In this particular instance, synchronization refers to the process by which two systems converge to the same dynamic. The master-slave strategy is the most commonly employed method of achieving the previously mentioned objective. In this scenario, the system exhibiting chaotic dynamics is referred to as the master system, while the system that is forced to track the dynamics of the master system is known as the slave [28]. Recently, extensive research has been conducted on master-slave synchronization within this framework to enhance the security of ECG signal transmission in telemedicine. For instance, in Ref. [29], the authors propose a novel encryption technique that utilizes signals generated in a chaotic system to encrypt information. The encrypted data can then be decrypted using a synchronization strategy incorporating the signals and a PD controller. The Lu system, a variant of the Lorenz oscillator, is employed. It consists of two chaotic systems arranged in a master-slave configuration that requires a PD controller synchronization. On the other hand, in Ref. [17], a secure communication system has been implemented using two embedded Chen chaotic systems, which are referred to as the master and slave systems, respectively. The ECG signal is encrypted using a master chaotic system. The original data are decrypted by using the slave system. To simplify the calculation of synchronization control design, the Takagi-Sugeno fuzzy method was employed to transform the master and slave components into a fuzzy format. A disturbance observer was developed to estimate the undesired signal present on public channels and the variations in parameters on both the master and slave sides. In addition, an adaptive sliding mode control was developed in combination with the disturbance observer to achieve synchronization between the master and slave systems. Both references demonstrate that synchronization errors are not exactly zero but remain close to zero. Nevertheless, this is important to the development of robust applications in chaotic systems [30; 31]. In furtherance of the perspective on _feedback_ methods discussed in the references given above, the synchronization problem is also closely related to the observer problem from control theory [32]. This paper aims to enhance the security and integrity of ECG data during RF wireless transmission for telemedicine applications by implementing a chaotic encryption strategy that relies on master-slave synchronization. This approach combines a multi-scroll chaotic system as the master system, with an extended state observer (ESO) acting as a slave system to estimate all states of the master, as well as the nonlinearity that generates the multi-scroll attractor. The ESO is a highly effective method that can estimate both the state vector and uncertainties in dynamical systems simultaneously [33]. In this proposal, the nonlinear term is seen as an uncertainty. Thus, in an encryption scheme, the user can modify the nonlinear term as desired, while the ESO can estimate the nonlinearity without knowing this adjustment. This feature enhances the reliability of the chaotic synchronization strategy by providing robustness. The Lyapunov stability analysis provides sufficient criteria to guarantee the boundedness of error synchronization dynamics. The proposed system supports OFDM and adaptive n-QAM schemes to optimize signal discretization. Experimentally validated, this approach prevents channel overlap during 2.5 GHz transmissions, ensuring robust and efficient data transmission in modern telemedicine environments. The structure of this article is organized as follows: Section 2 describes the synchronization design and dynamic chaos-based random key generator algorithm and decryption stage. The processing data, n-QAM algorithm, and RF transmission algorithms are all detailed in Section 2.2. Section 3 describes the main results obtained and the spectral and performance evaluations. Finally, Section 4 shows the conclusions obtained and future work.