Current Uses of 3D Printed Cardiac Models in Electrophysiology

In this episode of The EP Edit podcast, we’re talking with Alejandro Jimenez Restrepo, MD about his work utilizing three-dimensional (3D) printing in cardiac electrophysiology at the University of Maryland School of Medicine in Baltimore.

Dr. Restrepo is a cardiac electrophysiologist at the University of Maryland Medical Center and an Assistant Professor of Medicine at the University of Maryland School of Medicine.

For more information on this topic, see Dr. Restrepo's original work in EP Lab Digest's January 2020 issue. 

You can now listen to this episode on Spotify and Apple Podcasts.

Transcripts:

Tell us about the concept of 3D printing of cardiac models. 

Medical 3D printing is the process of taking diagnostic images such as CTs and MRIs, and creating a model using a 3D printer. The process involves several steps. The first step is what we call segmentation. Basically, you take an imaging file, which is usually in a DICOM format (a universal format for medical imaging), and then using an image processing software you choose the region of interest you want to display. For example, if you’re doing a model to guide a left atrial appendage closure procedure, you’re going to want to segment the left atrium, the pulmonary veins, and the left atrial appendage. If, in addition to that, you want to evaluate the interatrial septal anatomy to guide the transseptal access, then you would also add information from the right atrium and the IVC. The way you choose your region of interest is going through the 2D slices of the study and then selecting those images where the contrast delineates the endocardium — in this case, that would be the left atrium and the left atrial appendage. So essentially, using the software, you outline the anatomical areas of interest and assign them individual names — hence, the segmentation. One segment is the left atrium, another one is the pulmonary veins, and another one is the left atrial appendage. This process is facilitated with software algorithms that can automatically identify the endocardial contours, but you can also adjust it manually if there are any obvious discrepancies in the process. 

Once you have the file segmented into the regions of interest, the next step is called a file conversion. What this does is it essentially takes that segmented file that is still in a DICOM format and converts or saves it into a format that is readable by a 3D printer. The most common format worldwide is STL format, but there are other formats such as VRML and AMF that allow for your medical images to be printed.

Once you have converted the file into an STL file, the next steps are called fixing and design. Fixing is basically correcting small imperfections in the converted 3D file. The most common error is surface overlap, and this usually happens due to artifacts that occurred during the original scan. So as a rule, the better the scan quality — that is, the source quality of the image — the less fixing that will be required.

As for the design part, it’s basically selecting how you want to present the 3D printed file and how you want your model to be seen. Do you want a specific cutting plane to better show an intracardiac structure? Or, do you want to print certain regions in specific colors or have materials highlighted on your model? Once the fixing and design are completed, then you essentially have a virtual 3D model, which you can visualize on a computer and use for quality control. Before you print the model, you want to make sure that it’s accurate and without imperfections. It’s also useful at this point for the virtual 3D model to be used for preoperative planning. You can navigate the model and use virtual reality and other features to visualize the anatomy before you’ve even printed the model. 

Once you have the virtual file ready to go, then the next step is to print the file. You will choose the type of printer depending on what model and what printing material you want; the size and the complexity of the model will determine how long it takes for the printing process to occur. It could be anywhere from a couple of hours to 10-12 hours, again depending on all these variables.

Once the model is printed, then the last part of the process is curating the model. You must clean the model, remove any resin residue, add binders to detachable parts, and so on. You then have a workable model that you can use in clinical practice or for research or teaching purposes. 

What interested you about 3D printing, and why did you begin using this approach at the University of Maryland?

I have a special interest in cardiac anatomy, which I’ve found to be very useful in my practice, especially given the complexity of some of the procedures that we do. To give you an example, for congenital patients with arrhythmias and procedures that require detailed understanding of the cardiac anatomy — in particular, left atrial appendage occlusion and cardiac resynchronization therapy, as there are significant anatomical variability in some of these cases — knowing the anatomy beforehand is quite useful.

A number of years ago, a colleague and I started a 3D printing project in my previous job. It was basically a collaboration between the radiology and cardiology departments. We saw an unmet need to better understand patients’ individual anatomy before doing some of these complex cardiac interventions. Our first work was with preoperative transcatheter aortic valve replacements (TAVRs), atrial septal defect (ASD) and patent foramen ovale (PFO) closures, and complex transseptal access for left-sided ablations in congenital patients. 

At the University of Maryland, our 3D printing lab also started as a collaboration between radiology, interventional, pediatric, adult congenital cardiology, and EP. Our main goal is to provide both cardiologists and surgeons who perform complex procedures with the ability to evaluate a patient’s complex anatomy for optimal preoperative planning to help with the access planning and equipment selection, and identify potential barriers to achieving a successful procedure.

What are the current uses for 3D printing in your lab?

We use 3D printing for preprocedural planning, procedural simulation for fellow training, and didactic anatomy teaching. The preprocedural models are being used primarily for left-sided interventions, mainly left atrial appendage occlusions and in patients with unusual anatomical variance or with difficult anatomy undergoing either device implants or ablation procedures. For those particular models, we use an STL desktop printer. It’s a low-cost printer, and we print models in a single color and in one or two materials depending on the need.

We can simulate all the aspects of the procedure including the transseptal access, catheter manipulation, and device delivery. The model is very helpful for the rehearsal of all the preprocedural steps and in selecting the optimal equipment for each case. In addition to the actual hands-on simulation, we use the 3D virtual model to better understand the anatomy.

For fellow training, we have two areas that we focus on. One is the use of the printed models of both normal and abnormal anatomy to teach translational anatomy, which is basically integrating the information from cardiac anatomy that is relevant for electrophysiologists. We use didactic and interactive lectures that are currently part of our fellows curriculum, and this includes a combination of virtual models, printed models, correlation with histology, and anatomy slides. For the didactic area, we need more detailed anatomy on the models, so we use more expensive models and multicolor models printed on more sophisticated 3D printers. Usually, we use PolyJet and binder jetting printers that allow us to depict the anatomy in greater detail and to print different anatomical areas in different colors. The other part of the fellow training component for us is the fluoroscopy-guided simulations using the 3D printed models. The purpose of this is to familiarize the fellows with intracardiac catheter navigation, and it helps them develop muscle memory and hand-eye coordination, especially during the first year of their training. We do this in the EP lab using minimal fluoroscopy settings, and for these sessions, we use preprinted models of both the left and right atrial and ventricular anatomies. These 3D models are usually STL-printed models — they are very low cost and very robust. One model can often support multiple simulation sessions. Fellows find it very useful before they do their first cases because they get a sense of familiarity with an EP lab environment, and also with the catheter movement and manipulation needed to achieve placing the catheter in different positions.

Those are the main uses that we have in our lab. We also have some research projects related to device development where we use 3D printed models to understand specific anatomical characteristics.

What are some of the typical costs involved in 3D printing?

That is a very good question. The cost is variable depending on the equipment and the materials that you use. It can go from very basic equipment to more sophisticated equipment. But if you take aside the upfront cost of buying an STL printer, which is about $2,000 to $3,000, you’re talking about $10 to $20 per model in terms of the materials used. If you use more sophisticated printers and different resins or different materials, then you’re going to have increased costs. If you outsource the printing, then that obviously would be an additional cost. If you outsource the segmentation, that would also be an additional cost. But for the purposes of most of the ventures that I’ve mentioned — the modeling, preprocedural simulation, and didactic simulated sessions — you can get away with a very low-cost 3D printing setup.

The most important cost is essentially the time and the effort needed to print these models. You need some sort of a setup where you have the time or the human resources to do these printing models because for a full, four-chamber cardiac model on an STL printer, it can take about 10 to 12 hours of printing. The image processing beforehand takes one or two hours, and then finalizing the model after it’s been printed takes another one or two hours. So you’re looking at the overall time of printing a model, plus the time it takes to curate and prepare it. That is the main expense — the human capital expense — more so than the actual material.

So what is the value of 3D printing?

The obvious potential value is its personalized patient care around complex interventions. This personalized approach allows for a more tailored selection of materials. There is less guessing during the procedure itself, less guessing about what catheter to use, what device to use, and what movements are required to place or guide the catheter. You essentially know how to maneuver the catheter or the sheath before you start the case, because you’ve already rehearsed it in a patient’s accurate cardiac model. Selecting the right device size for each patient and factoring in the impact on all these procedural aspects can potentially reduce costs and also improve procedural outcomes.

What are the potential applications for this technology in the future? 

There are many applications for procedural simulation. You can look at integration of 3D printed models with augmented and virtual reality applications — this will allow for personalized patient-specific simulators. I strongly believe these two technologies are complementary rather than mutually exclusive. In the field of medical device development, 3D printed cardiac models and torso models are being used to develop novel implanting tools, devices, catheters, and leads. These can potentially bypass some of the animal testing phases of some of these devices that are being developed.

There is also the area of bioprinting, where essentially you use 3D-printed scaffolds to support regeneration of human tissue. This can be applied in cardiology for heart valves, myocytes and conduction tissue, for example. There is also the aspect of telemedicine and remote consultation, so you can apply 3D printing technology for expert opinion consultations. Three-dimensional virtual files can be sent via web-based applications. They can be reviewed in real time, and can even be printed in real time on the other side. An expert in a particular field can provide very valuable feedback regarding the feasibility of procedural techniques by having a model of the patient that is literally across the globe. So this is one aspect of global healthcare and globalized medicine that hasn’t been routinely done, but it’s perfectly feasible.

Finally, with academic institutions having enough resources, one can develop a complete anatomy library of normal and abnormal anatomical specimens for teaching, training, and clinical research purposes. Essentially, you’d have a complete cardiac anatomy library of virtual and printed models that physicians and students can access for learning anatomy and for training with accurate anatomical specimens.

What limitations still exist for 3D printing?

As I mentioned before, you need a close collaboration between different physicians with different levels of expertise, and in particular between radiologists and cardiologists. Because it is a very technology-specific application, the close collaboration with radiologists is essential. It is time and labor extensive to an extent, and there are setting upfront costs for building a lab. If you want to routinely print models, though, it is obviously a much better option than outsourcing the models, which is the more expensive route.

Ideally, you want to have a technician running your lab and facilitating the printing process, both for quality control as well as for troubleshooting and maintaining the equipment. Although this technology is not new, there is a lack of familiarity in general with 3D printing in the EP community. There is some reluctance to see or consider the added value of a personalized understanding of the patient’s cardiac anatomy to improve preoperative planning.

Perhaps because there isn’t a lot of robust clinical data, there isn’t randomized clinical data showing improved procedural outcomes with 3D printing used preprocedurally. But of course, there are case series and case reports showing its benefits. For simulation using 3D printing, there is even less data, and it’s hard to quantitatively measure the impact of simulation training for learning curves and its impact on actual procedural outcomes. So those are hard metrics to evaluate with these sort of simulation training experiences. It’s more of a qualitative assessment, but you can look at things like procedural outcomes, improving procedural times and complication rates, and so on. But these data are not yet available clinically.

Also, with the models, we’re talking about specific resins. There are tissue-like resins that simulate or mimic the compliance characteristics of myocardial tissue or arterial and venous structures. These resins, however, are more expensive and require the use of special printers, which are usually high-end printers. So, there is a cost to that.

As I mentioned before, some companies can be outsourced to segment very high-quality 3D printed models, but the cost of such models usually exceeds $3,000 per case. So yes, there are some limitations to just simply printing models. There are logistics and upfront costs that need to be considered, and then there is the applicability and whether your EP lab has the need for such a setup. It depends on the population that you serve and the type of cases that you do.

Thank you so much for speaking with me today. You have provided such a wonderful review of this concept and of your experience in your lab. Is there anything else that you’d like to add?

No. I want to thank you Jodie and EP Lab Digest for allowing us the opportunity to present our 3D printing workflow. I look forward to receiving feedback from the article, and I’m available to provide consultation and advice to anyone who is interested in using this in their practice or who sees the potential benefit of using it. We are currently collaborating with other centers and with some of the industry in device development and in clinical cases. We’re happy to welcome any comments or any potential collaborations with other EPs in the future.