Optimal electrocardiographic leads for detecting acute myocardial ischemia.

This study identifies the most sensitive electrocardiographic leads for monitoring ST-segment changes caused by acute coronary ischemia. The data set consisted of 120-lead electrocardiograms (ECGs) digitally recorded during balloon-inflation angioplasty in 3 groups of patients with single-vessel disease (left anterior descending [LAD], 32; right coronary artery [RCA], 36; left circumflex [LCx], 23). The ST deviation was measured in all recorded leads during baseline and ischemic states, and its difference between these 2 states (DeltaST) was calculated at 352 sites and plotted as DeltaST maps. The patients in each group were divided, by means of DeltaST criteria, into subgroups of "responders" and "nonresponders." Mean DeltaSTs for each group/subgroup were calculated and standardized by the corresponding standard deviation (SD); these values were plotted as mean DeltaST and t maps. Sites where extrema of DeltaST occurred most frequently were sought in bootstrap trials, performed in each group/subgroup. The results suggest that the optimal sites for the ischemia-sensitive leads are: V(3) (+) and just below V(8) (-) for LAD-related ischemia; the left iliac crest (+) and above V(3) at the third intercostal space (-) for RCA-related ischemia; and just below V(8) (+) and above V(2) at the third intercostal space (-) for LCx-related ischemia. Three "optimal" bipolar leads using these sites registered, in the responders from the LAD, RCA, and LCx groups, mean DeltaST (+/-SD) of 232 +/- 59, 245 +/- 96 and 158 +/- 91 microV, respectively; the corresponding t values were 15.14, 9.90, and 6.75. In the 12-lead ECG, only lead V(3) approached optimal DeltaST and t values for the LAD responders (187 +/- 61 microV; t = 11.75) and lead III for the RCA responders (191 +/- 76 microV; t = 9.73), but even these values were significantly suboptimal (P = 0.0011 and P = 0.0120, respectively). We found that the "optimal" bipolar leads can be derived, to an excellent approximation, from the 12 standard leads or from 3 EASI leads (with 3 electrodes at Frank's transverse level and 1 on the manubrium), by using precalculated regression coefficients. By means of bootstrap trials, we estimated the mean sensitivity (SE) and the mean positive predictive value (PPV) with which 3 "optimal" vessel-specific leads could identify ischemia related to the LAD, RCA, and LCx arteries, in the test set, as (SE/PPV) 94.7/92.8%, 78.7/80.9%, and 81.5/80.9%. A similar diagnostic performance can be achieved by vessel-specific leads derived from the 12-lead ECG (93.0/93.4%, 76.6/82.0%, and 82.7/77.1%) and, interestingly, from the EASI lead system (97.8/88.4%, 78.0/80.2%, and 76.8/83.2%). Thus, although the "optimal" bipolar leads for detecting ischemia related to each of the 3 coronary arteries were found to require sampling outside the 12-lead ECG, these leads can be derived from the full set of 12 standard leads or--for clinical monitoring applications--from the EASI lead system by using fewer electrodes at convenient locations.

Spatial features in body-surface potential maps can identify patients with a history of sustained ventricular tachycardia.

BACKGROUND: Regional disparities of ventricular primary-repolarization properties contribute to an electrophysiological substrate for arrhythmias. Such disparities can be assessed from body-surface distributions of ECG QRST areas. Our objective was to isolate and test those features of QRST-area distributions that would be suitable for identifying patients at risk for life-threatening ventricular arrhythmias. METHODS AND RESULTS: We recorded ECGs simultaneously from 120 leads during sinus rhythm for 204 patients taking no antiarrhythmic drugs: half had had sustained ventricular tachycardia (VT); the other half, a myocardial infarction but no history of VT. For each patient, we calculated the QRST area in each lead and, using Karhunen-Loeve (K-L) expansion, reduced these data to 16 coefficients (each relating to one spatial feature, an eigenvector, derived from the total set of 204 QRST-area maps). Using stepwise discriminant analysis, we selected feature subsets that best discriminated between the two groups, and we estimated by a bootstrap procedure using 1000 trials how these subsets would perform on a prospective patient population. The mean diagnostic performance of the classifier for 1000 randomly selected training sets (n = 102 in each, with both groups equally represented) increased monotonically with the number of features used for classification. The initial trend for the corresponding test sets (n = 102 in each) was the same but reversed when the number of features exceeded eight. For an optimal set of eight spatial features, the sensitivity and specificity of the classifier for detecting patients with VT in 1000 test sets were (mean +/- SD) 90.3 +/- 4.3% and 78.0 +/- 6.1%, and its positive and negative predictive accuracies were 80.7 +/- 4.2% and 89.2 +/- 4.2%, respectively. Use of QRS duration as a supplementary feature to eight K-L coefficients can, in the test sets, increase specificity to 80.9 +/- 5.4% and positive predictive accuracy to 82.8 +/- 3.9% compared with the results for the optimal number of eight K-L features alone. CONCLUSIONS: Multiple body-surface ECGs contain valuable spatial features that can identify the presence of an arrhythmogenic substrate in the myocardium of patients at risk for ventricular arrhythmias. Our results compare very favorably with those achieved by any other known test, invasive or noninvasive, for arrhythmogenicity.

Tropical diseases encountered in Canada: 1. Chagas' disease.

Chagas' disease, or South American trypanosomiasis, is an endemic South American disease now being seen in Canada in both acute and chronic forms. It is characterized by an initial parasitemia that elicits a brisk immune response. Evidence is mounting that the debilitating chronic form, which is characterized by cardiac and visceral organ failure, results from antigenic cross-reactivity between the parasite and the human host, which generates an aberrant, destructive, cell-mediated immune response. Diagnosis, treatment and potential areas for investigation are discussed.