Panoramic display of the orderly sequenced 12-lead ECG.

The standard 12-lead electrocardiogram (ECG) has been developed over many years. The ECG has had a long and successful history of providing diagnostic information in clinical medicine. Cardiac arrhythmias have been elucidated by deductive reasoning from continuous ECG recordings with confirmation from electrophysiologic studies. Recently, there has been renewed interest in the morphology of the QRS complex, ST-segment, and T wave, which raises the important question of considering whether the usual method of display provides maximal diagnostic capabilities. The conventional display provides a logical visualization of precordial lead recordings representing the horizontal plane, but does not provide a logical visualization of the limb lead recordings representing the frontal plane. Many clinical problems require the consideration of serial ECGs necessitating the comparison of separate pages. An alternate format presenting serial recordings on a single page would be advantageous. Some automated ECG analysis systems already include the capability for multiple display formats, but these have not yet been widely used in clinical practice. This point of view paper introduces a new display format for the standard 12-lead ECG that includes: (1) a presentation of an orderly sequence of leads to facilitate scanning through different points in space and (2) a presentation of recordings of 12-lead sequences to facilitate scanning through different points in time. This display format could either replace or supplement the conventional ECG format.

The dilemma of sensitivity versus specificity in computer-interpreted acute myocardial infarction.

The use of thrombolytic therapy and out-of-hospital electrocardiogram (ECG) acquisition capability has put even greater importance on the diagnostic accuracy of computerized ECG interpretation programs. Such programs must have extremely high specificity to minimize the possibility of clinicians treating inappropriate patients; thereby needlessly subjecting the patients to the risk of potentially life-threatening complications of the medication. At the same time, studies have shown that both prehospital personnel and emergency department (ED) physicians are aided by automated ECG interpretation programs with high sensitivity. These programs assist the attending personnel in rapidly identifying patients with suspected acute coronary thrombosis, which might otherwise have been undetected or not diagnosed until more obvious ECG abnormalities were present. In previous studies, clinically correlated databases have been used to develop and test sensitivity and specificity of the acute infarction detection algorithm in the Marquette 12SL ECG interpretation program. One program revision resulted in a marked increase in sensitivity (21-53%) without loss of specificity (99.5% to 99%). More recent studies have shown the sensitivity of the interpretation program to be influenced greatly by infarct location with sensitivity lower in anterior than inferior injury. Further refinement of the acute infarction interpretation criteria along with the methodology and data used are presented. Increased sensitivity without appreciable loss of specificity has been possible for detection of both acute inferior and anterior infarction; however, different methods were used for each location. Consideration of reciprocal or concomitant repolarization changes are found to be more useful for inferior than anterior injury. Methodological approaches are presented as they relate to the compromise between sensitivity and specificity.

A statistical analysis of the ECG measurements used in computerized interpretation of acute anterior myocardial infarction with applications to interpretive criteria development.

Computerized interpretation of the electrocardiogram (ECG) for detection of acute myocardial infarction (AMI) has been an area of active investigation for the past few years. Advances in the development of criteria for increased accuracy have resulted through the use of clinically correlated databases. Previously, using such databases, the sensitivity for interpretation of AMI in the Marquette 12SL ECG analysis program has increased from 21% to 65% with specificity remaining unchanged (99%). This study attempted to find measurements of the QRS and ST-segment from 7 of the 12 standard ECG leads to increase the sensitivity of detection of anterior AMI to the level of a trained physician while maintaining the current level of specificity. Regression analyses were performed on the measurements to see which ones could improve sensitivity and what effect they had on specificity. There was no clear separation of the individual measurements between the normal database or the true positive and true negative anterior AMI databases for maintaining high specificity. In a parallel study of the same data, deterministic criteria combining both ST and T wave information increased the sensitivity of the 12SL analysis program for detection of anterior AMI to 71% on a clinically correlated anterior AMI database and 75% on a physician interpreted anterior AMI database while maintaining the specificity at 99%.

Computerized recognition of acute infarction. Criteria advances and test results.

The advent of thrombolytic therapy has increased the desire for an accurate computerized recognition of the ST elevation associated with acute myocardial infarction (AMI). Quantified electrocardiographic (ECG) criteria for AMI, described in the literature and in computerized ECG criteria packages, have concentrated on only those leads that exhibit ST elevation. The accuracy of this lead-specific approach has been maximized by an analysis of the associated ST-segment and T wave. Further advancement of the Marquette 12SL program's ability to classify ST elevation due to AMI has required the inclusion of those leads that are not elevated. This global approach was developed by modifying the 12SL program so that it would properly diagnose a small training set of clinically correlated AMI ECGs that did not meet the lead-specific criteria. Further training, via an evaluation of the false-positive rate, was done with a large clinical database (greater than 30,000 ECGs). Both the new and the old criteria were tested with a separate ECG database taken from a total of 296 patients. Of these, 77 had an AMI (determined via the hospital discharge diagnosis). The lead-specific criteria resulted in a sensitivity of 21% and a specificity of 99.5%. The global approach resulted in over twice the sensitivity (53%), while continuing to maintain a high rate of specificity (98%).

Intraventricular conduction defect (IVCD), real or fancied, QRS duration in 1,254 normal adult white males by a multilead automated algorithm.

The QRS duration (QRSD) on a digital 12 simultaneous lead ECG was measured by a commercially available recording cart (Marquette MACII 12SL) in 1,254 white male safety workers (ages 19-65, mean 34). All had a negative history (including drugs known to affect the cardiovascular or pulmonary systems), a negative family history (in immediate family members before age 55), no physical findings suggestive of heart disease, a normal blood chemistry profile, pulmonary function tests, and symptom limited bicycle exercise test. The frontal QRS axis was between -30 and -65 in 22 of 1,254 (1.8%). Twenty-seven of 1,254 (2.1%) had QRSD greater than or equal to 120 ms-14 of these had normal morphology; 2 had RBB; 3 had atypical RBB; 5 had R' in V1, V2; 2 had WPW; and 1 had Superior Fascicular Block. Sixty-three (5%) had a QRSD greater than or equal to 112 and less than or equal to 116 ms-36 of this group had normal morphology; 1 had typical RBBB; and 26 had R' V1, V2 (considered a normal variant as it occurred in 360 of 1,164 remaining with QRSD less than or equal to 108). In 1,224 white men with normal QRS morphologies and frontal axis (-25 to 100), the 98% upper and lower bounds of QRSD with the 12SL algorithm, like that seen in BSMs, was 80-116 ms, peak 96 ms.(ABSTRACT TRUNCATED AT 250 WORDS)

Digital filtering of on-line evoked potentials.

Evoked potentials recorded automatically at frequent intervals are a useful adjunct for monitoring head injury patients; however, unaveraged residual noise due to patient movement and synchronization of th- stimulus to harmonics of the line frequency is sometimes present. A frequency analysis was performed on 23 records with varying degrees of unaveraged noise and the results were used to design a digital filter. The frequency content of the records analyzed was largely contained in a band from D.C. to 200 Hz. A zero phase shift lowpass digital filter with a cutoff frequency of 200 Hz eliminated the majority of noise. Despite the low frequency content, a wide-band amplifier is still required to avoid waveform distortion, particularly latencies. Digital filters can then be applied without causing distortion.