Congenital heart disease (CHD) is the most common birth defect among the newborn [1, 2, 3]. It has a broad spectrum of severity and morphology that is largely variable between individuals [2]. A strong foundation for education in CHD is therefore crucial among the medical students and young clinicians for the development and training of future cardiac specialists. Current teaching approach of heart anatomy and physiology relies heavily on two-dimensional (2D) medical images and cadaveric specimens, both of which have their own limitations and shortcomings. 2D medical images, or even three-dimensional (3D) digital reconstruction of heart presented on 2D plane requires the viewer to conceptually translate the information into 3D to understand the spatial relationship between the inter- and intra-cardiac structures. This is extremely challenging, especially for beginners who only just learn about CHD [1, 2, 3, 4, 5]. Cadaveric specimens are often inaccessible to students, expensive to maintain, and subjective to wear and tear overtime. Additionally, depending on the availability, the cadaveric specimens only demonstrate certain types of CHD (i.e., lesion-specific), and therefore cannot represent the whole spectrum of CHD [1, 3, 6, 7, 8].

3D printed heart models (3DPHM) have shown to be a novel teaching approach that can improve students’ and health providers’ learning experience and satisfaction [9]. The 3DPHM were reported with the advantages of being easily accessible, affordable, and the ability to reproduce any type of lesions, including those which are rare and more complex [1, 3, 7, 8]. Being tangible, the students can also assess the cardiac morphology up close at any viewing angle, achieving deeper understanding of the cardiac morphology without the need to master the knowledge of cardiac imaging [8]. A case-control study by Tan et al. [5] which involved 132 nursing students, reported that the 3DPHM group scored significantly higher in both objective and subjective evaluations. The study concluded that the 3DPHM were useful in improving the students’ knowledge acquisition on atrial septal defect (ASD) as well as students’ interest and satisfaction in their learning [5]. In a recently published randomized controlled trial which involved 5th year medical students, a significantly higher increase in test scores was observed in the 3DPHM group compared to the control group, regardless of the type of CHD being tested [9]. Similarly, in another study which involved 127 participants, Valverde et al. [10] reported that the use of 3DPHM have significantly improved the anatomical knowledge of criss-cross cardiac anatomy, compared to the use of imaging datasets as a teaching tool.

Despite these promising results, according to a recently published meta-analysis and systematic review, the use of 3D printed cardiac models do not necessarily increase the short-term knowledge gain among the students, even though their learning experience was enhanced [11]. To the best of our knowledge, none of the existing studies investigated the effect of 3D printed heart models on long-term knowledge gain among the students in the domain of CHD. This study aimed to investigate the immediate knowledge acquisition as well as long-term knowledge retention among the medical students with the use of 3DPHM incorporated in the teaching of CHD, compared to the conventional teaching approach.

Normality of test scores were met by Shapiro-Wilk’s test for Quiz 2 score (p = 0.25 and p = 0.08, respectively), but not for Quiz 1 score (p = 0.014). Both quiz scores met the assumption of homogeneity of variance by Levene’s test (p $>$ 0.05).

The Quiz 1 score was marginally higher in the 3DPHM group, with a median score of 17.5 and compared to median score of 16 in the control group, however Mann-Whitney U test demonstrates no statistical significance (U = 272, p = 0.16). Fig. 5 presents a boxplot of the scores achieved by both student groups in Quizzes 1 and 2.

Fig. 5.

Boxplot of the scores (out of 20) achieved by control and 3DPHM groups in Quiz 1 and Quiz 2. 3DPHM, three-dimensional printed heart model.

The 3DPHM group experienced slightly higher score difference between Quiz 1 and Quiz 2, with a mean score difference of 7.79 ($\pm$2.63), compared to the control group, 7.04 ($\pm$2.64). Fig. 6 illustrates the mean score differences between Quizzes 1 and 2 of both control and 3DPHM groups. The Pearson’s correlation between the score difference and type of group and year of recruitment was very weak and not significantly different, r = –0.143 (p = 0.15) and r = 0.043 (p = 0.379), respectively. The fitted regression equation for predicting the score difference of the two quizzes from the predictors was ŷ = –7.137 + 0.220$\chi$ – 0.743z, where ŷ is the score difference of Quiz 1 and Quiz 2, $\chi$ is the year of recruitment (coded as 0 = year 2020, 1 = year 2021), and z is the type of group (coded as 0 = control group, 1 = 3DPHM group). The r${}^2$ for the fitted regression was 0.022; that is, only 2% of the variance in score difference was predictable from the predictors. In other words, the result does not suggest improvement in long-term knowledge acquisition within the 3DPHM group when compared to the control group.

Fig. 6.

Mean changes in score between Quizzes 1 and 2 (Quiz 2 score – Quiz 1 score) for both control and 3DPHM groups. 3DPHM, three-dimensional printed heart model.

In comparing survey responses between the control and 3DPHM groups, the Mann-Whitney U test showed no significant difference in all of the questions. Figs. 7,8 illustrate the survey responses in percentage for the control group and 3DPHM group, respectively. Both groups of students indicated either ‘strongly agree’ or ‘agree’ that the teaching method was interactive and interesting (U = 346.5, p = 0.93). Slightly more students in 3DPHM group indicated ‘strongly agree’ that the education was easy to understand (82%) compared to the control group (76%), although this is not statistically significant (U = 331.5, p = 0.64). More students in 3DPHM indicated ‘strongly agree’ that their knowledge about CHD has improved (86%) compared to the control group (68%), and again this is not statistically significant (U = 292, p = 0.16). About 64% of the students in 3DPHM group indicated ‘strongly agree’ that the 3DPHM played an important role in helping them understand CHD. This is similar to the control group where 60% indicated ‘strongly agree’ that the 3DPHM would help them to understand CHD (U = 349.5, p = 0.99). However, one student in the 3DPHM group disagreed that the 3DPHM helped in his/her learning of CHD.

Fig. 7.

Survey responses (number of students, percentage) of the control group with regards to the education session. 3DPHM, three-dimensional printed heart model; CHD, congenital heart disease.

Fig. 8.

Survey responses (number of students, percentage) of the 3DPHM group with regards to the education session. 3DPHM, three-dimensional printed heart model; CHD, congenital heart disease.

This cohort study has evaluated the value of 3DPHM in both immediate and long-term knowledge acquisition among the medical students on the topic of CHD when compared to the conventional teaching tools. Even though there are published articles which assessed the role of 3DPHM in immediate knowledge gain on the topic of CHD, the present study is the first to investigate the effect of 3DPHM in long-term knowledge retention in the domain of CHD.

The results showed that the 3DPHM group scored slightly higher in Quiz 1, which indicated improvement in immediate knowledge acquisition compared to the control group. This difference however, did not achieve statistical significance. This finding echoes the finding in Jones et al.’s [16] study, in which 36 residents were divided into 3D printed model group and control group with their pre-test and post-test scores analyzed. In their study, the 3D printed model group experienced slightly greater improvement in the post-test compared to the control group, however the difference was not statistically significant [16]. In another study conducted by Loke et al. [2], the 3DPHM group did not show improvement in the immediate knowledge gain among the pediatric residents. Despite these positive reports, there are other studies documenting contrasting findings. In a study which involved 63 medical students, the 3DPHM group was reported to have a significant improvement in the test results when compared to the control group [17]. In another study by Lim et al. [7], 53 first year medical students were randomly assigned into three groups (cadaveric materials, 3DPHM, and combined materials) and were objectively tested in pre- and post-test for their knowledge acquisition on external cardiac anatomy. It was reported that the 3DPHM group had significant improvement in test scores (p = 0.003) [7]. This is not a surprising finding. In a meta-analysis conducted by Yammine et al. [18], physical models were reported to significantly improve the overall knowledge outcome and the spatial knowledge acquisition, but not the factual knowledge acquisition. In the present study, we focused on the topic of CHD using 3DPHM which feature 4 different types of CHD. Even though the result did not reach statistical significance, which likely was due to the small sample size, the role of 3DPHM in improving short-term knowledge gain on CHD should not be overlooked, as the effect of 3DPHM on immediate knowledge acquisition appears to vary with the complexity of the CHD. In the study by White et al. [19], residents were objectively tested on two types of CHD of different complexities to explore the usefulness of 3DPHM in improving residents’ knowledge on VSD and ToF. They were divided into 3DPHM and control groups for both VSD and ToF lecture. It was reported that the 3DPHM group scored higher in the ToF post-test (p = 0.037), but lower in the VSD post-test (p = 0.02) [19]. Similarly, in another study by Smerling et al. [3], first year medical students were subjectively tested to assess their perceived knowledge acquisition using 3DPHM of different lesion complexity. It was reported that with the use of 3DPHM, as the complexity of CHD increases, the mean knowledge also increases [3]. This however, was not validated in our study, which could contribute to the findings of no significant difference. This limitation could be addressed in future studies.

Surprisingly, the 3DPHM group performed slightly inferior to the control group for long-term knowledge retention, even though this was not statistically significant. This is in contrast to another study by Lombardi et al., in which plastic heart models were compared to organ dissection of a sheep heart and virtual dissection using physiology software program, to assess the students’ immediate knowledge acquisition and long-term knowledge retention on normal heart anatomy and physiology. It was found that the plastic model group performed significantly better during the initial exam and the 2-month follow-up exam [20]. This difference in findings might be due to the difference in methods of lecture being carried out in both studies. In Lombardi et al.’s [20] study, the students in plastic model group were allowed 45-minute of hands-on activity with the models as well as within-group discussions after 15-minute of PowerPoint lecture; whereas in our study, the students in the 3DPHM group learned individually and had full 1.5 hour of PowerPoint lecture with different teaching tools incorporated throughout the sessions. The amount of time that they spent on the models might not be enough. On the other hand, the study by Lombardi et al. [20] only focused on normal heart anatomy and physiology, whereas our study focused on CHD, which could justify the difference in findings.

As for the survey responses, although not statistically significant, greater percentage of students in 3DPHM group responded that the lecture was easy to understand, and that their knowledge on the topic of CHD has improved. In Loke et al.’s [2] study, the 3DPHM group rated significantly higher satisfaction score towards the teaching session, when compared to the control group. On the other hand, a meta-analysis found that the 3DPHM is associated with higher subjective evaluation scores and satisfactory level among the study participants [9]. This is also reflected in our study in which majority of the students responded (96% in the control group and 85% in the 3DPHM group) ‘agree’ or ‘strongly agree’ that the 3DPHM had helped them to gain a deeper understanding of CHD. Hence, the 3DPHM has contributed to improving students’ learning experience.

It is worthwhile to report that in the survey when the students were asked to provide additional comments, some of them mentioned that the coloured digital 3D models were helpful for them to understand CHD compared to the CT images (total of 9 from the control group and 4 from the 3DPHM group). This is not surprising. As a novice, the students may not have the ability yet to mentally reconstruct the heart anatomy in 3D views based on the 2D images, not to mention when it comes to CHD when the heart morphology is more complex than the normal anatomy [2, 4, 21]. Hence, the digital 3D models were helpful for the students to visualise the heart defects in 3D, and the colour on the digital 3D models were helpful for them to understand the hemodynamic changes in the heart for each type of CHD. In fact, a recently published study by Liddle et al. [22] found that the use of digital 3D heart models over tele-consultation had significantly improved the CHD patients’ knowledge about their disease as well as their cardiac surgical history. This has demonstrated the value of digital 3D heart models as an alternative or complementary teaching tool in medical education, especially when physical meeting is not possible during coronavirus disease 2019 (COVID-19) pandemic. In light of the pandemic, virtual education had formed an integral part of medical education [23]. While there are limited publications on virtual teaching of CHD, our group had compared the value of 3DPHM and virtual reality (VR) in medical teaching of CHD based on the opinions from radiologists, sonographers, and radiographers. It was found out that the VR heart models had comparable benefits with 3DPHM in medical teaching of CHD [15]. This is another area that can be explored further in future studies to investigate the use of virtual models in medical education.

This study has some limitations. Firstly, there were no pre-test done to test the students’ actual baseline knowledge on CHD, hence it remains unknown that if both groups are comparable. Secondly, the selection criteria for the study participants could not exclude those who had pre-existing tertiary education, which could affect the results to some extent. Thirdly, the amount of time that each student in the 3DPHM group spent on assessing 3DPHM was not controlled. Even though they were encouraged to share the 3DPHM among themselves, some students may not spend as much time on the models as others, therefore reducing the level of benefits they could gain from the 3DPHM. Fourthly, both Quizzes 1 and 2 are a mixture of questions on factual and spatial knowledge on CHD, which might be too generalised to evaluate the actual effect of 3DPHM on CHD knowledge acquisition. It is suggested that future studies should group the questions into different educational components, for example, knowledge acquisition and structural conceptualization [17], to investigate the effect of 3DPHM on these two components separately. Additionally, in the last question of the survey, the control group was being asked speculatively about their opinion on 3DPHM. This could have led to bias in the results, hence should be interpreted with caution. Lastly, it is unknown if the students had done any extra studies or revision on CHD during the 6-week’s duration between Quizzes 1 and 2, which could have affected their score in Quiz 2. Future similar studies should take this confounding variable into account.

The results of this study suggested no significant improvement in CHD knowledge acquisition and knowledge retention with the use of 3DPHM compared to the conventional teaching methods. The 3DPHM did not significantly enhance the self-perceived knowledge improvement either among the students when compared to the conventional teaching methods. However, the positive benefit that the 3DPHM could bring to enhance the students’ learning experience should not be overlooked. Future research should include larger number of sample size, and categorize the quiz questions into different educational components, allowing measurement of the true effect of 3DPHM on knowledge acquisition of different aspects of CHD.

IL and ZHS designed the research study. IL performed the research investigation. IL analysed the data. ZHS provided supervision of the study. All authors contributed to editorial changes in the manuscript. All authors read and approved the final manuscript.

The study was approved by the Human Research Ethics Committee of CURTIN UNIVERSITY (approval number: HRE 2017-0138). All participants signed inform consent prior to participating in the study.

The authors would like to thank Mauro Vaccarezza from Curtin University for his assistance in advertising this research project to the medical students.

This research received no external funding.

The authors declare no conflict of interest. Zhonghua Sun is serving as one of the Guest editors of this journal. We declare that Zhonghua Sun had no involvement in the peer review of this article and has no access to information regarding its peer review. Full responsibility for the editorial process for this article was delegated to Peter A. McCullough.