-Insensitive Contact Force Sensing in Bi-Directional Catheter Using Fiber Bragg Grating Pair

Bi-directional catheters are commonly used in electrophysiology mapping and ablation procedures. We have designed and demonstrated a temperature-insensitive contact force sensor for bi-directional catheters with variable curve diameter during deflection. The compact force sensor is based on a fiber Bragg grating (FBG) pair, where both FBGs have the same center wavelength and are fixed at two opposite deflection arcs of the bi-directional catheter. When the catheter is deflected or when contact force is applied to the catheter, bifurcation of the FBG pair spectrum is observed. The amount of spectral bifurcation and the applied contact force has a linear relationship. Contact force measurement, therefore, is accomplished by measuring the change in the spectral bifurcation of the FBG pair, i.e., the change in the Bragg wavelength difference between the two FBGs. Since the approach relies solely on the amount of spectral bifurcation of the FBG pair instead of the Bragg wavelength shift of one single FBG, the proposed contact force sensor is temperature insensitive.