To our knowledge, our study is the first to date to evaluate hypnosis by STAI before coronary angiography. It shows that carrying out a hypnosis session with self-hypnosis suggestions before coronary angiography did not result in a significant drop in the state anxiety score. With a median score of 45 in the hypnosis group and 46 in the control group, the anxiety levels of the patients included could be considered “average” [30]. These values ​​are higher than the norms reported for patients in medical stress situations such as patients hospitalized for various organic diseases, or undergoing medical examinations or surgery [30]. However, our results are in agreement with those of Lang et al., for patients hospitalized for a biopsy under hypnosis with suspicion of breast cancer or to perform a transesophageal ultrasound examination [21, 31]. The anxiety state score before the intervention, with alternative medicine, is on average comparable to that observed in our study [11, 14,15,16,17].

The lack of effectiveness of hypnosis in our study may be due to the timing of the assessment. Indeed, due to the constraints of the coronary angiography procedure, anxiety could not be measured during the procedure. It may also be due to the choice of the evaluation method. Indeed, if hypnosis is effective against anxiety, its statistical proof seems to be provided by an evaluation throughout the intervention and not in the moments preceding it [21, 23, 32, 33]. The patients were subjected to the Spielberger’s inventory on their arrival in the coronary angiography room, therefore before initiating a process of self-hypnosis. The evaluation carried out here therefore probably evaluates the effects of morning management and not the effectiveness of hypnosis during coronary angiography. This is in agreement with the results reported in several randomized clinical trials using STAI and involving interventional medicine showing a decrease in anxiety during an invasive examination but without significant difference in pre-interventional or during the first stages of the procedure. Lang et al., who also used the Spielberger inventory, found no significant difference in state anxiety scores before the procedure as well as during the first 0–15 min time interval [33]. A simple numerical rating scale is more sensitive to hypnosis-induced changes in anxiety [21, 32, 33]. Other scales, such as the Beck Anxiety Inventory or the Hamilton Anxiety Scale, also lead to the same conclusion [23]. These results therefore raise the possible interest of hypnosis during pre-coronary angiography since hypnosis showed a clear superiority compared to the groups receiving other additional measures such as "structured attention" or empathy [21, 32].

However, the main obstacle to the use of these techniques remains skepticism, maintained by the lack of scientific evidence, as it is difficult to measure the effectiveness of hypnosis or self-hypnosis, but also by the pejorative connotation disseminated, among others, by the entertainment world [34]. If self-hypnosis seems to be a promising tool for adapting to situations felt difficult (as demonstrated by Peter C. Keil in 2018 on chronic pain in hospitalized patients [35], its effectiveness must be objectively measured by standardized measures to expand its use and teaching. Our study found that patients' belief that "hypnosis works in general" prior to coronary angiography significantly influenced pre-intervention anxiety, regardless of the group to which they were assigned. This raises two important points: on the one hand, the beliefs and opinions of the patient vis-à-vis hypnosis and, on the other hand, the “hypnosis” label of the study. The general public develops ideas and expectations from different sources, including about medical care [36]. The cognitive model of hypnosis explains that variables such as participant motivation, beliefs or expectations are keys for patients' hypnotic receptivity [37, 38]. According to some authors, the reinforcement of these variables makes it possible to facilitate hypnotic reactivity [39]. On the other hand, Gandhi and Oakley highlighted the impact of the “hypnosis” label, whose title alone plays an anxiolytic role [40].

As observed by Dufresne et al., our study shows that one month after treatment, patients' opinions were influenced by the hypnotic experience [41]. This difference between the two arms of the study may suggest a use of self-hypnosis in the experimental group during the procedure. In any case, the improvement of the opinion regarding the hypnosis represents a positive reinforcement for the subsequent management. This hypothesis will require an evaluation of the effectiveness of hypnosis in patients who have previously benefited from this approach in the same procedure to confirm this hypothesis.

Our study has several limitations. First, it is monocentric and therefore there is a risk of bias of non-representativeness of practices and population. However, clinical activity within Mercy Hospital's cardiology department is significant, with 4,500 coronary angiograms and 2,314 percutaneous coronary angioplasties performed in 2016. In addition, the study included the intervention of 6 different cardiologists and was also carried out with the intervention of 6 health personnel qualified in hypnosis. Therefore, given the number of patients and operators, we believe that our results can be extrapolated to other centers.

Second, our study could not be double-blind because the hypnotherapist had to know whether to perform a hypnosis session or an interview with the patient. In order to avoid any follow-up bias, it would seem appropriate that the intervention in the control group not be limited to a simple interview with the hypnotherapist but also by another unconventional technique.

Third, pain assessment was only performed at peri-procedural times. It is therefore possible that such an assessment was not suitable since literature reviews highlight the positive effects of hypnosis on pain during medical or surgical procedures and often find no difference in anxiety before the procedure as in our study [21, 22, 32, 33, 42,43,44]. Therefore, it would have been more appropriate to assess pain by VAS during the procedure. It would also have been interesting to assess whether the patient had used self-hypnosis during the intervention by questioning him afterwards. These elements will have to be taken into account in another study. Finally, if none of our patients received specific premedication, the patients' usual treatment was not defined as an exclusion criterion. Under these conditions, patients on anxiolytics (benzodiazepines, antidepressants, etc.) could be included, which may induce a bias. However, these practices are usual in the coronary angiography center in which the study was conducted and we did not wish to modify them.