Design of ambulatory ECG monitoring system to detect ST pattern change

In this paper, we describe the hardware configuration for the ambulatory ECG monitoring device and the algorithm for detection of ST pattern change. The ambulatory ECG recording are available for diagnosis of the heart diseases such as myocardial infarction, arrhythmia, etc. It especially is important to detect the transient ECG pattern change caused by the unbalance between the oxygen supply and the oxygen demand in the cardiac muscle that is called myocardial ischemia. This is one of the reasons why the ambulatory ECG monitoring system is necessary. We designed the portable ECG measurement device with the analysis algorithm. The algorithm analyzes the ECG signal and detects the transient ST changes. The detection of QRS complex is accomplished using its the morphological characteristics such as the steep slope and high amplitude. The developed algorithm detects the ST level change, and then classify the ST shape type using the polynomial approximation. The algorithm finds the least squares curve for the data between S wave and T wave in ECG. This curve is used for the classification of the ST shapes. ST type is classified by calculating the difference between the reference ST type and the least square curve. Through the result from the developed algorithm, we can know when the ST level change occurs and what the ST shape type is. The portable ECG device consists of instrumentation amplifier, multiplexer, micro-controller, filter and transmitter module. The designed ECG device measures ECG with four electrodes on the body and transmits the measured ECG signal to the receiver connected in PC by digital radio way. The available range of wireless communication is 70m in building and 300m in open ground.