ECG Leads for Exercise Testing
ECG Leads for Exercise Testing
Source: Viik J, et al. Am J Cardiol 1998;81:964-969.
Exercise ecg testing is still favored by many physicians for screening subjects with a moderate risk of coronary artery disease (CAD), providing the resting ECG is normal and the patient can exercise adequately. Although 12 leads are usually recorded, the diagnostic value of each lead is unclear. Thus, Viik and associates studied 101 patients with catheterization proven CAD and interpretable ECGs and 100 patients with a low likelihood of CAD by bicycle ergometry with 12-lead ECG monitoring. Receiver operating curves for each lead were compared, and sensitivities were determined at a fixed specificity of 95%. Using these criteria, chest leads V4, V5, and V6 were the best, followed closely by limb leads I and aVL. The remainder of the leads were quite poor. Also, it was noted that a smaller threshold was better for the limb leads than the chest leads (e.g., 0.05 mV vs 0.10 mV). A formula using multiple leads improved the diagnostic ability, but the increment was small and of dubious value as compared to the effort. Viik et al conclude that the lateral pericardial leads are superior for diagnosing CAD, but equal performance could be obtained from the lateral limb leads if a cut-off of 0.05 mV is used.
Chest lead V5 has long been touted as the best single lead for exercise ECG testing. The inferior leads and V1-V3 are known to produce a high incidence of false-positives. The former was again confirmed by this study, but the value of the lateral limb leads with a lower threshold was also demonstrated. The poor specificity of the inferior leads and V1-3 could not be confirmed in this study because they set the specificity at 95% for their analysis. However, considering the poor sensitivity of these leads, any criteria adjustment to improve it would undoubtedly deteriorate the specificity. Interestingly, the best sensitivity they could obtain with specificity set at 95% was about 65%. If specificity was allowed to drift to 85%, sensitivities of about 75% could be realized. These data are consistent with previous studies and are disappointing. Since half the patients had known CAD, the results should have been better. -mhc
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