Supplementary Material for: Clinical Utility of the Electrocardiographic P-Wave Axis in Patients with Chronic Obstructive Pulmonary Disease

<b><i>Background:</i></b> The vertical P-wave axis on electrocardiography (ECG) is a useful criterion for screening patients with chronic obstructive pulmonary disease (COPD). This study aimed to investigate the clinical characteristics of patients with COPD with a vertical P-wave axis as they have not yet been elucidated. <b><i>Methods:</i></b> Keio University and its affiliated hospitals conducted an observational COPD cohort study over 3 years. We analyzed 201 patients using ECG and chest computed tomography. <b><i>Results:</i></b> The severity of airflow limitation was higher in patients with a P-wave axis &gt;75° than in those with a P-wave axis ≤75°. Patients with a P-wave axis &gt;75° exhibited significantly higher total COPD assessment test scores and increased St. George’s Respiratory Questionnaire total, activity, and impact scores than those with a P-wave axis ≤75°. The incidence of exacerbations over 1 and 3 years was significantly higher in patients with a P-wave axis &gt;75° than in those with a P-wave axis ≤75°. The optimal cutoff for the P-wave axis for a percentage of the predicted forced expiratory volume in 1 s &lt;50% and future exacerbations over 3 years was 70° (the areas under the curve [AUC]: 0.788; sensitivity: 65.3%; specificity: 78.3%) and 79° (AUC: 0.642; sensitivity: 36.7%; specificity: 92.6%). The ratio of the low attenuation area was also significantly higher in patients with a P-wave axis &gt;75° than in those with a P-wave axis ≤75°. However, the ratio of the airway wall area did not differ between the 2 groups. <b><i>Conclusions:</i></b> Patients with COPD with a vertical P-wave axis exhibited severe airflow limitation and emphysema, a worse health status, and more frequent exacerbation than patients without a vertical P-wave. Detection of the vertical P-wave axis by ECG is beneficial for the management of patients with COPD.