Evaluation of the Electrocardiographic Transitional Zone by Cardiac Computed Tomography
Yorio Tahara, MD, Haruyoshi Mizuno, MD, Akifumi Ono, MD, and Kyozo Ishikawa, MD, FACC
Abstract: The relationship between shift of the transitional zone on the standard 12-lead electrocardiogram (ECG) and anatomical rotation of the heart in one plane was studied by cardiac computed tomography (CT). Based on the position of the transitional zone, 102 subjects were divided into 3 groups: the normal transitional zone (NT) group (31 subjects), clockwise rotation (CWR) group (30 subjects), and counterclockwise rotation (CCWR) group (41 subjects). The left-sided angle between the interventricular septum and horizontal axis of the body (the septal angle) was determined on the cardiac CT and compared among the three groups. The angle was 5 1.8” ? 6.8” in the NT group, 38.2” + 8.4” in the CWR group, and 64.9” r 10.4” in the CCWR group. There were significant differences in the septal angle among the groups (p < 0.05). The mechanism of CWR and CCWR could be attributed to the septal angle in about two-thirds of the cases (24/30 in CWR and 27/41 in CCWR). However, those not explained by the septal angle amounted to 6 (20%) of the CWR group and 14 (34%) of the CCWR group. Relatively higher positions of the precordial ECG leads, as observed in the vertical heart, appeared to be responsible for CWR in the 6 patients, and left septal fascicular block was suspected to be responsible for CCWR in the 14 patients. These data indicate that about two-thirds of CWR and CCWR can be explained by anatomical rotation of the heart in one plane around the long axis, but other factors appear to be responsible for such electrocardiographic findings in the remaining one-third of cases. Key words: dockwise rotation, counterclockwise rotation, electrocardiographic transitional zone, computed tomography.
rotation of the heart around its long axis. Shift of the transitional zone to the left precordial leads is generally referred to as clockwise rotation (CWR) and that to the right precordial leads as counterclockwise rotation (CCWR); these terms are widely accepted in electrocardiographic terminology. ‘-’ However, the important question arises as to whether or not, and if so to what extent, electrocardiographic CWR and CCWR reflect anatomical rotation of the heart. In order to answer this question, there is a particular
The transitional zone in the precordial leads of the standard 124ead electrocardiogram (ECG) has long been considered to reflect the position of the interventricular septum (IVS) and to shift according to
From the Second Department of Internal Medicine, Kyorin University School of Medicine, Tokyo, Japan. Reprint requests: Kyozo Ishikawa, MD, The Second Department of Internal Medicine, Kyorin University School of Medicine, 6-20 Shinkawa, Mitaka-City, Tokyo- 18 1, Japan.
239
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Journal of Electrocardiology
Vol. 24 No. 3 July 1991
of the IVS. In recent years, the advent of cardiac computed tomography (CT) has provided an opportunity to approach a solution to this question.6-9 In the present study, therefore, an attempt was made to clarify the relation between the transitional zone on ECG and the IVS angle on cardiac CT. need
for precise
visualization
Materials
and Methods
The subjects were 102 cases, out of 8,000 outpatients in our department from 1983 to 1986, who gave their consent for cardiac CT for the purpose of detailed examinations due to displacement of the transitional zone on ECG. Cases that did not give their consent for economic reasons were excluded. One hundred two patients in whom the IVS was clearly delineated on CT comprised the study group. The group included 7 1 men and 3 1 women whose ages ranged from 30 to 8 1 years, with a mean of 62.5 years. IndividuaIs with a history of myocardial infarction and those who were diagnosed as having myocardial infarction on the basis of localized perfusion defects without redistribution by thallium 20 1 myocardial perfusion scintigraphy were excluded from the study. Patients showing fascicular block with a QRS width on the standard 12-lead ECG of 0.12 ms or higher and those showing aberrant conduction were excluded. The transitional zone was
Table
1.
Angle and Thickness
defined on the basis of position of the precordial ECG leads in which the amplitudes of the R and S waves were almost equal. The subjects were classified into three groups according to the position of the transitional zone (Table 1): the normal transitional zone (NT) group in which the transitional zone was observed in V3 or V4 (3 1 subjects), the CWR group in which it occurred in leads to the left of Vq (30 subjects), and the CCWR group in which it was found to the right of Vj (41 subjects) on ECG. In all of the 4 1 CCWR cases, the absence of posterior myocardial infarction was confirmed by myocardial scintigraphic imaging. The clinical background of the subjects is summarized in Table 2. The study was performed using a Toshiba computed tomograph (TCT60A- 30: exposure time of 4.5 seconds) whole body scanner. Seven to 15 sequential lOmm-thick scans were obtained from the aortic arch to the diaphragmatic level (Fig. 1A). The contrast medium (60% Angiographin or 30% Conray) was injected as a 20-30 ml bolus for each scan. The angle between the IVS and horizontal axis of the body (the septal angle) was determined as shown in Figure 1: the septal line was obtained by drawing a line from the origin of the posterior septum (0 point) to the midpoint on the midportion of the septum (M point). The maximum thickness of the septum was also measured. The ECG data and morphometric values obtained by CT were compared by the non-paired Student’s
of Interventricular
Age Number NT CWR CCWR NT = normal
of Cases
(years)
31 30 41 transitional
56.8 60.4 64.8
Male/Female
2 11.4 2 16.8 ? 7.2
zone; CWR = clockwise
21110 20110 30111 rotation;
CCWR
Normal Hypertension Angina pectoris Aortic aneurysm DCM HCM MSR + TR Atrial septal defect Lobectomy (right side) Emphysema Total
NT
CWR
9 4 4 9 3 1 1 0 0 0 31
6 1 0 0 4 1 15 1 0 2 30
CCWR 18 3 11 1 1 5 0 0 2 0 41
Angle of IVS (degrees)
Thickness of IVS (mm)
51.8 t 6.8 38.2 2 8.4 64.9 ” 10.4
11.4 2 3.8 10.1 ” 2.6 14.3 t 5.1
= counterclockwise
Table 2. Clinical Backgrounds Total 33 8 15 10 8 7 16 2 2 102
Septum
rotation;
QRS Axis (degrees) 48.6 88.9 76.4
IVS = intraventricular
2 9.7 ? 10.8 i 11.4
septum.
in 102 Cases IVS Angle 49.6 50.8 53.6 58.4 40.8 56.3 39.6 41.6 67.6 62.4
(degrees) -t 2 2 e ? + ? ? ? 2
QRS Axis
19.8 16.4 15.5 7.9 10.6 9.6 8.8 0.0 15.8 6.6
NT = normal transitional zone; CWR = clockwise rotation; CCWR = counterclockwise rotation; DCM = dilated HCM = hypertrophic cardiomyopathy; MSR = mitral valve stenosis and regurgitation; TR = tricuspid regurgitation.
42.4 50.4 45.6 44.6 -24.6 11.6 114.5 120.0 58.6 67.4
(degrees)
? 2 2 t -c ? 2 If: 2 2
10.5 20.3 12.4 10.6 18.7 11.6 26.5 00.0 12.7 10.4
cardiomyopathy;
Evaluation
of ECG Transitional
Zone by CT
l
Tahara
et al.
241
Fig. 1. Scanning levels and measurement of the septal angle. (A) The horizontal lines on the roentgenogram indicate the scanning levels by CT. Scanning was carried out from the aortic level to the diaphragm at 1.5 cm intervals. (B) The interventricular septum is clearly delineated in the contrast scan. (C) The schema illustrates the measurement of the angle between the horizontal axis of the body and septum (the septal angle). The angle between the horizontal axis and the line passing through the center of the septum was determined as the septal angle.
t test.
A value significant.
of p < 0.05
was considered
to be
Results Angle of the Interventricular Septum to the Horizontal Axis of the Body As shown in Table 1 and Figure 2, the septal angle was 51.8” t 6.8” (40”-59’) in the NT group, 38.2” t 8.4” (17”-56”) in the CWR group, and 64.9” + 10.4” (41”-90”) in the CCWR group. There were significant differences among the groups (p < 0.05). The septal angle fell within the narrow range of 40”59” in the NT group; the transitional zone in all patients of this group could be explained by the septal angle. The septal angle was significantly smaller in the CWR group than in the NT group, and as shown in Table 2, most of the patients with CWR had right
ventricular overload such as combined valvular disease. The septal angle was within the normal range in six (20%) of the CWR group, three of whom had dilated cardiomyopathy, one had chronic obstructive lung disease, and the remaining two were normal subjects. The septal angle was larger in 27 of 41 subjects (66%) of the CCWR group than in the NT group, but it was within the normal range in the remaining 14 (34%). Nine of these 14 subjects had angina pectoris and 5 had hypertrophic cardiomyopathy. CCWR was discriminated from the remaining two groups (CWR and normal) with a sensitivity of lOO%, a specificity of 82.4%, a positive predictive accuracy of 68%, and a negative predictive accuracy of 100% when the IVS angle was more than 60”. CWR was discriminated from the remaining two groups (CCWR and normal) with a sensitivity of 95.2%, a specificity of 87.6%, a positive predictive accuracy of 66.6% and a negative predictive accuracy of 98.6% when the IVS angle was less than 40”.
242
Journal
of Electrocardiology
Relationship Between Cardiac Rotation and Septal Thickness
A * 1
Vol. 24 No. 3 July 1991
* P
Yorio Tahara, MD, Haruyoshi Mizuno, MD, Akifumi Ono, MD, and Kyozo Ishikawa, MD, FACC
Abstract: The relationship between shift of the transitional zone on the standard 12-lead electrocardiogram (ECG) and anatomical rotation of the heart in one plane was studied by cardiac computed tomography (CT). Based on the position of the transitional zone, 102 subjects were divided into 3 groups: the normal transitional zone (NT) group (31 subjects), clockwise rotation (CWR) group (30 subjects), and counterclockwise rotation (CCWR) group (41 subjects). The left-sided angle between the interventricular septum and horizontal axis of the body (the septal angle) was determined on the cardiac CT and compared among the three groups. The angle was 5 1.8” ? 6.8” in the NT group, 38.2” + 8.4” in the CWR group, and 64.9” r 10.4” in the CCWR group. There were significant differences in the septal angle among the groups (p < 0.05). The mechanism of CWR and CCWR could be attributed to the septal angle in about two-thirds of the cases (24/30 in CWR and 27/41 in CCWR). However, those not explained by the septal angle amounted to 6 (20%) of the CWR group and 14 (34%) of the CCWR group. Relatively higher positions of the precordial ECG leads, as observed in the vertical heart, appeared to be responsible for CWR in the 6 patients, and left septal fascicular block was suspected to be responsible for CCWR in the 14 patients. These data indicate that about two-thirds of CWR and CCWR can be explained by anatomical rotation of the heart in one plane around the long axis, but other factors appear to be responsible for such electrocardiographic findings in the remaining one-third of cases. Key words: dockwise rotation, counterclockwise rotation, electrocardiographic transitional zone, computed tomography.
rotation of the heart around its long axis. Shift of the transitional zone to the left precordial leads is generally referred to as clockwise rotation (CWR) and that to the right precordial leads as counterclockwise rotation (CCWR); these terms are widely accepted in electrocardiographic terminology. ‘-’ However, the important question arises as to whether or not, and if so to what extent, electrocardiographic CWR and CCWR reflect anatomical rotation of the heart. In order to answer this question, there is a particular
The transitional zone in the precordial leads of the standard 124ead electrocardiogram (ECG) has long been considered to reflect the position of the interventricular septum (IVS) and to shift according to
From the Second Department of Internal Medicine, Kyorin University School of Medicine, Tokyo, Japan. Reprint requests: Kyozo Ishikawa, MD, The Second Department of Internal Medicine, Kyorin University School of Medicine, 6-20 Shinkawa, Mitaka-City, Tokyo- 18 1, Japan.
239
240
Journal of Electrocardiology
Vol. 24 No. 3 July 1991
of the IVS. In recent years, the advent of cardiac computed tomography (CT) has provided an opportunity to approach a solution to this question.6-9 In the present study, therefore, an attempt was made to clarify the relation between the transitional zone on ECG and the IVS angle on cardiac CT. need
for precise
visualization
Materials
and Methods
The subjects were 102 cases, out of 8,000 outpatients in our department from 1983 to 1986, who gave their consent for cardiac CT for the purpose of detailed examinations due to displacement of the transitional zone on ECG. Cases that did not give their consent for economic reasons were excluded. One hundred two patients in whom the IVS was clearly delineated on CT comprised the study group. The group included 7 1 men and 3 1 women whose ages ranged from 30 to 8 1 years, with a mean of 62.5 years. IndividuaIs with a history of myocardial infarction and those who were diagnosed as having myocardial infarction on the basis of localized perfusion defects without redistribution by thallium 20 1 myocardial perfusion scintigraphy were excluded from the study. Patients showing fascicular block with a QRS width on the standard 12-lead ECG of 0.12 ms or higher and those showing aberrant conduction were excluded. The transitional zone was
Table
1.
Angle and Thickness
defined on the basis of position of the precordial ECG leads in which the amplitudes of the R and S waves were almost equal. The subjects were classified into three groups according to the position of the transitional zone (Table 1): the normal transitional zone (NT) group in which the transitional zone was observed in V3 or V4 (3 1 subjects), the CWR group in which it occurred in leads to the left of Vq (30 subjects), and the CCWR group in which it was found to the right of Vj (41 subjects) on ECG. In all of the 4 1 CCWR cases, the absence of posterior myocardial infarction was confirmed by myocardial scintigraphic imaging. The clinical background of the subjects is summarized in Table 2. The study was performed using a Toshiba computed tomograph (TCT60A- 30: exposure time of 4.5 seconds) whole body scanner. Seven to 15 sequential lOmm-thick scans were obtained from the aortic arch to the diaphragmatic level (Fig. 1A). The contrast medium (60% Angiographin or 30% Conray) was injected as a 20-30 ml bolus for each scan. The angle between the IVS and horizontal axis of the body (the septal angle) was determined as shown in Figure 1: the septal line was obtained by drawing a line from the origin of the posterior septum (0 point) to the midpoint on the midportion of the septum (M point). The maximum thickness of the septum was also measured. The ECG data and morphometric values obtained by CT were compared by the non-paired Student’s
of Interventricular
Age Number NT CWR CCWR NT = normal
of Cases
(years)
31 30 41 transitional
56.8 60.4 64.8
Male/Female
2 11.4 2 16.8 ? 7.2
zone; CWR = clockwise
21110 20110 30111 rotation;
CCWR
Normal Hypertension Angina pectoris Aortic aneurysm DCM HCM MSR + TR Atrial septal defect Lobectomy (right side) Emphysema Total
NT
CWR
9 4 4 9 3 1 1 0 0 0 31
6 1 0 0 4 1 15 1 0 2 30
CCWR 18 3 11 1 1 5 0 0 2 0 41
Angle of IVS (degrees)
Thickness of IVS (mm)
51.8 t 6.8 38.2 2 8.4 64.9 ” 10.4
11.4 2 3.8 10.1 ” 2.6 14.3 t 5.1
= counterclockwise
Table 2. Clinical Backgrounds Total 33 8 15 10 8 7 16 2 2 102
Septum
rotation;
QRS Axis (degrees) 48.6 88.9 76.4
IVS = intraventricular
2 9.7 ? 10.8 i 11.4
septum.
in 102 Cases IVS Angle 49.6 50.8 53.6 58.4 40.8 56.3 39.6 41.6 67.6 62.4
(degrees) -t 2 2 e ? + ? ? ? 2
QRS Axis
19.8 16.4 15.5 7.9 10.6 9.6 8.8 0.0 15.8 6.6
NT = normal transitional zone; CWR = clockwise rotation; CCWR = counterclockwise rotation; DCM = dilated HCM = hypertrophic cardiomyopathy; MSR = mitral valve stenosis and regurgitation; TR = tricuspid regurgitation.
42.4 50.4 45.6 44.6 -24.6 11.6 114.5 120.0 58.6 67.4
(degrees)
? 2 2 t -c ? 2 If: 2 2
10.5 20.3 12.4 10.6 18.7 11.6 26.5 00.0 12.7 10.4
cardiomyopathy;
Evaluation
of ECG Transitional
Zone by CT
l
Tahara
et al.
241
Fig. 1. Scanning levels and measurement of the septal angle. (A) The horizontal lines on the roentgenogram indicate the scanning levels by CT. Scanning was carried out from the aortic level to the diaphragm at 1.5 cm intervals. (B) The interventricular septum is clearly delineated in the contrast scan. (C) The schema illustrates the measurement of the angle between the horizontal axis of the body and septum (the septal angle). The angle between the horizontal axis and the line passing through the center of the septum was determined as the septal angle.
t test.
A value significant.
of p < 0.05
was considered
to be
Results Angle of the Interventricular Septum to the Horizontal Axis of the Body As shown in Table 1 and Figure 2, the septal angle was 51.8” t 6.8” (40”-59’) in the NT group, 38.2” t 8.4” (17”-56”) in the CWR group, and 64.9” + 10.4” (41”-90”) in the CCWR group. There were significant differences among the groups (p < 0.05). The septal angle fell within the narrow range of 40”59” in the NT group; the transitional zone in all patients of this group could be explained by the septal angle. The septal angle was significantly smaller in the CWR group than in the NT group, and as shown in Table 2, most of the patients with CWR had right
ventricular overload such as combined valvular disease. The septal angle was within the normal range in six (20%) of the CWR group, three of whom had dilated cardiomyopathy, one had chronic obstructive lung disease, and the remaining two were normal subjects. The septal angle was larger in 27 of 41 subjects (66%) of the CCWR group than in the NT group, but it was within the normal range in the remaining 14 (34%). Nine of these 14 subjects had angina pectoris and 5 had hypertrophic cardiomyopathy. CCWR was discriminated from the remaining two groups (CWR and normal) with a sensitivity of lOO%, a specificity of 82.4%, a positive predictive accuracy of 68%, and a negative predictive accuracy of 100% when the IVS angle was more than 60”. CWR was discriminated from the remaining two groups (CCWR and normal) with a sensitivity of 95.2%, a specificity of 87.6%, a positive predictive accuracy of 66.6% and a negative predictive accuracy of 98.6% when the IVS angle was less than 40”.
242
Journal
of Electrocardiology
Relationship Between Cardiac Rotation and Septal Thickness
A * 1
Vol. 24 No. 3 July 1991
* P
