Development of a wearable device for the acquisition of a six-derivations ECG for self-monitoring of cardiovascular diseases.

Developed over a century ago, the electrocardiogram provides invaluable information about the state of health of the heart, aiding the diagnosis and management of various cardiovascular conditions. Cardiovascular diseases have significant impact on health, quality of life and economics, being the major cause of death and disability worldwide. In Europe, CVDs are the leading cause of death, accounting for 32% of all deceases, with an estimated cost of €210 billion annually. Addressing CVDs through monitoring and prevention is crucial to improve health expectancy and reduce the economic burden of these diseases. It is in this scenario that smart wearable devices fit: they allow self-monitoring of heart rate and activity. These information, together with other vital parameters, provide feedback to cardiologists, allowing them to remotely monitor patients, eventually detecting early warning signs of CVDs, and to intervene with cures before complications might occur. There are several devices that allow self monitoring of heart activity, but they are not designed to provide a comprehensive diagnosis of cardiac conditions. They commonly provide just numerical information about heart activity and, less frequently, reports a single-lead ECG. The aim of this thesis is thus to study and to realise an innovative wearable device capable of overcoming these limitations acquiring a six-leads medical ECG in a non invasive way. While a single-lead ECG offer limited diagnostic utility, as the electrical activity of the heart is reported from one direction only, a six-leads ECG records information from six different electrodes placed on specific locations of the chest and of the limbs. In this way, it allows more effective diagnosis of cardiac conditions such as arrhythmia, ischaemia and heart block. The device conceived in this thesis uses an ultra-compact design with just three electrodes, leveraging on the mathematical relationship between the six derivations. Going more into details of the signal elaboration system, the device simultaneously acquires two differential signals from the input electrodes. Common mode noise is reduced using an instrumentation amplifier and different analog filters have been tested to reduce other sources of noise. Signals are amplified and sampled with a high resolution 24-bit ADC. Acquired data are sent to a microcontroller and transmitted via Bluetooth to a smartphone application which displays acquisitions in real time. Furthermore, signal processing also involves the use of digital filters, such as Finite Impulse Response filters. In general, the development of the thesis project has gone through the following steps: • Pen and paper design of the different functional blocks of the circuit. • Schematic diagram and PCB layout realization using Cadence OrCAD. • Firmware development. • Implementation of digital signal processing techniques. The combination of digital and analog filtering of the acquired signals made it possible to create a device capable of acquiring a high quality six-leads electrocardiogram maintaining an extremely compact design. By offering an accessible and user-friendly solution, this device potentially simplifies and changes the current conception of ECG monitoring, improving prevention strategies, diagnosis, and treatments of cardiovascular diseases.