3D printing is a promising technology, with exciting potential applications in medicine. It creates the opportunity to examine a physical model of a patient’s anatomy before entering the operating room20. Various types of 3D printing technology have been used to fabricate cardiovascular models, and we have been exploring an economic, universally accessible type of technology for this purpose. To the best of our knowledge, FDM and SLA are the most common types of 3D printing technology. Considering the speed of FDM and the limitation of support removal, SLA is the most suitable technology for manufacturing rigid cardiovascular models. Rigid blood pool and myocardial models can be made by SLA, but their effectiveness in different types of CHD has not been evaluated. In this paper, we conducted a multicase study evaluating the application of 3D printing for the first time.
The improvement of 3D printing over CT in the diagnosis of CHDs was obvious, and it was equally effective for complex and simple CHDs; in contrast, in the diagnosis of CHDs based on CT, the accuracy was lower for complex than simple CHDs. However, when 3D-printed models were used for the diagnosis, the accuracy in the student group was significantly improved, becoming similar to that in the expert group, while the diagnosis rate in the expert group also increased. 3D printing improved the rate of CHD diagnosis, especially among students and inexperienced doctors, and this effect was more obvious for complex CHDs.
In the investigation of the necessity of 3D-printed models for the diagnosis and treatment of CHDs, most surgeons considered it necessary, although we were informed by a few experts that they could identify the diseases accurately relying on their rich experience. It is undeniable that experienced experts can correctly diagnose most CHDs using CT or echocardiography. However, we must admit that the distribution of these experts is extremely uneven, and their experience is based on extensive case training. For most doctors or students, 3D printing is necessary.
Both blood pool models and myocardial models improved the diagnostic accuracy, although they had different effects in different cases. In cases of ccTGA, DORV, WS, CAF, and TOF, blood pool models improved the diagnostic accuracy more than myocardial models. In the research on which of the two models is more suitable for different types of CHD, the results showed a difference. In cases of ccTGA, WS, CAF, TOF, PDA, and CoA, i.e., CHDs with “structural heterotopia”, blood pool models were considered to be more effective, as they were good at illustrating arteriovenous connections, vessel stenosis/obstruction, and chamber volumes. However, the results were the opposite in cases of VSD and DORV. In the case of VSD (Fig. 2h1), the location of the VSD was occluded by the left and right ventricles, so it was not easy to find. In the myocardial model (Fig. 2h2), the VSD was shown as a hole, which was easy to find and understand. Similarly, in the case of DORV (Fig. 2b1), the blood pool model was useful for finding the origin of the root of the aorta and the pulmonary artery. However, when we performed in-depth research, the surgical plan and myocardial model (Fig. 2b2) were found to be more important, as they helped doctors accurately estimate the exact location of the VSD (Fig. 4a) within the septum, the relationship of the VSD to the septal leaflet of the tricuspid valve, the subaortic or subpulmonary outflow tract, and the distance between the upper margin of the VSD and the nearest arterial valve (Fig. 4b). In addition, the model allowed the doctor to simulate channel establishment (Fig. 4c-4d) and estimate the volume of the remaining right ventricle after application. Furthermore, the ability to perform rapid demonstrations using the myocardial model is of great significance in surgical communication and education.
On the other hand, from the aspect of shape similarity, the myocardial model was more similar to the actual heart, with no significant difference in either group. The result is different from that of the demand for models in the diagnosis of some CHDs, such as ccTGA, WS, CAF, TOF, PDA, and CoA. This may have something to do with our habit of understanding the structure of the heart. Usually, each cavity, such as the left and right ventricles, is considered as an entity, which is the same as the structure of the blood pool. This could be why the students preferred the blood pool models. This habit gradually changed after they looked at the heart from the first perspective for a long time.
Compared with colorful blood pool models applied for the diagnosis of CHDs4, 21, monochrome blood pool models have a disadvantage on first glance, but they do not affect the accuracy of the diagnosis. In terms of surgical simulation, flexible myocardial models can better train doctors for surgery, which is a significant advantage of hard myocardial models. However, considering the cost of the models, this difference can be ignored. A study on the time and price of modeling, 3D printing, and postprocessing showed that the average cost of 3D printing of blood pool and myocardial models was approximately 41.8 dollars, which is much less expensive than printing multicolor models or soft models22. The average time of modeling for the blood pool and myocardial models was approximately 10 minutes and 20 minutes, respectively, and the average time of 3D printing and postprocessing was within 7 hours, which allows large-scale application.
Research on the average time of diagnosis using CT or 3D printing has shown that 3D printing allow a diagnosis to be made faster. The diagnosis of CHDs mainly depends on judgment of the cardiac structures. When diagnosing using CT or other tomographic images, 3D spatial relationships are produced through planar images, which is a very difficult and time-consuming process because it requires the comparison of almost every slice. However, 3D printing establishes and displays these spatial relationships, leaving only a judgment to be made based on the visible 3D model. In some cases, only one glance is needed to find the location and condition of the lesion, such as in cases of VSD, PDA, and CoA. Even though differences between 3D-printed models and normal models need to be determined, which may include the location affected by the disease, this approach greatly simplifies the diagnostic process, especially for inexperienced doctors and students.
Before 3D printing, the virtual model created can also be used for the diagnosis of CHDs. The advantages and disadvantages of augmented reality, mixed reality, virtual reality, and 3D printing have been compared23. On the whole, virtual models have the advantages of fast, low-cost, and repeatable application, but this method also requires more skills from the operator. The advantage of 3D printing lies in the physical characteristics of the model and high quality of simulation. The perception of spatial relationships will be biased on a virtual screen, but the 3D printing of objects can eliminate this bias because the objects can touched as if they were on a real operating table, and all the perceptions and simulations of the physical model can then be applied to the real heart.
Several limitations of this study must be noted. First, we compared two 3D printing methods with CT in the diagnosis of CHDs and did not compare them with echocardiography. The combination of 3D printing and echocardiography may offer new advantages in the diagnosis of CHDs. Second, only one case of each CHD was selected in the comparative study, while each CHD usually includes a wide spectrum of anatomical variations. Many other types of complex CHD should be considered in subsequent studies.