Stratifying Syncope - Which Rule Should You Trust?

Clinical Scenario

A 46-year-old man with hypertension and a fondness for double espressos and triple IPAs faints during his niece’s graduation in a sweltering gym. He has a quick recovery, is drenched in sweat,, and no seizure activity was witnessed. Was it the beverages and boring speeches - or something more concerning?

The San Francisco Syncope Rule offers a quick screen for short-term risk, while the Canadian Syncope Risk Score adds nuance and clinical context for a more comprehensive assessment.

Summary

SFSR: Fast but fallible - simple to use, but prone to errors and weak external validation.

CSRS: Comprehensive and reliable – More robust and broadly validated, but is more complex and includes subjectivity.

Tool Comparison

	San Francisco Syncope Rule (SFSR)	Canadian Syncope Risk Score (CSRS)
Purpose	Identify patients at risk for serious outcomes within 7 days of ED presentation for syncope.	Stratify risk of serious adverse events (SAEs) within 30 days, including arrhythmias and death.
Use When...	…your patient has true syncope (not “near syncope” or lightheadedness/weakness) with no alternative cause identified.	…your patient has true syncope ((not “near syncope” or lightheadedness/weakness) and is being considered for discharge from the ED.
Scoring	Binary rule: positive if ≥1 high-risk feature present.	Risk score from –3 to +11, stratified into 5 risk categories (very low to very high).
Action	If any high risk feature present, consider further investigation.	Medium, high, or very high risk (≥1 point) patients should undergo further investigation.
Performance	After validation, pooled sensitivity ~86% for SAEs, and poor specificity, which may lead to over-admission.	Sensitivity >99% for SAEs, externally validated. Better risk stratification utility (any score ≥4 achieves a (+)LR >10, and any score <1 achieves a (-) LR- of 0.1.
Workup	Requires: • ECG • Vital signs (SBP) • History (CHF, SOB) • Laboratory: Hematocrit	Requires: • ECG • Laboratory: Troponin • ED clinical diagnosis • History & vital signs
Common Pitfalls	• Often misused as a “rule-out” tool rather than a tool to aid overall clinical judgment. • Misapplication of criteria can lead to overestimation of risk and unnecessary admissions. • Did not perform as well outside its original cohort, limiting its generalizability.	• Subjectivity in clinician judgement of “ED diagnosis” input. • Be cognizant of variability in troponin cutoffs and local lab standards. • Not all syncope patients necessarily require troponin testing.
Serious Outcomes (San Francisco) = Death, myocardial infarction, arrhythmia, pulmonary embolism, stroke, subarachnoid hemorrhage, significant hemorrhage, or any condition causing a return ED visit and hospitalization for a related event." SAEs (Canadian) = Death, arrhythmia, myocardial infarction, serious structural heart disease, aortic dissection, pulmonary embolism, severe pulmonary hypertension, severe hemorrhage, subarachnoid hemorrhage, or any other serious condition causing syncope and procedural interventions for the treatment of syncope.

Case Resolution

In the ED, his BP was 190/110, and his ECG showed nonspecific ST-T changes compared to his previous one. Labs were WNL. On MDCalc, the San Francisco Syncope Rule flagged him as not low-risk, and the Canadian Syncope Risk Score combined with your clinical gestalt pushed him into the medium risk category. Instead of discharge papers, he earned a telemetry observation stay - because sometimes it’s not just the heat and boring speeches!