INCORPORATING RIGHT PRECORDIAL LEADS IN EXERCISE ELECTROCARDIOGRAPHY.
Clinical question Does the addition of right precordial leads to the standard 12-lead exercise electrocardiogram improve detection of coronary artery disease?
Background Coronary artery disease (CAD) is one of the leading causes of morbidity and mortality in the United States. Exercise electrocardiographic treadmill testing (ETT) is a frequently employed screening test. However, its sensitivity for the detection of single-vessel CAD is only 35% to 61% in various studies. This study evaluates the incorporation of right precordial leads as a noninvasive method for improving the sensitivity of ETT.
Population studied Participants of this study included 245 adults (218 men, 27 women) who were referred to a cardiology department with symptoms suggestive of angina. Exclusion criteria included left or right bundle branch block; left or right ventricular hypertrophy; ventricular pre-excitation; valvular or congenital heart disease; history of bypass surgery, coronary angioplasty, or myocardial infarction; and use of digitalis.
Study design and validity This was an investigator-blinded cross-sectional study. All participants underwent multistage Bruce protocol ETT with the standard 12 electrocardiogram leads as well as 3 right precordial leads ([V.sub.3R], [V.sub.4R], and [V.sub.5R]) and thallium-201 scintigraphy. During ETT, ischemia was defined as: a horizontal or downsloping ST-segment depression of at least 1 mm 60 [micro] sec after the J point; an upsloping ST-segment with a depression at least 1.5 mm 80 [micro] sec after the J point; in the presence of ST-segment depression at rest, an additional 2 mm of ST-segment depression; or an ST-segment elevation of at least 1 mm. Exercise was terminated if the patient developed severe angina, fatigue, dyspnea or arrhythmias; 3-mm ST-segment depression; 2-mm ST-segment elevation; or a decrease in systolic blood pressure of 20 mm Hg or more. Thallium-201 scintigraphy stress and redistribution images were analyzed by standard qualitative and quantitative techniques. CAD was defined by a narrowing of at least 70% of the left anterior descending, left circumflex, or right coronary arteries, or narrowing of at least 50% of the left main coronary artery, as determined by arteriography.
Results of the 12-lead set and right precordial set were interpreted separately as well as in combination. All medications were discontinued 5 half-lives before testing. Within 2 months of ETT, all patients underwent coronary arteriography and left ventriculography. Investigators in each of the 3 diagnostic arms (ETT, thallium scintigraphy, and coronary arteriography) were blinded to results of the other diagnostic studies. Arteriography was the reference standard for defining CAD.
Outcomes measured The primary outcomes were the sensitivity and specificity of the ETT. Likelihood ratios were calculated by the authors.
Results Arteriography revealed that 14% of patients had normal coronary arteries, 35% had single-vessel disease, 34% had 2-vessel disease, and 17% had 3-vessel disease. In comparison with the standard 12-lead ETT, the additional right precordial leads increased sensitivity for detection of single-vessel disease from 52% to 89%, for 2-vessel disease from 71% to 94%, for 3-vessel disease from 83% to 95%, and for all cases of CAD from 66% to 92% (P [is less than] .001). Moreover, sensitivity of detection of single-vessel right CAD increased from 25% to 89% (P [is less than] .001) and the sensitivity of left circumflex CAD increased from 45% to 86% (P [is less than] .004). Differences in sensitivity between ETT with right precordial leads and thallium-201 scintigraphy were not statistically significant; neither were differences in specificity between the standard 12-lead ETT, ETT with the addition of right precordial leads, and thallium scintigraphy (88%). The positive and negative likelihood ratios for detection of any CAD were 5.5 and 0.4 for standard ETT, and 7.7 and 0.1 with the addition of right precordial leads.
Recommendations for clinical practice The addition of 3 right precordial leads to the conventional 12-lead exercise electrocardiogram improves detection of CAD, as defined by coronary arteriography, such that sensitivity rivals exercise thallium-201 scintigraphy. This modification also significantly improves the negative likelihood ratio, a measure of how well a negative test rules out disease. These results are intriguing because they propose a low-cost, widely available, and noninvasive improvement to current CAD screening tools. Nonetheless, a prospective randomized controlled trial is needed to determine if this technique has a meaningful impact on mortality and morbidity when compared with standard 12-lead ETT or thallium-201 scintigraphy. A study incorporating more women would also be important, since preliminary findings suggest that greater sensitivity in CAD detection may also be achieved for this group.
Jennifer Edgoose, MD, MPH Sharon Dobie, MD, MCP University of Washington-Seattle E-mail: firstname.lastname@example.org
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|Author:||Edgoose, Jennifer; Dobie, Sharon|
|Publication:||Journal of Family Practice|
|Date:||May 1, 1999|
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