Screening for latent coronary artery disease by exercise testing

NONLINEAR ANALYSIS OF CORONARY ARTERY DISEASE, MYOCARDIAL INFARCTION, AND NORMAL ECG SIGNALS

In this study, we analyze nonlinear feature extraction methods in terms of their ability to support the diagnosis of coronary artery disease (CAD) and myocardial infarction (MI). The nonlinear features were extracted from electrocardiogram (ECG) signals that were measured from CAD patients, MI patients as well as normal controls.

We tested 34 recurrence quantification analysis (RQA) features, 14 bispectrum, and 136 cumulant features. The features were extracted from 10,546 normal, 41,545 CAD, and 40,182 MI heart beats. The feature quality was assessed with Student’s [Formula: see text]-test and the [Formula: see text]-value was used for feature ranking.

We found that nonlinear features can effectively represent the physiological realities of the human heart.

Nonlinear dynamics analysis of electrocardiograms for detection of coronary artery disease

A computerized approach of nonlinear dynamics analysis of electrocardiogram (ECG) signals was applied for the detection of coronary artery disease (CAD). The proposed nonlinear dynamics descriptors were derived from 12-lead rest ECG data, and evaluated by originally developed computer software. Fluctuations of potentials of ECG leads that occur during the period of 20 ms with a magnitude of 5-20 microV were significantly less beat-to-beat predictable in ischemic versus non-ischemic patients. The well-known nonlinear dynamics descriptors, recurrences percentage, mutual information, fractal dimension, and a new descriptor, next embedding dimension error, were good quantitative descriptors of fluctuations. They were significantly different (< p = 0.00001) in males with (108 patients) and without (54 patients) coronary artery lesions. The analysis of small fluctuations required a careful preprocessing technique based on knowledge of specifics of measurement errors and physiology of ECG signals. We considered finite differences of measured potentials with the time step of 20 ms as the initial source for nonlinear analysis. In nonlinear dynamics analysis, we also included such time moments that only belong to P- and T-waves or baseline drift with small positive slopes that allowed us to extract, under normal conditions, initial halves of P- and T-waves that displayed a better capacity to classify ischemic patients.

Accuracy of heart rate-adjusted ST segments in populations with and without posttest referral bias

We compared the accuracy of the ST segment/heart rate (STHR) index and slope to standard criteria (> or =1 mm horizontal/downsloping ST-segment depression at J + 60 msec) in 1358 patients (152 underwent angiography). All exercise tests used the Cornell protocol and computer measurements of maximum ST-segment depression at J + 60 msec. Test accuracy was determined for the entire group with a probability-based method. Thresholds with equal specificity to standard criteria were determined. By using only patients who underwent angiography, neither STHR index nor slope was more accurate than standard criteria (maximum sensitivity: standard criteria, 42%; STHR index, 51%; STHR slope, 40%). However, by using the entire group, both STHR index and slope were more accurate than standard criteria, but only STHR index achieved statistical significance (maximum sensitivity: standard criteria, 31%; STHR index, 60%; STHR slope, 47%). We conclude that heart rate-adjusted ST-segment criteria are more accurate than standard ST-segment criteria. A lack of demonstration of improved accuracy of STHR index and slope only occurs in patients affected by posttest referral bias.

Diagnostic accuracy of heart rate-adjusted ST segments compared with standard ST-segment criteria

We compared the accuracy of ST segment/heart rate (ST/HR) index with that of standard criteria (> or = 0.1 mV horizontal/downsloping ST depression 80 ms after the J point) in 121 patients who had undergone angiography (49 with > or = 1 lesion with > or = 50% stenosis) and 50 clinically normal subjects. All exercise tests used the Cornell protocol and computer measurements of maximal ST depression 80 ms after the J point. Thresholds with equal specificity to standard criteria were determined for ST/HR index using each of the 2 normal groups (those who were normal by angiography and those who were clinically normal). In using only patients who underwent angiography, we found that the ST/HR index had a sensitivity that was not significantly greater than that of standard criteria (standard criteria 51%, ST/HR index 59%; p = 0.21). However, the receiver-operating characteristic curve area increased from 64 +/- 4 to 68 +/- 4 (p < 0.02). When clinically normal subjects were used instead of patients without angiographic disease, there was a clearly discernible improvement in sensitivity of ST/HR index over standard criteria (standard criteria 51%, ST/HR index 69%; p < 0.05). The associated curve areas were 69 +/- 4 and 79 +/- 3 (p < 0.001). Therefore, accuracy of the ST/HR index was marginally better than standard criteria only in patients who underwent angiography. When clinically normal subjects were used, the accuracy of the ST/HR index was definitely better than standard criteria. We conclude that the demonstration of improved accuracy of the ST/HR index depends on the population being tested.

Hyperventilation in Patients Who Have Sustained Myocardial Infarction after a Work Injury

Patients who present with acute myocardial infarction after a work injury (AMI-WI) often report symptoms consistent with chronic hyperventilation which date back as far as the work injury itself, rather than to the AMI. The aim of the study was to test the hypothesis that hyperventilation significantly contributes to the symptoms of AMI-WI patients.

The prevalence of hyperventilation was assessed by clinical capnography in 12 AMI-WI patients, 20 normal controls, 15 AMI patients whose AMI was conventional and not subsequent to a work injury (AMI-C) and 14 patients with post-traumatic stress disorder (PTSD). End-tidal carbon dioxide partial pressure (PetCO2) was measured at rest, after 1 min hyperventilation (FHPT), after recall of the relevant stressor (Think) and when the breathing was felt to be normal (MBIN).

PetCO2 levels after FHPT were: 29.0±1.5 (mean±SD) mmHg for AMI-WI; 26.7±1.9 mmHg for PTSD; 32.1± 4.1mmHg for AMI-C and 33.7±1.4 mmHg for the controls ( P< 0.05 and P< 0.01 for AMI-WI and PTSD, respectively, versus controls). After Think, the levels were 25.8±1.6 mmHg for AMI-WI, 24.6±1.4 mmHg for PTSD, 31.2±4.1mmHg for AMI-C and 31.2± 1.5 mmHg for normals ( P<0.05 and P<0.01 for AMI-WI and PTSD, respectively, versus controls). For MBIN, values of PetCO2 were 26.8±1.7 mmHg and 26.7±1.5mmHg for AMI-WI and PTSD versus 33.8±1.2 mmHg for normals, ( P< 0.01 for both versus controls). Ten AMI-WI and 12 PTSD were positive for hyperventilation versus four AMI-C patients and four controls ( P< 0.01). The implications for rehabilitation, compensation and pathophysiology of AMI-WI are discussed, both from a medical-scientific perspective and in terms of admissible legal evidence.

Accuracy of ST/heart rate index in the diagnosis of coronary artery disease

The accuracy of ST/heart rate (ST HR) index was evaluated in patients presenting for exercise electrocardiography with suspected coronary disease. In all, 420 patients (235 men and 185 women) with normal electrocardiograms at rest underwent exercise testing, followed within 3 months by coronary angiography. The sensitivity and specificity for standard ST criteria (greater than or equal to 1 mm horizontal or downsloping depression) were 48% (78 of 162) and 81% (208 of 258), respectively. An ST HR-index threshold of 1.86 microV/beta/min had the exact same specificity with a sensitivity of 44% (71 of 162; p = not significant). Consideration of greater than or equal to 1.5 mm upsloping depression had no significant impact on the aforementioned results. Using multivariate logistic regression analysis, age, sex, symptoms, cigarette smoking, diabetes mellitus, qualitative ST slope, rate-pressure product, METs achieved and exercise angina were evaluated with and without ST HR index and ST depression. According to this analysis, age, sex, symptoms and ST slope were good predictors of presence or absence of disease. Neither ST HR index nor ST depression had significance in the multivariate analysis. However, when a separate analysis was performed in men and women, the 2 quantitative ST variables showed significance in men, but not in women. Comparisons of discriminative accuracy using receiver-operating characteristic curves demonstrated differences between men and women, but no difference between ST HR index and ST depression. Therefore, concerning questions of coronary disease diagnosis, consideration of ST HR index was not better than standard ST criteria, and added nothing to multivariate analysis of other available variables.

Variability in the accuracy of the exercise ST-segment in predicting the coronary angiogram: how good can we be?

In order to evaluate the variability in the diagnostic accuracy of the exercise electrocardiogram, a meta-analytic database derived from a review of 147 publications and a multicenter database derived from 2,826 angiographic referrals were analyzed. Wide variability in sensitivity and specificity were found from the meta-analytic review (standard deviations of 16% and 15%, respectively). No improvement in reported sensitivities and specificities has been seen over the past 22 years. The sensitivities and specifities derived from the multicenter database also showed wide variability (standard deviation 13% and 5%). These results suggest that despite obvious technologic strides in acquiring, processing, and interpreting exercise ECG signals, the accuracy of the exercise induced ST depression has not increased greatly and is difficult to ascertain a priori in a given laboratory. Individual anatomic and physiologic differences are postulated as limiting factors in the accuracy that can be obtained from this noninvasive test.