Standardizing electrocardiographic leads: introduction to a symposium

Abstract

Since Einthoven introduced the string galvanometer in 1902, electrocardiography has evolved as one of the most widely used tests in the practice of medicine. The routine 12-lead electrocardiogram (ECG), comprising limb leads, augmented frontal plane leads, and precordial leads, has been standardized for half a century. Routine electrocardiography is a fundamental tool for establishing cardiac rhythm and for the diagnosis of acute and chronic diseases of the heart. Comparison of serial ECGs is important in clinical decision making, and this requires technical consistency to minimize nonbiologic variability. Important elements of technical consistency include choice of leads and accuracy of electrode placement. To identify Q waves of prior myocardial infarction and to quantify QRS amplitudes to diagnose ventricular hypertrophy, proper lead placement of the standard electrodes can be extremely important. Electrode placement can have a profound effect on the quantitative variability of serial ECG findings. For example, to evaluate changing ST-segment deviation in patients with acute coronary syndromes, consistent electrode placement is essential. For most rhythm diagnoses, precise lead placement is less critical, but electrode placement is important when QRS morphology is used to determine whether a wide QRS complex tachycardia is ventricular tachycardia or supraventricular tachycardia with aberrancy or bundle branch block. Before the modern era of acute coronary care and hospital-based monitoring and telemetry, nearly all ECGs recorded in the course of practice used a standard 12-lead electrode array that evolved by empirical consensus in the 1930s and 1940s. Early exercise tests conducted with the master 2-step protocol used supine limb lead tracings recorded before and after effort, but exceptions began to occur in the last third of the 20th century when bipolar torso electrodes were introduced to allow activity-compatible