a b s t r a c t

Objective: This was a pilot retrospective case-series study performed to investigate whether synthesized 18-lead electrocardiogram (ECG) could improve the accuracy of infarction site diagnosis in patients presenting with ST- elevation myocardial infarction (STEMI).

Method: Of 103 consecutive patients with acute coronary syndrome who underwent emergency coronary angi- ography between October 1, 2014 and December 10, 2015, 33 patients fulfilling the diagnostic criteria for STEMI were enrolled in this study.

Results: Comparison by the infarct-related coronary artery revealed that ST elevation in the 6 synthesized leads (any of syn-V_3R-V_5R and syn-V₇-V₉ leads), in addition to ST elevation in the standard 12-lead ECG, was lower in patients in whom the left anterior descending coronary artery (LAD) was the infarct-related coronary artery LAD vs. right coronary artery vs. left circumflex coronary artery (LCX): 3/11 [27.3%] vs. 4/6 [66.7%] vs. 11/16 [68.6%], p = 0.007). The above data indicate that the synthesized 18-lead ECG was useful for diagnosing STEMI in 18 of the 33 patients (54.5%). Furthermore, in 17 of the 18 patients (94.4%), the area of myocardium sup- plied by the infarct-related coronary artery was consistent with the site of infarction estimated from the ST ele- vation profile in the 6 synthesized leads.

Conclusion: The diagnosis of STEMI by synthesized 18-lead ECG is useful to identify the site of infarction in pa-

tients with infarction of the right ventricular wall (supplied by the RCA) or posterior wall of the left ventricle (supplied by the LCX), which often fail to be diagnosed by the standard 12-lead ECG.

(C) 2016 The Authors. This is an open access article under the CC BY-NC-ND license

(http://creativecommons.org/licenses/by-nc-nd/4.0/).

Introduction

The 2013 Guidelines for the management of ST-elevation myocardial infarction of the Japanese Circulation Society (JCS) and American Heart Association[1,2] recommend a standard 12-lead elec- trocardiogram (ECG) be obtained as soon as possible after hospital ar- rival in patients with suspected acute myocardial infarction (AMI) (Class 1). Guidelines of JCS recommends that a standard 12-lead ECG and a right chest lead (V_4R) be recorded in STEMI patients (Class I, evi- dence level B). The guidelines also recommend obtaining recordings from the posterolateral chest leads (V₇, V₈ and V₉) in patients with suspected AMI, when the diagnosis cannot be confirmed by the initially recorded ECG (Class IIa, evidence level B). A Scientific Statement from the American Heart Association[3] also describes that recordings from right-sided and posterior leads increase the diagnostic sensitivity for STEMI (Page 1760). However, electrode repositioning is required to ob- tain recordings from the right chest (V_3R, V_4R and V_5R) and

* Corresponding author at: Department of Cardiology, Nihon University Hospital, 1-6 Kanda-Surugadai, Chiyoda-ku, Tokyo 101-8309, Japan.

E-mail address: [email protected] (S. Tani).

posterolateral chest (V₇, V₈ and V₉) leads, with additional position change of the patient to lateral recumbent position also required for obtaining recordings from the posterolateral chest leads. Therefore, these leads are not recorded in a standard manner in clinical practice.

Recently, synthesized 18-lead electrocardiography, which can easily provide recordings from 6 synthesized leads, namely, right chest and posterolateral chest leads (syn-V_3R, syn-V_4R, syn-V_5R, syn-V₇, syn-V₈ and syn-V₉), using an algorithm based on the standard 12-lead ECG has been developed and begun to be used clinically[3]. Its principle is that instantaneous cardiac electromotive force vectors are continually calculated from the leads of a 12-lead ECG and can be processed to ob- tain recordings from the 6 synthesized leads, i.e., right chest and pos- terolateral chest leads (syn-V_3R, syn-V_4R, syn-V_5R, syn-V₇, syn-V₈ and syn-V₉)[4]. Wei et al. compared the ECG waveform parameters between the actually recorded right chest/posterolateral chest leads and those of the 6 synthesized leads, and reported a mean correlation coefficient of as high as 0.91[4].

Synthesized 18-lead ECG has the big advantage that it does not re- quire the complicated maneuvers needed for obtaining recordings from the right chest and posterolateral leads during 12-lead ECG, such as repositioning of the electrodes, thereby enabling rapid diagnosis of

http://dx.doi.org/10.1016/j.ajem.2016.11.052

0735-6757/(C) 2016 The Authors. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

ACS n = 103

AMI

n = 57 (55%)

UA

n = 33 (32%)

Cardiac arrest n = 13 (13%)

STEMI (n = 36) non-STEMI (n = 21 )

Exclusion

Patients did not undergo ECG within 10 minutes of seeing a doctor (n = 1), those in whom the ECG showed bundle branch block (n = 2).

STEMI (n = 33)

LAD (n = 11) LCX (n = 6) RCA (n = 16)

Fig. 1. Study flow chart. ACS = acute coronary syndrome; AMI = acute myocardial infarction; STEMI = ST-elevation myocardial infarction; non-STEMI = non-ST-elevation myocardial infarction.

left posterior ventricular infarction or of inferior infarction associated with Right ventricular infarction[5-8]. However, not many studies have been carried out to investigate the usefulness of synthesized 18-lead ECG for improving the rate of diagnosis of the site of infarction in STEMI patients presenting in cardiovascular emergency[9-11]. We hy- pothesized that synthesized 18-lead ECG is an excellent tool for improv- ing the rate of diagnosis of the site of MI, being particularly useful for the diagnosis in cases with right ventricular or left posterior wall infarction, which are often difficult to diagnose by the standard 12-lead ECG.

The purpose of this study was to investigate whether synthesized

18-lead ECG, which enables recordings to be obtained from 6 synthe- sized leads (syn-V_3R, syn-V_4R, syn-V_5R, syn-V₇, syn-V₈ and syn-V₉) dur- ing a standard 12-lead ECG, is useful to improve the diagnosis rate of the site of infarction in patients with STEMI.

Materials and methods

Study design and population

This study was a pilot retrospective case-series study conducted to investigate the efficacy of synthesized 18-lead ECG in the diagnosis of STEMI. Of 103 consecutive patients with acute coronary syndrome (ACS) who presented to Nihon University Hospital and underwent emergency coronary angiography, 33 with STEMI were enrolled in this study after excluding the remaining patients who fulfilled the exclusion criteria described below. The observation period was from October 1, 2014, to December 10, 2015. The definitive diagnosis of STEMI was made according to the criteria described in the guidelines for the man- agement of patients with ST-elevation acute myocardial infarction (JCS

(%)

P = 0.007

66.7%

68.6%

27.3%

3/11

4/6

11/16

n =15

45.5%

n =18

54.5%

100

90

80

70

60

50

40

30

20

10

0

LAD LCX RCA

Fig. 2. Comparison of the incidence of ST elevation in the 6 synthesized leads by the infarct-related coronary artery. LAD = left anterior descending; LCX = left circumflex; RCA = right coronary artery;

N=33

Fig. 3. Diagnosis of the site of infarction by the synthesized 18-lead ECG and standard 12- lead ECG. In 54.5% of the cases, while the standard 12-lead ECG proved insufficient to diagnose the site of infarction, the synthesized 18-lead ECG was provided the correct diagnosis.

Table 1

Relationship between the sites of infarction estimated from the ST elevation profile in the 6 synthesized leads and the area of the myocardium supplied by the infarct-related artery on coronary angiography.

Case IRA Infarct-related

lesion (AHA classification)

ST elevation in synthesized leads

Leads with ST elevation Cause of ST elevation in synthesized leads

RCA # 1 Synthesized right chest leads II?III?aV_F

syn-V_3R?syn-V_4R?syn-V_5R

# 3 Synthesized right chest leads II?III?aV_F

syn-V_3R?syn-V_4R?syn-V_5R

# 2 Synthesized right chest leads II?III?aV_F

syn-V_4R?syn-V_5R

The patient had right ventricular infarction.

Hypoperfusion of the right ventricular branch associated with reduced right Coronary blood flow due to contrast media-induced anaphylactic shock.

Delayed enhancement of the right ventricular branch (myocardial

hypoperfusion).

# 1 Synthesized posterolateral chest leads

# 1 Synthesized posterolateral chest leads

# 1 Synthesized right chest and synthesized posterolateral chest leads

# 2 Synthesized right chest and synthesized posterolateral chest leads

# 2 Synthesized right chest and synthesized posterolateral chest leads

# 3 Synthesized right chest and synthesized posterolateral chest leads

# 4AV Synthesized right chest and

synthesized posterolateral chest leads

# 3 Synthesized right chest and synthesized posterolateral chest leads

LCX # 13 Synthesized posterolateral chest leads

# 11 Synthesized posterolateral chest leads

# 13 Synthesized posterolateral chest leads

# 13 Synthesized right chest and synthesized posterolateral chest leads

II?III?aVF

syn-V7?syn-V8?syn-V9

II?aVF

syn-V7?syn-V8?syn-V9

II?III?aVF?V5?V6

syn-V4R?syn-V5R?syn-V7?

syn-V8?syn-V9

II?III?aVF?V₆,?syn-V4R? syn-V5R?syn-V7?syn-V8? syn-V9

II? III?aVF?

syn-V4R?syn-V5R?syn-V7? syn-V8?syn-V9

II? III?aVF?syn-V3R?

syn-V4R?syn-V5R?syn-V7? syn-V8?syn-V9

II?III?aV_F

syn-V_4R?syn-V_5R?syn-V₇?

syn-V₈?syn-V₉

II?III?aV_F

syn-V_4R?syn-V_5R?

syn-V₇?syn-V₈?syn-V₉ I?aV_L?V₅?V₆

syn-V₇?syn-V₈?syn-V₉

V5?V6

syn-V₇?syn-V₈?syn-V₉

II?III?aV_F

syn-V₈?syn-V₉

II?III?aV_F

syn-V_3R?syn-V_4R?syn-V_5R? syn-V₈?syn-V₉

The right coronary artery perfused up to the left ventricular posterior wall (There was collateral circulation from the conus branch to the right ventricular branch, resulting in no ST elevation in syn V3R-V5R).

The right coronary artery perfused up to the left ventricular posterior wall (The infarct vessel was spontaneously recanalized, resulting in no ST elevation in syn V3R-V5R).

The patient had right ventricular infarction. The right coronary artery perfused up to the left ventricular posterior wall.

Delayed enhancement of the right ventricular branch. The right coronary artery perfused up to the left ventricular posterior wall.

Delayed enhancement of the right ventricular branch. The right coronary artery perfused up to the left ventricular posterior wall.

Delayed enhancement of the right ventricular branch. The right coronary artery perfused up to the left ventricular posterior wall.

The right coronary artery perfused up to part of the left ventricular posterior wall (the coronary angiographic findings were inconsistent with the ECG findings, probably because a thrombus occluding the proximal right coronary artery moved distally to occlude the #4AV at the time of the coronary angiography).

Delayed enhancement of the right ventricular branch. The right coronary artery perfused up to the left ventricular posterior wall.

The left circumflex coronary artery perfused up to the left ventricular posterior. The left circumflex coronary artery perfused up to the left ventricular posterior.

The left circumflex coronary artery perfused up to part of the left ventricular posterior and inferior walls.

The left circumflex coronary artery perfused up to the left ventricular posterior and inferior walls and right ventricle.

LAD # 6 Synthesized right chest leads V₁?V₂?V₃?V₄

syn-V_3R?syn-V_4R

# 6 Synthesized right chest leads II? III?aVF

V₁?V₂?V₃?V₄

syn-V_3R?syn-V_4R?syn-V_5R

# 6 Synthesized right chest leads V₂?V₃?V₄?V₅?V₆

syn-V₇

There were branches originating from #7 and perfusing the right ventricle. There were branches originating from #7 and perfusing the right ventricle.

The left anterior descending coronary artery perfused up to part of the left ventricular posterior wall.

IRA = infarct-related coronary artery; AHA = American Heart Association; RCA = right coronary artery; LCX = left circumflex coronary artery; LAD = left anterior descending coronary artery.

2013)[1]. ECG-1450 (Nihon Kohden Corporation, Tokyo, Japan) was the device used in this study for obtaining the synthesized 18-lead electro- cardiographic recordings. The relevant data of the patients enrolled in the study were collected from the medical records of the patients and cardiac catheterization database.

The primary endpoint was comparison, by the infarct-related cor- onary artery (IRA), of the incidence of ST elevation in the 6 synthe- sized (syn-V_3R-V_5R or syn-V₇-V₉ leads). The secondary endpoint was comparison between the site of infarction as estimated from the ST elevation profile in the 6 synthesized leads and the area of the myocardium supplied by the IRA as assessed by coronary angiography.

Exclusion criteria consisted of patients who did not undergo electro- cardiography within 10 min of seeing a doctor, those in whom the ECG showed evidence of bundle branch block, and those who did not wish to provide consent for participation in this study.

Coronary risk factors were defined as follows for the purpose of this study: Hypertensive patients with an office systolic blood pressure of

>= 140 mm Hg or office diastolic blood pressure of >= 90 mm Hg or those receiving any antihypertensive drug; dyslipidemic patients with a serum low density lipoprotein (LDL) cholesterol level of >= 40 mg/dL, serum high density lipoprotein (HDL) cholesterol level of b 40 mg/dL or fasting serum triglyceride level of >= 150 mg/dL, or those receiving any drugs used to treat dyslipidemia; Diabetic patients with a fasting blood glucose level of >= 126 mg/dL and hemoglobin A1c (HbA1c) of

>= 6.5% or those receiving any antidiabetic agents or insulin, and current smokers.

Assessment of the ECG

The finding of synthesized 18-lead ECGs were determined in a blinded manner by a cardiologist who did not participate in this study

and was not informed of the purpose of the study. The ECG diagnostic criteria for STEMI were ST elevation (>= 1 mm; 1 mV = 10 mm) in 2 or more adjacent leads in the 12-lead ECG. ST elevation in the synthesized right chest leads (syn-V_3R, syn-V_4R and syn-V_5R), II, III and aV_F was de- fined as being diagnostic of inferior infarction associated with right ven- tricular infarction. ST elevation in the synthesized posterolateral chest leads (syn-V₇, syn-V₈ and syn-V₉) in addition to ST depression in V₁, V₂, V₃ and V₄ was defined as being diagnostic of acute high posterior in- farction. ST elevation in the synthesized posterolateral chest leads (syn- V₇, syn-V₈ and syn-V₉), V₅ and V₆ was defined as being diagnostic of an- terior and posterior infarction. ST elevation in the synthesized

posterolateral chest leads (syn-V₇, syn-V₈ and syn-V₉), I, aV_L and V₁- V₆ was defined as being diagnostic of extensive anterior and posterior infarction.

This study was conducted with the approval of the Ethics Committee of Nihon University Hospital (approval number, 160102).

Statistical analysis

For the statistical analysis, continuous variables were represented as mean +- standard deviation and nominal variables in nominal scales (%). Chi-square test was used for comparing 2 or 3 groups, with the

Fig. 4. a: Case 6; ECG showed ST elevation in leads syn-V_4R-V_5R and syn-V₇-V₉ in addition to that in leads II, III, aV_F, V₅ and V₆ (upper panel). Initial coronary angiography revealed complete occlusion of the RCA #1 (lower left panel, arrow). After reperfusion therapy, coronary angiography revealed that the area of the myocardium supplied by the IRA covered the right ven- tricle, inferior wall and left ventricular posterior wall (lower right panel). b: Case7; ECG showed ST elevation in leads syn-V_4R, V_5R and syn-V₇-V₉, in addition to that in leads II, III, aV_F and V₆ (upper panel). Initial coronary angiography (lower left panel) revealed complete occlusion of the RCA #2 (arrow). The right ventricular branch showed delayed enhancement, but no in- terruption of the blood flow was found (arrowheads). Six months later, coronary angiography revealed that the area of the myocardium supplied by the IRA covered the left ventricular inferior and posterior walls (lower right panel). Even the slight ischemia of the right ventricle caused ST elevation in the right chest leads. Coronary artery computed tomography (CT) shows similar findings (panel b-2). c: Case 13; ECG shows leads V_1,2 with an R/S ratio of N 1 and ST elevation in leads V₅, V₆ and syn-V₇-V₉ (upper panel). Initial coronary angiography (lower left panel) shows complete occlusion of the proximal LCX (arrow). After reperfusion therapy, coronary angiography revealed that the area of the myocardium supplied by the IRA covered the left ventricular posterior and lateral walls (lower right panel). d: Case 15; ECG shows ST elevation in leads II, III, aV_F, syn-V_3R-V_5R and syn-V₈-V₉ (upper panel). Before reperfusion (lower left panel), coronary angiography revealed subtotal occlusion of the middle LCX associated with delayed enhancement (arrow). After reperfusion therapy (lower right panel), coronary angiography revealed branches originating from the LCX and perfusing part of the inferior wall, right ventricle and left ventricular posterior and lateral walls (ar- rowheads). e-1: Case 17; ECG shows ST elevation in leads V₁-V₄, II, III, aV_F and syn-V_3R-V_5R (upper panel). Before reperfusion (lower left panel), coronary angiography revealed complete occlusion of the LAD #6 (arrow). After reperfusion therapy (lower right panel), coronary angiography revealed branches originating from the LAD and perfusing part of the right ventricle (arrowheads). Coronary artery CT shows similar findings (arrows; panel-e-2).

Fig. 4 (continued).

Fig. 4 (continued).

level of statistical significance set at p b 0.05. The statistical analysis soft- ware SPSS Windows, version 12.0 (Statistical Package for the Social Sci- ences, SPSS Ins., Chicago, IL), was used.

Results

Patients

The study flow chart is shown inFig. 1. We included the ECG and cor- onary artery angiographic findings of 33 patients with STEMI (IRA: left anterior descending coronary artery (LAD) in 11 cases, left circumflex coronary artery (LCX) in 6 cases, and right coronary artery in 16 cases) for the analysis in this study.

The mean age of the subjects enrolled was 64.2 +- 23.5 years, and 32 (97.0%) of the patients were male. The mean body mass index was

23.9 +- 5.7 kg/m². Of the 33 subjects, 23 (69.7%) had hypertension, 22

(66.7%) had dyslipidemia, 11 (33.3%) had diabetes and 12 (36.4%) were smokers.

Comparison of the incidence of ST elevation in the 6 synthesized leads by the infarct-related coronary artery

Comparison by the IRA revealed that the proportion of patients with ST elevation in any of the 6 synthesized leads was lower in patients in whom the LAD was the IRA, with significant differences (p = 0.007) among the 3 groups divided according to the IRA (i.e., the LAD, LCX, and RCA groups) (Fig. 2).

The incidence of ST elevation in the synthesized leads (any of the syn-V_3R-V_5R and syn-V₇-V₉ leads) was significantly higher in patients in whom the RCA or the LCX was the IRA (15 of 22 patients [68.2%]) than in those in whom the LAD was the IRA (3 of 11 patients [27.3%]) (p b 0.0001).

The proportion of patients with ST elevation in any of the 6 synthe- sized leads in addition to ST elevation in the standard 12-lead ECG was 54.5% (18 of the 33 patients). In addition, the proportion of patients in whom the site of infarction could be diagnosed from the standard 12- lead ECG alone, i.e., when there was no ST elevation in the 6 synthesized leads, was 45.5% (15 of the 33 patients) (Fig. 3).

Fig. 4 (continued).

Relationship between the sites of infarction estimated from the ST ele- vation profile in the 6 synthesized leads and the area of the myocardium supplied by the infarct-related artery on coronary angiography

Of the patients in whom the LAD was the IRA, 2 had ST elevation in only one or more of the syn-V_3R-V_5R leads, 1 had ST elevation in only one or more of the syn-V₇-V₉ leads, and 0 had ST elevation in one or more of the syn-V_3R-V_5R leads and one or more of the syn-V₇-V₉ leads. Of the pa- tients in whom the LCX was the IRA, 3 had ST elevation in only one or more of the syn-V_3R-V_5R leads, 0 had ST elevation in only one or more of the syn-V₇-V₉ leads, and 1 had ST elevation in one or more of the syn-V_3R-V_5R leads and one or more of the syn-V₇-V₉ leads. Of the pa- tients in whom the RCA was the IRA, 3 had ST elevation in only one or more of the syn-V_3R-V_5R leads, 2 had ST elevation in only one or more of the syn-V₇-V₉ leads, and 6 had ST elevation in one or more of the syn-V_3R-V_5R leads and one or more of the syn-V₇-V₉ leads.

Furthermore, the relationship between the site of infarction estimat- ed from the ST elevation profile in the 6 synthesized leads and the area of the myocardium supplied by the IRA on coronary angiography was investigated in each patient (Table 1). The site of infarction estimated from the ST elevation profile in the 6 synthesized leads was consistent with the area of the myocardium supplied by the IRA on coronary

angiography in the majority of the patients. Namely, of the patients with evidence of STEMI on the 12-lead ECG, those in whom the right ventricle was the perfusion area of the IRA showed ST elevation in the synthesized right chest leads and those in whom the left ventricular posterior wall was the perfusion area of the IRA showed ST elevation in the synthesized posterolateral chest leads (Fig. 4a-d).

However, this relationship was inconsistent in one of the 18 patients (Case 10). This was eventually attributed to a thrombus occluding the proximal right coronary artery moving distally at the time of the coro- nary angiography.

Discussion

The main findings of the study were as follows: 1) The incidence of ST elevation in the 6 synthesized leads was significantly higher in pa- tients in whom the RCA or the LCX was the IRA than in those in whom the LCX was the IRA, consistent with the anatomical feature of the RCA and LCX perfusing the right ventricle and left ventricular posterior wall, respectively; 2) In 54.5% of the patients, ST elevation was seen only in any of the 6 synthesized leads, i.e., the standard 12-lead ECG alone was insufficient to diagnose the site of infarction, while the synthesized 18-lead ECG was effective for diagnosing the site of infarction; 3) In the

Fig. 4 (continued).

majority of patients with ST elevation in any of the 6 synthesized leads, the site of infarction estimated from the ST elevation profile in the 6 syn- thesized leads was consistent with the area of the myocardium supplied by the IRA on coronary angiography, and this information could not be obtained from the 12-lead ECG.

The above findings suggest that synthesized 18-lead ECG is more useful than the standard 12-lead ECG for diagnosis of the site of infarc- tion in STEMI patients, particularly, those presenting with infarction of the right ventricle or left ventricular posterior wall, lending support to the hypothesis proposed by us in this study. Furthermore, no previous studies have compared the site of infarction estimated from the ST ele- vation profile in the 6 synthesized leads and the area of supply of the infarct-related artery determined by coronary angiography, and this is a new finding. In future studies, further close comparison of the findings of synthesized 18-lead ECG and coronary angiography is necessary.

Standard 12-lead ECG findings are essential for early diagnosis and early therapeutic intervention in patients with ACS (Class 1, evidence level A)[1,2]. However, the standard 12-lead ECG does not provide suf- ficient information about the status of the right ventricle or posterior surface of the heart[12]. Zalenski et al. reported that the addition of re- cordings from right chest (V_3R, V_4R and V_5R) and posterolateral chest (V₇, V₈ and V₉) leads to the standard 12-lead ECG increased the diag- nostic sensitivity for AMI by 8%[13] and that a 15-lead ECG containing V_4R, V₈ and V₉ leads in addition to the 12 standard leads increased the diagnostic rate of AMI by approximately 22% as compared to the stan- dard 12-lead ECG[14]. Melendez et al. reported that in approximately 7% of AMI patients, ECG changes were found only in the posterolateral chest leads (V₇, V₈ and V₉), with no ST changes in the standard 12- lead ECG[15].

In addition, Katoh et al. reported that comparison between the waveforms obtained from the synthesized 18-lead ECG and the actually recorded waveforms in patients transported to the coronary care unit complaining of chest pain revealed high correlations in all ECG parame- ters, such as the P-wave, QRS, QT time and T-wave characteristics[16]. Recently, Tamura et al. reported that there was a strong positive corre- lation between the degree of ST elevation in syn-V_3R, syn-V_4R and syn- V_5R and the actually recorded degree of ST elevation in V_3R, V_4R and V_5R when the relevant coronary artery was occluded[17].

To obtain ECG recordings from the posterolateral chest leads, the electrodes have to be repositioned to the posterior axillary line, inferior angle of the scapula and left edge of the spinal column for obtaining V₇, V₈ and V₉ lead recordings, respectively, necessitating a change of the pa- tient’s position to lateral recumbent position. It is assumed that holding a posture is difficult for patients complaining of severe chest symptoms. In addition, electrode repositioning is also required to obtain recordings from the right chest leads. However, recording from the 6 synthesized leads has the advantage that it does not require a change in the patient’s position or electrode repositioning.

Synthesized 18-lead ECG, unlike the standard 12-lead ECG, covers the entire heart, thereby enabling estimation of the size of the myocar- dial ischemic area by monitoring the ST elevation profile in the ECG leads. This estimation during the Hyperacute phase may lead to a de- crease in STEMI mortality. In addition, in a previous study, we placed a synthesized 18-lead electrocardiograph in the emergency department to investigate whether it would improve the diagnostic rate of STEMI, and found that synthesized 18-lead ECG improved the diagnostic rate of STEMI by 13% as compared to the standard 12-lead ECG[18]. The placement of a synthesized 18-lead electrocardiograph in the emergen- cy department may increase the early diagnosis rate of STEMI and en- able Rapid treatment, thereby minimizing the extent of infarction and reducing the incidence of associated cardiac events.

In addition, it should be noted that ST elevation in the synthesized right chest leads was not only seen in patients with complete occlusion of the right ventricular arterial branch causing right ventricular infarc- tion, but also in patients with decreased perfusion associated with de- layed enhancement of the right ventricular arterial branch. Namely, ST

elevation in the synthesized right chest leads in synthesized 18-lead ECG may also be useful for detecting hypoperfusion of the right ventri- cle (Fig. 4-b).

Furthermore, in this study we encountered a patient with complete occlusion of the proximal LAD who showed ST elevation in the synthe- sized right chest leads. This patient had anterior infarction with branches originating from the LAD and perfusing the right ventricle, which is difficult to detect by coronary angiography[19,20]. James re- ported that side branches of the LAD perfuse 30% of the right ventricular free wall in 24% of human hearts[21]. Synthesized 18-lead ECG can ad- ditionally record right chest leads, and is therefore probably useful for identifying such patients (Fig. 4-e).

Study limitations

First, this was a single-center retrospective case-series study, with no established protocol for the initial treatment of patients presenting with ACS, and there may have been a patient selection bias. Second, the duration of ST elevation in the right chest leads depends on the time from the onset of myocardial infarction, and there may have been some patients in whom the ST elevation had regressed by the time of arrival at the hospital[22,23]. Third, it is necessary to compare the measured ST changes in the right chest and posterolateral chest leads with the ST changes in the 6 synthesized leads. Lastly, it cannot be clearly said that the results of this study represent a whole picture of the usefulness of synthesized 18-lead ECG in the diagnosis of STEMI. It is necessary to conduct further studies with a larger number of patients.

Conclusion

We showed that synthesized 18-lead ECG, which compensates for the weaknesses of the standard 12-lead ECG, considered to be useful for the emergency diagnosis of STEMI, may be an excellent tool for early and accurate diagnosis of the site of STEMI. We think that dissem- ination of the easily usable synthesized 18-lead ECG is necessary to im- prove the quality of emergency cardiovascular care in the future.

Disclosure

The authors have no conflicts of interest to disclose.

Acknowledgment

The authors wish to express their gratitude to the CCU staff doctors for their great assistance in collecting ECG data. The authors also wish to thank the following physicians for their gracious assistance and coop- eration with this study; Dr. Shori Takahashi, Dr. Shinichiro Kokubun, Dr. Hiroaki Nakazawa, and Dr. Masami Takei. The authors would like to thank International Medical Information Center (www.imic.or.jp/ services/translation.html) for the English language review.

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