Part I of this series,8-10 evaluating the relationship of the ECG to its technology, appeared in March 2007. Its purposes are: 1) to examine the relation of the resting ECG to its technology; 2) to increase understanding of how the modern ECG is derived and recorded; and 3) to promote standards that will improve the accuracy and usefulness of the ECG in practice.8-10 In this document, special emphasis is placed on digital recording methods and computer-based signal processing, which are used in current electrocardiographs to provide automated measurements and computer-generated diagnostic statements. The distinction between measurements made from single ECG lead data and newer global measurements obtained from simultaneous analysis of all leads and the impact of this difference on detection of the earliest onset and latest offset of the QRS complex and the QT interval is stressed. Common technical recording deficiencies such as improper filter settings and misplacement of the precordial electrodes, which can reduce the diagnostic value of the recorded ECG, are reviewed. The major recommendations in the document include the following: Regarding the ECG signal and its processing, it is recommended that manufacturers should continue to develop improved algorithms for the identification and quantitative presentation of pacemaker stimulus outputs and for their preservation during ECG storage and retrieval. Low-amplitude pacemaker stimulus outputs should not be artificially increased in amplitude to aid recognition, because this would distort the form of the recorded ECG. Instead, it is recommended that manufacturers incorporate a separate representation of detected pacemaker stimulus outputs into 1 row only of the standard output tracing that would aid the identification of atrial, ventricular, and biventricular pacing signals.8-10 To reduce artifactual distortion of the ST segment, the low-frequency ECG filter cutoff should be 0.05 Hz, but this can be changed to 0.67 Hz or below for linear digital filters with zero phase distortion. To correctly measure amplitudes and durations used for detection of hypertrophy and infarction, the high-frequency ECG filter cutoff should be at least 150 Hz for all standard 12-lead ECGs, with extension of the high-frequency cutoff to 250 Hz in children. In addition, ECGs should automatically alert the user when a suboptimal high-frequency cutoff, such as 40 Hz, is used, and a proper high-frequency cutoff should automatically be restored between routine standard ECG recordings.8-10 Although it may be necessary to retain the ability to examine beat-to-beat changes in the ECG for special detection purposes, the formation of a single and stable representative complex for analysis of each lead is desirable. It is recommended that digital ECGs provide beat alignment that allows selective averaging or formation8-10 of individual lead representative complexes with fidelity that is acceptable for diagnostic ECG computer programs. The ability to acquire data from 12 leads simultaneously, which provides a method for identification of the earliest onset and latest offset of waves that are used for duration measurements,8-10 requires major reconsideration of measurement standards and reference values for intervals that were originally derived from analog, single-channel recording.8-10 These global waveform measurements will be systematically greater than the corresponding measurements made from single leads or measurements averaged from several leads.8-10 It is recommended that technicians and other personnel responsible for recording ECGs have periodic retraining in skin preparation, proper electrode positioning, and proper patient positioning in order to prevent precordial electrode misplacement. It is noted that one common error is superior misplacement of V1 and V2 in the second or third intercostal space,8-10 rather than in the fourth interspace. This error can result in poor R-wave progression and/or the incorrect diagnosis of anterior infarction. Periodic retraining regarding avoidance of lead switches should also be provided, and lead-switch detection algorithms should be added into digital ECGs to correct the problem as the tracing is recorded. In addition, it is recommended that diagnostic statements alerting the reader to the presence of different types of lead switches should be incorporated into preliminary interpretive reports.8-10 Routine use of the orderly frontal plane sequence for display of the limb leads, arrayed from lead aVL to III with insertion of inverted aVR between leads I and II, is recommended as an alternative to the standard ECG presentation in which leads I, II, III, and leads aVR, aVL and aVF are grouped together. However, it is recognized that the current limb lead array is already long-established, so an acceptance of such a change could take years. Therefore, manufacturers are encouraged to make this display available as a routine option. Regarding alternative lead applications, ECGs recorded with torso placement of the extremity electrodes cannot be considered equivalent to standard ECGs for all purposes and should not be used interchangeably with standard ECGs for serial comparison.8-10 In addition, tracings that use torso limb lead placement must be clearly labeled as such, including 12-lead tracings derived from torso limb lead placement in neonates or in young children and during ambulatory and exercise electrocardiography in adults.8-10 Synthesized 12-lead electrocardiograms that are derived from reduced monitoring lead sets are not considered equivalent to standard 12-lead ECGs, so they cannot be substituted for routine use. All such synthesized 12-lead tracings must be clearly labeled as such. Recording of right-sided precordial leads during acute inferior wall left ventricular infarction is also suggested, since treatment of acute MI may vary with right ventricular involvement. However, it is noted in the document that routine recording of these leads in the absence of acute inferior infarction is not recommended.8-10 Part II of this series is an electrocardiographic diagnostic list.11-13 It was prompted by the existence and characteristics of multiple commercial computerized ECG interpretation algorithms and customized diagnostic statement lists that are used in local laboratories throughout the world and that commonly contain redundant, imprecise and incorrect or misleading terms. The list differs from most others by its brevity, its absence of overlapping or redundant terms, and the elimination of terms that have little or unclear clinical meaning. A total of 117 primary diagnostic statements are grouped under 14 diagnostic categories. An additional group of secondary statements are included to allow reference to underlying mechanisms or clinical conditions, and modifier terms are presented in a third list to add precision to primary or secondary statements. In addition, a fourth list provides a small number of comparison statements that are used to signal changes between electrocardiograms that might be indicative of significant clinical events. The Committee is hopeful that this ECG statement list will be implemented as an available vocabulary in commercial ECG recording devices. The Committee also recognizes that this lexicon cannot remain fixed, as new knowledge will lead to modification of existing terms and/or addition of new terms. Parts 3-6 of this series are currently in review and will be published soon. They consist of sections concerning Intraventricular Conduction Disturbances (Part III), ST, T and U wave Abnormalities (Part IV), Hypertrophy (Part V) and Ischemia/Infarction (Part VI).