Diagnostic Overshadowing in Chronic Obstructive Pulmonary Disease: A Case of Recurrent Syncope.

Acute exacerbation of chronic obstructive pulmonary disease (AECOPD) is a frequent cause of acute medical presentations. However, misattribution of the cause of such episodes based on bias from pre-existing diagnostic history (i.e., diagnostic anchoring) can lead to poor appraisal of co-existing life-threatening pathology unrelated to COPD. We present a 67-year-old male with a known background of severe COPD who presented with sudden-onset breathlessness but also recurrent syncope, where a presumed AECOPD served as a diagnostic red herring. Driven by implicit framing biases, the admitting team prematurely closed the diagnostic process and empirically initiated intravenous corticosteroids and nebulised bronchodilators without fully exploring alternative diagnoses. Multidisciplinary team review noted the absence of hypoxia or hypercapnia on arterial blood gas analysis and identified syncope as an atypical diagnostic feature of AECOPD, prompting a pivot away from respiratory management. A pre-hospital ECG had captured an irregularly irregular tachycardia suggestive of a focal atrial tachycardia with variable block or a multifocal atrial tachycardia (MAT), and a subsequent electrocardiography (ECG) revealed a consistently short PR interval (110 ms), raising the possibility of an underlying arrhythmic cause of the event. Corticosteroids were safely discontinued, and an outpatient implantable loop recorder (ILR) was arranged for long-term tachyarrhythmia surveillance. This report highlights the risks of diagnostic anchoring and premature closure in patients in the context of a known background diagnosis, the necessity of holistic clinical assessment with maintenance of a broad differential, and the importance of reassessing atypical clinical features through multidisciplinary review.