Common electrocardiographic artifacts mimicking arrhythmias in ambulatory monitoring Manlio F. Ma ´rquez, MD, Luis Colı ´n, MD, Milton Guevara, MD, Pedro Iturralde, MD, and Antonio G. Hermosillo, MD, FACC Mexico City, Mexico Background Ambulatory electrocardiographic monitoring is used in clinical practice as a means of detecting car- diac arrhythmias during daily activities. Current equipment provides analysis for the detection of arrhythmias, ST-segment deviation, and more sophisticated analyses (late potentials, Q-T behavior, and heart-rate variability). However, despite the system used, a number of artifacts could mislead diagnosis. Methods and Results We prospectively searched for artifacts during ambulatory electrocardiography in pa- tients referred for monitoring to our institution, a tertiary referral center. Patients were ambulatory at home, work, school, or within the hospital. We divided artifacts according to Krasnow and Bloomfield’s classification (pseudoarrhythmia, non- arrhythmia), and we added a new category, artifacts in patients with pacemakers. Artifacts encountered mimicked sinus arrest, supraventricular arrhythmias, ventricular arrhythmias, and aberrancy. Examples of each one and diagnostic clues are provided to recognize these artifacts properly. Conclusions A substantial amount of invalid data (false-positive findings because of electrocardiographic artifacts) were identified during ambulatory electrocardiographic monitoring that can lead to inappropriate interpretation and may result in severe diagnostic errors. (Am Heart J 2002;144:187-97.) Ambulatory electrocardiographic monitoring (AEM) is used in clinical practice as a means of detecting, documenting, and characterizing cardiac arrhythmias, usually during ordinary daily activities. 1 Its major appli- cation is in the diagnosis of tachyarrhythmias, brady- arrhythmias, and conduction disturbances that are not detected by means of 12-lead resting electrocardiogra- phy. Electrocardiographic artifacts can occur during AEM; although some do not represent diagnostic prob- lems because they can be readily identified, others can easily simulate ventricular or atrial arrhythmias. 2 The largest series of artifacts during AEM was published by Krasnow and Bloomfield in 1976, 3 and several case reports are found in the literature, many of which de- scribe severe iatrogenic problems caused by misdiag- nosis. 4-11 Recognition of artifacts during AEM requires the competence of both the interpreting cardiologist and the referring physician, who needs the results to guide management. In this article, we describe a num- ber of artifacts encountered during AEM that could lead to inappropriate interpretation. Methods Patients were eligible when they were consecutively re- ferred to our department for 24-hour AEM by their attending physician and their studies showed abnormalities compatible with some kind of artifact. The equipment used for electro- cardiographic monitoring at our hospital was the New Wave Holter device (HP43420A, Hewlett Packard, Sunnyvale, Calif) with digital electrocardiographic recorders. For this monitor- ing, the electrodes were positioned with the exploring elec- trodes at the V1 and V5 positions. Rhythm strips consisted of 2 channels, A (superior) and B (inferior), corresponding to V 1 and V 5 , respectively, unless otherwise specified. We also report the results of patients referred to our department be- cause of abnormal results on a ambulatory electrocardiogram performed in another center. Artifacts discovered were di- vided according to Krasnow and Bloomfield’s original classifi- cation 3 into 2 general categories, pseudoarrhythmias and nonarrhythmias, and a new category was added, artifacts in patients with pacemakers (Table I). Whenever possible, we tried to provide clues to the interpreting physician for recog- nizing these artifacts. Results Although the most frequent artifacts do not repre- sent a diagnostic problem when present only in one channel (in Figure 1, A, the gross artifacts seen on channel A are not seen in channel B, and in Figure 1, B, the electrical signal shows such irregularity that it is almost impossible not to consider it as an artifact), we found a number of artifacts that had the potential for misdiagnosis because they can sim- From the Department of Electrocardiography and Cardiac Electrophysiology, Instituto Nacional de Cardiologı ´a “Ignacio Cha ´ vez.” Submitted October 29, 2001; accepted February 11, 2002. Reprint requests: Manlio F. Ma ´ rquez, MD, Servicio de Electrofisiologı ´a, Instituto Nacio- nal de Cardiologı ´a “Ignacio Cha ´ vez,” Juan Badiano 1, Seccio ´n XVI, Tlalpan, CP 14080, Me ´xico DF, Me ´xico. E-mail: manliomarquez@yahoo.com © 2002, Mosby, Inc. All rights reserved. 0002-8703/2002/$35.00 + 0 4/1/124047 doi:10.1067/mhj.2002.124047 Curriculum in Cardiology