A PC-based system for visualization of the electrical axis and vectocardiogram

Presents a simple and low-cost PC-based system, designed and implemented with the idea of providing specialists with an automated tool for the monitoring of cardiac electrical activity, specifically the heart electrical axis. Previous studies have shown that, after obtaining the voltage from some specific points, it is possible to numerically compute the electrical axis, which represents the average of the instantaneous vectors corresponding to the QRS, T and P signals. A vectocardiogram (VCG) is a plot which shows the time-evolution of the resultant obtained from the ECG signals generated during a single cardiac cycle. The system works with an IBM-compatible personal computer and consists of an extension board connected to the expansion slot of the PC. The ECG signals are obtained at a sampling frequency of 500 Hz and are stored in memory. The digital signals are processed through some algorithms which compute the desired result. These operations include: detection of the QRS and T signals from the ECG, digital filtering of the signals, vector construction for each derivation, and the final operations required to obtain the instantaneous electrical axis for each set of signals. The average electrical axis is computed and plotted in the last step. Data processing is performed through an application program written in Borland C. The system was checked with a test group of 50 patients under the supervision of a cardiologist, with excellent results. Concluding remarks regarding the operation and functionality of the system are discussed.