Optimal interpretation of the supine exercise electrocardiogram in patients with right bundle branch block. A detailed analysis of the exercise ECG was performed in 82 patients with right bundle branch block who underwent supine exercise equilibrium radionuclide angiography. The sensitivity and specificity of each individual electrocardiographic lead for the detection of a positive radionuclide angiogram was determined. Leads V5 and V6 had a sensitivity of 58 percent and a specificity of 89 percent. The limb leads and lead V4 had a lower sensitivity, but an equivalent specificity. Leads V1 and V3 each had a clearly lower specificity that ranged from 56 to 67 percent. Receiver operating characteristic curve analysis demonstrated that the optimal interpretation of the exercise ECG included the limb leads and V4 to V6, but not V1 to V3. The results of coronary angiography in the subset of 16 patients who underwent this procedure confirmed these findings. 