Peripheral Interventions Radiation Exposure Reduction Using a Sensor-Based Navigation System: A Proof-of-Concept Study.

BACKGROUND: Intravascular catheter positioning is done with radiography imaging. Increasing evidence indicates excessive ionizing radiation exposure for patients and physicians during catheterization procedures, making solutions to reduce radiation exposure a priority. This study evaluated the feasibility and impact of using sensor-based magnetic navigation on (i) fluoroscopy time and (ii) positioning accuracy and safety of a peripheral angioplasty balloon catheter. METHODS: All patients (n = 10) underwent a balloon-positioning protocol using 2 navigation methods sequentially: (i) magnetic navigation with minimal fluoroscopy; (ii) fluoroscopic navigation. The navigation method order was randomized, and 4 consecutive placements per method were performed. A target vascular bifurcation was used as a fiduciary landmark for both methods to determine accuracy. RESULTS: Balloon placements were successful with both navigation methods in all subjects, and no adverse events occurred. Magnetic guidance led to significant reductions in fluoroscopy time (0.37 ± 1.5 vs 15.0 ± 8.1 seconds, P < 0.001) and dose (0.3 ± 1.2 vs 24.1 ± 23.8 µGy.m2, P < 0.01). The time duration for balloon alignment was similar for the 2 navigation methods (4.8 ± 1.4 vs 4.8 ± 2.3 seconds, P = 0.89), and the accuracy was almost identical (0.51 ± 0.41 vs 0.51 ± 0.32 mm, P = 0.97). CONCLUSIONS: These results demonstrate the feasibility of using sensor-based magnetic guidance during simple peripheral interventional procedures; a significant reduction in ionizing radiation was achieved, with excellent positioning accuracy and safety. The clinical applications of magnetic guidance for device navigation during more complex percutaneous procedures should be evaluated.

CONTEXTE: Le positionnement d'un cathéter intravasculaire fait appel à l'imagerie radiographique. De plus en plus de données probantes indiquent que les patients et les médecins subissent une surexposition aux rayonnements ionisants pendant le cathétérisme, ce qui fait des solutions de réduction de l'irradiation une priorité. Cette étude a permis d'évaluer la faisabilité du guidage magnétique par capteur et son effet sur (i) la durée de la fluoroscopie et (ii) la précision et la sécurité du positionnement d'un cathéter d'angioplastie périphérique à ballonnet. MÉTHODOLOGIE: Chez tous les patients (n = 10), le positionnement du ballonnet a été effectué en fonction d'un protocole fondé sur deux méthodes de guidage mises en œuvre séquentiellement : (i) guidage magnétique avec fluoroscopie minimale; (ii) guidage fluoroscopique. L'ordre dans lequel les méthodes de guidage ont été mises en œuvre a été randomisé, et quatre positionnements consécutifs par méthode ont été effectués. Une bifurcation vasculaire cible a servi de repère de fond de chambre afin de déterminer la précision des deux méthodes. RÉSULTATS: Les deux méthodes de guidage ont permis un positionnement adéquat du ballonnet chez tous les patients, et aucun événement indésirable n'est survenu. Le guidage magnétique a entraîné des réductions significatives de la durée de la fluoroscopie (0,37 ± 1,5 vs 15,0 ± 8,1 secondes, p < 0,001) et de la dose de rayonnement (0,3 ± 1,2 vs 24,1 ± 23,8 µGy.m2, p < 0,01). La durée de l'alignement du ballonnet était similaire lors de la mise en œuvre des deux méthodes de guidage (4,8 ± 1,4 vs 4,8 ± 2,3 secondes, p = 0,89), et la précision était presque identique (0,51 ± 0,41 vs 0,51 ± 0,32 mm, p = 0,97). CONCLUSIONS: Ces résultats démontrent la faisabilité du guidage magnétique par capteur dans le cadre d'angioplasties périphériques simples. L'exposition aux rayonnements ionisants a été réduite de façon significative, et la précision ainsi que la sécurité du positionnement se sont avérées excellentes. Les applications cliniques du guidage magnétique dans le contexte d'interventions percutanées plus complexes représentent une avenue de recherche à explorer.

Electroanatomical Navigation to Minimize Contrast Medium or X-Rays During Stenting: Insights From an Experimental Model.

Stents can be effectively implemented with no x-rays or contrast medium. Modified stents were successfully implanted in 9 of 11 attempted targets (82%) (7 carotid and 4 coronary arteries) using an impedance-sensitive navigation system and optical coherence tomography. Electroanatomical navigation systems can be used to assist interventionalists in performing arterial stenting while minimizing x-ray and contrast use, thereby potentially enhancing safety for both patients and catheterization laboratory staff members.

Integration of 3D nuclear imaging in 3D mapping system for ventricular tachycardia ablation in patients with implanted devices: Perfusion/voltage retrospective assessment of scar location.

Background: The identification of low-voltage proarrhythmic areas for catheter ablation of scar-mediated ventricular tachycardia (VT) remains challenging. Integration of myocardial perfusion imaging (single-photon emission computed tomography/computed tomography; SPECT/CT) and electroanatomical mapping (EAM) may improve delineation of the arrhythmogenic substrate. Objective: To assess the feasibility of SPECT/CT image integration with voltage maps using the EnSite Precision system (Abbott) in patients undergoing scar-mediated VT ablation. Methods: Patients underwent SPECT/CT imaging prior to left ventricular (LV) EAM with the EnSite Precision mapping system. The SPECT/CT, EAM data, and ablation lesions were retrospectively co-registered in the EnSite Precision system and exported for analysis. Segmental tissue viability scores were calculated based on SPECT/CT perfusion and electrogram bipolar voltage amplitude. Concordance, specificity, and sensitivity between the 2 modalities as well as the impact of SPECT/CT spatial resolution were evaluated. Results: Twenty subjects (95% male, 67 ± 7 years old, left ventricular ejection fraction 36% ± 11%) underwent EAM and SPECT/CT integration. A concordance of 70% was found between EAM and SPECT/CT for identification of cardiac segments as scar vs viable, with EAM showing a 68.5% sensitivity and 76.4% specificity when using SPECT/CT as a gold standard. Projection on low-resolution 3D geometries led to an average decrease of 38% ± 22% of the voltage points used. Conclusion: The study demonstrated the feasibility of integrating SPECT/CT with EAM performed retrospectively for characterization of anatomical substrates during VT ablation procedures.

Cervical vagosympathetic and mediastinal nerves activation effects on atrial arrhythmia formation.

In anesthetized dogs both epi-and endocardial atrial activation maps and corresponding isointegral repolarization maps were created before and during right or left mediastinal nerve (RMN and LMN) and cervical vagus nerve (CVN) stimulation. Right mediastinal nerve stimulation typically caused sinus slowing, atrial tachycardia (AT), followed by atrial fibrillation (AF). Activation maps during AT showed epicardial breakthroughs from the right atrial free wall or Bachmann's bundle. Left mediastinal nerve stimulation (LMN) rarely caused sinus slowing and ATs originated mostly from Bachmann's bundle or from the pulmonary vein ostial region. Atrial repolarization changes induced by neural stimulation were measured by integrating the area subtended by 161 epicardial unipolar electrograms. Atrial tachycardia epicardial breakthrough sites were closely associated with the border zone where repolarization changes occurred. Both AT and AF were abolished by I.V. atropine, as were sinus bradycardia and atrial repolarization effects of nerve stimulation. Shortening of latency of onset and duration of AT by I.V. timolol suggest concurrent activation of adrenergic efferent neurons. In conclusion, juxta-cardiac mediastinal nerve stimulation can induce atrial fibrillation from multiple, discrete right and left atrial sites, which correspond to localized repolarization changes. Secondly, sinus bradycardia is not a necessary index of parasympathetic neurally induced atrial fibrillation.

Origin and pharmacological response of atrial tachyarrhythmias induced by activation of mediastinal nerves in canines.

We sought to determine the sites of origin of atrial tachyarrhythmias induced by activating mediastinal nerves, as well as the response of such arrhythmias to autonomic modulation. Under general anaesthesia, atrioventricular block was induced after thoracotomy in 19 canines. Brief trains of 5 electrical stimuli were delivered to right-sided mediastinal nerves during the atrial refractory period. Unipolar electrograms were recorded from 191 right and left atrial epicardial sites under several conditions, i.e. (i) with intact nervous systems and following (ii) acute decentralization of the intrathoracic nervous system or administration of (iii) atropine, (iv) timolol, (v) hexamethonium. Concomitant right atrial endocardial mapping was performed in 7 of these dogs. Mediastinal nerve stimulation consistently initiated bradycardia followed by atrial tachyarrhythmias. In the initial tachyarrhythmia beats, early epicardial breakthroughs were identified in the right atrial free wall (28/50 episodes) or Bachmann bundle region (22/50), which corresponded to endocardial sites of origin associated with the right atrial subsidiary pacemaker complex, i.e. the crista terminalis and dorsal locations including the right atrial aspect of the interatrial septum. Neuronally induced responses were eliminated by atropine, modified by timolol and unaffected by acute neuronal decentralization. After hexamethonium, responses to extra-pericardial but not intra-pericardial nerve stimulation were eliminated. It is concluded that concomitant activation of cholinergic and adrenergic efferent intrinsic cardiac neurons induced by right-sided efferent neuronal stimulation initiates atrial tachyarrhythmias that originate from foci anatomically related to the right atrial pacemaker complex and tissues underlying major atrial ganglionated plexuses.

Simultaneous epicardial and noncontact endocardial mapping of the canine right atrium: simulation and experiment.

Epicardial high-density electrical mapping is a well-established experimental instrument to monitor in vivo the activity of the atria in response to modulations of the autonomic nervous system in sinus rhythm. In regions that are not accessible by epicardial mapping, noncontact endocardial mapping performed through a balloon catheter may provide a more comprehensive description of atrial activity. We developed a computer model of the canine right atrium to compare epicardial and noncontact endocardial mapping. The model was derived from an experiment in which electroanatomical reconstruction, epicardial mapping (103 electrodes), noncontact endocardial mapping (2048 virtual electrodes computed from a 64-channel balloon catheter), and direct-contact endocardial catheter recordings were simultaneously performed in a dog. The recording system was simulated in the computer model. For simulations and experiments (after atrio-ventricular node suppression), activation maps were computed during sinus rhythm. Repolarization was assessed by measuring the area under the atrial T wave (ATa), a marker of repolarization gradients. Results showed an epicardial-endocardial correlation coefficients of 0.80 and 0.63 (two dog experiments) and 0.96 (simulation) between activation times, and a correlation coefficients of 0.57 and 0.46 (two dog experiments) and 0.92 (simulation) between ATa values. Despite distance (balloon-atrial wall) and dimension reduction (64 electrodes), some information about atrial repolarization remained present in noncontact signals.

Engineering and therapeutic application of single-chain bivalent TGF-ß family traps.

Deregulation of TGF-ß superfamily signaling is a causative factor in many diseases. Here we describe a protein engineering strategy for the generation of single-chain bivalent receptor traps for TGF-ß superfamily ligands. Traps were assembled using the intrinsically disordered regions flanking the structured binding domain of each receptor as "native linkers" between two binding domains. This yields traps that are approximately threefold smaller than antibodies and consists entirely of native receptor sequences. Two TGF-ß type II receptor-based, single-chain traps were designed, termed (TßRII)2 and (TßRIIb)2, that have native linker lengths of 35 and 60 amino acids, respectively. Both single-chain traps exhibit a 100 to 1,000 fold higher in vitro ligand binding and neutralization activity compared with the monovalent ectodomain (TßRII-ED), and a similar or slightly better potency than pan-TGF-ß-neutralizing antibody 1D11 or an Fc-fused receptor trap (TßRII-Fc). Despite its short in vivo half-life (<1 hour), which is primarily due to kidney clearance, daily injections of the (TßRII)2 trap reduced the growth of 4T1 tumors in BALB/c mice by 50%, an efficacy that is comparable with 1D11 (dosed thrice weekly). In addition, (TßRII)2 treatment of mice with established 4T1 tumors (100 mm(3)) significantly inhibited further tumor growth, whereas the 1D11 antibody did not. Overall, our results indicate that our rationally designed bivalent, single-chain traps have promising therapeutic potential.

Alpha-adrenoceptor blockade modifies neurally induced atrial arrhythmias.

Our objective was to determine whether neuronally induced atrial arrhythmias can be modified by alpha-adrenergic receptor blockade. In 30 anesthetized dogs, trains of five electrical stimuli (1 mA; 1 ms) were delivered immediately after the P wave of the ECG to mediastinal nerves associated with the superior vena cava. Regional atrial electrical events were monitored with 191 atrial unipolar electrodes. Mediastinal nerve sites were identified that reproducibly initiated atrial arrhythmias. These sites were then restimulated following 1 h (time control, n = 6), or the intravenous administration of naftopidil (alpha(1)-adrenergic blocker: 0.2 mg/kg, n = 6), yohimbine (alpha(2)-adrenergic blocker: 1 mg/kg, n = 6) or both (n = 8). A ganglionic blocker (hexamethonium: 1 mg/kg) was tested in four dogs. Stimulation of mediastinal nerves sites consistently elicited atrial tachyarrhythmias. Repeat stimulation after 1 h in the time-control group exerted a 19% decrease of the sites still able to induce atrial tachyarrhythmias. Hexamethonium inactivated 78% of the previously active sites. Combined alpha-adrenoceptor blockade inactivated 72% of the previously active sites. Bradycardia responses induced by mediastinal nerve stimulation were blunted by hexamethonium, but not by alpha(1,2)-adrenergic blockade. Naftopidil or yohimbine alone eliminated atrial arrhythmia induction from 31% and 34% of the sites (similar to time control). We conclude that heterogeneous activation of the intrinsic cardiac nervous system results in atrial arrhythmias that involve intrinsic cardiac neuronal alpha-adrenoceptors. In contrast to the global suppression exerted by hexamethonium, we conclude that alpha-adrenoceptor blockade targets intrinsic cardiac local circuit neurons involved in arrhythmia formation and not the flow-through efferent projections of the cardiac nervous system.