Variance ECG detection of coronary artery disease--a comparison with exercise stress test and myocardial scintigraphy

"ECG variability contour" method reveals amplitude changes in both ischemic patients and normal subjects during Dipyridamole stress: a preliminary report

To detect and quantify consistent ECG amplitude changes, the "ECG variability contour" (EVC) method was proposed. Using this method we investigated amplitude changes in subjects undergoing myocardial perfusion imaging (MPI) with Dipyridamole (Dp). Fifty-three patients having reversible perfusion defects and 19 normal subjects (NS) who were free of: perfusion defects on their MPI, standard ST-T changes during Dp stress, and a negative clinical follow up. Mean ∏¹(<∏¹>) was similar for the NS and patient group (6.2 ± 6.1 vs. 6.3 ± 6.2, P = 0.95). <∏¹> was 4.6 ± 3.0 in patients not having ST-T changes during Dp stress (n = 42), whereas in patients having ST-T changes (n = 11) it was 13.1 ± 10.2 (P < 0.001). For both groups <∏(QRS)> was smaller than <∏(ST)>, which in turn was smaller than <∏(T)>. The values of <∏(QRS)>, <∏(ST)>, and <∏(T)> for the NS, patients without and with ST-T changes were: 26.8 ± 28.6, 42.6 ± 41.8, 44.9 ± 36.5; 19.6 ± 20.8, 26.4 ± 31.4, 38.7 ± 27.3; 51.0 ± 30.0, 71.0 ± 36.8, 75.1 ± 20.9, respectively (P < 0.05 for all comparisons of patients with versus without ST-T changes). This study showed that Dp stress, with or without hypoperfusion, had a clear effect on myocyte electrophysiology, expressed by consistent ECG amplitude changes, detected by the EVC method. The EVC method did not distinguish between NS and patients in this clinical setting.

Changes in the initial slope of the QRS in ischemic patients and normal subjects undergoing scintigraphy with dipyridamole

The effect of dipyridamole (Dp) on the linear portion of the first major deflection of the QRS in human electrocardiograms (which we refer to as Fslope) was investigated in the context of myocardial perfusion imaging (MPI), in normal subjects (NS, n=19) and in patients with cardiovascular ischemia (as manifested by a positive MPI scan, n=53). In the majority of participants, Fslope decreased (84% of 19 NS and 77% of 53 patients, p=0.69). The decrease in Fslope was more pronounced in patients with ST-T deviation as compared to those without (32.6±24.5 vs. 22.4±23.1, p=0.24), and in patients vs. NS (24.9±23.5 vs. 19.6±23.4, p=0.44). A change in Fslope is a sensitive (but not specific) measure for detecting the effect of Dp on the myocardium in the setting of scintigraphy.

Anatomy of a meta-analysis: a critical review of "exercise echocardiography or exercise SPECT imaging? A meta-analysis of diagnostic test performance"

BACKGROUND

Accurate diagnosis of coronary heart disease has the potential to contribute substantially to cost-effective delivery of health services. Recent work by Fleischmann et al (JAMA 1998;280:913-20) represents an effort to summarize the accuracy of exercise echocardiography and exercise single photon emission computed tomography (SPECT).

METHODS AND RESULTS

A critique of the previous work was constructed, obtaining the 44 articles used. These articles were reviewed and summarized with established techniques for meta-analysis. The studies summarized by Fleischmann et al were found to be significantly heterogeneous (echocardiography and SPECT, both P<.001). In the SPECT cohort, combination of different radioisotopes and reading techniques, and inclusion of reports using experimental techniques, were sources of heterogeneity. In the echocardiography cohort, experimental techniques and an individual series were identified. When the sample was stratified for sources of heterogeneity, it was found that there was no significant difference in diagnostic accuracy between the echocardiography and SPECT techniques used in current clinical practice. Meta-regression with summary receiver operating characteristic curve techniques, after adjustment of the model for multicolinearity and outliers, revealed that there were no significant differences between SPECT as used in current clinical practice and echocardiography.

CONCLUSION

The report by Fleischmann et al contains serious flaws that limit its validity and generalizability.

Beat-to-beat QRS variability in the 12-lead ECG and the detection of coronary artery disease

The aim of this article was to study beat-to-beat QRS variability in patients with ischemia and old myocardial infarction using the 12-lead resting electrocardiogram (ECG). The variability analysis was based on beats that have been synchronized in time with an iterative alignment technique. The QRS variability was measured in patients submitted for myocardial scintigraphy. Those with a normal myocardial scintigraphy (called NO, n = 34, mean age 57 years, 23 women) were compared with a group with both myocardial infarction and exercise-induced ischemia (called ISCINF, n = 27, mean age 57 years, 5 women). The mean QRS variability was somewhat smaller in lead I in ISCINF than in NO, and there was no statistically significant difference in QRS variability among the groups in leads II, III, and V1-V6. Using a multivariate approach, the joint variability in leads I, II, II, and V1-V6 was used for calculating receiver operating characteristics based on a leave-one-out procedure. The sensitivity for detecting coronary artery disease was 75% at a specificity of 50%. It is concluded that beat-to-beat QRS variability in the 12-lead ECG does not discriminate between the presence and absence of coronary artery disease sufficiently well for clinical purposes.

Beat-to-beat QRS amplitude variability after acute myocardial infarction and coronary artery bypass grafting

Ischemic myocardial injury has been demonstrated to be associated with increased beat-to-beat electrical variability of the depolarization phase. This can be quantified by electrocardiographic (ECG) signal variance analysis, a technique that has proven its diagnostic value in the detection of coronary artery disease (CAD). This study evaluates QRS amplitude variability during a 6-month follow-up period in 73 patients with acute myocardial infarction (AMI) and in 56 patients subjected to coronary artery bypass grafting (CABG). The beat-to-beat QRS amplitude variability was quantified with variance electrocardiography. The equipment allows computerized time domain analysis of high-fidelity ECG signals from 24 leads, and the detected electrical heterogeneity is then expressed as a nondimensional index ranging from 0 to 150, with values >90 being indicative of ischemic myocardial involvement. One week after AMI 55% of the patients presented with an abnormal QRS variability index >90. A significant (p <0.01) increase in the index values occurred during the follow-up period, but only in the patients with an initial index <70. In the CABG group 44% of the patients had a preoperative QRS variability index >90. The values increased (p <0.05) in all patients after surgery; the increase was transient in patients with an initial index <70 (p <0.01). The results demonstrate that the myocardial injury in patients with CAD is often associated with increased electrical variability of myocardial depolarization. The QRS amplitude variability index can be used as a marker of such an injury, and analysis of its changes in the course of ischemic cardiac events may provide new insights into the dynamics of ischemic heart disease and the myocardial healing process.