Performance Testing of the Modified Electrocardiogram Lead Placement

Background and Rationale Electrocardiogram (ECG) monitoring is essential during general anesthesia to assess heart rate, arrhythmias, and myocardial ischemia, alongside blood pressure. Standard Lead II, derived from limb leads placed on the torso (both clavicles below and left anterior superior iliac spine, outside the heart boundary), aligns best with the heart's electrical axis for accurate rhythm and ischemia detection. However, in shoulder surgeries like arthroscopic rotator cuff repair, surgical incisions overlap these sites, forcing electrode relocation (e.g., to the sternum instead of the shoulder). This inward shift distorts ECG signals, potentially missing normal or abnormal heart changes during surgery. To address this, modified Lead II placements are needed for reliable cardiac surveillance in shoulder surgery patients.

Study Overview This prospective, single-group interventional study evaluates the performance of two modified ECG Lead II configurations compared to the standard during general anesthesia for non-shoulder surgeries (to simulate placement feasibility). The modifications test alternative sites for the left shoulder electrode: sternum center (modified Sternum-Chest Lead II, mSC2) versus temple (modified Temple-Chest Lead II, mTC2). Left-side versions are assessed post-induction in supine position; right-side versions post-surgery. Outcomes focus on ST segment morphology similarity (visual and quantitative) to ensure modified leads maintain diagnostic accuracy without artifacts.

Methods Summary Eligible adults (19-65 years) scheduled for general anesthesia in non-shoulder sites undergo standard monitoring (ECG, NIBP, SpO2) per institutional protocols. After induction and hemodynamic stabilization, three ECG configurations are recorded simultaneously using Vital Recorder software (VitalDB, Republic of Korea) for at least 10 noise-free waves: (1) Standard Lead II; (2) Left mSC2 (sternum, right shoulder, left iliac spine); (3) Left mTC2 (left temple, right shoulder, left iliac spine). Post-surgery, right-side mSC2 and mTC2 are added. Recordings capture preoperative ST segment status (normal/abnormal). Blinded assessors (two researchers, third for ties) evaluate ST similarity visually; quantitative area differences use R/RStudio.

Statistical Considerations Sample size (n=84, 10% dropout) is calculated via McNemar test for paired comparisons, stratified by ST status (normal: 38 pairs; abnormal: 46 pairs), yielding 80% power at $\alpha=0.05$ based on pilot data. Analysis: Stratified McNemar for agreement; R for area differences.

Safety and Ethics Modifications involve brief additional recordings with no added risk beyond standard care. IRB-approved (Dongguk University Ilsan Hospital); informed consent obtained. Data anonymized (case numbers); stored securely for 3 years per regulations.