Comparison between measured and synthesized posterior lead electrocardiograms during percutaneous coronary intervention-induced myocardial ischemia

Background Posterior/inferolateral myocardial ischemia is frequently underrecognized on standard 12‑lead electrocardiography (ECG). Synthesized posterior leads derived from the standard 12‑lead ECG have been proposed as an alternative to directly measured posterior leads; however, their accuracy under controlled ischemic conditions has not been fully validated. Methods We prospectively enrolled 26 consecutive patients undergoing percutaneous coronary intervention (PCI) in whom simultaneously recorded measured and synthesized posterior lead ECGs (V 7 –V 9 ) were obtained during balloon-induced myocardial ischemia. ST-segment deviation was measured at the ST junction (STJ), 40 ms (ST1), and 80 ms (ST2) thereafter. Agreement between measured and synthesized posterior leads was assessed using Pearson correlation and Bland–Altman analyses. As an exploratory patient-level analysis, diagnostic performance was compared with reciprocal anterior ST-segment depression (V 1 –V 4 ). Results Strong correlations were observed between measured and synthesized posterior lead ST-segment deviations (V 7 : r = 0.89; V 8 : r = 0.86; V 9 : r = 0.83; all P < 0.001). Bland–Altman analysis demonstrated minimal systematic bias (within ±0.004 mV) and narrow limits of agreement. Synthesized posterior leads showed higher diagnostic performance than reciprocal anterior ST-segment depression (AUC 0.917 vs. 0.708), although the difference was not statistically significant (DeLong test, P = 0.197). Using a 0.05 mV threshold, synthesized posterior leads demonstrated 83.3% sensitivity, 100% specificity, and 96.2% overall accuracy. Conclusions Synthesized posterior leads closely reproduced measured posterior lead ST-segment deviations during percutaneous coronary intervention (PCI)-induced myocardial ischemia, supporting the technical validity of posterior lead reconstruction. Larger prospective studies are warranted to determine whether synthesized posterior leads provide incremental diagnostic value beyond careful interpretation of the standard 12‑lead ECG.