Intracardiac Echocardiography for Percutaneous Mitral Valve Repair in a Swine Model

Dos and don'ts in large animal models of aortic insufficiency

Aortic insufficiency caused by paravalvular leakage (PVL) is one of the most feared complications following transcatheter aortic valve replacement (TAVI) in patients. Domestic pigs (Sus scrofa domestica) are a popular large animal model to study such conditions and develop novel diagnostic and therapeutic techniques. However, the models based on prosthetic valve implantation are time intensive, costly, and often hamper further hemodynamic measurements such as PV loop and 4D MRI flow by causing implantation-related wall motion abnormalities and degradation of MR image quality. This study describes in detail, the establishment of a minimally invasive porcine model suitable to study the effects of mild-to-moderate “paravalvular“ aortic regurgitation on left ventricular (LV) performance and blood flow patterns, particularly under the influence of altered afterload, preload, inotropic state, and heart rate. Six domestic pigs (Swiss large white, female, 60–70 kg of body weight) were used to establish this model. The defects on the hinge point of aortic leaflets and annulus were created percutaneously by the pierce-and-dilate technique either in the right coronary cusp (RCC) or in the non-coronary cusp (NCC). The hemodynamic changes as well as LV performance were recorded by PV loop measurements, while blood flow patterns were assessed by 4D MRI. LV performance was additionally challenged by pharmaceutically altering cardiac inotropy, chronotropy, and afterload. The presented work aims to elaborate the dos and don'ts in porcine models of aortic insufficiency and intends to steepen the learning curve for researchers planning to use this or similar models by giving valuable insights ranging from animal selection to vascular access choices, placement of PV Loop catheter, improvement of PV loop data acquisition and post-processing and finally the induction of paravalvular regurgitation of the aortic valve by a standardized and reproducible balloon induced defect in a precisely targeted region of the aortic valve.

Baseline intracardiac echocardiography predicts haemodynamic changes and Doppler velocity patterns during follow-up after percutaneous pulmonary valve implantation

BACKGROUND

Intracardiac echocardiography Doppler-derived gradients have previously been shown to correlate with post-procedure echocardiographic evaluations when compared with invasive gradients measured during percutaneous pulmonary valve implantation, suggesting that intracardiac echocardiography could offer an accurate and predictable starting point to estimate valve function after percutaneous pulmonary valve implantation.

METHODS

We performed a retrospective chart review of 51 patients who underwent percutaneous pulmonary valve implantation between September 2018 and December 2019 in whom intracardiac echocardiography was performed immediately after valve implantation. We evaluated the correlation between intracardiac echocardiography gradients and post-procedural Doppler-derived gradients. Among the parameters assessed, those which demonstrated the strongest correlation were used to create a predictive model of expected echo-derived gradients after percutaneous pulmonary valve implantation. The equation was validated on the same sample data along with a subsequent cohort of 25 consecutive patients collected between January 2020 and July 2020.

RESULTS

All the assessed correlation models between intracardiac echocardiography evaluation and post-procedure transthoracic echocardiographic assessments were statistically significant, presenting moderate to strong correlations. The strongest relationship was found between intracardiac echocardiography mean gradients and post-procedural transthoracic echocardiographic mean gradients. Therefore, an equation was created based on the intracardiac echocardiography-derived mean gradient, to allow prediction of the post-procedural and follow-up transthoracic echocardiographic-derived mean gradients within a range of ±5 mmHg from the observed value in more than 80% of cases.

CONCLUSIONS

There is a strong correlation between intracardiac echocardiography and post-procedure transthoracic echocardiographic. This allowed us to derive a predictive equation that defines the expected transthoracic echocardiographic Doppler-derived gradient following the procedure and at out-patient follow-up after percutaneous pulmonary valve implantation.

Transesophageal Echocardiography in Swine: Establishment of a Baseline

The porcine model is a commonly used animal model in cardiovascular research. Along with new innovative operative techniques, choice of the optimal imaging technique is crucial. Transesophageal echocardiography (TEE) is a reliable imaging tool is highly important in a large number of experimental evaluations. But so far, TEE data for swine are limited, and few standard values have been established for the porcine model. The experience and baseline results for TEE in 45 swine are presented in this study. A full TEE examination was conducted in 45 German landrace or German large white swine, with an average body weight of 49 ± 3 kg, before experimental off-pump mitral valved stent implantation. Additionally hemodynamic measurements were evaluated. The valve implantation procedure was guided solely by real-time 3-D TEE. Baseline values of standard echocardiographic parameters are provided and, where appropriate, compared with human reference values. TEE proved to be an adequate imaging technique in this experimental porcine animal model. The baseline TEE and hemodynamic parameters established for the widely used porcine model can serve as a reference in future studies.

Usefulness of intracardiac echocardiography with a mechanical probe for catheter-based interventions: a 10-year prospective registry

BACKGROUND

The clinical outcome benefit of intracardiac echocardiography (ICE) with a mechanical probe during congenital heart disease interventions has not been fully investigated. We reported the long-term results of a prospective registry of interatrial shunt closure guided by mechanical ICE.

METHODS

We enrolled 537 patients (mean age 48 ± 19.0 years, 378 females) submitted to ICE-aided procedures in a prospective registry over a 10-year period (September 2003-September 2013). All patients underwent transesophageal echocardiography (TEE) before the planned procedure. We evaluated (1) structure identification capability, (2) fossa ovale and interatrial septum component measurement, (3) procedure monitoring capability, (4) procedural and fluoroscopy times, and radiograph dose, (5) probe-related complications.

RESULTS

ICE was successfully performed and was able to correctly identify the structures previously assessed by TEE in all patients. In 24 patients (4.5%), ICE allowed better anatomy definition than TEE. In 35 other patients (6.5%), ICE identified structures not observed by TEE, which led to change indications to interventions or the operative technique to be used. In 131 patients (24.4%), ICE evaluation led to change the planned device to be implanted. There was only one probe-related complication (0.2%).

CONCLUSIONS

Mechanical ICE may offer a valid alternative to conventional TEE in guiding congenital heart disease interventional procedures.

Intracardiac echocardiography: evolving use in interventional cardiology

Intracardiac echocardiography (ICE) uses a catheter-based steerable ultrasound probe that is passed into the right heart chambers to image intracardiac structures. The transducer can be variably positioned for optimal imaging: in the inferior vena cava to visualize the abdominal aorta; in the right atrium for the interatrial septum, aortic, mitral, and tricuspid valves, and pulmonary veins; or in the right ventricle for the left ventricular function, outflow tract, or pulmonary artery. Intracardiac echocardiography is primarily used for imaging during an invasive cardiac procedure using conscious sedation, when transthoracic image quality would likely be inadequate, and transesophageal imaging would require general anesthesia. Intracardiac echocardiography is generally well tolerated and provides adequate images and sufficient information for the procedure performed. In the cardiac catheterization laboratory, ICE is routinely used for patent foramen ovale, atrial septal defect, and ventricular septal defect closures, allowing adequate percutaneous placement of septal occluders. It is now being considered in the current era of transcatheter aortic valve implantation necessitating improved imaging approaches for accurate placement. It is also routinely used for trans-septal punctures during mitral valvuloplasty and, more recently, with the advent of left atrial appendage closure devices. This article provides a comprehensive review of the current technology for ICE and its growing applications in the realm of interventional cardiology.

New coaxial transseptal needle for creation of atrial septal defects in adult sheep

OBJECTIVES

To introduce a new transseptal (TS) needle assembled in our laboratory--the coaxial TS (CTS) needle--and describe our experience with it in creating experimental atrial septal defects (ASD) in adult sheep.

BACKGROUND

With commercially available TS needles, we were not able to consistently perform TS puncture at the fossa ovalis in adult sheep.

MATERIAL AND METHODS

Ten adult sheep with a mean weight of 63.5 kg were used. The CTS needle consists of four components: a 9F Teflon catheter, a 14-gauge blunt curved-tip metal cannula, a 4F tapered catheter, and a 20-gauge open needle. A transjugular 5F pigtail catheter was used to display the septal anatomy by angiocardiography and was left in place to mark the level of the fossa ovalis. The septum was then probed by a transfemoral 5F curved-tip end-hole catheter. The CTS needle was aligned with the tip of the transjugular catheter, and the TS puncture was performed under fluoroscopic guidance. After documenting a left atrial position, a balloon angioplasty catheter was used for creation of the ASD.

RESULTS

A small patent foramen ovale was discovered by septal probing in one sheep. All sheep underwent successful TS punctures without complications. The ASD size ranged from 13 to 15 mm. In eight sheep, the ASD was in fossa ovalis. In the first two sheep where the needle was not well aligned with the marking catheter, the ASD was in the septum secundum. No damage to the atrial or other heart structures was found at necropsy.

CONCLUSION

The CTS needle is a suitable needle for TS puncture and ASD creation in adult sheep. Proper alignment of the CTS needle with a catheter marking the fossa ovalis is essential for successful puncture.

Evaluation of model-enhanced ultrasound-assisted interventional guidance in a cardiac phantom

Minimizing invasiveness associated with cardiac procedures has led to limited visual access to the target tissues. To address these limitations, we have developed a visualization environment that integrates interventional ultrasound (US) imaging with preoperative anatomical models and virtual representations of the surgical instruments tracked in real time. In this paper, we present a comprehensive evaluation of our model-enhanced US-guidance environment by simulating clinically relevant interventions in vitro . We have demonstrated that model-enhanced US guidance provides a clinically desired targeting accuracy better than 3-mm rms and maintains this level of accuracy even in the case of image-to-patient misalignments that are often encountered in the clinic. These studies emphasize the benefits of integrating real-time imaging with preoperative data to enhance surgical navigation in the absence of direct vision during minimally invasive cardiac interventions.

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. The feature-based registration technique was employed to fuse pre- and intra-operative data during in vivo intracardiac procedures on porcine subjects.

RESULTS

This method was found to be suitable for in vivo applications as it relies on easily identifiable landmarks, and hence, it ensures satisfactory alignment of pre- and intra-operative anatomy in the region of interest (4.8 mm RMS alignment accuracy) within the VR environment. Our initial experience in translating this work to guide intracardiac interventions, such as mitral valve implantation and atrial septal defect repair demonstrated feasibility of the methods.

CONCLUSION

Surgical guidance in the absence of direct vision and with no exposure to ionizing radiation was achieved, so our virtual environment constitutes a feasible candidate for performing various off-pump intracardiac interventions.

Beating-heart percutaneous mitral valve repair using a transcatheter endovascular suturing device in an animal model

BACKGROUND

The edge-to-edge (Alfieri) technique for mitral valve repair is a versatile method of treating mitral insufficiency. Because of its simplicity, it has been applied in minimally invasive surgery, and recently, in the design of endovascular closed-heart devices.

AIM

The purpose of this study was to evaluate the acute in-vivo safety and feasibility of a novel percutaneous mitral valve repair system based on Alfieri technique in an animal model.

METHODS

Under general anesthesia, 11 pigs (90-100 kgs), underwent percutaneous Alfeiri procedure. The right femoral vein was punctured and the mitral valve was approached via a standard transeptal puncture. Combined intracardiac echo and fluoroscopic guidance was used. The procedure included: the positioning of a guide catheter for multiple access to the left atrium and for directing devices; the use of a therapy device to capture the free edge of the mitral valve leaflets using vacuum, and to deliver the suture to the valve and finally the fixation with a Nitinol suture clip, and trimming of the suture with a fastener catheter.

RESULTS

Leaflet capture, suture placement, and suture-clip deployment was successful in all 11 animals. There were no acute cardiac or access site complications. Procedural time (from wire in left atrium to completion of the procedure was 18 +/- 9 min (range 9-30 min). Blood loss was 67 +/- 44 ml (range 0-125 ml). A double orifice configuration was visible by echocardiography at the end of the procedure in all animals.

CONCLUSION

This acute animal study demonstrated the feasibility of a beating heart percutaneous Alfieri procedure in a non-diseased porcine valve using an endovascular suturing device to safely access the mitral valve, place a stitch through the mitral valve leaflets, and deploy a suture-clip that reproduces the surgical technique. Clinical application of this device in humans needs to be evaluated.