Correspondence
Exercise Electrocardiography with Right Precordial Leads
N Engl J Med 1999; 341:208-210July 15, 1999
- Article
To the Editor:
The key to the validity of any study of a diagnostic test is a systematic comparison with an accepted gold standard. Using the coronary angiogram as the gold standard, Michaelides et al. (Feb. 4 issue)1 conclude that the use of right-sided leads improves the diagnostic performance of the exercise electrocardiogram.
Most studies of exercise electrocardiography that use coronary angiography as a gold standard suffer from a sequential workup bias: the decision whether or not to perform coronary angiography rests in the hands of clinicians who are aware of the results of exercise electrocardiography. Patients with normal results are unlikely to undergo coronary angiography. This workup bias leads to inflated sensitivity and deflated specificity.2 The clinical importance of this bias was reported in a recent study by Froelicher et al.,3 in which a population of more than 800 men with chest pain prospectively agreed to undergo both exercise electrocardiography and coronary angiography, irrespective of the stress-test results. In this group of patients, the sensitivity of the exercise electrocardiogram was only 45 percent, whereas in another group of patients who were studied in a more traditional way, the sensitivity was 65 percent.
It is noteworthy that in the study by Michaelides et al., the sensitivity of the standard exercise electrocardiogram was 66 percent, which is in line with the results in the traditional group in the study by Froelicher et al. and with the results in most studies with this workup bias.4 Unfortunately, Michaelides et al. do not provide essential information that would allow an evaluation of the internal validity of the study. They do not state whether the clinicians were aware of the results of the analyses involving right precordial leads. If the clinicians were aware, it is possible that patients with abnormalities in those leads might have been more likely to be referred for coronary angiography.
This study has the potential to have an important effect on our assessment of coronary artery disease. However, an assurance that a sequential workup bias was not present in this study would go a long way toward confirming its internal validity.
4 ReferencesMichael S. Lauer, M.D.
Christopher Cole, M.D.
Cleveland Clinic Foundation, Cleveland, OH 44195Harlan M. Krumholz, M.D.
Yale University, New Haven, CT 06520-80251
Michaelides AP ,Psomadaki ZD ,Dilaveris PE , et al. Improved detection of coronary artery disease by exercise electrocardiography with the use of right precordial leads. N Engl J Med 1999;340:340-345
Full Text | Web of Science | Medline2
Choi BC . Sensitivity and specificity of a single diagnostic test in the presence of work-up bias. J Clin Epidemiol 1992;45:581-586
CrossRef | Web of Science | Medline3
Froelicher VF ,Lehmann KG ,Thomas R , et al. The electrocardiographic exercise test in a population with reduced workup bias: diagnostic performance, computerized interpretation, and multivariable prediction. Ann Intern Med 1998;128:965-974
Web of Science | Medline4
Gianrossi R ,Detrano R ,Mulvihill D , et al. Exercise-induced ST depression in the diagnosis of coronary artery disease: a meta-analysis. Circulation 1989;80:87-98
CrossRef | Web of Science | Medline
To the Editor:
Michaelides et al. suggest that the sensitivity of their technique using right precordial leads was “similar to that of thallium-201 scintigraphy for the detection of disease.” In the accompanying editorial, Wellens1 comments that the technique “improves the sensitivity of exercise electrocardiography and is less expensive than thallium-201 exercise testing.”
These conclusions are defensible with respect to the study population but cannot be extrapolated to a general group of patients referred for assessment of chest pain. This point is important because the following groups of patients were excluded from the study: patients with left or right bundle-branch block, left or right ventricular hypertrophy, ventricular preexcitation, a history of myocardial infarction, valvular or congenital heart disease, or a history of bypass surgery or angioplasty and those who were receiving digitalis.
Thallium-201 scintigraphy has a major role in the management of coronary artery disease because it is far less susceptible to false positive findings in all the groups of patients that were excluded from the study. The excluded groups represent a considerable proportion of the patients who are seen in general cardiologic practice. Therefore, the conclusions that the diagnostic yield of the two methods is equivalent and that the new technique costs less than thallium imaging clearly do not apply to the general population. Those conclusions are an example of the overextrapolation of findings from a specific group to the general population.
1 ReferencesDudley Pennell, M.D.
Royal Brompton Hospital, London SW3 6NP, United Kingdom1
Wellens HJJ . The value of the right precordial leads of the electrocardiogram. N Engl J Med 1999;340:381-383
Full Text | Web of Science | Medline
To the Editor:
In his excellent editorial on the value of right anterior chest leads in electrocardiography, Wellens does not mention recent studies that used left posterior chest leads. Right anterior chest leads can be used to show which acute transmural inferoposterior myocardial infarctions are complicated by right ventricular infarction, whether occlusion of the right coronary artery or of the left circumflex artery caused the infarction, and the site of the occlusion in the involved coronary artery. Agarwal et al. have shown that left posterior chest leads can be used to indicate which acute myocardial infarctions with anterior ST-segment depression that could be misconstrued as non–Q-wave infarction are actually due to transmural myocardial infarction related to occlusion of the circumflex artery.1 The combination of these two approaches should now enable us to identify transmural infarction more accurately and to pinpoint the diseased artery that has caused the infarction. Such a three-vessel classification should yield more accurate information on clinical variation than the standard two-wall electrocardiographic classification.2
2 ReferencesHerbert E. Cohen, M.D.
Thomas Jefferson University Hospital, Philadelphia, PA 191071
Agarwal JB ,Khaw K ,Aurignac F ,LoCurto A . Importance of posterior chest leads in patients with suspected myocardial infarction, but nondiagnostic, routine 12-lead electrocardiogram. Am J Cardiol 1999;83:323-326
CrossRef | Web of Science | Medline2
Cohen HE . Myocardial infarction classification. Am J Cardiol 1984;53:651-651
CrossRef | Web of Science | Medline
To the Editor:
Michaelides et al. and Wellens describe the usefulness of right-chest electrocardiographic leads in the analysis of exercise stress tests for the detection of coronary heart disease. Our only concern is the use of the term “right precordial leads” throughout the article and the editorial. Clearly, the adjective “precordial” refers to the area “situated or occurring in front of the heart.”1 Because the heart is almost always in the left side of the chest, the term “right precordial leads” should be reserved for patients with dextrocardia. We suggest that leads V1R through V6R be called “right chest leads” and that “left chest leads” be used in the rare case of dextrocardia. We have been recommending this nomenclature for many years to students, house staff, and attending physicians in our heart station and in our weekly electrocardiographic conferences, with little success. The term “right precordial” seems more firmly entrenched than ever. If we can convert editors and authors to our belief in the value of precise terminology, perhaps others will follow.
1 ReferencesHarold Smulyan, M.D.
C. Thomas Fruehan, M.D.
State University of New York Health Science Center at Syracuse, Syracuse, NY 13210Author/Editor Response
The authors reply:
To the Editor: Drs. Smulyan and Fruehan suggest that leads V1R to V6R should preferably be termed “right chest leads.” Although we followed the paradigm of many previous investigators1,2 who also used the term “right precordial leads,” we have to admit that this term may be misleading. Since we respect the value of precise terminology, we shall take into serious consideration the use of the term “right chest leads” in future publications.
Lauer et al. note that the fact that patients with normal exercise electrocardiograms are the most likely to refuse to undergo coronary angiography may cause a workup bias, which could lead to inflated sensitivity. In our study, which was undertaken in a referral center affiliated with Athens University, only 23 of 268 eligible patients (8.6 percent) refused to undergo coronary angiography and were consequently excluded from the study population. Taking into account that six of them (26 percent) had positive exercise tests on the basis of ST-segment deviation on the standard 12-lead electrocardiogram and that the clinicians were blinded to the results of analyses involving right chest leads, we hypothesize that our results could have been only marginally affected by this bias. Moreover, the fact that the sensitivity of the standard exercise electrocardiogram in our study was similar to that of the traditional group in the study by Froelicher et al.3 is not necessarily indicative of a workup bias; it may reflect substantial differences between the two study populations with respect to both exclusion criteria and base-line clinical characteristics.
Like Dr. Pennell, we also believe that thallium-201 scintigraphy has a major role in the management of coronary artery disease, particularly in the groups of patients that were excluded from our study. Indeed, we did not include a variety of patients who may represent a substantial proportion of the patients who are seen in general cardiologic practice. Thus, because we were aware of the clinical implications of our findings, we avoided direct extrapolation of our conclusions to the general population. Furthermore, the contribution of right chest leads in each one of the excluded groups of patients should be tested separately in specifically designed studies.
3 ReferencesAndreas P. Michaelides, M.D.
George K. Andrikopoulos, M.D.
Pavlos Toutouzas, M.D.
Athens University, Athens, Greece1
Braat SH ,Brugada P ,de Zwaan C ,Coenegracht JM ,Wellens HJ . Value of electrocardiogram in diagnosing right ventricular involvement in patients with an acute inferior wall myocardial infarction. Br Heart J 1983;49:368-372
CrossRef | Web of Science | Medline2
Yoshino H ,Udagawa H ,Shimizu H , et al. ST-segment elevation in right precordial leads implies depressed right ventricular function after acute myocardial infarction. Am Heart J 1998;135:689-695[Erratum, Heart J 1998;136:5.]
CrossRef | Web of Science | Medline3
Froelicher VF ,Lehmann KG ,Thomas R , et al. The electrocardiographic exercise test in a population with reduced workup bias: diagnostic performance, computerized interpretation, and multivariable prediction. Ann Intern Med 1998;128:965-974
Web of Science | Medline
Author/Editor Response
Dr. Pennell is correct. Exercise electrocardiography cannot be used to identify regional reversible ischemia in patients with abnormal ventricular depolarization such as those with left bundle-branch block, preexcitation, and ventricular pacing. Its use in patients with old myocardial infarctions is also limited. At best, “normalization” of the ST-T segment in the area of scarring during exercise may indicate the presence of viable tissue, but it could also represent ischemia in the opposite ventricular wall. Nuclear techniques are indeed much more helpful under those circumstances.
Drs. Smulyan and Fruehan make a plea for the use of the term “right chest leads” rather than “right precordial leads.” The problem is that the right side of the chest has an anterior, a lateral, and a posterior aspect. I would not object to the use of “right anterior chest leads.”
Dr. Cohen calls attention to the use of left posterior chest leads to identify left circumflex disease. A pilot study using right anterior, left anterior, and left posterior chest leads during exercise should be done to assess the value of such an approach in identifying the diseased coronary artery.
Hein J.J. Wellens, M.D.
Academic Hospital Maastricht, 6202 AZ Maastricht, the Netherlands
