Revisiting heart activation-conduction physiology, part I: atria.

This discussion paper re-examines the conduction-activation of the atria, based on observations, with respect to the complexity of the heart as an organ with a brain, and its evolution from a peristaltic tube. The atria do not require a specialized conduction system because they use the subendocardial layer to produce centripetal transmural activation fronts, regardless of the anatomical and histological organization of the transmural atrial wall. This has been described as "two-layer" physiology which provides robust transmission of activation from the sinus to the AV node via a centripetal transmural activation front.

Revisiting right atrial isolation rationale for atrial fibrillation: functional anatomy of interatrial connections.

Introduction: Direct catheter ablation for atrial fibrillation does not yield reproducible permanent control as for other atrial arrhythmias. Therefore, there is a need for an alternative intervention, i.e.

Surface-Based CT-TEE Registration of the Aortic Root.

Transcatheter aortic valve implantation (TAVI) is a minimally invasive alternative to conventional aortic valve replacement for severe aortic stenosis in high-risk patients in which a stent-based bioprosthetic valve is delivered into the heart via a catheter. TAVI relies largely on single-plane fluoroscopy for intraoperative navigation and guidance, which provides only gross imaging of anatomical structures. Inadequate imaging leading to suboptimal valve positioning contributes to many of the early complications experienced by TAVI patients, including valve embolism, coronary ostia obstruction, paravalvular leak, heart block, and secondary nephrotoxicity from excessive contrast use.

Augmented reality image guidance improves navigation for beating heart mitral valve repair.

Objective: Emerging off-pump beating heart valve repair techniques offer patients less invasive alternatives for mitral valve (MV) repair. However, most of these techniques rely on the limited spatial and temporal resolution of transesophageal echocardiography (TEE) alone, which can make tool visualization and guidance challenging.

Methods: Using a magnetic tracking system and integrated sensors, we created an augmented reality (AR) environment displaying virtual representations of important intracardiac landmarks registered to biplane TEE imaging.

A navigation platform for guidance of beating heart transapical mitral valve repair.

Traditional surgical approaches for repairing diseased mitral valves (MVs) have relied on placing the patient on cardiopulmonary bypass (on pump), stopping the heart and accessing the arrested heart directly. However, because this approach has the potential for adverse neurological, vascular, and immunological sequelae, less invasive beating heart alternatives are desirable. Emerging beating heart techniques have been developed to offer high-risk patients MV repair using ultrasound guidance alone without stopping the heart.

Hybrid access to atria via the Guiraudon Universal Cardiac Introducer for arrhythmia ablation after total cavopulmonary derivation.

We report the first use of a new platform, the Guiraudon Universal Cardiac Introducer (GUCI), in humans for accessing the left atrium for catheter-based ablations in patients with resistant atrial arrhythmias after total cavopulmonary derivation. The GUCI was originally designed for intracardiac access for closed, beating instrumental intracardiac surgery.The patient was a 29-year-old man with problematic atrial arrhythmias resistant to antiarrhythmic drugs because of severe uncontrolled bradycardia and because his pacemaker was explanted for infection.

US-fluoroscopy registration for transcatheter aortic valve implantation.

Transcatheter aortic valve implantation is a minimally invasive alternative to open-heart surgery for aortic stenosis in which a stent-based bioprosthetic valve is delivered into the heart on a catheter. Limited visualization during this procedure can lead to severe complications. Improved visualization can be provided by live registration of transesophageal echo (TEE) and fluoroscopy images intraoperatively.

Augmented reality image guidance during off-pump mitral valve replacement through the guiraudon universal cardiac introducer.

Objective: : We report our experience with ultrasound augmented reality (US-AR) guidance for mitral valve prosthesis (MVP) implantation in the pig using off-pump, closed, beating intracardiac access through the Guiraudon Universal Cardiac Introducer attached to the left atrial appendage.

Methods: : Before testing US-AR guidance, a feasibility pilot study on nine pigs was performed using US alone. US-AR guidance, tested on a heart phantom, was subsequently used in three pigs (∼65 kg) using a tracked transesophageal echocardiography probe, augmented with registration of a 3D computed tomography scan, and virtual representation of the MVP and clip-delivering tool (Clipper); three pigs were used to test feature-based registration.

Spinal cord stimulation causes potentiation of right vagus nerve effects on atrial chronotropic function and repolarization in canines.

Introduction: Experimental evidence suggests that spinal cord stimulation (SCS) can cause augmentation of parasympathetic influences on the heart via enhanced vagus nerve (VgN) activity. Herein, we investigated whether this might lead to enhanced inducibility of vagally mediated atrial tachyarrhythmias (AT) and whether such actions depend on intact autonomic neural connections with central neurons.

Method And Results: Epidural SCS electrodes were implanted at T1-T4 in anesthetized canines.

Virtual and augmented medical imaging environments: enabling technology for minimally invasive cardiac interventional guidance.

Virtual and augmented reality environments have been adopted in medicine as a means to enhance the clinician's view of the anatomy and facilitate the performance of minimally invasive procedures. Their value is truly appreciated during interventions where the surgeon cannot directly visualize the targets to be treated, such as during cardiac procedures performed on the beating heart. These environments must accurately represent the real surgical field and require seamless integration of pre- and intra-operative imaging, surgical tracking, and visualization technology in a common framework centered around the patient.

Inside the beating heart: an in vivo feasibility study on fusing pre- and intra-operative imaging for minimally invasive therapy.

Objective: An interventional system for minimally invasive cardiac surgery was developed for therapy delivery inside the beating heart, in absence of direct vision.

Method: A system was developed to provide a virtual reality (VR) environment that integrates pre-operative imaging, real-time intra-operative guidance using 2D trans-esophageal ultrasound, and models of the surgical tools tracked using a magnetic tracking system. Detailed 3D dynamic cardiac models were synthesized from high-resolution pre-operative MR data and registered within the intra-operative imaging environment.

Off-pump positioning of a conventional aortic valve prosthesis through the left ventricular apex with the universal cardiac introducer under sole ultrasound guidance, in the pig.

Objective: : To test an alternative to catheter and open-heart techniques, by documenting the feasibility of implanting an unmodified mechanical aortic valve (AoV) in the off pump, beating heart using the universal cardiac introducer (UCI) attached to the left ventricular (LV) apex.

Methods: : In six pigs, the LV apex was exposed by a median sternotomy. The UCI was attached to the apex.

Mapping of cardiac electrophysiology onto a dynamic patient-specific heart model.

Electrophysiological cardiac data mapping is an essential tool for the study of cardiac rhythm disorders, such as atrial fibrillation. Over the past decade, various advanced cardiac mapping systems have been developed to create detailed cardiac maps and assist physicians in diagnosis and therapy guidance. While these systems have increased the ability to study and treat cardiac arrhythmias, inherent limitations exist.

Surgeon-controlled visualization techniques for virtual reality-guided cardiac surgery.

Surgeon-to-computer interaction difficulties in using virtual reality (VR)-guided surgical environments arise from disorientation, insufficient depth information, and delegation of view control. This study focuses on optimizing information delivery for VR-guided beating heart surgery. Initial human factors evaluation and participatory design has provided insight for developing an effective surgeon-controlled interface for VR-guided cardiac interventions.

Dynamic 2D ultrasound and 3D CT image registration of the beating heart.

Two-dimensional ultrasound (US) is widely used in minimally invasive cardiac procedures due to its convenience of use and noninvasive nature. However, the low quality of US images often limits their utility as a means for guiding procedures, since it is often difficult to relate the images to their anatomical context. To improve the interpretability of the US images while maintaining US as a flexible anatomical and functional real-time imaging modality, we describe a multimodality image navigation system that integrates 2D US images with their 3D context by registering them to high quality preoperative models based on magnetic resonance imaging (MRI) or computed tomography (CT) images.

Off-pump atrial septal defect closure using the universal cardiac introducer®: creation of models of atrial septal defects in the pig access and surgical technique.

Objective: : Optimal atrial septal defect (ASD) closure should combine off-pump techniques with the effectiveness and versatility of open-heart techniques. We report our experience with off-pump ASD closure using the Universal Cardiac Introducer (UCI) in a porcine model. The goal was to create an ASD over the fossa ovale (FO) and position a patch over the ASD under ultrasound (US) imaging and augmented virtual reality guidance.

Dynamic cardiac mapping on patient-specific cardiac models.

Minimally invasive techniques for electrophysiological cardiac data mapping and catheter ablation therapy have been driven through advancements in computer-aided technologies, including magnetic tracking systems, and virtual and augmented-reality environments. The objective of this work is to extend current cardiac mapping techniques to collect and display data in the temporal domain, while mapping on patient-specific cardiac models. This paper details novel approaches to collecting spatially tracked cardiac electrograms, registering the data with a patient-specific cardiac model, and interpreting the data directly on the model surface, with the goal of giving a more comprehensive cardiac mapping system in comparison to current systems.

Ultrasound image and augmented reality guidance for off-pump, closed, beating, intracardiac surgery.

Our project is the reintroduction of off-pump intracardiac surgery using the Universal Cardiac Introducer (UCI) for safe intracardiac access. The purpose of this study was to evaluate multimodality visualization using three ultrasound modalities and ultrasound augmented with virtual reality. Image guidance was tested on implanting a mitral valve prosthesis via the UCI in 12 pigs.

Dynamic 3-D virtual fixtures for minimally invasive beating heart procedures.

Two-dimensional or 3-D visual guidance is often used for minimally invasive cardiac surgery and diagnosis. This visual guidance suffers from several drawbacks such as limited field of view, loss of signal from time to time, and in some cases, difficulty of interpretation. These limitations become more evident in beating-heart procedures when the surgeon has to perform a surgical procedure in the presence of heart motion.

Anatomical pitfalls during encircling cryoablation of the left atrium for atrial fibrillation therapy in the pig.

We previously published encircling endocardial cryo-isolation of the pulmonary vein (PV) region. This study documented mechanisms of isolation failure using CARTO mapping. Cryo-isolation used a modified Surgifrost introduced via a Universal Cardiac Introducer on the left atrial appendage.

Rapid dynamic image registration of the beating heart for diagnosis and surgical navigation.

Dynamic cardiac magnetic resonance imaging (MR) and computed tomography (CT) provide cardiologists and cardiac surgeons with high-quality 4-D images for diagnosis and therapy, yet the effective use of these high-quality anatomical models remains a challenge. Ultrasound (US) is a flexible imaging tool, but the US images produced are often difficult to interpret unless they are placed within their proper 3-D anatomical context. The ability to correlate real-time 3-D US volumes (RT3D US) with dynamic MR/CT images would offer a significant contribution to improve the quality of cardiac procedures.

Towards subject-specific models of the dynamic heart for image-guided mitral valve surgery.

Surgeons need a robust interventional system capable of providing reliable, real-time information regarding the position and orientation of the surgical targets and tools to compensate for the lack of direct vision and to enhance manipulation of intracardiac targets during minimally-invasive, off-pump cardiac interventions. In this paper, we describe a novel method for creating dynamic, pre-operative, subject-specific cardiac models containing the surgical targets and surrounding anatomy, and how they are used to augment the intra-operative virtual environment for guidance of valvular interventions. The accuracy of these pre-operative models was established by comparing the target registration error between the mitral valve annulus characterized in the pre-operative images and their equivalent structures manually extracted from 3D US data.

On enhancing planning and navigation of beating-heart mitral valve surgery using pre-operative cardiac models.

In an effort to reduce morbidity during minimally-invasive cardiac procedures, we have recently developed an interventional technique targeted towards off-pump cardiac interventions. To compensate for the absence of direct visualization, our system employs a virtual reality environment for image guidance, that integrates pre-operative information with real-time intra-operative imaging and surgical tool tracking. This work focuses on enhancing intracardiac visualization and navigation by overlaying pre-operative cardiac models onto the intra-operative virtual space, to display surgical targets within their specific anatomical context.

Spatial distribution of fibrosis governs fibrillation wave dynamics in the posterior left atrium during heart failure.

Heart failure (HF) commonly results in atrial fibrillation (AF) and fibrosis, but how the distribution of fibrosis impacts AF dynamics has not been studied. HF was induced in sheep by ventricular tachypacing (220 bpm, 6 to 7 weeks). Optical mapping (Di-4-ANEPPS, 300 frames/sec) of the posterior left atrial (PLA) endocardium was performed during sustained AF (burst pacing) in Langendorff-perfused HF (n=7, 4 micromol/L acetylcholine; n=3, no acetylcholine) and control (n=6) hearts.