Clinical guidelines systematically assist practitioners with providing appropriate health care for specific clinical circumstances. Today, a significant number of guidelines and protocols are lacking in quality. Indeed, ambiguity and incompleteness are more likely anomalies in medical practices. Our objective is to find anomalies and to improve the quality of medical protocols using well-known mathematical formal techniques, such as Event-B. In this paper, we use the Event-B modeling language to capture guidelines for their validation. Our main contributions are : to apply mathematical formal techniques to evaluate real-life medical protocols for quality improvement; verification proofs for the protocol and properties according to the medical experts; and perspectives of the potentials of this approach. An assessment of the proposed approach is given through a case study, relative to a real-life reference protocol (ECG Interpretation) which covers a wide variety of protocol characteristics related to the several heart diseases. We formalise the given reference protocol, verify a set of interesting properties of the protocol and finally determine anomalies.