## 2 Related Works
### Complexity of the System: VAD, Patient, and Medical Team  
One of the fundamental characteristics for identifying complexity in systems is emergent behavior [35; 36; 37]. Therefore, the approach to solving problems in complex systems (CS) cannot rely on solutions that consider well-defined, restricted problems with known solution paths and convergent answers. Instead, an approach that can handle the challenges imposed by these systems is more recommended [38]. According to [PERSON] [36], CSs have a particular behavior of interacting with the external environment, being classified as open systems. These interactions lead to changes in the global behavior of the system, which are linked to another characteristic of complexity, adaptation and resilience, in response to external changes [35; 36; 37]. Considering the use of VADs, the influence of the external environment is observed, especially in response to stimuli generated by changes in physical activity. For example, during physical exertion, the increased metabolic demand requires VAD controllers to adjust blood flow to ensure adequate circulatory support. This highlights the importance of effective integration between the VAD operation and the hemodynamic behavior of the system, as discussed by [PERSON] et al. [39] and [PERSON] et al. [40]. An important characteristic of complexity in VADs is their dynamic interaction with the cardiovascular system, which has its own control mechanisms [13; 41; 42]. Therefore, the VAD operates within a complex system, where the regulation of the heart rate and respiratory rate, as highlighted by [PERSON] [42], is mediated by the actions of the parasympathetic and sympathetic systems, which cooperate to maintain homeostasis. This sophisticated system is essential for ensuring physiological stability. Based on the context provided regarding patients with an implanted VAD, a complexity is observed resulting from the interaction among three fundamental entities: the VAD, the patient, and the medical team. The following presents some of the characteristics of this system formed by the patient, VAD, and medical team, considering the interactions described and the complexity principles explored in refs. [35; 36]. * Interactivity: The system involves the participation of the 'VAD' and its subsystems (blood pump, cannulas, controller, driveline, and power supply), the 'patient' and their various subsystems (composed of organs, tissues, and cells that interact with each other), and the'medical team', which interacts with the other two elements to monitor and supervise processes that may occur in the patient. The numerous interactions between the elements of the system are a complexity attribute that highlights the impacts of undesirable events. These impacts include both the effects that AEs can have on the functioning of the DAV and the effects on the patient, both involving potential risk. * Adaptability: The system is dynamic, and behavior changes are driven by interactions between its entities. This attribute is related to other characteristics, such as the influences of interaction with the external environment [37] and the emergence of the system [35]. These dynamics highlight adaptations and self-organization of the elements, resulting in a sophisticated synergy capable of inducing changes in global behavior. * Non-deterministic: The system's response is unpredictable, and its behavior is stochastic, meaning that the observed phenomena are random. This characteristic is evident in the occurrence of AEs, which emerge unpredictably. There is no predefined sequence nor a way to accurately predict when or which patient will experience a specific AE. After examining the characteristics of the studied system, the diversity of processes related to the operation domains and interactions between the DAV, the patient's body, and the medical team stands out.