Evaluation of serial QRS changes during acute inferior myocardial infarction using a QRS scoring system

Evaluation of Serial QRS Changes During Acute Inferior Myocardial Infarction Using a QRS Scoring System CHRISTINE I. ANDERSON, BA, DAVID G. HARRISON, MD, NANCY C. STACK, BA, NANCY B. HINDMAN, BA, RAYMOND E. IDEKER, MD, PhD, SEBASTIAN T. PALMERI, MD, RONALD H. SELVESTER, MD, and GALEN S. WAGNER, MD

The evolution of changes in the QRS complex during the initial 3 days after the onset of an initial inferior myocbrdial infarction (Ml) was studied in 82 consecutive patients. Each patient’s standard 12-lead electrocardiogram was assigned points (a QRS score) according to the absolute duration of the Q and R waves and the amplitude ratios of R-to-Q and R-to-S waves. This QRS score has been demonstrated to correlate (r = 0.74) with the anatomic extent of single inferior Ml. By this sytem, 43 patients (53 % of the study group) had an initial electrocardiogram that registered a score of 0 and developed QRS points only after admission. The QRS scores of

18 additional patients (22% of the study group) changed after admission. Forty-nine score changes were noted on Day 2 and 18 on Day, 3. All of these changes resulted in an increased QRS score. Alteration of the QRS complex during initial inferior MI evolves over 2 to 3 days in many patients. There is a distinct pattern to this evolution, which results in sequential increases in a QRS score based upon electrocardiographic indicators of the extent of myocardial necrosis. This QRS scoring system might be applied to evaluate clinically interventions aimed at limiting the extent of necrosis in patients with initial acute inferior MI.

The effects of myocardial infarction (MI) on the scalar electrocardiogram have been recognized almost since the advent of electrocardiography.lJ In the QRS complex, R waves diminish and Q waves develop.3-s The temporal course of these changes has not been completely elucidated. In Heart Disease, a 1982 textbook of cardiovascular medicine,7 QRS evolution is discussed only in reference to a hand-drawn diagram originally published by Lepeschkin in 1951.8 This diagram suggests that acute QRS changes are limited to the first day after the onset of MI. Other reports have described changes in the QRS complex occurring over several

days.gJO The present study examines the incidence, timing, and quantitative appearance of QRS changes during the first 3 days after the onset of initial, acute, inferior MI. A recently developed1’J2 and simplified13 QRS scoring system quantifies the QRS changes which occur as a result of MI. In the absence of other factors affecting the QRS complex, the magnitude of the QRS score correlates well with the size of both anterioP4 and inferior15 MI determined at autopsy. It also correlates with decreases in left ventricular ejection fraction that result from MI.ls The electrocardiograms of patients included in the present study were evaluated according to this QRS scoring system.

From the Division of Cardiology, Department of Medicine, and the Department of Pathology, Duke University Medical Center, Durham, North Carolina, and the Ranch0 Los Amigos campus of the University of Southern California, Downey, California. This study was supported in part by Contract HRA-230-76-0300 from the National Center of Health Services Research; by Research Grants HL-17670 and HL-00546 from the National Heart, Lung, and Blood Institute, the National Institutes of Health, Bethesda, Maryland, and by grants from the Prudential Insurance Company of America and the Kaiser Family Foundation. Manuscript received October 1, 1982; revised manuscript received February 25, 1983, accepted May 2, 1983. Address for reprints: Galen S. Wagner, MD, Box 31211, Duke University Medical Center, Durham, North Carolina 27713.

Methods Patient population: During an &year period, 271 patients with acute inferior MI were admitted to the Duke University Medical Center Coronary Care Unit. Twelve-lead electrocardiograms were performed in these patients on admission and at least once daily for the first 3 hospital days. Serum

enzymes, including creatine kinase (CK) and the nearly cardiac-specific isoenzyme CK-MB, were measured at varying intervals in all patients. The 82 patients included in this study met the following criteria: (1) no MI by history or electrocardiogram, (2) acute

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TABLE I

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ORS Scoring System Maximum Category

Criterion for IMI required for inclusion in study Additional criteria for IMI

Duration (ms)

Lead

II

v5

: cl Q R R R R Q

V6

QL30(1)

Vi v2

Criteria for apical involvement

Criteria for anterior and lateral involvement used for exclusion from this study

Points 1

Q r 30 (1)

aVF

aVF Criteria for posterior involvement

Amplitude Ratio (ms)

I aVL VI v2 v3 v4

5 z r r > I L 1

f; 50 40 50 40 60 50 30

[:I (3) (2) (2) (1) (2) (1) (1)

Q L 30 (1) QZ30(1) Any Q (1) AnyQorRI 10(l) Any Q or R _<20 (1) Q 1 20 (1)

2 R/Q I R/Q I

R/Q R/Q R/Q R/Q

1 (2) 2 (1)

4

R/S 1 1 (1)

3

R/S I or R/S or R/S or R/S or R/S R/Q 5 R/Q I

1.5 (1) I 1 (2) I 2 (1) I 1 (2) I 3 (1) 1 (1) l(1)

R/Q or R/S I R/Q or R/S I

0.5 (2) 1 (1)

3

MI = inferior myocardial infarction.

infarction as indicated by elevation of S-T segments and the appearance of CK-MB in the serum sample, (3) definite inferior infarction as marked by the appearance of a Q wave 130 ms in lead aVF, (4) the absence of a concurrent anterior or lateral infarct (Table I), and (5) records of daily, storable electrocardiograms for at least the first 3 hospital days. Electrocardiographic storability required the absence of left and right ventricular hypertrophy, ventricular tachycardia, paced rhythms, left or right bundle branch block, and left anterior or posterior fascicular block. Electrocardiogram and enzyme analysis: Electrocardiograms were recorded in the standard manner at 25 mm/s paper speed and 10 mm/mV amplitude. QRS complexes were measured with calipers and scored according to the system developed by Selvester et a11rJs and simplified’s and evaluated14J5 by Wagner, Ideker, and their co-workers. Points were assigned according to the duration of Q and R waves and the amplitude ratios of R-to-Q or R-to-S waves (Table I). The amplitude ratios of R-to-Q waves were considered in a given lead only when a Q-wave duration criterion was satisfied in that lead. QRS points achieved in leads II and aVF were attributed to inferior infarction; lead III is not considered in the QRS scoring system. When FL-wave duration and R/S amplitude ratios were sufficiently increased to be assigned points in leads Vr, Vz, or both, the adjacent posterior myocardium was considered to be involved in the infarct. Adjacent apical involvement was identified by points in leads V5 and Vs. Although multiple electrocardiograms were performed in a single day on some patients, only 1 per day was consistently available in the populati’on of this study. For that reason, only 1 QRS score per day could be applied in data analysis. When more than one electrocardiogram was available, the admission QRS score was used for !Day 1 and the highest daily score was used for Days 2 and 3. CK determinations were performed by the method of Rosalki17 using the modified reagent substrate prepared by Eskalab. CK isoenzymes were identified using the Corning method with agarose electrophoresis. Definitions: A QRS change refers to a score increase or decrease of L2 points compared with a previous observation. Minor fluctuations in R-wave and Q-wave dimensions resulted

in frequent, transient, l-point variations which were attributed to uncontrolled variables such as respiration, abdominal

distention, and patient position. When sequential l-point variations accrued to 2 points, thereby meeting the criterion for QRS change, the day on which the second point was observed was arbitrarily considered to be the day of QRS change. Day 1 began at the time of admission if CK-MB appeared in the serum sample within 24 hours. When no CK-MB appeared, the episode prompting admission was considered to have been unstable angina and Day 1 of the acute infarct was defined as beginning 12 hours before the first appearance of CK-MB. Day 1 always ended at 790 A.M. and every day thereafter

lasted 24 hours. Results

Eighty-two patients met the criteria for inclusion in this study, 72 of them with the QRS characteristics of inferior infarction alone. These patients’ QRS changes occurred only in leads II and aVF, and they consisted of abnormal Q-wave durations and Q- to R-wave amplitude ratios (Table I). In 10 patients, these signs of inferior infarction were accompanied by changes in the chest leads, which indicated involvement of adjacent apical (1 patient), posterior (4 patients), or both apical and posterior areas of the myocardium (5 patients) (Table I). Figure 1A illustrates the mean QRS scores observed during the first 3 hospital days. The 82 patients in the study had an average of 1.6 QRS points at admission, 3.8 points on Day 2, and 4.3 points on Day 3. Figure 1B provides the same information with the study group divided according to infarct location. The 10 patients with apical or posterior involvement or both had higher average QRS scores than those with only localized inferior infarcts (difference approximately 4 QRS points). QRS score changes during the first 3 hospital days are summarized in Table II. Forty-three patients (53% of

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QRS SCORING SYSTEM

82-

70 -

z 60> c): z

,

,1’

so-

0” :

40-

: 4 v

/

d 2

30-

20-

L I

J

Adn

Day2

Dar3

Adm.

1

Doy2

10 -

Day3

DAY OF OBSERVATION FIGURE 1. Daily mean QRS scores (* 1 standard deviation). A, all patients in the study (n = 82). B, patients with localized inferior infarction (solid lines; n = 72) compared with patients with apical or posterior involvement, or both, with inferior infarction (dashed lines; n = 10).

_.

mm.

I Dal

_Jl Dar3

DAY CHANGES OBSERVED

FIGURE 2. Days on which QRS changes were observed. Changes in relation to the admission QRS score are outlined; changes from the Day

2 score are shaded.

the study population) were admitted with a QRS score of 0. In 39 of these patients, the QRS score changed once after admission; in 4 it changed twice. The other 39 patients in the study were admitted with 11 QRS points. In 21 of them the QRS score did not change, in 16 it changed once, and in 2 it changed twice during the first 3 hospital days. All 61 changes during this period resulted in increased QRS scores. As Table III indicates, patients with adjacent apical or posterior infarct involvement, or both, were more

TABLE ii

QRS Score Changes During the First 3 Hospital Days Admission Score = 0 (n = 43) (53%)

Admission Score >0 (n = 39) (47%)

Total (n = 82)(100%)

likely than those with localized inferior infarcts to have been admitted with a QRS score >O. The number of patients in the apical or posterior groups, or both, was too small for consideration of statistical significance. The incidences of 0, 1, and 2 score changes were similar in the 2 groups of patients. The timing of QRS score changes is summarized in Figure 2. The electrocardiograms of 49 patients indicated a change in QRS score between admission and Day 2. By Day 3,12 more patients’ scores had changed from admission. Six of the patients whose QRS scores had changed by Day 2, changed a second time by Day 3. Electrocardiograms were available after Day 3 in a diminishing number of patients. Table IV shows that the incidence of change in QRS scores decreased markedly after Day 3, but a few changes in QRS scores were observed as late as Day 7. The score increases

No change Single change Two changes

TABLE IV TABLE Ill

QRS Changes In Patients With and Without Posterior or Apical involvement Inferior Infarct Only

Patients (n) Admission score = 0 Admission score >0 No score change Single score change Two score changes

41 (Z%)

4 (8%)

Frequency of QRS Score Changes

Posterior and/or Apical Involvement

Day

Patients With Data Available

3’

t;

2 (:ooqg)

: 6 7

::

2 (20%)

:z

Patients With Changes Observed (n)* 48 18 1

Patients With Data Available Observed to

Change(%) 59 22 r!l

-Y 3

;

Positive numbers indicate QRS score increases; negative numbers indicate QRS score decreases. l

August 1983

noted after Day 3 all f,ollowed a period of 2 to 6 days without a score change. One patient’s QRS score decreased on Day 6 from a higher score observed on Day 2. Discussion This study demonstrates that (1) changes in the QRS complex after the onset of MI often evolve over a longer period than that previously described, and (2) these changes follow a pattern. More than half of the patients studied were admitted1 before the development of abnormal Q waves. After admission, QRS changes were observed on Day 2 or :3 in most patients. All of the 61 observed changes during the first 3 days and 4 of the 5 late changes yielded increased QRS scores. The appearance of t:he QRS complex after an infarct varies with the location,18 the transmural depth,8 and the subendocardial areal of the necrotic myocardium. The QRS scoring system devised by Selvester et a111,12 and simplified by Wagner et all3 quantifies the effects of these variables on the electrocardiogram. This scoring system correlates well with the size of anterior and inferior infarcts measured at autopsy when other factors such as previous infarcts, conduction disturbances, and ventricular hypertrop:hy are absent.14p15 In the present stud.y, the QRS scoring system was used to analyze daily electrocardiograms of patients with acute inferior infarcts. The difference of at least 2 QRS points required for diagnosing a score change exceeds the observer variability previously documented in this 1aboratory.l” B’ecause all the observed changes during the first 3 days resulted in increased scores, and because the QRS score has been correlated with anatomic infarct size, it is likely that the observed increases indicate increasing necrosis. Other explanations for QRS score changes cannot be excluded. One mechanism might be “infarct expansion,” a process described by Hutchins and Bulkley,2e in which the infarcted myocardial wall stretches and thins. This process potentially increases the proportion of infarcted myocardium exposed to surface electrodes, possibly altering the QRS complex. Such expansion, however, has been considered to become significant only by the fourth to fifth day after the onset of infarction. Almost all of the QRS changes observed in this study were noted during the second or third days. Moreover, infarct expansion has been observed much more frequently in patients with anterior infarcts; only 19% of the patients in the series of Hutchins and BulkleyZo had inferior infarcts. On the basis of timing and location, therefore, it seems unlikely that many of the QRS changes observed in the present. study resulted from infarct expansion. Another possible cause of QRS change may be found in experimental studies which have identified increased extravascular fluid in infarcted myocardium.21-23 Reimer and Jennings21 have demonstrated in the canine model that this fluid can cause a 25% increase in infarct weight after 4 days. The fluid disappears after 28 days. Extravascular hemorrhage and edema might therefore have caused temporary QRS score increases during Days 5 to 7 of the present study, but very few changes

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were observed after Day 3. Extravascular fluid, like infarct expansion, occurs too late to correspond to the major period of QRS score change observed in the present study. Late electrocardiograms were unavailable, so resolution of QRS changes after 28 days could not be determined. A concurrent study in our laboratory, however, has documented minimal regression in QRS score during the initial 2 months after acute nonoperative infarcts.24 Ganz et a1,25Beller et a1,26and others27,28 have performed experimental and clinical studies describing the sudden development of Q waves after myocardial reperfusion. These studies have shown that S-T segments diminish rapidly upon reperfusion, and Q waves concurrently increase. The investigators describing these events have suggested that Q waves may be “masked” by an injury current and “unmasked” by its resolution. In the present retrospective study, the relative timing of QRS change and S-T segment resolution could not be determined because of infrequent sampling. In experimental studies, however, Q waves have been shown to develop before injury currents resolve.29 In addition, Q waves produced by coronary arterial occlusion were not diminished when reocclusion produced recurrent S-T segment elevation. 3oOn the basis of these findings, it seems unlikely that QRS score changes result from injury current resolution. The significance of QRS changes during the days after the onset of infarction remains uncertain. The changes probably reflect ongoing necrosis. Experimental studies in the canine model have yielded results which substantiate this possibility. A border zone of viable but ischemic tissue has been shown to exist within the perfusion field of an occluded vesse1.31-34Lee et al35 reported that this border zone may be of substantial size in man. Its source of perfusion is probably quite tenuous, being either collateral blood flow or flow through a highly stenosed epicardial vessel. In either circumstance, small disturbances in hemodynamic parameters may result in progressive myocardial necrosis during the early days after the onset of infarction. Unfavorable alterations in hemodynamic parameters may result in necrosis several days after the onset of infarction. If ongoing necrosis is the determining factor in QRS score changes, such as those described in the present study, the infarction process may not be limited to a 24-hour period but may continue for 2 to 3 days in a significant proportion of patients. Moreover, among patients who are admitted with QRS scores of 0, the myocardium may not have undergone any necrosis before admission. Interventions initiated later than the first few hours after the onset of symptoms may have a greater potential for limiting infarct size than previously considered. Further investigation is required to determine the period in which such interventions can be effective. The standard 12-lead electrocardiogram may provide an important tool for evaluating interventions intended to limit infarct size, possibly with the goal of maintaining the minimal QRS score observed at the time of hospital admission. Acknowledgment: tance of Gail McKinnis

The authors acknowledge the assisin preparation

of the manuscript.

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