Predicting Poor Outcomes After Syncope

Syncope is a classic good news/bad news presenting complaint. It can be highly distressing to patients and family members, but rarely does it relate to an acutely serious underlying cause. That’s the good news. The bad news, however, is that for those with the worst prognosis, most of the poor prognostic features are unmodifiable.

This is a prospective, observational study of patients presenting with syncope to Emergency Departments in Canada, with the stated goal of developing a risk model for poor outcomes after syncope. The composite outcome of interest was death, arrhythmia, or interventions to treat arrhythmias within 30 days of ED disposition. Follow-up was performed by structured telephone interview, networked hospital record review, and Coroner’s Office record search.

To achieve a lower bound of the 95% confidence interval for sensitivity of 96.4%, these authors targeted a sample size of 5,000 patients, and ultimately enrolled 5,010 with complete outcome assessments. The mean age was 53.4, had a low incidence of comorbid medical conditions, and only 9.5% were admitted to the hospital. Within 30 days, 22 had died, 15 from unknown causes and the others from the pool of 91 patients diagnosed with a “serious arrhythmia” – sinus node dysfunction, atrial fibrillation, AV block, ventricular arrhythmia, supraventricular tachycardia, or requiring a pacemaker insertion.

These authors ride the standard merry-go-round of statistical analysis, bootstrapping, and logistic regression to determine a prediction rule – the Canadian Syncope Arrhythmia Risk Score – an eight element additive and subtractive scoring system to stratify patients into one of eleven expected risk categories. They report the test characteristics of their proposed clinically useful threshold, greater than 0, to be a sensitivity of 97.1% and a specificity of 53.4% – a weak positive predictive value of 4.4% considering the low incidence of the composite outcome.

This is yet another product of obviously excellent work from the risk model machines in Canada, but, again, of uncertain clinical value. The elements of the risk model are frankly those that are quite obvious: elevated troponin and conduction delays on EKG, along with an absence of classic vasovagal features. These are patients whose cardiac function is obviously impaired, but short a time machine to go back and fix those hearts before they became sick, it’s a bit difficult to see the path forward. These authors feel their prediction rule aids in safe discharge of patients with syncope, although these patients are already infrequently admitted to the hospital in Canada. The various members of their composite outcome are not equally serious, preventable, or treatable, limiting the potential management options for even those falling into their high-risk group.

As with any decision instrument, its value remains uncertain until it is demonstrated the clinical decisions supplemented by this rule lead to better patient-oriented outcomes and/or resource utilization than our current management in this cohort.

“Predicting Short-Term Risk of Arrhythmia among Patients with Syncope: The Canadian Syncope Arrhythmia Risk Score”

https://www.ncbi.nlm.nih.gov/pubmed/28791782

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