Electrocardiographic tall R waves in the right precordial leads

ElectrocardiographicTall R Waves in the Right PrecordialLeads Comparison of Recently Proposed ECG and VCG Criteria for Distinguishing Posterolateral Myocardial Infarction From Prominent Anterior Forces in Normal Subjects

Michael J. Zema, MD

Abstract: Electrocardiographic tall R waves in the right precordial leads may be present in patients with posterior myocardial infarction, right ventricular hypertrophy, various conduction disturbances, and some forms of cardiomyopathy and in clinically otherwise normal subjects with prominent anterior electromotive forces. Clinical uncertainty most often arises in distinguishing possible prior posterolateral myocardial infarction (PMI) from the unusual normal variant (PAF). The ECGs and VCGs of 15 subjects with posterolateral infarction were compared with tracings from 12 subjects with no evidence of cardiac disease, all individuals demonstrating tall R waves (R/S > 1.O in Vr and/or V,) in the right precordial leads on surface ECG. By standard ECG, the infarction group was characterized by taller T waves in leads V, and Vl, shorter T waves in V6, greater T2-T6 index, and a more negative two variable function as described by Nestico. By VCG, the infarction group was characterized by a more anteriorly oriented T loop, more leftward maximal frontal plane QRS vector and a lower calculated -45”lab. as described by Suzuki. An algorithm was proposed that permitted proper classification (PAF vs. PMI) based on ECG criteria in 75% of subjects with 90% accuracy. This compared favorably with performance of the Frank vectorcardiogram, including using more recently proposed criteria. Routine use of the VCG, therefore, in this clinical setting may no longer be justified. Key words: posterolateral myocardial infarction, prominent anterior electromotive forces, anterior conduction delay, left septal fascicular block.

The differential diagnosis of a tall R wave in the right precordial leads remains an important problem in clinical electrocardiography. The ECG pattern may

be present in subjects with right ventricular hypertrophy (RVH),’ hypertrophic cardiomyopathy,2 Wolff-Parkinson-White preexcitation,3-5 Duchenne’s progressive muscular dystrophy,” right ventricular infarction,’ and true poste;olateral left ventricular infarction (PMI).‘-lo However, some in-

From the Department of Medicine. Division of Cardiology, Brookhaven Memorial Hospital Medical Center, Patchogue, New York.

Reprint requests: Michael J. Zema, MD, 101 Hospital Road, Patchogue, NY 11772.

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APICAL

Fig. 1. Subdivisions

of the heart as recommended in the Report of the Committee on Nomenclature of Myocardial Wall Segments” by the International Society of Computerized Electrocardiography. This 12 segment left ventricular (LV) subdivision is based on the Ideker 24 LV segment subdivision and consists of eight circumferential (octant) subdivisions, starting with the center of the septum in serial bread loaf cross-sections of the heart as seen in the lower right of the figure. Each two adjacent octants are combined to provide a quadrant subdivision consisting of four walls: anteroseptal, anterosuperior, posterolateral, and inferior. The LV is further subdivided into three regions from the apex to me base-apical, middle, and basal-by passing three planes at right angles to the internal long axis of the LV in such a way as to divide it into three equal parts that produce the final 12 segments of approximately equal volume shown.

similarly

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anterior QRS electromotive difficulty arises largely in distinguishing patients with PMI from otherwise normal subjects with PAF, since RVH and other distinct causes can frequently be identified by history and examination. Although a vectorcardiogram (VCG) may be performed to aid in diagnosis, l1 its predictive value in this situation remains unclear.“-I5 Radionuclide techniques, such as thallium perfusion, scintigraphy, or multiple-view radionuclide cineangiography, will often establish the diagnosis. Such testing, however, requires sophisticated equipment and highly trained technical personnel and may be quite costly if indiscriminantly applied to all subjects with ECG tall R waves in the right precordial leads. The purpose of this study was twofold: ( 1) to assess in a validation “test” group of subjects whether

forces (PAF) . Clinical

recently proposed ECG and VCG criteria for PM1 are effective in the group of patients with electrocardiographic tall R waves in the right precordial leads, and (2) to assess whether performance of the Frank vectorcardiogram in these subjects, including using the most recently proposed criteria, offers any diagnostic advantage over the standard electrocardiogram with regard to sensitivity, specificity, or predictive value for PM1 (ISCE segments lo-12 of Fig. l).”

Materials

and Methods

Patient Selection Data were reviewed from patients seen at the Brookhaven Memorial Hospital Medical Center outpatient Cardiology Department during the period

Tall Right Precordial 19831986, in whom at least two ECGs had revealed a tall R wave in the right precordial leads (defined as R/S > 1.0 in V1 and/or V,) and in whom it was thought clinically necessary to exclude the presence of coronary artery disease. This was not a study to distinguish PM1 from obvious right ventricular hypertrophy. Patients who had possible right ventricular hypertrophy based upon history, physical examination, chest radiograph, echocardiogram, or a measured pulmonary arterial peak pressure of 40 mm Hg or greater were excluded from analysis. All patients with classic intraventricular conduction defects, including Wolff-Parkinson-White preexcitation, ’ 6,l7 also were excluded. Patients with hypertrophic cardiomyopathy were excluded by previously suggested M mode1”i9 and two-dimensional echocardiographic2’ criteria. No patient had clinical or enzymatic evidence of Duchemre’s progressive muscular dystrophy. The data were derived from consecutive patients, except in two cases where a degree of ambiguity still remained regarding the correct diagnosis (PM1 or PAF) even after appropriate studies had been performed. Such cases were deleted a priori and the detailed ECG and VCG statistical analysis performed subsequently. The final study population consisted of 2 1 men and 6 women aged 17-79 years. Fifteen had PM1 and 12 had PAF with no evidence of previous myocardial infarction.

PMI Group The terminology used to describe segments of left ventricular myocardium is taken from the Report of the Committee on Nomenclature of Myocardial Wall

R Waves

l

Zema

149

Segments of the International Society of Computerized Electrocardiography (ISCE).” Thirteen men and two women with a history of typical angina pectoris and/or clinical myocardial infarction were selected. Ten subjects with a history of previous myocardial infarction had hospitalization records available demonstrating abnormal CK isoenzyme elevation accompanied by ECG evolution of PM1 consisting of initial ST-segment depression followed subsequently by development of tall R and peaked T waves in precordial leads V1 an&or V2. Three of the remaining five patients had a history compatible with remote myocardial infarction (see Table 1). Ten subjects had thallium-201 perfusion scintigraphy, and nine demonstrated abnormalities. Scintigraphic defects, either at rest or upon redistribution after exercise, were noted in the posterolateral (ISCE segments 1 O-12) left ventricular wall on the 45” left anterior oblique and/or left lateral views in seven. Defects were also seen in two subjects in the area of the inferior (ISCE segments 7-9) left ventricular wall on the anterior view and in six subjects in the area of apex (ISCE segments 4, 7, 10) on the anterior and left lateral views. No patient had scintigraphic defects confined to the inferior (ISCE segments 7-9) left ventricular wall alone. Only a single patient (patient 14) had a scintigraphic defect confined to the area of the left ventricular apex (ISCE segments 4, 7, 10) alone. Eleven subjects had radionuclide ventriculography performed at rest.21-25 Two of these studies were performed in the 45” modified ( 15” caudal tilt) left anterior oblique position only and in one contraction of the posterolateral (ISCE segments 11, 12) left ventricular wall was diminished. The remaining nine

Table 1. Inclusion Criteria for Subjects in PM1 Group

Subject 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Clin Hx of MI

+MB-CK Isoenzyme

Evolutionary PM1 ECG

X X

X X

X X

X X X X

X X X X X

X X X X X X X X X X X

X X X X

Abnormal Exercise ECG

Posterolateral Thallium Defect

X X X X

X X X X

X X X X X X X X X

X

Posterolateral Asynergy RNCA

X

X X X X X

X X

Angio LAD

CX

RCA

X X x

x X

LAO V-gram Asynergy X X

x

X x

x

X

X X

X X

X

RNCA, radionucIide cineangiography; LAD, left anterior descending coronary artery; CX, circumflex coronary artery; RCA, right coronary artery; LAO V-Gram, left anterior oblique contrast ventriculogram.

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studies were performed in four views (45” modified left anterior oblique, 30” right anterior oblique, 70” left anterior oblique and left lateral), and all of these exhibited a contraction abnormality involving at least the middle and ba.sal posterolateral left ventricular wall (ISCE segments 11 and 12, respectively) seen on the 70” left anterior oblique or left lateral views. Contraction abnormalities were also noted involving the posterolateral (ISCE segments 10-12) and apical (ISCE segments 4, 7, 10) left ventricular walls on the 45” modified left anterior oblique view. Ten patients had cardiac catheterization with selective coronary arteriography. A significant coronary arterial stenosis was defined as a 70% or greater decrease in luminal diameter. Nine had obstruction of the left circumflex coronary artery or one of its major branches. Three had obstruction of the right coronary artery, with two of these also having significant circumflex artery disease. Four had left anterior oblique contrast ventriculography performed at the time of catheterization, which demonstrated regional asynergy of the posteriolateral (ISCE segments 11, 12) left ventricular wall. Nine of the fifteen patients had diagnostic abnormalities on at least two types of testing (thallium perfusion scintigraphy, radionuclide ventriculography, and coronary arteriography). Of those with abnormalities confined to a single test, one involved thallium perfusion scintigraphy, two multiple-view radionuclide ventriculography, and three cardiac catheterization. Two of three subjects with abnormal findings on a single noninvasive study also had documented clinical myocardial infarction (elevated CK-MB and LD- 1 isoenzymes) accompanied by ECG evolution of tall R waves in the right precordial leads while hospitalized. The third (patient 3, Table 1) had posterolateral akinesia seen on all three views (45” left anterior oblique, 70” left anterior oblique and left lateral) during radionuclide cineangiography and was, therefore, included in the PM1 group (Table 1).

PAF Group Eight men and four women with a history of atypical angina were selected who met electrocardiographic entry criteria but who had not had a clinical myocardial infarction. All 12 subjects had stress thallium-20 1 perfusion scintigraphy with redistribution. Eleven studies were completely normal and one revealed a possible fured apical (ISCE segments 4, 7, 10) perfusion defect on the 45” left anterior oblique view only. However, coronary arteriography in this individual revealed only a 50% stenosis of the an-

terior descending coronary artery without evidence of regional contraction abnormality on the right anterior oblique contrast ventriculogram. Of four patients who had, in addition, radionuclide ventriculography at rest, two were multiview studies and all four demonstrated normal global left ventricular ejection fraction values without evidence of regional contraction abnormalities. Nine of 12 subjects had an entirely normal 85% maximal treadmill exercise test without production of their atypical angina or electrocardiographic ST-segment abnormalities.

Equipment and Method of Analysis All subjects had standard 12-lead ECGs recorded at 25 mm/set paper speed in the supine position, using a MAC 2 three-channel automatic electrocardiograph (Marquette Electronics). Manual measurements were made of the QRS and T wave complexes. The recorded data included the width of the Q wave in lead aVF ( QavF), in seconds, and the height of the T wave in leads Vr, VZ, and V6 (Tvr, Tv2, Tv6), in millivolts. The direction of the frontal plane QRS axis was determined to the nearest 15” by a common vectoral approach using a hexaxial reference system.26 Concomitant ECG inferior myocardial infarction (IMI) was diagnosed by the presence of Q waves in leads II, III, and aVF, with the Q wave in lead aVF being at least 0.04 set in duration with a depth greater than 25% of the amplitude of the following R wave in the same lead.27 The TZ-T6 index was calculated by subtracting Tva from TV2 and expressing the result in millivolts ( 10 mm = 1 mV).28 The value Y of the two variable discriminant model was calculated as Y = 0.65 - 65.1 (QavF) - 6.0 (Tw), where QavF and Tvl are expressed in units of seconds and millivolts, respectively.29 Each of the study patients had a VCG performed within 48 hours of the standard 12-lead ECG. VCGs were recorded using the Frank lead system with an Instruments for Cardiac Research VCG-1B direct writer vectrocardiograph. The chest electrodes (A, C, E, I) were placed in the fourth intercostal space as recommended for the supine position.30 Calibrations of 1 mV per 2-8 cm deflection were used in displaying the total QRS and T loops, the P loop having been deleted. The dash times were 2.0 and 4.0 msec. Initial QRS forces were displayed with a high magnification technique ( 1 mV = 16 cm deflection). Manual measurements of the scalar representation of the orthogonal leads as well as QRS and T loops were carried out in a blinded manner. The VCG data recorded (Fig. 2) included the max-

Tall Right Precordial R Waves

imal posteriorly directed QRS voltage (MVP), anterior QRS duration (AD), magnitude and direction of the maximal QRS (MAX QRS) and T loop (MAX T) vector, direction of T loop rotation, speed of T loop inscription, ratio of maximal width to maximal length (w/l) of the T loop, and - 45”/ab ratio-all in the horizontal plane (HP). The direction of the maximal amplitude QRS vector in the frontal plane and the presence of concomitant VCG inferior wall myocardial infarction were also recorded. The MVP was determined as the maximum voltage projected posteriorly, on the 90”-270” axis. The position of the afferent limb was determined by inspection. The magnitude of the vector directed to - 45” ( + 3 15”) in the HP QRS loop was measured. In determining the magnitude of the line ab, points a and b were the most prominent points of the HP QRS loop in the left anterior and right posterior quadrants, respectively. The -45”lab value was determined by their quotient.31 The VCG criteria for diaphragmatic inferior myocardial infarction were those previously proposed by Stam3’ Previously proposed ECG and VCG criteria for PM1 were studied with regard to their ability to differentiate accurately subjects with PM1 from those with merely PAF among the 27 subjects (“test” group) with electrocardiographic tall R waves in the right precordial leads.

Statistics Means are expressed with 1 standard deviation, not the standard error, as the index of dispersion. Significant differences between means were sought using the two-tailed Student’s t-test.33 The ECG and VCG criteria were evaluated with regard to sensitivity, specificity, positive predictive value, and negative predictive value. McNemar’s test with Yate’s correction for continuity was used to compare the diagnostic accuracy of each of the criteria. If the expected Table 2.

TVI (mV) TVZ(mv) Tv~ (mV) T2-T6 (mV) Y function

Myocardial Infarction @‘MU

0.35 0.78 0.11 0.67 -2.51

‘f 2 f f

0.16 0.52 0.20 0.46 1.27

Tvl (V,, V,) = height T wave in leads VI, Vz, and Vg, respectively. T2-T6 = Tvl - Tvb. QavF = width of Q wave in lead aVF. Y = 0.65 - 65.1 (Qav~) - 6.0 (T,,).

Zema

151

frequencies were less than 5, the binomial test was substituted for McNemar’s test with p = Q = 0.5.34 When applied to differentiate patient groups, the chisquare test uncorrected for continuity3’ was used. Where the expected frequencies were less than 5, Fisher’s exact probability test was substituted.34 An alpha level of 0.05 was established as the level of significance.

Results The mean age of the PM1 subjects (61.0 + 11.4 years) did not differ from that of PAF subjects (52.7 + 15.4 years) (p = NS). The proportion of men in the PM1 group (13 of 15) also did not differ from that of the PAF group (8 of 12) (p = NS).

Electrocardiogram TV2was greater (0.78 k 0.52 vs. 0.42 k 0.26) (p < 0.05) and TV6less (0.11 k 0.20 vs. 0.33 + 0.14) (p < 0.05) in PM1 when compared to PAF subjects. Combining both of these measures, the T2-T6 index was greater for PM1 (0.67 k 0.46) than for PAF (0.09 t 0.23) subjects (p < 0.001). Tvl was greater (0.35 + 0.16 vs. 0.06 k 0.14) (p < 0.0001) in PM1 than in PAF patients. The Y value derived from the previously described two-variable function also differed (p < 0.01) (-2.51 2 1.27 vs. -0.33 t_ 0.94) in patients with PM1 and PAF (p < 0.01) (Table 2). The discriminant model (Y), which is composed of both depolarization and repolarization variables, was more sensitive for the detection of PM1 than any other ECG discriminator examined. Tvl 20.25 mV also surpassed in sensitivity at least two of the more complex ECG discriminators examined and did not differ in this regard from the two-variable function Y (p = NS) (Table 3).

ECG Findings in Patients With Tall R Waves in the Right Precordial Posterolateral

l

Leads

Clinically Normal Subjects With Prominent Anterior QRS Forces (PAF) 0.06 0.42 0.33 0.09 -0.33

a ‘* f 2

0.14 0.26 0.14 0.23 0.94

on ECG

P
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Table 3. Predictive Value of Various ECG Findings for the Diagnosis of Posterolateral Myocardial Infarction in Subjects With Tall R Waves in the Right hecordial Leads on ECG Sensitivity Criteria Y < -0.5 T2-T6 > 0.38 Tv, 2 0.25 IMI ECG and iso or t T wave V1 ECG QRS axis < 30” and iso or t T wave V1 ECG QRS axis < 30” and IMI ECG

Positive hedictive Value

Specificity

Negative Predictive Value

No.

%

No.

%

No.

%

No.

%

15/15 11/15 12/15 ?/15

100 73 80 47

7112 10/12 1 l/12 12112

58 83 92 100

15120 11/13 12/13 717

75 85 92 100

7/7 10114 1 l/14 12120

100 71 79 60

9115

60

B/12

67

9113

69

B/l4

57

5115

33

1 l/12

92

5/6

83

1 l/26

42

IMI. inferior myocardial infarction; iso, isoelectric or equiphasic; Q, width of Q wave in lead aVF; t T, upright (or predominantly positive) T wave; Tvl (V2, V6), height of T wave in leads VI, Vz, and Vb, respectively; TZ-T6, Tvz-Tvs (in mV); Y, 0.65 - 65.1 (QavF) - 6.0 (TV,).

No significant differences in the positive predictive values of any of the proposed ECG discriminators were noted. The values ranged from 69% to 100%. The negative predictive value of the two-variable function (7 of 7; 100%) was greater than any other discriminator that used a measure of myocardial depolarization (p < 0.05 in all cases) (Table 3). It did not, however, differ from that of the T2-T6 index (10 of 14; 71%) or Tvl 2 0.25 mV (11 of 14; 79%) (p = NS).

Vectorcardiogram Significant group differences on the VCG were found between individuals with PM1 and PAF. As we showed previously, in a separate “criteria” group of subjects, the maximal amplitude HP T loop vector was more anterior (p < 0.0005) and the maximal

amplitude FP QRS loop vector was more leftward (p < 0.01) in PMI patients. The previously reported lower-magnitude HP MVP in PMI subjects was not confirmed. Unlike our previously reported results,35 the - 45”/ab ratio of Suzuki was significantly less in patients with PM1 than PAF (p < 0.02) (Table 4). Because, however, late rightward and posterior QRS forces could not be demonstrated in 37% (10 of 27) of our subjects, calculation of the -45”/ab ratio in patients was often not possible, clearly limiting its potential application as a useful discriminator (Table 5). The specificity and positive predictive value of the four VCG discriminators examined did not differ (p = NS) . The sensitivity of the Max HP T vector > 50” for PMI (15 of 15; 100%) exceeded all other, more complex VCG discriminators (p < 0.05 for all comparisons), even those involving depolarization variables. The negative predictive value of the Max HP T vector 550” (8 of 8: 100%) surpassed all other VCG

Table 4. VCG Findings in Patients With Electrocardiographic Tall R Waves in the Right Precordial Leads Posterolateral Maximum HP T vector (“) Maximum FP QRS vector (“) - 45’lab Maximum HP T voltage (mV) T max Maximum HP QRS voltage (mV) QRS max QRS max (mV)n max (mV) Anterior duration (ms) Maximum posterior QRS voltage (mV) QRS-T” (HP) w/l T loop (HP)

Myocardial Infarction (PMI)

71.8 9.7 0.11 0.40

2 17.3 -c 19.5 f 0.08 2 0.24

1.27 f

Clinically Normal Subjects with Prominent Anterior QRS Forces (PAP) 33.9 31.7 0.23 0.43

2 25.8 f 19.6 * 0.11 +- 0.21

P <0.0005 co.01 co.02 NS

0.43

1.21 2

0.39

NS

4.35 -+ 2.78 55.3 f 12.4 0.30 2 0.16

3.65 2 52.5 f 0.36 ”

2.14 9.3 0.19

NS NS NS

34.9 -c 14.4 0.20 + 0.20

27.5 f 17.1 0.18 + 0.15

NS NS

FP, frontal plane; HP, horizontal plane; QRS-T”, angle formed by the direction of the maximal amplitude QRS and T vectors; w/l, ratio of maxima1 width to maximal length.

Tall Right Precordial R Waves

l

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153

Table 5. Predictive Value of Various VCG Findings for the Diagnosis of Posterolateral Myocardial Infarction in Subjects With Tail R Waves in the Right Precordial Leads on ECG Sensitivity

Criteria Max HP T Vector> 50” Max FP QRS Vector < 30” and IMI VCG -45”/ab 5 0.20 Max HP T Vector 260” and at least 2 of the following 3 (HP): QRS maxA? max 5 3.0 QRS-T” 5 75” w/l T loop 5 0.15

Positive Predictive Value

Specificity

Negative Predictive Value

15/15

100

67

15119

79

818

6115

40

1 l/12

92

617

86

1 l/20

9115

60

5/12

42

9116

56

6115

40

1 l/12

92

6f7

86

8112

5/l 1

1 l/20

100 55 45

55

FP, frontal plane; HP, horizontal plane; QRS max. magnitude of maximal amplitude instantaneous QRS loop vector; T max. magnitude of maximal amplitude instantaneous T loop vector; QRS-T”, angle formed by the direction of the maximal amplitude instantaneous QRS and T vectors; w/l, ratio of maximal width to maximal length.

discriminators (p < 0.025 for all comparisons) in its ability to exclude patients with PM1 (Table 5).

Electrocardiograms Versus Vectorcardiogram The best VCG discriminator (Max HP T vector > 50’) did not differ from the best ECG discriminators (two-variable discriminant model Y and T2-T6 index) with regard to sensitivity, specificity, positive predictive value, or negative predictive value for the detection of PM1 (Tables 3, 4).

Discussion A tall R wave in the right precordial leads is a frequent electrocardiographic finding with clinical and pathologic correlates that are quite diverse. It is seen with posterolateral wall myocardial infarction (PMI), right ventricular hypertrophy, right bundle branch block, type A Wolff-Parkinson-White syndrome, several forms of cardiomyopathy, and in otherwise clinically normal subjects with prominent anterior forces (PAF). Most difficulty arises in attempts to distinguish PMI from PAF, since clinical and laboratory examination are often capable of excluding RVH, hypertrophic cardiomyopathy, and Duchenne’s progressive muscular dystrophy. Electrocardiographic PAF, moreover, is not an uncommon finding. An unpublished review of the electrocardiograms of 100 consecutive patients who had demonstrated entirely normal findings at cardiac catheterization performed at a major university teaching hospital between the years 1973 and 1977

revealed R > S pattern in leads V1 and/or VZ in three subjects (3 %). None of these patients were catheterized, moreover, as a direct consequence of the appearance of their electrocardiogram. This figure agrees well with the 2.4% incidence recently reported by Paparelli36 in a retrospective study. In a previous publication,35 we demonstrated that existing ECG and VCG criteria for PM18,‘2-‘5 lacked specificity and predictive value in this group of patients. We proposed, moreover, based upon examination of our “criteria” subject group, the existence of previously undescribed ECG and VCG discriminators of PM1 and PAF. Subsequent to our publication, at least three other studies have been reported, emphasizing, as we had done earlier, the importance of the ECG T wave and VCG T loop in the diagnosis of PM1 in genera1.28*29,37While the specific criteria developed in each of these latter studies claim improved sensitivity and specificity for the diagnosis of angiographically proven PMI, they do not deal exclusively or even predominantly with the subgroup of patients characterized by electrocardiographic tall R waves in the right precordial leads. In the paper by Nestico et a1.,29 only 33 (7 PM1 and 26 PAF) of 180 subjects in the validation subgroup had IUS z 1.0 in V1 and/or V2. Likewise, in the study by Eisenstein et a1.,28 only 12 of 27 patients with angiographic PM1 had R/S > 1.0 in V1 and/or VZ. The number of control subjects with ECG R/S > 1.0 in V1 and/or V2 is not reported. The current study population, while somewhat limited in size, is composed entirely of subjects with prominent anterior QRS electromotive forces on ECG in the transverse plane. While comprising a minority of all patients with previous posterolateral myocardial infarction,21,22,28,38 it is the individual with ECG tall R waves in the right precordial leads who most often comes to medical

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Journal of Electrocardiology Vol. 23 No. 2 April 1990

attention in the chronic care setting, being referred after routine performance and physician interpretation of the ECG. The use of such qualifying terms as “cannot rule out” and “doubtful” highlight the reluctance of physicians to equate the presence of tall R waves in the right-sided chest leads with posterolateral myocardial infarction. The sensitivity, specificity, and predictive value of various criteria for PM1 are dependent upon the population studied.39 For example, Takatsu et a1.37 showed the VCG QRS-T angle (HP), w/l T loop (HP) ratio, and maximal amplitude HP T loop vector (T max) all to be significantly different in patients with PMI versus “normal controls.” No differences in any of these variables was noted, however, when our patients with PM1 were compared to subjects with PAF (Table 4). While a single previous publication had examined specifically patients presenting with ECG tall R waves in the right precordial leads and had reported significant ECG and VCG differences among patients with PM1 and PAF,35 it remained to be demonstrated prospectively in a separate “test” group of subjects whether those discriminators (Tables 3, 5) could indeed accurately separate individuals with PM1 from PAF. With perhaps a single exception (the presence of concomitant VCG or ECG LMI, the latter being reflected also in the first term of the two-variable Y function),29 repolarization as opposed to depolarization criteria were found to be more useful discriminators. Unlike other criteria tested, Tvl has not been shown, by us or others, to be a discriminator in a previous “criteria” group of subjects. The cut-off value of Tvl 2 0.25 mV (Table 3) was arbitrarily chosen from the current data best to affect a separation of patients with PMI from PAF. The true potential of this seemingly simple discriminator must await further confirmation, therefore, in yet another separate “test” group of subjects. Use of the vectorcardiogram was not associated with improved ability to differentiate PMI from PAF subjects when compared with the best of the more recently proposed electrocardiographic discriminators. Based upon results from our current study, an algorithm can be developed whereby a patient presenting with electrocardiographic tall R waves in the right precordial leads (in whom routine clinical and laboratory evaluation has revealed no evidence of RVH, hypertrophic cardiomyopathy, or Duchenne’s muscular dystrophy) can be approached in an attempt to differentiate PM1 from PAF, conditions with extremely different long-term prognoses. Measuring the width of the q(Q) wave in lead aVF along with the height of the T wave in lead V1 allows easy calculation of the associated Y value. If Y 2 - 0.5, then PM1 in our series of patients was essentially ex-

\ Fig. 2.

Anteriorly oriented horizontal plane QRS and T loop. ab, length of segment ab as defined in Methods; AD, anterior QRS durations (msec); MAX QRS, magnitude (mV) and direction (“) of maximal amplitude instantaneous QRS vector; MAX T, magnitude (mV) and direction (“) of maximal amplitude instantaneous T vector: MVP, maximum posterior QRS voltage (mV); -45”, length of segment as defined in Methods.

eluded. If Y < - 0.5, then measurement of the T wave amplitude in leads V2 and Vg allows simple calculation of the TZ-T6 index, and if >0.38, a diagnosis of “probable PMI” can be made. Such an approach permitted a correct diagnosis to be made in 78% (7 of 9) of PAF cases and 73% ( 11 of 15) of PMI cases. Approximately 25% of cases still remain unclassifiable, as “possible PMI” or “cannot rule out PMI.” This simple flow scheme (Fig. 3) permits reliable exclusion of PM1 in patients with “probable PAF,” delineates others (“probable PMI”) who may be assumed to have coronary artery disease, and defines a third group (“cannot rule out PMI”) upon

Figure 3. Approach to the patient with tall R waves in the right precordial leads. PAF, prominent anterior forces; PMI, posterolateral myocardial infarction; T2-T6, T2-T6 index28; Y, two-variable Y function.*’

Tall Right Precordial R Waves whom more sophisticated diagnostic studies may be appropriately performed in a cost-effective manner. Because of the limited number of individuals studied, the true usefulness of the algorithm described above will be known only after long-term extensive clinical application. The preliminary results described above in this prospectively studied “test” group of subjects, however, appear encouraging.

14.

15.

16.

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