Is the pre-balloon inflation ECG representative of the true baseline state before percutaneous coronary angioplasty?

The electrocardiogram (ECG) is widely used to assess myocardial ischemia in both clinical and research settings. In percutaneous transluminal coronary angioplasty (PTCA), it remains unclear which ECG should be regarded as the true baseline reference, because several factors, including catheter presence, contrast injection, and procedural stress may already change the pre-balloon inflation tracing. We analyzed 44 patients (24 men, 20 women; mean age 60 ± 11.8 years) from the STAFF III Physionet database who underwent PTCA. Each patient had an ECG recorded in the hospital room before the procedure. In the catheterization laboratory, a continuous ECG recording was obtained, extending from before balloon inflation to after balloon deflation. For analysis, pre-inflation ECG segments were compared with room tracings and classified into four grades of change. Differences between the room ECG and the pre-inflation ECG were found in 37 of 44 patients (84%). Changes were overt in 20 patients (45.5%) and subtle in 17 (38.6%), and no difference was observed in 7 patients (16%). Alterations included T-wave modifications as well as ST-segment shifts. Importantly, all patients demonstrated significant ischemic changes during the interval of balloon occlusion (between the pre-inflation and the pre-deflation recordings), indicating severe ischemia. These findings demonstrate that the pre-balloon inflation ECG does not consistently represent the baseline state, but rather an intermediate stage already affected by the presence of the catheter, baseline state, contrast, or procedural stress. Misinterpretation of this tracing as baseline may bias the evaluation of ischemic burden and post-angioplasty improvement. We suggest that the true baseline ECG should be defined as the resting tracing obtained outside the catheterization laboratory, before the procedure.