Evaluation of a QRS scoring system for estimating myocardial infarct size☆IV. Correlation with quantitative anatomic findings for posterolateral infarcts

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  Evaluation of a QRS scoring system for estimating myocardial infarct size☆IV. Correlation with quantitative anatomic findings for posterolateral infarcts
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   valuation of a QRS Scoring System for stimating Myocardial Infarct Size III Correlation With Quantitative Anatomic Findings for Inferior Infarcts STEVEN F. ROARK MD RAYMOND E. IDEKER MD PhD GALEN S. WAGNER MD DANIEL R. ALONSO MD SANFORD P. BISHOP DVM PhD COLIN M. BLOOR MD DEAN A. BRAMLET MD JESSE E. EDWARDS MD JOHN T. FALLON MD PhD GEOFFERY J. GOTTLIEB MD DONALD B. HACKEL MD HARRY R. PHILLIPS MD KEITH A. REIMER MD PhD WILLIAM J. ROGERS MD WAYNE K. RUTH MD ROBERT M. SAVAGE MD RICHARD D. WHITE MD and RONALD H. SELVESTER MD This study evaluated by quantitative autopsy cor- relation a previously developed scoring system for estimating the size of myocardial infarcts based on the QRS complex of the electrocardiogram. This system was tested using electrocardiograms from patients with infarcts shown by autopsy to predominate in the inferior third of the left ventricle. The study was limited to patients whose electro- cardiogram did not indicate left or right ventricular hypertrophy, left or right bundle branch block, or left anterior or posterior fascicular block. Thirty-one pa- tients from 6 medical centers met these criteria. In the electrocardiogram of 28 of the 31 patients (90 ), lead aVF exhibited a Q wave of at least 30 ms. The correlation coefficient between the total QRS score and the percent infarction of the left ventricle was 0.74. In patients without confounding factors in the electrocardiogram and with single infarcts, the electrocardiogram provides a marker for infarcts in the inferior third of the left ventricle and a quantitative QRS scoring system provides an es- timate of infarct size. While several new, sophisticated methods are poten- tially capable of determining the size of myocardial in- farcts, it is still important to evaluate the standard 12-lead electrocardiogram because it is readily available, inexpensive, and noninvasive. Although changes in the QRS complex are recognized for their ability to docu- ment the presence of various locations of myocardial infarcts, relatively little has been determined about their ability to indicate infarct size. Recent studies from From the Departments of Pathology and Medicine at Duke University Medical Center Durham North Carolina; University of Alabama Medical Center Birmingham Alabama; Cornell University Medical College New York New York; University of California at San Diego School of Med- icine La Jolla California; Massachusetts General Hospital Boston Massachusetts; United Hospitals of St. Paul St Paul Minnesota; and the Department of Medicine at University of Southern California Rancho Los Amigos Campus Downey California. This study was supported in part by Contract PH-43-NHLI-67-1440 by Research Grants HI_-17670 HL-17667 HL-17682 HL-11310 HL-14688 HL-17532 HL-00546 MO-RROOO-13 and 5R01-HL05694 from the National Heart Lung and Blood Institute the National Institutes of Health Bethesda Maryland and by Contract HRA-230-76-0300 from the National Center for Health Research and the National Center for Health Care Technology Hyattsville Maryland. Manuscript received January 12 1982; revised manuscript received September 23 1982; accepted October 18 1982. Address for reprints: Raymond E. Ideker MD Box 3140 Duke Uni- versity Medical Center Durham North Carolina 27710. a multicenter collaboration have demonstrated that a simplified version of a previously developed scoring system based on quantitative aspects of the QRS com- plex attains a correlation of 0.80 with the size of anato- mically documented anterior infarcts. 1,~ Previous studies have suggested that the electrocardiogram might be less capable of defining infarcts in the other principal locations in which they occur, that is, inferior and pos- terolateral aspects of the left ventricle. 3 It is important that the capability of any method for indication of in- farct size be evaluated for all infarct locations. Ac- cordingly, this study was performed to determine the correlation between the simplified version of the QRS scoring system and anatomically documented inferior myocardial infarcts. Methods Criteria for inclusion Deceased patients from the Mas sachusetts General Hospital, Cornell University Medical College, the University of Alabama at Birmingham, the Uni- versity of California at San Diego, United Hospitals of St. Paul, and Duke University Medical Center were included i~ the study if they met the following criteria: 1) quantitative postmortem examination revealed a myocardial infarct pri- marily in the inferior third of the left ventricle Fig. 1). It was required that this infarct either be the only infarct present or 38  February 1983 THE AMERICAN JOURNAL OF CARDIOLOGY Volume 51 383 FIGURE 1. Division of the left ventricle into thirds A) and octants B). This study includes all cases in which the inferior third of the left ventricle had the largest percent infarction. C = centroid of the outline of the left ventricular epicardium and right septal border; MS = point in the mid-septum halfway between the anterior and posterior endocardial in- sertions of the right ventricle into the septum. B, the dashed line MS to C bisects octant 1. A. that it be fibrotic and clearly distinguished from a second and fatal acute infarct. In this latter instance only the fibrotic infarct was considered for this study. (2) An electrocardiogram was available that was taken when only the infarct considered in the study was present. This electrocardiogram could not exhibit left or right ventricular hypertrophy, left or right bundle branch block, or left anterior or posterior fascicular block as defined by the IBM program for electrocardiographic analysis. 4 The electrocardiogram must have been taken within 1 year of the paient s death. The final available electrocardi- ogram was used for the study. Quantitative anatomic evaluation: The hearts, all ob- tained between 1969 and 1979, were initially dissected by similar protocols at the 6 institutions. The ventricles were cut transverse to the long axis into 5 to 7 slices of approximately equal thickness. Coronary dominance, amount of athero- sclerotic coronary arterial disease, and transmural extent of infarction were determined as previously described. 2 To be considered transmural, an infarct had to extend from the endocardium to involve at least 1 cm of the epicardial sur- face. 2 The size of the infarct was quantified by computer-assisted planimetry as described previously. 5 Infarct size excludes viable muscle within the infarcted region. For infarcts at least I week old at the time of the patient s death, the method in- cludes a correction for estimated wall thinning caused by the infarct. No correction was made for wall thinning in infarcts <1 week old because such thinning was assumed to be caused by expansion and stretching of the infarcted tissue 6 rather than by phagocytosis and scar contraction. The dominant location of the infarct was determined by COmparing the percent infarction of the anterior, posterolat- eral, and inferior thirds of the left ventricle (Fig. 1A). This study includes all hearts in which the greatest percent in- farction was in the inferior third. The percent infarction for each of 24 sectors of the left ventricle was also calculated. The sectors divide the heart into octants in the transverse plane (Fig. 1B) for basal, middle, and apical thirds of the left ven- tricle as described in the second study in this series. 2 Electrocardiographic evaluation: The point score to ~i[~.raate infarct size developed by Selvester et al 7-9 and sim- ned and modified by Wagner et al 1 (Table I) was deter- mined for each electrocardiogram. Points are awarded for duration of Q or R waves and for R to Q and R to S ratios from 10 of the 12 standard leads. R to Q ratio points may only be awarded if Q-wave duration criteria have been satisfied for that lead. However, R to S ratio points may be awarded without consideration of any other criteria for that lead. If there are multiple criteria of a single type (such as Q-wave duration) for a lead, the points achieved by the maximal sat- isfied criterion are awarded. Results Thirty-one patients met the criteria for inclusion in the study. Twenty-seven were men (mean age 56) and 4 were women (mean age 65). Eighteen of the infarcts were >30 days old when the patient died, 6 between 7 and 30 days old, and 7 were <7 days old. Of the 18 pa- tients with infarcts >30 days old, 10 had a second, fatal infarct. TABLE I Simplified QRS Scoring System Maximal Lead Duration ms) Amplitude Ratios Points I Q >30 1) R/Q <1 1) 2 II e >40 2) e >30 1) 2 aVL Q >30 1) R/Q <1 1) 2 aVF Q >50 3) R/Q -<1 2) Q >40 2) Q >30 1) R/Q <2 1) 5 V~ Any Q 1) R >50 2) R >40 1) R/S >1 1) 4 V2 Any Q or R <10 1) R >60 2) R >50 1) R/S >1.5 1) 4 V3 Any Q or R <20 1) 1 V4 Q >20 1) R/Q or R/S <0.5 2) R/Q or R/S <1 1) 3 V5 Q >30 1) R/Q or R/S <1 2) R/Q or R/S <2 1) 3 V6 Q >30 1) R/Q or R/S <1 2) R/Q or R/S <3 1) 3   84 QRS SCORING SYSTEM FOR ESTIM TING MYOC RDI L INF RCT SIZE TABLE II Transmural Extent of Infarcts Number of Hearts Level of LV TM SEn SEp IM Zero Base 12 19 0 0 0 Middle 17 12 1 1 0 Apex 4 12 5 6 4 IM = intramural; LV = left ventricle; SEn = subendocardial; SEp -- subepicardial; TM = transmural; zero = no infarct in that level. Anatomic evaluation The mean total heart weight was 462 g. The right coronary artery was dominant in 29 hearts. Maximal narrowing in the dominant coronary artery was 90 to 100% in all cases. The percentage of the left ventricle that was infarcted ranged from 4 to 41% (mean 15). Eighteen hearts had transmural involvement in at least I level of the left ventricle. Sixteen of 18 infarcts involving >10% of the left ventricle had transmural involvement in at least 1 level. Eleven of 13 infarcts involving < 10% of the left ventricle had no levels with transmural involvement. Infarcts were more often transmural in the basal and middle thirds than in the apical third (Table II). Eleven of the 13 (85%) non- transmural infarcts in the basal and middle thirds were subendocardial. In the apical third, however, 11 of the 23 (48%) nontransmural infarcts were intramural or subepicardial. Four hearts had no apical involve- ment. The inferior free wall (octant 7) was the most com- monly involved area with the basal and middle levels containing infarct in 100 and 97% of the hearts, re- spectively (Table III). The infarcts involved the inferior aspect of the septum and immediately adjacent free wall (octant 8) in 94% of the hearts. Involvement of the midseptum (octant 1) was uncommon, with only 2 in- farcts reaching all 3 levels. Many infarcts extended laterally into octant 6 but fewer infarcts extended more laterally into the middle of the free wall (octant 5) (Table III). In contrast to anterior infarcts, 2 no infarct predominating in the inferior third had circumferential apical involvement. Electrocardiographic evaluation: Q waves in leads II, III, and aVF are commonly considered indicative of inferior infarcts. Table IV indicates the Q wave dura- tions observed in these 3 leads in the study patients. Q waves of >30 ms were present in leads II, aVF, and III in 20, 28, and 22 electrocardiogramg, respectively. Forty ms or greater Q waves were present in leads II, aVF, and III in 3, 19, and 14 electrocardiograms, respectively. Thus, 28 of the 31 patients (90%) had a 30 ms Q wave in at least 1 inferiorly oriented electrocardiogram lead, while only 19(61%) had a 40 ms Q wave in at least 1 of these leads. The mean QRS score for the 31 patients was 5 points, with a range of 0 to 11 (Fig. 2). All but 1 of the patients received points and 26 patients (84%) received ~2 points. Of the total of 150 points received by all 31 pa- tients, 119 points (80%) were gained from leads aVF and II. Three patients had no QRS points from either leads aVF or II. One of these patients had no points and 2 had only 1 point, contributed by a Q wave in lead V1. The anatomic size of these infarcts varied from 4 to 10% of the left ventricle and the 2 with a Q wave in V1 did not have more anteroseptally located infarcts. Five of the 31 patients (16%) received points for in- creased duration or amplitude of the R wave in leads V1 or V2 (Fig. 2) which has been reported to indicate true posterior infarction, 1°-12 Ten other patients (32%) received points for a Q wave in lead V1 or a diminished R wave in leads V2 or Va, which have been reported to indicate anteroseptal infarction. 13 Eleven of the 31 patients (35%) met criteria for points in leads V4, V5, or V6 which have been reported to indicate apical infarc- tion. 1,14,15 None of the patients met criteria for points from leads I or aVL, which have been reported to indi- cate high lateral infarction. 14,15 Comparison of antomic and electrocardiographic estimated infarct size A diagram of the location of the infarct and the electrocardiogram is shown for 1 rep- resentative patient in Figure 3. The percent infarction of the left ventricle versus the total point score is plotted for all patients in Figure 4. For the 26 patients in whom the electrocardiograms scored >2 points, the mean in- farct occupied 17% of the left ventricle (range 4 to 41%). For the 5 patients with electrocardiogram scores of < 2 points, the mean infarct occupied 7% of the left ventricle (range 4 to 10%). The correlation coefficient between the number of points and infarct size was 0.74. The slope of the re- gression line was 2.5, indicating that each QRS point represents infarction of 2.5% of the left ventricle. The standard error of the estimate was 6.6%. Twenty-seven of the 31 hearts contained infarcts in the apical third of the left ventricle, although only 11 electrocardiograms received points for leads V4 to ¥~ (Fig. 2). In many patients, however, the amount of apical infarction was small. In the 11 patients receiving points in leads V4 to V6, the mean infarct extent in the apical third of the left ventricle was 12%, significantly greater TABLE III Number and Percentage of Hearts With Infarction of Each Octant 2 3 4 5 6 7 8 Base 9 0 0 3 15 26 31 29 (29 ) (0 ) (0 ) (10 ) (48 ) (84 ) (100 ) (94 ) Middle 5 0 0 1 10 24 30 29 (16 ) (0 ) (0 ) (3 ) (32 ) (77 ) (97 ) (94 ) Apex 3 0 0 0 6 15 24 19 (10 ) (0 ) (0 ) (0 ) (19 ) (46 ) (77 ) (61 °/o~.~-)  February 1983 THE AMERICAN JOURNAL OF CARDIOLOGY Volume 51 385 (p -- 0.04) than the mean infarct extent of 6 in the 20 patients without QRS points in leads V~ to V6. Eighteen of the 31 hearts contained infarcts which extended laterally (octant 5). Only 5 electrocardiograms received points for increased R-wave duration in lead V1 or V2. The mean percent infarction of octant 5 in these hearts was 32 , significantly greater (p = 0.005) TABLE iV incidence of Q Waves in Inferior Leads Q Wave Lead Duration II aVF III No Q 4 2 1 >0 but <30 ms 7 1 8 >30 but <40 ms 17 9 8 >40 ms 3 19 14 t aVL aVF v2 v3 v4 v5 v6 _ > or oo o S ooo; oo- S ; S -- At C~ AI AI I A I AI AI ^1 AI ~ VI ^1 Vl ^U ~ q.~ ^1 ~ ~ ^1 ~1 ~ O r I ; • • • 5 • 22 I 2 • • • • • • 8 • 41 I 3 • • • 4 11 I 4 • • 3 7 I 5 • • • • • • • • 11 38 I 6 • • • 3 14 I 7 • • • 4 18 I 8 • • • • 5 10 I 9 • • • • • 8 16 11 • • • • • • 1 26 111 • • • go • • 6 1 112 • • • 3 9 113 • • • • • 21 I 14 • • • 4 16 115 • • • • • 7 11 116 • • • 3 17 I 17 • • • 5 4 I 18 • • • 5 13 I 19 • oo 4 • 9 I 2 • • • • • • 1 • 37 I 21 • • 3 1 i 22 • • • 6 • 13 I 23 • 1 5 I 24 • • • • 8 • 22 t25 • • oo • 5 • 9 I 26 • • • 4 12 127 • 1 4 I 28 4 23 129 0 10 I 3 • 1 1 I 31 • I 4 PATIENTo 317 6139142 .51 11 04053 14 40003 1000250013 i OTAL FIGURE 2. QRS point scores for each patient. Anatomically estimated infarct size is at the right of the figure. MI = myocardial infarct; LV = left ventricle.  386 QRS SCORING SYSTEM FOR ESTIMATING MYOCARDIAL INFARCT SIZE than the mean infarct size of 5 in the 26 patients not receiving such points. Eleven of the 31 hearts contained infarct in > 1 level of octant 1 within the mid-septum, although only 8 electrocardiograms received points for Q waves or di- minished R waves in leads V1 to V3. The amount of the middle third of octant 1 infarcted in the 8 patients re- ceiving points for Q waves or diminished R waves in leads Vt to V3 (mean infarction of 0 ) was not signifi- cantly greater than the mean amount infarcted for the 23 patients not receiving these points (mean infarction of 4 ). iscussion Terminology of infarct location The inferior as- pect of the left ventricle is the site of approximately 40 of all myocardial infarcts. This incidence is similar to that for anterior infarcts, but both the anatomic location and electrocardiographic changes for inferior infarcts are less well understood than for anterior infarcts. The term inferior or di phr gm tic is applied when the frontal plane leads II, III, and aVF are involved, and the term true posterior is applied when the right precordial leads are involved. However, it has not been clear pre- - -4-4--I-i4 1-- J , ' I L ~_ :11 , , r VR~ V1 ' I 't :il ~ii' V2 ~~ 7' ~., t J t i t I i AVF ~11 E ~. =t ~ii 11 :i ' .u ,i ~ ' L FIGURE 3. Myocardial infarct (MI) location and electrocardiogram for Patient 22. The infarct was acute, solid, and occupied 13% of the left ventricle. Six QRS points were awarded; Q >50 ms and R/Q >1 in lead aVF, and a Q >30 ms in lead I1.
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