Spatial variation of QT intervals in normal persons and patients with acute myocardial infarction

It is now well established that the vulnerability of the ventricular myocardium to repetitive dysrhythm increases in the presence of greater than normal disparity local recovery times. Local recovery is reflected in the electrocardiographic waveform as an area of the ventricular deflection (QRST time integral), and thus disparate ventricular recovery may be manifested in the body surface distribution of this quality. To assess this possibility, we obtained simultaneous 120-lead electrocardiograms from both the anterior and posterior torso in 140 subjects (ages 8 to 75) grouped as follows: group A, 97 normal subjects; group B, 16 patients resuscitated from ventricular fibrillation or sustained ventricular tachycardia; and group C, 27 patients 6 to 12 months after myocardial infarction but without clinically significant arrhythmia. In each subject, the QRST integral was evaluated for each lead and isointegral contour maps were plotted. A score was assigned to each map, based on the number of extrema; each maximum or minimum scored one point, with the exception of simultaneously occurring anterior and posterior minima on the right shoulder (frequently occurring in normal subjects), which scored together only one point. All but one group A subject had dipolar QRST integral maps (mean +/- SD score 2.11 +/- 0.2). Conversely, 10 of 16 (62.5%) group B patients had scores of 3 or more (mean 3.16 +/- 1.08; p less than .01 vs group A). Group C patients had intermediate values, with eight of 27 (29.6%) scoring 3 or more (mean 2.46 +/- 83); this was less than in group B (p less than .01), but more (p less than .05) than in group A.(ABSTRACT TRUNCATED AT 250 WORDS)

Vulnerability to ventricular arrhythmia: assessment by mapping of body surface potential.

Physiologic bases for anterior ST segment depression in patients with acute inferior wall myocardial infarction.

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.

Spatial Features in Body-Surface Potential Maps Can Identify Patients With a History of Sustained Ventricular Tachycardia

To determine the depolarization and repolarization time-integral patterns in patients with first acute inferior myocardial infarction, we acquired body surface potential maps in 28 men and eight women, ages 36–76 years, a mean of 76 hours after the onset of symptoms. Based on technetium-99m pyrophosphate myocardial scans, patients were divided into two groups. Group 1 included 22 patients with scintigraphic activity limited to the left ventricle who were considered to have exclusive left ventricular infarction, and group 2 included 14 patients with scintigraphic activity involving the right ventricle in addition to the left ventricle, considered to have both left and right ventricular infarction.Isointegral plots of the first 50% of the QRS complex (Q zone) were characterized by negative areas over the inferior torso with concomitant extension of positive areas to the superior precordium. Group 2 patients had greater leftward and superior extension of the negative inferior distributions than group 1 patients. Subtraction of the mean Q-zone map of group 1 patients from that of group 2 patients confirmed a mean area of difference over the right anterior-inferior torso. The average Q-zone integral value within this area of difference was 5.9 + 7.2, uVsec (±+ SD) for group 1 patients compared with 1.7 + 5.2, V-sec for group 2 patients (p < 0.05). ST-segment isointegral maps revealed positive inferior distributions in all subjects; however, 29 patients also had abnormal negative ST-segment distributions over the precordium. The area of negative precordial values in group 2 patients extended further rightward and inferiorly compared with group 1 patients. There were two large areas of difference seen on subtraction: one over the precordium, in which the mean ST-segment integral value for group 1 patients was -0.6 + 3.8 AV-sec, compared with –3.2 3.2 tkVNsec for group 2 patients (p < 0.025), and another over the inferior torso, where the mean value for group 1 was 1.2 ± 1.6, uV-sec, compared with 3.3 ± 3.5, xV sec for group 2 (p < 0.05).Thus, in acute inferior infarction, there is a characteristic distribution of negative Q-zone and positive ST-segment time integrals over the inferior torso and a reciprocal development of positive Q-zone and negative ST-segment integrals over the anterior-superior torso. Patients with right ventricular involvement, however, have spatial and quantitative abnormalities of both depolarization and repolarization that distinguish them from patients with infarction limited to the left ventricle.

Body surface electrocardiographic mapping in inferior myocardial infarction. Manifestation of left and right ventricular involvement.

Although ST-segment abnormalities during acute myocardial infarction are clinically important, the total thoracic distribution of these repolarization potentials has not been reported To provide this information, 24 patients with acute myocardial infarction were studied Isopotential body surface maps were constructed from potentials sensed by 150 anterior and posterior electrodes Patterns from 12 patients with anterior lesions demonstrated the appearance of repolarization potentials 213 +/- 46 msec before the end of the QRS complex During the ST segment, potential distributions were characterized by a single anterior maximum that remained fixed in location but increased in intensity as repolarization progressed Distributions in the remaining subjects with inferior lesions were analogously characterized by (1) the onset of repolarization 346 +/- 124 msec before termination of the QRS complex and (2) a single anterior minimum located on the left anterior superior thorax, with positive potentials distributed around the lower thoracic margins These data suggest that electrocardiographic changes after acute myocardial infarction include (1) marked overlap between activation and recovery patterns and (2) isopotential surface patterns with relatively simple topographic configurations, such as expected of a single-dipole equivalent cardiac generator

D M Mirvis

Papers

Body surface distributions of repolarization forces during acute myocardial infarction. I. Isopotential and isoarea mapping.