Prevalence of ST-elevation in right precordial leads in patients presenting with acute coronary syndrome without ST-elevation in standard 12-lead electrocardiography.

ABSTRACT

Objective: The aim of this preliminary study was to determine the prevalence of isolated ST-elevation in the right precordial leads and the potential impact the addition had to risk stratification in patients with acute coronary syndrome.

Methods: Right-sided precordial leads (V4R, V5R and V6R) were routinely added to standard 12-lead electrocardiogram (ECG) on all patients presenting with acute coronary syndrome at the Tygerberg cardiac unit for a 7-month period. Patients without ST-elevation on standard 12-lead ECG were selected and evaluated for isolated right-sided ST-elevation. Demographic data, ECG-characteristics and cardiac enzymes were also recorded. Risk scoring using the TIMI-risk score was done and patients with isolated ST-elevation in right-sided leads without ST-changes (i.e. depression) in 12-lead ECG were experimentally awarded another point. Coronary angiography if performed was also noted.

Results: Seventy-seven patients were selected, among them 4 patients (5.19%) had isolated ST-elevation in right-sided ECG. Only 1 patient (1.3%) was awarded an additional point for ST-elevation in right-sided leads without ST-depression on 12-lead ECG increasing the TIMI score from 6 to 7. Angiography revealed no patients with isolated right-sided ST-elevation with non-dominant right coronary artery occlusion.

Conclusion: The addition of right-sided leads did not alter risk scoring significantly and therefore the results of this study do not support the routine addition of such leads. This study also did not prove that isolated ST-elevation occurs in right-sided leads in patients with occluded non-dominant right coronary arteries. (Anadolu Kardiyol Derg 2007: 7 Suppl 1; 182-5)

Key words: electrocardiography, coronary artery disease 

Introduction

With the limited availability of specialist referral and equipment in developing countries like South Africa there is a continuous need to develop ready available ways of early identification of high-risk acute coronary syndrome (ACS) patients that will benefit from early referral and treatment. Due to the ready availability of electrocardiograms (ECG) in most emergency units in developing countries, electrocardiography remains an essential tool for initial risk stratification and consequently the decision on further management. Developing ways to improve risk stratification using ECG will therefore be beneficial in developing countries.

The use of right precordial leads (V4R, V5R and V6R) to identify right ventricular infarction in the setting of an inferior left ventricular ST-elevation infarction has been well studied and documented (1-6) with a sensitivity reported between 70-100% and specificity between 68-100% (7). Right myocardial infarction tends to occur in conjunction with inferior myocardial infarction (8, 9) with proximal occlusion of the right coronary artery (RCA) which can be explained on the anatomical basis of the RCA supplying both the right ventricle and inferior left ventricle in right dominant coronary circulations (1) (Fig. 1).

[FIGURE 1 OMITTED]

Approximately 25% (range 20-60%) of inferior left ventricle infarctions are complicated by right ventricular infarction (10). Due to the markedly higher occurrence of right dominant coronary circulations (89%) in the general population (11), association with left inferior ventricular infarcts is the most common presentation of right ventricular infarction (Fig. 2). The usage of right precordial leads are therefore traditionally indicated when inferior myocardial infarction is identified on standard 12-lead ECG.

[FIGURE 2 OMITTED]

Isolated right ventricular infarction does however occur but is rare (8, 9, 12) (less than 3% of myocardial infarctions). Case studies suggest that this tends to occur in patients with non-right dominant coronary circulation (12-18). Occlusion of such a RCA (Fig. 3) will lead to infarction of the right ventricle while the inferior left ventricle is perfused by the left coronary artery. Isolated right ventricular infarction with significant ST-segment elevation only in right precordial leads with little or no elevation on standard 12 lead ECGs have also been reported (19, 20).

[FIGURE 3 OMITTED]

It was this hypothesis that lead to the initiation of this study. We postulated that patients presenting with ACS without ST-elevation in standard 12-lead ECG may have isolated right ventricular infarction with ST-elevation in right precordial leads due to occlusion of a non-dominant RCA. Furthermore, we postulate that this finding could identify an additional higher risk group for further myocardial events and consequently alter risk assessment.

Previous studies suggest that the addition of right precordial leads to standard 12-lead ECG improves sensitivity (by 6.7%) but decreases specificity (by 5.4%) for detecting acute myocardial infarction in patients (20, 21). It is suggested that the addition of such leads are probably only beneficial in determining prognosis and therefore risk stratification rather increased detection of infarction (21). A survey done on emergency department physicians concluded that physicians felt that the addition of such leads only adds information regarding the extent of myocardial injury rather than altering diagnostic or therapeutic issues (22). These studies however entailed the use of both posterior and single (V4R) right-sided precordial leads and assessed the use of such leads in detecting myocardial infarction and not risk stratification per se. The routine use of right-sided ECGs for determining risk stratification therefore remains an unresolved issue.

The aim of this pilot study was to determine the prevalence of ST-elevation in right precordial leads in patients presenting with ACS without ST-elevation in standard 12-lead ECGs (therefore unstable angina pectoris and non-ST-elevation myocardial infarction) and the impact the addition had on risk assessment. Risk scoring and prognostication by means of the TIMI risk score (23) (Table 1) for unstable angina or non-ST elevation myocardial infarction has recently been introduced and is widely implemented. The impact the addition of right-sided ECGs have on TIMI scores will be evaluated and whether it contributed towards identifying a potential group at higher risk for further events that would normally be missed. This could give an indication of the potential usefulness of performing routine right precordial leads electrocardiography in all patients presenting with ACS.

As right-sided precordial leads are placed with little additional effort when performing standard ECGs, such routine use could be easily implemented. If the addition of right-sided leads were to alter the risk assessment in patients, it may assist the physician faced with the decision on further management of patients with ACS without ST-elevation on standard 12-lead ECG.

Methods

The study design was that of an observational study. Patients presenting to the cardiac unit of Tygerberg hospital were studied during a period of 7 months (January--July 2006). All patients admitted to the coronary unit underwent routine conventional 12-lead electrocardiography with the routine addition of right-sided precordial leads (V4R, V5R and V6R).

Patients deemed to have ACS (typical chest pain, associated symptoms) according to the attending registrar were selected but excluded if ST-elevation was present on the initial standard 12-lead ECG according to the investigator or the attending registrar. ST-elevation was considered to be present if elevation of the ST-segment was more than 1 mm (0.1mV) above the isoelectric line in two or more anatomically adjacent leads. Patients were furthermore excluded if right-sided leads were not performed on presentation, were not clearly indicated on the electrocardiogram, if the ECG was not interpretable (e.g. presence of left bundle branch block, severe arrythmias) or if the patient had chest pain due to proven other causes.

The ECGs were furthermore evaluated by a cardiologist blinded to all aspects of the patient's clinical picture and management, who confirmed the absence of ST-elevation on 12-lead ECG and either the presence or absence of ST elevation on right-sided leads.

Risk scoring was done retrospectively according to the TIMI risk scoring system (23) (Table 1) using the standard 12-lead ECG. This includes scoring a point if ST-segment changes (i.e. depression more than 0.5mm) occurred. Patients were experimentally awarded another point if ST-elevation of more than 1mm (0.1mV) was present in more than 2 adjacent right-sided leads without any ST-changes in standard 12-lead ECG (i.e. ST-depression >0.5mm).

The age, sex, characteristics of the ECG (rhythm, axis, P-waves, PR interval, QRS-complex, ST-segment, T-waves and QT time) of the standard 12-lead electrocardiograms, initial cardiac enzymes (troponin-I and creatinine kinase) and coronary angiography (if performed) were also recorded.

Results

Overall, 109 patients were selected but 32 were excluded for the following reasons: 3 were proven to have other diagnoses than ACS, 1 had an uninterpretable rhythm, 16 had a left bundle branch block, right-sided leads were not appropriately indicated in 3 patients and 9 patients had ST-elevation on the standard 12-lead ECG (verified by a cardiologist). Seventy-seven patients were therefore selected and initial electrocardiograms were evaluated for the presence of ST-elevation in the right precordial leads.

The mean age of the patients was 62.15 [+ or -] 2.05 years with an age rage from 28 to 89 years. Gender distribution was slightly shifted towards male with 54.4% of patients being male and 45.5% female. Among 77 patients 63 (81.8%) had positive cardiac enzyme markers contributing a point to the TIMI-risk score and 29 of the 77 patients (37.7%) had ST-segment changes contributing towards TIMI-risk scoring. In 48 patients (62.3%) ECG changes did not contribute to risk scoring. Of 77 patients 52 (67.5%) of the study group underwent coronary angiography. A summary of the data is presented in Table 2.

Patients were stratified in all 8 the TIMI score-groups (0-7) with the majority of patients stratified in the intermediate risk group. TIMI scores are summarized in Table 3 and graphically represented in Figure 4.

Four patients (5.19%) had isolated ST-elevation in right-sided leads (Fig. 5). All four patients had positive cardiac markers. In 3 of the 4 patients ST-segment depression occurred in the standard 12-leads. Two of patients' (50%) scores were 4 points and 2 patients' (50%)--were 6 points. Therefore, only 1 patient was awarded an additional point where ST-depression was absent in the 12-lead ECG but right-sided ST-elevation was present in the right-sided leads. This increased the patient's score from 6 to 7. Angiography on this patient was not justified due to end stage ischemic disease previously demonstrated and was therefore unavailable. The addition of the right-sided leads therefore only altered risk scoring in 1 patient (1.30%). Three of the 4 patients underwent coronary

[FIGURE 5 OMITTED]

Coronary angiography findings in the remaining 3 patients are as follows: the first patient had a moderately obstructed left anterior descending artery (LAD) with an unobstructed non-dominant RCA (Fig. 3). The second patient revealed a totally occluded left circumflex coronary artery, proximal stenosis of the LAD and a critical lesion in a dominant RCA occluding one of the right ventricular branches (Fig. 6). The last patient had a complex angiogram with evidence of a previous coronary artery bypass with complete occlusion of the left circumflex artery and LAD with diffuse disease of the RCA.

[FIGURE 6 OMITTED]

Discussion

Experience from this study showed that the probability of having right-sided precordial leads available in patients with ACS is increased by performing right-sided ECGs routinely on all patients presenting to an emergency unit. This is done with little additional effort and cost.

However, only a small percentage (5.19%) of patients presenting with ACS have isolated ST-elevation in right precordial leads. This addition minimally contributed to risk stratification as experimentally set out in our study design. In only one patient (1.30%) did the addition alter risk scoring and this did not change the risk group for this patient who was stratified already into the high risk group with a TIMI score of 6 before the addition of right- sided precordial leads was made.

The study did not support our hypothesis that isolated ST-elevation in right-sided leads occurs in patients with occluded non-dominant right coronary arteries, as none of the patients with isolated right-sided ST-elevation revealed to have such pathology on angiography. Angiographic data however suggested the possibility that occlusion in a dominant RCA, which involves right ventricular branches could also manifest as isolated right-sided ST-elevation or that isolated right sided ST-elevation may be a non-specific finding. This is however a topic for future research.

Due to the low yield of significant findings, this study does not support the routine use of right-sided electrocardiography in emergency units for risk stratification if the initial ECG does not show ST-elevation. However due to low cost and low effort involved in performing such ECGs routinely and the previously reported increased sensitivity for identifying myocardial infarction by performing routine right-sided ECGs, routine addition of right-sided ECG to standard 12-lead ECG cannot be discouraged.

Study limitations

The principle investigator was not a cardiologist with limited experience in assessing ECGs and was not blinded to the patient's clinical picture or management, and could therefore have lead to selection bias. All ECGs were however evaluated by a blinded cardiologist in order limit such error.

References

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(21.) Zalenski RJ, Rydman RJ, Sloan EP, Hahn K, Cooke D, Tucker J, et al. ST segment-elevation and the prediction of hospital life-threatening complications. J Electrocardiol 1998; 31 (Suppl): 164-71.

(22.) Brady WJ, Hwang V, Sullivan R, Chang N, Beagle C, Carter CT, et al. A comparison in ED chest pain patients: Impact on diagnosis, therapy and disposition. Am J Emerg Med 2000; 18: 239-43.

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Elmo Pretorius, Anton F. Doubell

Cardiology unit, Internal Medicine Division, Department of Medicine, Faculty of Health Sciences, University of Stellenbosch and Tygerberg Hospital, Tygerberg, South Africa

Address for Correspondence: Dr. Elmo Pretorius, PO Box 73623 Fairland 2030, South Africa Professor Anton Doubell, Cardiology unit, PO Box 19063, Tygerberg, 7505, South Africa Phone: [phone] Fax: [phone] E-mail: [e-mail], [e-mail]

* This study was performed as an undergraduate student assignment at the abovementioned institution

Table 1. TIMI risk score for unstable angina/non-ST
elevation myocardial infarction (adapted from www.timi.org)

Historical                           Points

Age [greater than or                   1
equal to] 65 years

[greater than or                       1
equal to] 3 Coronary
artery disease
risk factors
(family history,
hypertension,
hypercholesterolemia,
diabetes mellitus,
active smoker)

Known coronary                         1
artery disease
(more than
50% stenosis)

Aspirin use in                         1
past 7 days

Presentation

Recent ([less than                     1
or equal to] 24
hours) severe angina

Raised cardiac markers                 1
ST-deviation =0.5 mm                   1

TOTAL SCORE = TOTAL POINTS (0-7)

Table 2. Summary of patient data

Number of patients                     77

Age range, years                     28-89

Mean age, years               62.15 [+ or -] 12.05

Males, n (%)                       42 (54.5)

Females, n (%)                     35 (45.5)

Patients with ST-segment           29 (37.7)
changes on standard
12- lead ECG, n (%)

Enzyme markers                     63 (81.8)
positive, n (%)

Patients that underwent            52 (67.5)
coronary angiography, n (%)

ECG- electrocardiogram

Table 3. Summary of TIMI-scores

TIMI score            0         1         2         3

All patients          1         8        15        19
(n=77), n (%)      (1.30)    (10.39)   (19.40)   (24.68)

Patients without      1         8        15        19
right-sided ST-    (1.37)    (10.96)   (20.55)   (26.03)
elevation
(n=73), n (%)

Patients with         0         0         0         0
right-sided        (0.00)    (0.00)    (0.00)    (0.00)
ST-elevation
(n=4), n (%)

TIMI score            4         5         6         7

All patients         21         7         4         2
(n=77), n (%)      (27.27)    9.09)    (5.19)    (2.60)

Patients without     19         7         2         2
right-sided ST-    (26.03)   (9.59)    (2.74)    (2.74)
elevation
(n=73), n (%)

Patients with         2         0         2         0
right-sided        (50.00)   (0.00)    (50.00)   (0.00)
ST-elevation
(n=4), n (%)

Figure 4. Graphic representation of TIMI scores

TIMI Score                  Number of patients

             All patients    Patients without   Patients with
                               right-sided       right-sided
                               ST-elevation      ST-elevation

0                  1                1                 0
1                  8                8                 0
2                 15               15                 0
3                 19               19                 0
4                 19               19                 2
5                 7                 7                 0
6                 4                 2                 2
7                 2                 2                 0

Note: Table made from bar graph.