Background: Focused cardiac ultrasound (FOCUS) is insensitive for pulmonary embolus (PE). However, when a clot is large enough to cause vital sign abnormalities, it is more likely to show signs on FOCUS. A rapid bedside test that could quickly and reliably exclude PE in patients with abnormal vital signs could be of high utility in ED patients. We hypothesized that in patients with tachycardia or hypotension FOCUS would be sensitive for excluding PE.
Methods: We performed a prospective observational multi-center cohort study involving a convenience sample of patients from five urban academic EDs. Patients suspected to have PE with tachycardia (heart rate (HR) ≥100) or hypotension (sBP < 90 mmHg) underwent FOCUS before computed tomographic angiography (CTA). FOCUS includes assessment for right ventricular dilation, McConnell’s sign, septal flattening, tricuspid regurgitation, and tricuspid annular plane systolic excursion (TAPSE). If any of these were abnormal, FOCUS was considered positive, while if all were normal, FOCUS was considered negative. We defined two apriori cutoffs for abnormal vital signs (HR ≥ 100 BPM or sBP < 90) and HR ≥ 110 BPM, and determined sensitivity and specificity of abnormal FOCUS for PE on CTA. Inter-rater reliability (IRR) of FOCUS was determined by blinded review of images by an EP with fellowship training in ultrasound.
Results: 143 subjects were assessed for enrollment and 136 were enrolled; three were excluded because of poor FOCUS windows and four because they were non-English speaking. The mean age of enrolled subjects was 56 (SD 17) years, mean HR was 114 (SD 12) BPM, and 37 (27.2%) were diagnosed with PE on CTA. In all subjects, FOCUS was 92% (95%CI 78-98) sensitive and 64% specific (95%CI 53-73) for PE. In 98 subjects with a HR ≥ 110 BPM, FOCUS was 100% (95%CI 88-100) sensitive and 63% specific (95%CI 51-74) for PE. IRR of FOCUS demonstrated substantial agreement between observers (Kappa = 1.0, 95% CI 0.72-1.0).
Conclusion: FOCUS can reliably exclude PE in most patients with suspected PE and abnormal vital signs. This study included a convenience sample with FOCUS performed by investigators with significant expertise in ultrasound, which limits its generalizability. Results suggest that FOCUS may be an important tool in the initial assessment of the emergency department patient with tachycardia and/or hypotension and suspected PE.