A Simple Device to Illustrate the Einthoven Triangle

Abstract

Objective: Einthoven's Triangle is a crucial concept for the proper understanding of electrocardiography but the electrical vector of the heart is often difficult for students to grasp. In order to illustrate this principle, we constructed a device that simulates the ECG orientation and frontal plane vectors to simulate the heart's electrical activity for the main electrocardiographic leads (I, II and III). Materials & Methods: We built a box connected to a headboard with three analog voltmeters and a battery that simulates the electrical activity of the heart. Placed on the top of the box is an acrylic board with a diagram of the Einthoven Triangle, consisting of an equilateral triangle with an inscribed concentric circle. The voltmeters were connected to the corners of the triangle, mirroring the standard ECG leads. Silver-chlorided electrodes were placed at the center and at twelve equally spaced positions (30 degrees apart) along the circle. All electrodes were electrically “connected” by submergence in a 10 mM saline solution (NaCl). A particular position of the heart's electrical vector was simulated by connecting the negative terminal of the battery to the center of the circle and the positive terminal to an electrode along the circumference. At every position, readings from meters I, II and III were taken. We built a total of six devices for a class of thirty students and tested them in the HPH 400 Human Physiology course at the UC Davis School of Medicine. Conclusions: This device enabled students to verify the Einthoven Triangle principle; namely, that Lead I + Lead III = Lead II, independent of the heart's electrical vector position. Combined with the traditional demonstration with ECG machines, this equipment helps medical students to obtain a solid foundation of the basic principles of electrocardiography.