Urgent Care Approach to the Syncopal Patient

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San Francisco Syncope Rule

• Introduction
• About the Score
• Calculator Review Author
• Evidence Appraisal
• Instructions
• Calculator Creator
• References

Introduction

The San Francisco Syncope Rule predicts risk for serious outcomes at 7 days in patients presenting with syncope or near syncope.

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About the Score

Syncope may be relatively benign, or it may be a manifestation of serious underlying pathology. The gestalt of the emergency clinician is highly sensitive but poorly specific for predicting high-risk patients. The creators of the San Francisco Syncope Rule designed it to improve specificity while maintaining high levels of sensitivity. This tool can be utilized to predict low-risk syncope patients who are unlikely to benefit from aggressive workup and hospitalization, thus reducing unnecessary testing, healthcare costs, and potential harms associated with hospitalization.

The most common serious outcome in the studies of the San Francisco Syncope Rule was cardiac dysrhythmia; most of those were bradydysrhythmias or sick sinus syndrome, and the remainder were supraventricular or ventricular dysrhythmias. Other common serious outcomes in patients misclassified as low-risk were stroke and intracranial hemorrhage. Validation studies were not able to replicate the high sensitivity found in the original studies published by the creators of the rule.

A commonly used mnemonic to recall the 5 variables of the San Francisco Syncope Rule is “CHESS”:

• Congestive heart failure history
• Hematocrit <30%
• Electrocardiogram (ECG) abnormal
• Shortness of breath
• Systolic blood pressure <90 mm Hg

Calculator Review Authors

Cullen Clark, MD

Marc Probst, MD, MS

Evidence Appraisal

Since its inception, the San Francisco Syncope Rule has undergone considerable scrutiny and has been evaluated in validation trials and meta-analyses (key studies include Sun 2007 and Birnbaum 2008). The initial derivation study (Quinn 2004) was a single-center, prospective cohort study of 684 patients with a chief complaint of syncope or near-syncope. Fifty predictor variables selected from literature review and expert consensus were incorporated into a survey completed by the physician evaluating the patient after a syncopal episode. The patients were followed through hospital admission and/or contacted at 7 days after the initial presentation to assess for serious outcomes. The predictor variables associated with serious outcomes were identified on univariate analysis. Recursive partitioning was used to find the best combination of predictor variables that would maximize specificity while preserving high sensitivity. Once the combination of predictors was identified, the rule was applied to the derivation set of patients, resulting in sensitivity of 96% and specificity of 62%.

The rule was validated by Quinn et al 2 years later with another single-center, prospective cohort study of 760 patients. Physicians treated patients with syncope or near-syncope in their usual manner and were then asked to fill out a questionnaire about the patients, which included the 5 San Francisco Syncope Rule syncope predictors. After following the patients for 30 days, the San Francisco Syncope Rule was able to predict serious outcomes in all but 1 patient (98% sensitivity). The rule had higher specificity than physician judgment (56% specificity), with an estimated decrease in overall admission rate by 7%, if applied. The single missed patient was suspected to have had transient ischemic attack related to extensive carotid and vertebral artery disease requiring a stent.

Several external validation studies and meta-analyses have also examined the San Francisco Syncope Rule since the derivation study. Sun et al externally validated the rule with a single-center, prospective cohort study with a sample size of 477 patients. Using definitions, exclusion criteria, and methods similar to the internal validation study, the authors found a sensitivity of 89% and a specificity of 42%. Of the 6 patients misclassified as low-risk, 3 had dysrhythmias, 1 had a cerebrovascular accident, 1 had an intracerebral hemorrhage, and 1 had hypertrophic obstructive cardiomyopathy. This study also compared physician judgment to the clinical decision rule. Physician judgment had a sensitivity of 100% and a specificity of 30% for predicting serious outcomes at 7 days.

Another single-center, prospective, observational cohort study by Birnbaum et al performed at a large urban academic center found that the San Francisco Syncope Rule did not perform as well as previously reported. The study found the rule had a sensitivity of 74% and specificity of 54% for predicting serious outcomes at 7 days. The rule would have decreased the overall admission rate by 41%, but it misclassified 16 of the 61 patients who had serious outcomes as low-risk. Physician judgment in this study was 100% sensitive. In a written response to the study published in the Annals of Emergency Medicine, the derivation study authors criticized the validation study for incorrect application of ECG criteria used to define “high risk” in the study. The original study authors argued that the subjective interpretation of the ECG is enhanced when performed by a treating physician who is familiar with the clinical context. They posited that the sensitivity of the rule in the New York study was reduced because ECGs were evaluated retrospectively by experts rather than by the physician seeing the patient.

Meta-analyses published in the Annals of Emergency Medicine and the Canadian Medical Association Journal found sensitivity and specificity similar to the external validation study by Sun et al. The Annals of Emergency Medicine meta-analysis found 86% sensitivity and 49% specificity, while the Canadian Medical Association Journal meta-analysis found 87% sensitivity and 52% specificity. The most commonly missed serious outcome in all of the studies assessing the predictive value of the San Francisco Syncope Rule was cardiac dysrhythmia.

Instructions

Use this score in adult patients presenting with syncope or near-syncope who are back to their neurologic baseline. Do not use it in patients with persistent or new neurologic deficits, alcohol- or drug-related loss of consciousness, definite seizure, or transient loss of consciousness from head trauma.

Calculator Creator

Ian Stiell, MD, MSc, FRCPC

James V. Quinn, MD, MS

References

Original/Primary Reference

• Quinn JV, Stiell IG, McDermott DA, et al. Derivation of the San Francisco Syncope Rule to predict patients with short-term serious outcomes. Ann Emerg Med. 2004;43(2):224-232. DOI: 10.1016/s0196-0644(03)00823-0

Validation References

• Quinn J, McDermott D, Stiell I, et al. Prospective validation of the San Francisco Syncope Rule to predict patients with serious outcomes. Ann Emerg Med. 2006;47(5):448-454. DOI: 10.1016/j.annemergmed.2005.11.019
• Sun BC, Mangione CM, Merchant G, et al. External validation of the San Francisco Syncope Rule. Ann Emerg Med. 2007;49(4):420-427. DOI: 10.1016/j.annemergmed.2006.11.012

Other References

• Birnbaum A, Esses D, Bijur P, et al. Failure to validate the San Francisco Syncope Rule in an independent emergency department population. Ann Emerg Med. 2008;52(2):151-159. DOI: 10.1016/j.annemergmed.2007.12.007
• Serrano LA, Hess EP, Bellolio MF, et al. Accuracy and quality of clinical decision rules for syncope in the emergency department: a systematic review and meta-analysis. Ann Emerg Med. 2010;56(4):362.e1-373.e1. DOI: 10.1016/j.annemergmed.2010.05.013
• Quinn J, McDermott D. ECG criteria of the San Francisco Syncope Rule. Ann Emerg Med. 2011;57(1):72-73. DOI: 10.1016/j.annemergmed.2010.06.570
• Saccilotto RT, Nickel CH, Bucher HC, et al. San Francisco Syncope Rule to predict short-term serious outcomes: a systematic review. CMAJ. 2011;183(15):E1116-E1126. DOI: 10.1503/cmaj.101326