What is Einthoven's triangle theory?
Einthoven's triangle is a conceptual model I developed to interpret the electrical signals of the heart from limb leads. I proposed that the heart's electrical activity can be represented as a dipole—a vector of electrical force—projected onto an equilateral triangle formed by the two arms and the left leg. The three standard limb leads (I, II, and III) measure the potential differences between these points: Lead I from right arm to left arm, Lead II from right arm to left leg, and Lead III from left arm to left leg. The fundamental law I derived states that the voltage in Lead II equals the sum of the voltages in Leads I and III. This geometric framework allowed clinicians to deduce the direction and magnitude of the heart's electrical axis, which is essential for diagnosing conditions like ventricular hypertrophy or myocardial infarction. Every deflection tells a story of potential difference.
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