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Response by Thiruganasambandamoorthy et al to Letters Regarding Article, "Duration of Electrocardiographic Monitoring of Emergency Department Patients With Syncope".

September 17, 2019 e655 Venkatesh Thiruganasambandamoorthy, MBBS, MSc Brian H. Rowe, MD, MSc Marco L.A. Sivilotti, MD, MSc Andrew D. McRae, MD, PhD Kirtana Arcot, MSc Marie-Joe Nemnom, MSc Longlong Huang, PhD Muhammad Mukarram, MBBS, MPH Andrew D. Krahn, MD George A. Wells, PhD Monica Taljaard, PhD In Response: We thank Dr Muller and his team for their questions. First, the 5581 patients who were enrolled in our study had a median emergency department (ED) length of stay of 4 hours (interquartile range, 3–7 hours). Because our study was a pragmatic prospective cohort study,1 and because there were no clear previous guidelines or criteria for ED or post-ED cardiac monitoring, this was left to the discretion of the treating team: initially the triage nurse, then the treating emergency physician. Hence, not all patients in our study had their cardiac rhythm monitored after ED arrival or after discharge. Second, with respect to overfitting, the derivation of the Canadian Syncope Risk Score was based on a cohort of 4030 patients, and the current study includes approximately an additional 40% of patients (N=5581). Hence, we believe that overfitting is less of a concern. We are in the process of publishing the validation of the Canadian Syncope Risk Score. Third, because this was a pragmatic study, the treating physician decided which patients might benefit from troponin testing based on their clinical judgment. The patients who did not have troponin levels measured were younger, with a low prevalence of comorbidities. Because the missing troponin values were not at random, imputing as normal is more appropriate than imputing on the assumption that they are missing at random. Fourth, to mitigate the risk of verification bias attributable to patients presenting with obvious arrhythmia, we did exclude those patients who had arrhythmia identified in the prehospital setting. Given the robust risk stratification by Canadian Syncope Risk Score for arrhythmias after ED disposition, we have no reason to believe that the results of our study are biased. Finally, we used visual inspection of the Kaplan–Meier curves, estimates of survival functions, and arrhythmic outcomes frequency distributions to develop the time cut points. We thank Dr Egerton-Warburton and her team for these important questions. Although we are advocating for the adoption of the Canadian Syncope Risk Score, we are not encouraging routine cardiac monitoring or troponin measurement in all patients with syncope, in particular, not for the low-risk patients. We agree that patients with vasovagal syncope and a normal ECG most likely do not require troponin measurement performed; however, more evidence is required before this is advocated. In addition, if any arrhythmias were to be identified among such low-risk patients, approximately half were identified within the first 2 hours of ED arrival. Hence, a brief period of ED observation (2 hours) will suffice for these patients. Finally, we agree with the authors that the role of troponin measurement in patients with syncope is complex and requires further research. We plan to address this in a future study. © 2019 American Heart Association, Inc. RESPONSE TO LETTER TO THE EDITOR