- Email: [email protected]
Importance of the terminal portion of the QRS in the electrocardiographic diagnosis of inferior myocardial infarction
Importance of the Terminal Portion of the QRS in the Electrocardiographic Diagnosis of Inferior Myocardial Infarction ROBERT A. WARNER, MD, JOSEPH BATTAGLIA,
MD, NORMA E. HILL, RN,
SAKTI MOOKHERJEE, MD, and HAROLD SMULYAN,
MD
The scalar electrocardiograms of 64 patients with inferior wail myocardiai infarction (MI) and 67 normal subjects were quantitatively analyzed to determine the respective contributions of the initial and terminal portions of the QRS to the diagnosis of inferior Ml. Of the 10 best individual eiectrocardiographic criteria for inferior Ml, 7 were Q-wave criteria and 3 were criteria that consisted of delayed termination of the QRS in leads II or III. Combining the best terminal QRS criterion (the QRS in lead Iii ending at least 20 ms later than the QRS in lead I) with the 7 best Q-wave criteria and the best Q-wave criterion (Q wave ,40 ms or longer in lead aVF) with the 3 best terminal QRS criteria, resulted in criteria
with better sensitivities and overall diagnostic performances than those of the individual criteria. Analyzing the vectorcardiograms that were also available in 26 of the patients with inferior MI and 34 of the normal subjects showed that the delayed inscription of the end of the QRS in leads Ii and III tn patients with inferior MI is due to redirection of the terminal forces of ventricular depolarization. The terminal portions of the QRS complexes in the limb leads, considered both alone and in conjunction with traditional measurements of Q waves, contain information that is useful for diagnosing inferior MI.
Traditional electrocardiographic criteria for diagnosing myocardial infarction (MI) emphasize abnormalities of the initial portions of the QRS complexes of appropriate leads. For example, inferior MI often produces abnormally large Q waves in leads II, III and aVF, but electrocardiographers have generally ignored the terminal portion of the QRS complex as a possible source of information for diagnosing myocardial infarction. However, our group has observed that many patients with inferior MI have, in addition to Q waves of various sizes in leads II, III and aVF, unusually broad terminal R waves in the same leads. Since it appeared that broad terminal R waves confined to these leads were uncommon in patients without inferior MI, we hypothesized that such a pattern of R waves might constitute specific electrocardiographic evidence for inferior MI. Therefore, we designed the present study to determine
empirically whether analyzing the terminal portion of the QRS is useful in the diagnosis of inferior MI. If so, it could provide a new set of diagnostic criteria for inferior MI that could be used either alone or in conjunction with traditional Q-wave criteria for this important abnormality.
From the Syracuse Veterans Administration and Upstate Medical Centers, Syracuse, New York. Manuscript received September 28, 1984; revised manuscript received December 7, 1984, accepted December 10,1984. Address for reprints: Robert A. Warner, MD, Cardiology Section: Syracuse Veterans Administration Medical Center, 800 Irving Avenue, Syracuse, New York 13210.
(Am J Cardiol 1965;55:696-699)
Methods Patients: The patients studied wereselectedfrom a total of 749 patients who had undergonecardiac catheterization between January 1, 1976, and December31, 1983, at the SyracuseVeteransAdministration Medical Center and who had no electrocardiographicevidenceof left bundle branch block, right bundle branch block or left anterior hemiblock. Group A consisted of 84 patients with inferior MI as indicated by 75% or greater narrowing of the dominant coronary artery and either akinesia or dyskinesia of the inferior left ventricular wall detected by contrast ventriculography in the right anterior oblique projection. Group B consisted of 87 patients with normal coronary arteries and normal motion of the left ventricular wall. Collection of electrocardiographic and vectorcardiographic data: On the day before catheterization of each pa-
tient, 12-leadelectrocardiogramswereobtained using either a Hewlett-Packard model 1517A or a Marquette model MAC 1-T electrocardiograph. These devices are 3-channel elec-
April 1, 1985
trocardiographic machines that simultaneously record from leads I, II and III, then from leads aVR, aVL and aVF, then from leads VI, Vs and Vs and finally from leads VJ, Vs and Vs. The simultaneous recording of 3 leads permits one to study the relative times of inscription of corresponding portions of the electrocardiographic complexes in those leads. To be certain that all 3 channels were operating simultaneously, we inspected the relative times of onset of the 1.0 mV standardization marks. If the times of onset of the marks were dissimilar, then a correction for the discrepancy was made in comparing the times of inscription of the QRS complexes. For example, if the standardization mark in channel 1 began 10 ms before the marks in channels 2 and 3, then the QRS complex in lead I was considered to have actually begun 10 ms later than it appeared on the tracing. We also recorded vectorcardiograms from 26 of the patients in group A and 34 of the patients in group B, using an Instruments for Cardiac Research model 1001recorder with the QRS loops in each plane interrupted every 2 ms. Analysis of electrocardiographic data: To compare the contributions of each portion of the QRS complex to the diagnosis of inferior MI, we analyzed both the initial and terminal deflections of the QRS in various leads. Therefore, we measured the following parameters of the QRS complexes of the electrocardiograms in all the patients in groups A and B: the total duration of the QRS complexes; the durations of the individual Q, R and S waves recorded in leads I, II, III, aVL and aVF; and the differences between the times of the termination of the QRS complexes in leads I and II, leads I and III and leads aVL and aVF. To measure the components of the QRS complexes more accurately, we used a 5X magnifier. From the measured values previously mentioned, we calculated the following additional parameters in each patient: the sums of the durations of the Q and R waves in each of leads I, II, III, aVL and aVF and the differences in each of these measured and calculated parameters between leads I and II, leads I and III, leads I and aVF, leads aVL and II, leads aVL and III and leads aVL and aVF. By analyzing the distributions of the values of each of these measured and calculated parameters in groups A and B, we determined the sensitivity and specificity of each of the values for the diagnosis of inferior MI. We then calculated the relative odds of these values using the formula: Relative odds =
(sensitivity) (specificity) (100 - sensitivity) (100 - specificity)
The relative odds exhibited by a diagnostic test for a particular disease are the odds that a subject with a positive test result actually has that diseasecompared with those of a subject with a negative test result. Because the relative odds incorporate both the sensitivity and specificity of a test, they measure the overall performance of the test. Also, in contrast to the positive or negative predictive value, the significance of a particular value of relative odds of a diagnostic test is independent of the prevalance of the disease in the group being studied.’ When either the sensitivity or the specificity of a test is high, a small change in the sensitivity or specificity, respectively, produces a large change in the relative odds exhibited by the test. The statistical significance of the differences between the overall diagnostic performances of 2 tests was assessedusing McNemar’s test with the Yates correction for continuity.2 Analysis of vectorcardiographic data: To help determine the reason for the broad terminal R wave in electrocardiographic leads II, III and aVF in somepatients with inferior MI, we measured the time occupied by the vectorcardiographic QRS loop in each of the 4 quadrants of the frontal plane (right superior, left superior, left inferior and right inferior) of the patients in groups A and B for whom vectorcardiograms were
THE AMERICAN
TABLE I
JOURNAL
OF CARDIOLOGY
Volume 55
897
Performances of the 10 Best Individual Electrocardiographic Criteria for Myocardial Infarction
Criterion QF 140 %FiMlj 120 QF 135 TERM13 225 Q2 225 Q2 230 g$WoFo’30 Q3 245 TERM12 220
Sensitivity (%)
Specificity (%I
Relative Odds
36
99
z: 36 ;:
% 2:
z: 31 38
E 97 94
56: __.1 36: 1 35: 1 26:l 27:l 25: 1 21:l 2O:l
97
15:l
1O:l
02 225 = L25-ms Q wave in lead II; Q2.130 = L30-ms Q wave i;F;d II; Q2,3&F 130 = 130-ms Q waves In leads II, Ill and aVF; Q3 = L40-ms Q wave in lead Ill; Q3 245 = L45-ms Q wave in lead 111; QF 135 = Z35-rns Q wave in lead aVF; QF 240 = 14O-rns Q wave in lead aVF; TERM12 120 = the QRS in lead II terminates 120 rns later than the QRS in lead I; TERM13 120 = the QRS in lead Ill terminates 120 ms later than the QRS in lead I; TERM13 225 = the QRS in lead Ill terminates 225 ms later than the QRS in lead I.
available. A possible cause of these broad terminal R waves is slowing of the late forces of ventricular depolarization when they are inferior to the E point (and are thus being recorded as positive deflections by leads II, III and aVF). If so, then the terminal portions of the vectorcardiographic loops of the patients in group A should spend more time in 1 or both of the inferior quadrants of the frontal plane than those of the patients in group B. To evaluate the additional possibility that inferior MI redirects rather than slows the terminal forces of ventricular depolarization, we measured the terminal angles exhibited by the vectorcardiographic loops in the frontal plane in groups A and B. The terminal angle is measured by drawing a line between the E point and the point 10 ms from the end of the QRS loop in the frontal plane. The absolute value of the angle formed by that line and the positive half of the Y axis is the terminal angle. Therefore, the smaller the terminal angle, the more nearly the terminal forces of ventricular depolarization are inferior and perpendicular to lead X. The statistical significance of any differences between groups A and B with respect to each of the vectorcardiographic parameters was determined using the Student t test.
Results The 10 best individual electrocardiographic criteria (as indicated by the relative odds exhibited by each) for diagnosing inferior MI are listed in Table I. Table I shows that the best individual criterion is a Q wave 40 ms or longer in lead aVF and that the second best is a QRS complex in lead III that ends at least 20 ms later than the QRS complex in lead I. Table I also shows that of the 10 best individual criteria for inferior MI, 7 are traditional Q-wave criteria and 3 are criteria that involve the relative times of termination of the QRS complexes in leads II and III. Since the best Q-wave and terminal forces criteria in Table I each exhibited high specificities (99% and 97%, respectively), we reasoned that we could combine each of them as disjunctions with other individual criteria, and thus develop combined criteria with improved sensitivities and acceptably high specificities. Table II lists the results of combining the best Q-wave criterion
899
TERMINAL
TABLE II
QRS IN INFERIOR MYOCARDIAL
INFARCTION
Performances of the Combined Electrocardiographic Criteria for Inferior Myocardial Infarction
Criterion OF 140 or TERM13 220 TERM13 220 or QF 140 QF 235 or TERM13 220 TERM13 225 or QF 140 Q2 125 or TERM13 220 Q2 130 or TERM13 220 02,3&F 130 or TERM13 220 Q3 140 or TERM13 120 Q3 145 or TERM13 220 TERM12 120 or QF 240
TABLE III
Sensitivity (%I
Specificity (%I
Relative DddS
73
95
51:l
73
95
51:l
78
93
47:i
81
97
51:l
88
87
49:l
83
91
49:l
81
92
49:l
84
87
35:l
70
93
31:l
88
93
28: 1
Q2 225 = 125-ms Q wave in lead II; 02 130 = 130~ms 0 wave in lead II; Q2,3&F 130 = 130-ms Q waves in leads II, Ill and aVF; Q3 240 = 14O-m~ Q wave in lead Ill; Q3 145 = 245-n’s Q wave in lead III;QF 135=135+nsQwaveinleadaVF;QF 140=?4O-msQwave in lead aVF; TERM12 120 = the QRS in leed II terminates 120 ms later than the QRS In lead I; TERM13 220 = the QRS In lead Ill terminates 120 me later than the QRS in lead I; TERM 13 225 = the QRS In lead Ill terminates 225 ms later then the QRS In lead I.
with the 3 best terminal forces criteria and the best terminal forces criterion with the 7 best Q-wave criteria.. Table II shows that in each case, these combinations resulted in higher sensitivities and usually in higher relative odds than those exhibited by the individual criteria. Furthermore, in 8 of the 10 cases,the specificities remained greater than 90%. For example, combining the best terminal forces criterion with the best Q-wave criterion raised the sensitivity of the latter from 36 to 73% and only reduced its specificity from 99 to 95%.This change represents a significant improvement in the overall performances of the best Q wave and the best terminal forces criteria for inferior MI (x2 = 16.3, p
The propensity of inferior MI to produce Q waves in leads II, III and aVF is well known. However, inferior MI can also alter the later portions of the QRS. In 1950, First et ale introduced the term “peri-infarction block” to describe a generalized prolongation of the QRS complex associated with MI. Subsequently, Grant4 and Grant and Dodge5 distinguished between anterolateral and inferior peri-infarction block to refer to changes confined to the terminal portions of the QRS complexes
Vectorcardiographic Parameters in Groups A and B
Parameter Right initial time Left initial time Total initial time Left terminal time Right terminal time Total terminal time Total time 1 Terminal anole
Group A (mean f SD) 8f9 18f 28f 43 f 19 f 85f i: 2
11 10 22 15 18 it
Group 6 (mean f SD) 9f 7f8 18 l 48f 18 f 71 f 87 f 89 f
P
10 10 18 17 10 9 53
1: NS <::05
lnitiil time = the time (in milliseconds) spent by the QRS loop before. it goes inferior to the E point; terminal time = the time (in millieeconds) spent by the QRS loop after it goee inferior to the E point; terminal angle (in degrees) Is described in the text. NS = not significant; SD = standard deviation.
of specifc leads. Because their descriptions of anterolateral and inferior peri-infarction blocks correspond to what are now called left anterior and posterior hemiblock, the term peri-infarction block has lost favor. However, the prominent terminal R waves in leads II, III and aVF that stimulated the present study are identical to those described by Grant et a14a5 in their discussions of inferior peri-infarction block. Grant et aP8 speculated that inferior MI produces prominent terminal R waves in leads II, III and aVF by damaging the portion of myocardium normally activated directly by the posterior fascicle. This results in a pattern of ventricular depolarization similar to that seen when the posterior fascicle itself is interrupted. We believe that this is an attractive hypothesis for the following reasons: First, because the posterior fascicle terminates in the inferior wall of the left ventricle, infarction in that location could easily disrupt the interface between that fascicle and the myocardiurn of the inferior wall. Second, the development of more prominent R waves in the terminal portions of the QRS complexes of leads II, III and aVF tends to make the QRS frontal-plane axis deviate toward the right-a change similar to that seen with left posterior hemiblock. Third, because of the spatial relations of the anterior and posterior fascicles, blockage in the latter produces clockwise rotation of the electrical forces of ventricular depolarization in the frontal plane.7 This could help explain why inferior MI (in the absence of left anterior hemiblock) is frequently associated with a similar direction of rotation of both the initial and terminal forces of depolarization.8 The present study not only confirms that inferior MI often alters the terminal portion of the QRS, but also shows that such alterations are diagnostically useful. A systematic evaluation of our patients’ tracings revealed that 3 of the 10 best (including the second best) overall electrocardiographic criteria for inferior MI consist of relative delays in the terminations of the QRS complexes in leads II and III. Of still greater clinical importance, the study also demonstrates that these new terminal QRS criteria can be combined with traditional Q-wave criteria for inferior MI and thus improve the sensitivity and overall diagnostic performances of each.
April 1, 1985
I
+ I
THE
AMERICAN
JOURNAL
OF CARDIOLOGY
Volume 55
a99
illustrates how such a change causes delayed termination of the QRS complexes in the inferior leads. Previous work by our group has demonstrated that it is useful to analyze the temporal relations among corresponding portions of the QRS complexes of simultaneously recorded electrocardiographic leads.s-11 The present study shows that applying this type of analysis to the terminal portions of the QRS complexes facilitates the diagnosis of inferior MI. Applying the criteria of Warner et al.9 to the electrocardiograms of the patients in the present study yielded results similar to those originally reported by us (sensitivity 88%, specificity 90%, relative odds 66:1).gThus, the terminal QRS criteria yield lower sensitivities but higher specificities than our previously published criteria for inferior MI. References
FIGURE 1. The vectorcardiogram CBS loop in the frontal plane of a patient with inferior myocardiil infarction. The triaxial reference figure is superimposed on the loop and the arrow shows the direction of inscription of the loop. To the ri@i of the loop are diagrams of the same patient’s QRS complexes, which have been recorded simultaneously by leads I and Ill. The magnitude of the deflection of a given portion of a QRS complex by a lead is directly related to the extent to which the corresponding segment of the vectorcardiographic loop parallels the axis of that lead.6*12Therefore, because the tennina pintion of the loop Is nearly parallel to the positive half of the axis of lead Ill, lead Ill exhibits an R wave during this phase of depolarization. At the same time, the terminal portion of the loop is perpendicular to the axis of lead I, so that lead I is isoelectric. Therefore, when leads I and Ill are recorded sirnukaneously,the CBS in lead Ill appears to terminate later than the ORS in lead I.
The vectorcardiographic data indicate that inferior MI redirects the late forces of ventricular depolarization. Specifically, these forces tend to be more nearly inferior and perpendicular to the axis of lead I in patients with than in those without inferior MI. Figure 1
1. lpeen J, Feigl P. Bancroft’s Introduction to Biostatistlcs. New York: Harper and Row, 1970:149-151. 2. Glantz SA. A Primer of Biostatistics. New York: McGraw-HIII, 1981: 262-264. 3. Fimt SR, Bayley RH, Beferd DR. Periiinfarction blodq electrocardiogaphic abnormallty occasionally resembling bundle branch block and local ventricular block of other types. Circulation 1950;2:31-36. 4. Grant RP. Left axis deviation-an electrocardiographic-pathologic correlation study. Circulation 1956;14:233-249. 5. Grant RP, Dodge HT. Mechanisms of QRS complex prolongation in man-left ventricular conduction disturbances. Am J Med 1956;20: 634-652. 8. Grant RP, Murray RH. The QRS complex deformity of myocardial infarctlon in the human subject. Am J Med 1954;17:567-609. 7. Hoffman I. Clinical vectorcardiography in adults. Part 2. Am Heart J 1980;100:373-396. 8. Starr JW, Wagner OS, Behar VS, Walaton A, Greentleld JC Jr. Vectorcardiographic criteria for the diagnosis of inferior myocardial infarction. Circulation 1974;49:629-636. 9. Warner R, Hill NE, Sheehe PR, Mookherjee S, Fruehan CT, Smulyan H. Improved electrocardiographic criteria for the dlagnosls of inferior myocardial infarction. Circulation 1982:66:422-428. 10. Warner RA, Hill NE, Mookerjee S, Smulyan H. Improved electrocardiographic criteria for the diagnosis of left anterior hemiblock. Am J Cardiol 1963;51:723-726. 11. Warner RA, Hill NE, Mootcherjee S, Smutyan H. Electrocardi aphic criteria for the diagnosis of combined inferior myocardial infarct7 on and left anteriw hemiblock. Am J Cardiol 1963;51:716-722. 12. Grant RP, Edes EH. Spatial Vector Electrocardiography. Philadelphia: The Blakiston Company, 1952:7-Q.
MD, NORMA E. HILL, RN,
SAKTI MOOKHERJEE, MD, and HAROLD SMULYAN,
MD
The scalar electrocardiograms of 64 patients with inferior wail myocardiai infarction (MI) and 67 normal subjects were quantitatively analyzed to determine the respective contributions of the initial and terminal portions of the QRS to the diagnosis of inferior Ml. Of the 10 best individual eiectrocardiographic criteria for inferior Ml, 7 were Q-wave criteria and 3 were criteria that consisted of delayed termination of the QRS in leads II or III. Combining the best terminal QRS criterion (the QRS in lead Iii ending at least 20 ms later than the QRS in lead I) with the 7 best Q-wave criteria and the best Q-wave criterion (Q wave ,40 ms or longer in lead aVF) with the 3 best terminal QRS criteria, resulted in criteria
with better sensitivities and overall diagnostic performances than those of the individual criteria. Analyzing the vectorcardiograms that were also available in 26 of the patients with inferior MI and 34 of the normal subjects showed that the delayed inscription of the end of the QRS in leads Ii and III tn patients with inferior MI is due to redirection of the terminal forces of ventricular depolarization. The terminal portions of the QRS complexes in the limb leads, considered both alone and in conjunction with traditional measurements of Q waves, contain information that is useful for diagnosing inferior MI.
Traditional electrocardiographic criteria for diagnosing myocardial infarction (MI) emphasize abnormalities of the initial portions of the QRS complexes of appropriate leads. For example, inferior MI often produces abnormally large Q waves in leads II, III and aVF, but electrocardiographers have generally ignored the terminal portion of the QRS complex as a possible source of information for diagnosing myocardial infarction. However, our group has observed that many patients with inferior MI have, in addition to Q waves of various sizes in leads II, III and aVF, unusually broad terminal R waves in the same leads. Since it appeared that broad terminal R waves confined to these leads were uncommon in patients without inferior MI, we hypothesized that such a pattern of R waves might constitute specific electrocardiographic evidence for inferior MI. Therefore, we designed the present study to determine
empirically whether analyzing the terminal portion of the QRS is useful in the diagnosis of inferior MI. If so, it could provide a new set of diagnostic criteria for inferior MI that could be used either alone or in conjunction with traditional Q-wave criteria for this important abnormality.
From the Syracuse Veterans Administration and Upstate Medical Centers, Syracuse, New York. Manuscript received September 28, 1984; revised manuscript received December 7, 1984, accepted December 10,1984. Address for reprints: Robert A. Warner, MD, Cardiology Section: Syracuse Veterans Administration Medical Center, 800 Irving Avenue, Syracuse, New York 13210.
(Am J Cardiol 1965;55:696-699)
Methods Patients: The patients studied wereselectedfrom a total of 749 patients who had undergonecardiac catheterization between January 1, 1976, and December31, 1983, at the SyracuseVeteransAdministration Medical Center and who had no electrocardiographicevidenceof left bundle branch block, right bundle branch block or left anterior hemiblock. Group A consisted of 84 patients with inferior MI as indicated by 75% or greater narrowing of the dominant coronary artery and either akinesia or dyskinesia of the inferior left ventricular wall detected by contrast ventriculography in the right anterior oblique projection. Group B consisted of 87 patients with normal coronary arteries and normal motion of the left ventricular wall. Collection of electrocardiographic and vectorcardiographic data: On the day before catheterization of each pa-
tient, 12-leadelectrocardiogramswereobtained using either a Hewlett-Packard model 1517A or a Marquette model MAC 1-T electrocardiograph. These devices are 3-channel elec-
April 1, 1985
trocardiographic machines that simultaneously record from leads I, II and III, then from leads aVR, aVL and aVF, then from leads VI, Vs and Vs and finally from leads VJ, Vs and Vs. The simultaneous recording of 3 leads permits one to study the relative times of inscription of corresponding portions of the electrocardiographic complexes in those leads. To be certain that all 3 channels were operating simultaneously, we inspected the relative times of onset of the 1.0 mV standardization marks. If the times of onset of the marks were dissimilar, then a correction for the discrepancy was made in comparing the times of inscription of the QRS complexes. For example, if the standardization mark in channel 1 began 10 ms before the marks in channels 2 and 3, then the QRS complex in lead I was considered to have actually begun 10 ms later than it appeared on the tracing. We also recorded vectorcardiograms from 26 of the patients in group A and 34 of the patients in group B, using an Instruments for Cardiac Research model 1001recorder with the QRS loops in each plane interrupted every 2 ms. Analysis of electrocardiographic data: To compare the contributions of each portion of the QRS complex to the diagnosis of inferior MI, we analyzed both the initial and terminal deflections of the QRS in various leads. Therefore, we measured the following parameters of the QRS complexes of the electrocardiograms in all the patients in groups A and B: the total duration of the QRS complexes; the durations of the individual Q, R and S waves recorded in leads I, II, III, aVL and aVF; and the differences between the times of the termination of the QRS complexes in leads I and II, leads I and III and leads aVL and aVF. To measure the components of the QRS complexes more accurately, we used a 5X magnifier. From the measured values previously mentioned, we calculated the following additional parameters in each patient: the sums of the durations of the Q and R waves in each of leads I, II, III, aVL and aVF and the differences in each of these measured and calculated parameters between leads I and II, leads I and III, leads I and aVF, leads aVL and II, leads aVL and III and leads aVL and aVF. By analyzing the distributions of the values of each of these measured and calculated parameters in groups A and B, we determined the sensitivity and specificity of each of the values for the diagnosis of inferior MI. We then calculated the relative odds of these values using the formula: Relative odds =
(sensitivity) (specificity) (100 - sensitivity) (100 - specificity)
The relative odds exhibited by a diagnostic test for a particular disease are the odds that a subject with a positive test result actually has that diseasecompared with those of a subject with a negative test result. Because the relative odds incorporate both the sensitivity and specificity of a test, they measure the overall performance of the test. Also, in contrast to the positive or negative predictive value, the significance of a particular value of relative odds of a diagnostic test is independent of the prevalance of the disease in the group being studied.’ When either the sensitivity or the specificity of a test is high, a small change in the sensitivity or specificity, respectively, produces a large change in the relative odds exhibited by the test. The statistical significance of the differences between the overall diagnostic performances of 2 tests was assessedusing McNemar’s test with the Yates correction for continuity.2 Analysis of vectorcardiographic data: To help determine the reason for the broad terminal R wave in electrocardiographic leads II, III and aVF in somepatients with inferior MI, we measured the time occupied by the vectorcardiographic QRS loop in each of the 4 quadrants of the frontal plane (right superior, left superior, left inferior and right inferior) of the patients in groups A and B for whom vectorcardiograms were
THE AMERICAN
TABLE I
JOURNAL
OF CARDIOLOGY
Volume 55
897
Performances of the 10 Best Individual Electrocardiographic Criteria for Myocardial Infarction
Criterion QF 140 %FiMlj 120 QF 135 TERM13 225 Q2 225 Q2 230 g$WoFo’30 Q3 245 TERM12 220
Sensitivity (%)
Specificity (%I
Relative Odds
36
99
z: 36 ;:
% 2:
z: 31 38
E 97 94
56: __.1 36: 1 35: 1 26:l 27:l 25: 1 21:l 2O:l
97
15:l
1O:l
02 225 = L25-ms Q wave in lead II; Q2.130 = L30-ms Q wave i;F;d II; Q2,3&F 130 = 130-ms Q waves In leads II, Ill and aVF; Q3 = L40-ms Q wave in lead Ill; Q3 245 = L45-ms Q wave in lead 111; QF 135 = Z35-rns Q wave in lead aVF; QF 240 = 14O-rns Q wave in lead aVF; TERM12 120 = the QRS in lead II terminates 120 rns later than the QRS in lead I; TERM13 120 = the QRS in lead Ill terminates 120 ms later than the QRS in lead I; TERM13 225 = the QRS in lead Ill terminates 225 ms later than the QRS in lead I.
available. A possible cause of these broad terminal R waves is slowing of the late forces of ventricular depolarization when they are inferior to the E point (and are thus being recorded as positive deflections by leads II, III and aVF). If so, then the terminal portions of the vectorcardiographic loops of the patients in group A should spend more time in 1 or both of the inferior quadrants of the frontal plane than those of the patients in group B. To evaluate the additional possibility that inferior MI redirects rather than slows the terminal forces of ventricular depolarization, we measured the terminal angles exhibited by the vectorcardiographic loops in the frontal plane in groups A and B. The terminal angle is measured by drawing a line between the E point and the point 10 ms from the end of the QRS loop in the frontal plane. The absolute value of the angle formed by that line and the positive half of the Y axis is the terminal angle. Therefore, the smaller the terminal angle, the more nearly the terminal forces of ventricular depolarization are inferior and perpendicular to lead X. The statistical significance of any differences between groups A and B with respect to each of the vectorcardiographic parameters was determined using the Student t test.
Results The 10 best individual electrocardiographic criteria (as indicated by the relative odds exhibited by each) for diagnosing inferior MI are listed in Table I. Table I shows that the best individual criterion is a Q wave 40 ms or longer in lead aVF and that the second best is a QRS complex in lead III that ends at least 20 ms later than the QRS complex in lead I. Table I also shows that of the 10 best individual criteria for inferior MI, 7 are traditional Q-wave criteria and 3 are criteria that involve the relative times of termination of the QRS complexes in leads II and III. Since the best Q-wave and terminal forces criteria in Table I each exhibited high specificities (99% and 97%, respectively), we reasoned that we could combine each of them as disjunctions with other individual criteria, and thus develop combined criteria with improved sensitivities and acceptably high specificities. Table II lists the results of combining the best Q-wave criterion
899
TERMINAL
TABLE II
QRS IN INFERIOR MYOCARDIAL
INFARCTION
Performances of the Combined Electrocardiographic Criteria for Inferior Myocardial Infarction
Criterion OF 140 or TERM13 220 TERM13 220 or QF 140 QF 235 or TERM13 220 TERM13 225 or QF 140 Q2 125 or TERM13 220 Q2 130 or TERM13 220 02,3&F 130 or TERM13 220 Q3 140 or TERM13 120 Q3 145 or TERM13 220 TERM12 120 or QF 240
TABLE III
Sensitivity (%I
Specificity (%I
Relative DddS
73
95
51:l
73
95
51:l
78
93
47:i
81
97
51:l
88
87
49:l
83
91
49:l
81
92
49:l
84
87
35:l
70
93
31:l
88
93
28: 1
Q2 225 = 125-ms Q wave in lead II; 02 130 = 130~ms 0 wave in lead II; Q2,3&F 130 = 130-ms Q waves in leads II, Ill and aVF; Q3 240 = 14O-m~ Q wave in lead Ill; Q3 145 = 245-n’s Q wave in lead III;QF 135=135+nsQwaveinleadaVF;QF 140=?4O-msQwave in lead aVF; TERM12 120 = the QRS in leed II terminates 120 ms later than the QRS In lead I; TERM13 220 = the QRS In lead Ill terminates 120 me later than the QRS in lead I; TERM 13 225 = the QRS In lead Ill terminates 225 ms later then the QRS In lead I.
with the 3 best terminal forces criteria and the best terminal forces criterion with the 7 best Q-wave criteria.. Table II shows that in each case, these combinations resulted in higher sensitivities and usually in higher relative odds than those exhibited by the individual criteria. Furthermore, in 8 of the 10 cases,the specificities remained greater than 90%. For example, combining the best terminal forces criterion with the best Q-wave criterion raised the sensitivity of the latter from 36 to 73% and only reduced its specificity from 99 to 95%.This change represents a significant improvement in the overall performances of the best Q wave and the best terminal forces criteria for inferior MI (x2 = 16.3, p
The propensity of inferior MI to produce Q waves in leads II, III and aVF is well known. However, inferior MI can also alter the later portions of the QRS. In 1950, First et ale introduced the term “peri-infarction block” to describe a generalized prolongation of the QRS complex associated with MI. Subsequently, Grant4 and Grant and Dodge5 distinguished between anterolateral and inferior peri-infarction block to refer to changes confined to the terminal portions of the QRS complexes
Vectorcardiographic Parameters in Groups A and B
Parameter Right initial time Left initial time Total initial time Left terminal time Right terminal time Total terminal time Total time 1 Terminal anole
Group A (mean f SD) 8f9 18f 28f 43 f 19 f 85f i: 2
11 10 22 15 18 it
Group 6 (mean f SD) 9f 7f8 18 l 48f 18 f 71 f 87 f 89 f
P
10 10 18 17 10 9 53
1: NS <::05
lnitiil time = the time (in milliseconds) spent by the QRS loop before. it goes inferior to the E point; terminal time = the time (in millieeconds) spent by the QRS loop after it goee inferior to the E point; terminal angle (in degrees) Is described in the text. NS = not significant; SD = standard deviation.
of specifc leads. Because their descriptions of anterolateral and inferior peri-infarction blocks correspond to what are now called left anterior and posterior hemiblock, the term peri-infarction block has lost favor. However, the prominent terminal R waves in leads II, III and aVF that stimulated the present study are identical to those described by Grant et a14a5 in their discussions of inferior peri-infarction block. Grant et aP8 speculated that inferior MI produces prominent terminal R waves in leads II, III and aVF by damaging the portion of myocardium normally activated directly by the posterior fascicle. This results in a pattern of ventricular depolarization similar to that seen when the posterior fascicle itself is interrupted. We believe that this is an attractive hypothesis for the following reasons: First, because the posterior fascicle terminates in the inferior wall of the left ventricle, infarction in that location could easily disrupt the interface between that fascicle and the myocardiurn of the inferior wall. Second, the development of more prominent R waves in the terminal portions of the QRS complexes of leads II, III and aVF tends to make the QRS frontal-plane axis deviate toward the right-a change similar to that seen with left posterior hemiblock. Third, because of the spatial relations of the anterior and posterior fascicles, blockage in the latter produces clockwise rotation of the electrical forces of ventricular depolarization in the frontal plane.7 This could help explain why inferior MI (in the absence of left anterior hemiblock) is frequently associated with a similar direction of rotation of both the initial and terminal forces of depolarization.8 The present study not only confirms that inferior MI often alters the terminal portion of the QRS, but also shows that such alterations are diagnostically useful. A systematic evaluation of our patients’ tracings revealed that 3 of the 10 best (including the second best) overall electrocardiographic criteria for inferior MI consist of relative delays in the terminations of the QRS complexes in leads II and III. Of still greater clinical importance, the study also demonstrates that these new terminal QRS criteria can be combined with traditional Q-wave criteria for inferior MI and thus improve the sensitivity and overall diagnostic performances of each.
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illustrates how such a change causes delayed termination of the QRS complexes in the inferior leads. Previous work by our group has demonstrated that it is useful to analyze the temporal relations among corresponding portions of the QRS complexes of simultaneously recorded electrocardiographic leads.s-11 The present study shows that applying this type of analysis to the terminal portions of the QRS complexes facilitates the diagnosis of inferior MI. Applying the criteria of Warner et al.9 to the electrocardiograms of the patients in the present study yielded results similar to those originally reported by us (sensitivity 88%, specificity 90%, relative odds 66:1).gThus, the terminal QRS criteria yield lower sensitivities but higher specificities than our previously published criteria for inferior MI. References
FIGURE 1. The vectorcardiogram CBS loop in the frontal plane of a patient with inferior myocardiil infarction. The triaxial reference figure is superimposed on the loop and the arrow shows the direction of inscription of the loop. To the ri@i of the loop are diagrams of the same patient’s QRS complexes, which have been recorded simultaneously by leads I and Ill. The magnitude of the deflection of a given portion of a QRS complex by a lead is directly related to the extent to which the corresponding segment of the vectorcardiographic loop parallels the axis of that lead.6*12Therefore, because the tennina pintion of the loop Is nearly parallel to the positive half of the axis of lead Ill, lead Ill exhibits an R wave during this phase of depolarization. At the same time, the terminal portion of the loop is perpendicular to the axis of lead I, so that lead I is isoelectric. Therefore, when leads I and Ill are recorded sirnukaneously,the CBS in lead Ill appears to terminate later than the ORS in lead I.
The vectorcardiographic data indicate that inferior MI redirects the late forces of ventricular depolarization. Specifically, these forces tend to be more nearly inferior and perpendicular to the axis of lead I in patients with than in those without inferior MI. Figure 1
1. lpeen J, Feigl P. Bancroft’s Introduction to Biostatistlcs. New York: Harper and Row, 1970:149-151. 2. Glantz SA. A Primer of Biostatistics. New York: McGraw-HIII, 1981: 262-264. 3. Fimt SR, Bayley RH, Beferd DR. Periiinfarction blodq electrocardiogaphic abnormallty occasionally resembling bundle branch block and local ventricular block of other types. Circulation 1950;2:31-36. 4. Grant RP. Left axis deviation-an electrocardiographic-pathologic correlation study. Circulation 1956;14:233-249. 5. Grant RP, Dodge HT. Mechanisms of QRS complex prolongation in man-left ventricular conduction disturbances. Am J Med 1956;20: 634-652. 8. Grant RP, Murray RH. The QRS complex deformity of myocardial infarctlon in the human subject. Am J Med 1954;17:567-609. 7. Hoffman I. Clinical vectorcardiography in adults. Part 2. Am Heart J 1980;100:373-396. 8. Starr JW, Wagner OS, Behar VS, Walaton A, Greentleld JC Jr. Vectorcardiographic criteria for the diagnosis of inferior myocardial infarction. Circulation 1974;49:629-636. 9. Warner R, Hill NE, Sheehe PR, Mookherjee S, Fruehan CT, Smulyan H. Improved electrocardiographic criteria for the dlagnosls of inferior myocardial infarction. Circulation 1982:66:422-428. 10. Warner RA, Hill NE, Mookerjee S, Smulyan H. Improved electrocardiographic criteria for the diagnosis of left anterior hemiblock. Am J Cardiol 1963;51:723-726. 11. Warner RA, Hill NE, Mootcherjee S, Smutyan H. Electrocardi aphic criteria for the diagnosis of combined inferior myocardial infarct7 on and left anteriw hemiblock. Am J Cardiol 1963;51:716-722. 12. Grant RP, Edes EH. Spatial Vector Electrocardiography. Philadelphia: The Blakiston Company, 1952:7-Q.