Easily Neglected Manifestations in Electrocardiogram in the Prone Position

A patient in their 70s with chronic obstructive pulmonary disease and hypertension presented with a 2-day history of cough, expectoration, and shortness of breath. On admission, their heart rate was 91/min, and their blood pressure was 126/65 mm Hg. An arterial blood gas analysis on supplemental low-flow oxygen (2 L/min) revealed a partial pressure of arterial oxygen level of 51 mm Hg, which suggested a diagnosis of moderate acute respiratory distress syndrome (ARDS), according to the profound degree of hypoxemia (the ratio of partial pressure of arterial oxygen to the fraction of inspired oxygen was 175.9 mm Hg). The patient was immediately placed in a prone position and received mechanical ventilation. On the second day of hospitalization, blood test results revealed a troponin I level of 0.68 ng/mL (reference range, <0.16 ng/mL) and a creatine kinase isoenzyme level of 18.70 U/L (reference range, <16 U/L). (To convert troponin I to μg/L, multiply by 1.0; creatine kinase to μkat/L, multiply by 0.0167.) To exclude acute myocardial infarction, an electrocardiogram (ECG) was obtained in the prone position with mirror lead placement (Figure, A). In brief, V₁ and V₂ leads were placed on the 2 sides of the seventh thoracic vertebra. The V₃ lead was located at the midpoint between V₂ and V₄. The location of V₆ was in the fifth intercostal space, at the left midaxillary line. The V₄ and V₅ leads were positioned at the same level as V₆, with V₄ in the left midscapular line and V₅ in the left posterior axillary line.