Diagnostic value of 12-lead electrocardiogram during dobutamine echocardiographic studies

Diagnostic value of 12-lead electrocardiogram during dobutamine echocardiographic studies Joseph Shaheen, MD, David Luria, MD, Marc W. Klutstein, MD, David Rosenmann, MD, and Dan Tzivoni, MD Jerusalem, Israel

Background The diagnostic value of 12-lead electrocardiography during dobutamine stress echocardiography (DSE) is not well documented.

Methods and Results We reviewed the records of 116 patients referred for DSE and coronary angiography, 52 of whom were excluded because of abnormal ST segment or inadequate DSE. Of the analyzed 65 patients, 42 had angiographic evidence of significant coronary disease, 41 had evidence of ischemia according to the echocardiographic criteria, and 30 had ST changes during the study. DSE had sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of 88%, 81%, 90%, and 78%, respectively. Twelve-lead electrocardiography had sensitivity, specificity, PPV, and NPV of 52%, 64%, 72%, and 41%, respectively. NPV increased to 92% in patients with negative DSE and negative ST changes. PPV increased to 95% if both DSE and 12-lead electrocardiographic ischemic changes were observed.

Conclusions Twelve-lead electrocardiography has an incremental diagnostic value when used during DSE. (Am Heart J 1998;136:1061-4.)

Dobutamine stress echocardiography (DSE) is a widely used method for diagnosis of the presence of coronary artery disease (CAD) and for prognostic assessment in patients with known CAD.1-5 Dobutamine, by its positive inotropic and chronotropic effects, increases myocardial oxygen demand and can cause ischemia and segmental wall motion abnormalities in patients with significant CAD.1 The sensitivity of DSE for diagnosis of CAD ranges from 68% to 86%,2-4 being lower (50% to 69%) in patients with single-vessel disease.2-4 Specificity of the test ranges from 60% to 100%.2-4 The electrocardiogram is recorded during intravenous infusion of dobutamine.2-7 Most previous studies have focused only on the echocardiographic findings of the test. The incremental diagnostic value of 12-lead electrocardiography during DSE has not been carefully evaluated. Daoud et al8 retrospectively analyzed their experiment and concluded that the incremental diagnostic value of the electrocardiogram during DSE study is poor, and the elimination of the 12-lead electrocardiogram during the study is unlikely From the Department of Cardiology, Jesselson Heart Center, Shaare Zedek Medical Center. Submitted November 24, 1997; accepted April 10, 1998. Reprint requests: Joseph Shaheen, MD, Bendheim Department of Cardiology, Jesselson Heart Center, Shaare Zedek Medical Center, POB 3235, Jerusalem 91031 Israel. Copyright © 1998 by Mosby, Inc. 0002-8703/98/$5.00 + 0 4/1/91141

to affect its results. In their study, only 41 patients had an interpretable electrocardiogram at baseline. The purpose of our study was to assess the diagnostic value of 12-lead electrocardiography in a larger number of patients.

Methods We retrospectively reviewed the records of 804 consecutive patients who underwent DSE at the Shaare Zedek Medical Center between June 1993 and March 1996. One hundred sixteen patients who underwent coronary angiography within 1 month of the DSE made up our study population. Fifty-two patients were excluded from analysis, 38 because of resting ST changes including right or left bundle branch block or ST elevation with Q wave, 4 because of poor-quality echocardiograms, 5 because target heart rate was not achieved, and 5 because the DSE was performed after the angiography. The remaining 64 patients with interpretable electrocardiograms, diagnostic DSE, and coronary angiography were the population for this study.

DSE protocol Dobutamine was administered intravenously at a starting dose of 5 µg/kg per minute and was incrementally increased at 3-minute intervals to 10, 20, 30, and 40 µg/kg per minute. Atropine up to a maximal dose of 2 mg was added if the target heart rate was not achieved at maximal dobutamine dose. Transthoracic echocardiography was performed with the patient in the left lateral decubitus position. Standard 2-

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Conventional 12-lead electrocardiography, with slight modification of lead placement to allow access to echocardiographic acoustic windows, was recorded every 3 minutes during the study. The electrocardiogram was interpreted at a later stage by a senior cardiologist blinded to the results of the DSE and the coronary angiography. An ischemic response to dobutamine was defined as ≥1 mm horizontal or downsloping ST-segment depression or ST-segment elevation (in leads without Q waves) measured 80 ms after the J-point.

cant CAD on coronary arteriography. Of the 23 patients with negative DSE, 18 had normal coronary arteries. Thus DSE had a sensitivity of 88%, specificity of 82%, positive predictive value (PPV) of 90%, and negative predictive value (NPV) of 78%. ST changes during DSE had sensitivity of 52% and specificity of 64%, with PPV of 73% and NPV only 41%. Four patients had CAD with negative DSE and positive ST changes, all had single-vessel disease, 3 had left anterior descending coronary artery disease, and 1 had right coronary artery disease. Chest pain during the DSE study had a sensitivity of 40%, 77% specificity, 77% PPV, and 40% NPV (Table I). Fifty-two patients had positive DSE or electrocardiographic changes and 41 had CAD; only 1 of 12 patients with normal DSE and no ST changes had significant CAD with high sensitivity and NPV of 98% and 92%, respectively (Table II). Fifty-five patients had positive DSE or ST changes or chest pain during the DSE study and 42 had CAD; none of the 9 patients with normal DSE, no chest pain, and no ST changes had significant CAD, with 100% sensitivity and 100% NPV for prediction of CAD (Table II). Patients with positive DSE and ischemic electrocardiographic changes had 95% specificity and PPV but had low sensitivity and NPV, 43% and 47%, respectively (Table II). The presence of chest pain in patients with both positive DSE and ST changes did not change the specificity (95%) but was associated with a lowered sensitivity of 17% (Table II).

Coronary angiography

Discussion

Coronary angiograms were reviewed by a senior interventional cardiologist blinded to the DSE or electrocardiography results. Coronary lesions were visually estimated. Coronary lesions >70% were considered significant.

The goal of this study was to assess the incremental diagnostic value of 12-lead electrocardiography during dobutamine stress echocardiography in 116 patients who had coronary arteriography. Of these patients, in only 64 the electrocardiogram enabled interpretation of ischemic changes; these patients make up the population for this study. This study demonstrates that the information obtained from 12-lead electrocardiography during DSE increased the diagnostic value of the test. When positive DSE for ischemia was accompanied by ischemic ST changes, specificity of the test increased from 82% to 95%, and when both DSE and electrocardiography were negative for ischemia, the NPV of the test increased from 78% to 92%. As reported previously,8,9 the sensitivity and NPV of electrocardiographic changes alone during DSE study were very low (52% and 41%, respectively),

dimensional echo views were acquired in the parasternal short- and long-axis and apical 4- and 2-chamber views. Images were digitized for display in a quad-screen format. The standard quad-screen views included images at baseline, 10 µg/kg per minute, peak dobutamine (with and without atropine) dose, and recovery phase at 6 minutes after the completion of dobutamine infusion. This format allowed playback in a continuous loop and facilitated comparison of each echo view during different stages of the DSE study. During each stage, patient complaints, heart rate, blood pressure, and a 12-lead electrocardiogram were obtained. DSE studies were interpreted by 2 experienced cardiologists blinded to the angiography or electrocardiography results. The left ventricle was divided into 16 segments. A normal wall motion response during DSE study was defined as an increase in myocardial thickening. An ischemic response was defined as a decrease in contractility in 2 or more segments as compared with baseline images. Dyskinetic response in an akinetic segment at baseline was not defined as ischemic. The DSE study was considered uninterpretable if the images were of poor quality.

Electrocardiography interpretation

Results Sixty-four patients who had diagnostic coronary angiography and DSE were retrospectively analyzed. Twenty-two (34%) patients had nonsignificant CAD and 42 (66%) patients had significant CAD, 1 with left main coronary disease, 21 with single-vessel disease, and 20 with multivessel disease. Twenty-three (36%) patients had negative DSE study and 41 (64%) had a positive test for ischemia. Thirty-four (53%) patients had no ST changes, whereas 30 had ST changes, 24 exhibited ST depression ≥1 mm, and 6 had ST elevation >1 mm. During the DSE study, 22 (34%) patients had chest pain. Of the 41 patients with positive DSE, 37 had signifi-

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Table I. Predictive value of DSE and ST changes True positive

False positive

True negative

False negative

Sensitivity

Specificity

PPV

NPV

37 22 17

4 8 5

18 14 17

5 20 25

88% 52% 40%

82% 64% 77%

90% 73% 77%

78% 41% 40%

DSE ST changes Chest pain

Table II. Predictive value of combined DSE and ST changes

DSE or ST changes DSE or ST changes or chest pain DSE and ST changes DSE, ST changes, and chest pain

True positive

False positive

True negative

False negative

Sensitivity

Specificity

PPV

NPV

41 42

11 13

11 9

1 0

98% 100%

50% 41%

79% 76%

92% 100%

18 7

1 1

21 21

24 35

43% 17%

95% 95%

95% 88%

47% 38%

with acceptable specificity and PPV (64% and 73%, respectively). Mazieka et al9 compared the diagnostic accuracy of electrocardiographic changes with that of DSE for the detection of >70% stenosis in 54 patients referred for coronary angiography. They reported low sensitivity and NPV of electrocardiography alone of 47% and 34%, respectively, and better specificity and PPV of 71% and 81%. Daoud et al8 reported their results in 41 patients with interpretable electrocardiography, DSE, and coronary angiography. They found that DSE is more sensitive and specific than electrocardiographic changes, with low sensitivity and NPV of 47% and 25% of electrocardiographic changes and better specificity and PPV of 53% and 75% of patients with >70% coronary lesions. According to their definitions, the combined results of both DSE and electrocardiographic changes slightly increased the sensitivity of the test but markedly reduced its specificity. According to their definition, the test was regarded as positive for ischemia if either the DSE or the electrocardiogram was ischemic. According to this definition, our results also showed reduced specificity (50%), but the specificity of the test increased to 95% if both the DSE and the electrocardiogram were positive for ischemia. On the other hand, the negative predictive value of the test increased to 92% if both tests were negative for ischemia (78% for DSE alone) and to 100% if the patient had no chest pain. Mairesse et al10 reported the accuracy of electrocardiography during DSE and found that the conventional

electrocardiographic criteria of 1 mm ST shift 80 ms after the J-point gave a sensitivity of 18%, a specificity of 93%, and overall accuracy of 45%. They reported that of 83 patients with CAD, 63 were correctly identified by DSE (76% sensitivity), whereas 3 patients had negative DSE but positive ST changes. Sensitivity of 83% was found with the use of either criteria for diagnosis of CAD. Only 4 patients with CAD had both negative electrocardiographic changes and negative DSE. They concluded that DSE had higher sensitivity and diagnostic accuracy than any electrocardiographic criteria and that the addition of electrocardiography did not significantly improve the accuracy of DSE. A limitation of their study was the use of a modified electrocardiographic Frank lead system instead of conventional 12-lead electrocardiography.

Limitations of the study This was a retrospective study designed to evaluate the incremental diagnostic value of 12-lead electrocardiography during DSE studies. As would be expected for non–exercise stress testing, almost one third of the patients had noninterpretable electrocardiograms for ST changes. We believe that this study represents the standard practice of performing DSE and thus reflects the value of 12-lead electrocardiography during these studies.

Conclusions Our results support the routine use of 12-lead electrocardiography as an integral part of DSE study, that

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ischemic electrocardiographic changes increase the specificity of the test if combined with ischemic DSE, and that negative electrocardiography for ischemia increases the NPV of the test if combined with a negative DSE.

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