Paul Peter Elko

Maximal Ascending and Descending Slopes of the T Wave in Men and Women

To investigate possible sex differences in the dynamics of T wave generation, the maximum instantaneous slope of the ascending and descending limbs of the T wave (max dV/dt and min dV/dt, respectively), were calculated. These rate of repolarization parameters, as well as more traditional repolarization duration parameters (QT, JT, Q to T wave peak [QTm] and J to T wave peak [JTm]), were measured by computer using digitized electrocardiograms (ECGs) from the V5 lead in 562 normal subjects (443 men and 119 women; mean age 37 years), whose heart rates (HRs) were confined to one of three narrow ranges, namely 60 +/- 1, 70 +/- 1, or 80 +/- 1 beats/min. In both men and women, for each HR range absolute values of min dV/dt exceeded those of max dV/dt (P < .0001). However, absolute values of both max dV/dt and min dV/dt were consistently greater in men than in women for each HR range (P < .0001 at HR 60 +/- 1; P < .02 at HR 70 +/- 1, or 80 +/- 1). By using correlation analysis, max dV/dt and min dV/dt were shown to be independent of the repolarization duration variables (r < .30). Thus, whereas in both men and women the descending limb of the T wave is steeper than the ascending limb, the maximum slope of each limb of the T wave is steeper in men than in women. These findings add to a growing body of data indicating fundamental sex differences in the physiology of cardiac repolarization and propensity to torsade de pointes.

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%.

Using directly acquired digital ECG data to optimize the diagnostic criteria for anterior myocardial infarction

The use of a newly developed method of directly transferring digital data from Marquette electrocardiogram (ECG) systems (Milwaukee, Wisconsin) to personal computers for subsequent storage and analysis is illustrated. This method can eliminate the slowness and inaccuracy associated with measuring relevant ECG parameters from analog tracings and manually entering the data into a computer. In this study, the new method was used to derive ECG criteria for anterior myocardial infarction and to compare their performances to those of the current Marquette 12SL diagnostic program and of a group of cardiologists who had also interpreted the ECGs. Using angiographic data, 82 normal subjects and 55 patients with anterior myocardial infarction were identified. The digital ECG data from the patients in each group were transferred to a personal computer and frequency distributions of these data were generated. From these frequency distributions, the ECG criteria that most reliably separated the two groups were identified. The diagnostic performance of the best of these empirically derived criteria appears clinically superior to the performances of both the 12SL program and the cardiologists who had also interpreted the ECGs.