6. Syncope

Syncope is a common condition (lifetime risk > 35%) that affects men and women equally and comprises approximately 1% of all presentations to the emergency department.^[115],[116] The underlying mechanism is important because it might predict future events. Syncope can be categorized as either reflex-mediated (carotid sinus syndrome, situational syncope, and vasovagal), orthostatic (primary or secondary autonomic dysfunction), and cardiac (tachyarrhythmia, bradyarrhythmia, valvular, or obstructive pathologies).

Question 6: In persons who have experienced at least 1 syncopal episode, who are considering driving, what is the risk of motor vehicle accidents (MVAs), syncope while driving, or injuries or fatalities as a result of motor vehicle collisions?

Societal tolerance

The preceding CCS guidance documents^[3],[4] include recommendations on the basis on a calculated societal risk tolerance of < 1/20,000 or 0.005% per year for a risk of serious injury or death due to a syncope event causing an MVA. This led to a modelled target of a societal risk tolerance of < 1% per year for a risk of syncope while driving. These assumptions were on the basis of Ontario driving data in the 1980s. Although the standard acceptable risk for cardiac patients appears to have stood the test of time insofar as its ongoing acceptance by provincial regulatory bodies in Canada, it is less clear that this standard represents society’s “acceptable” risk for MVAs (from any cause) across a broad range of noncardiac medical or other circumstances. This is drawn from societal acceptance of current rates of MVA in the general population. Large, governmental data sets from the United Kingdom and Canada from 2009-2013 and retrieved from the internet showed a mean risk of serious injury or death due to syncope while driving to be 0.067% in the general population (Table 9). Similarly, data from a large group health plan in Washington state in 1987-1988^[117] showed that in individuals older than 65 years that the risk of serious injury due to an MVA was 0.08%. The estimate in all of the United States was > 0.013%. The unweighted mean average of these data is 0.075% per year, 15-fold higher than the risk tolerance assumed by the CCS in its previous documents.^[3],[4]

The national yearly population risks of an MVA in the same period (Table 10) in Canada,^[118] the United States,^[118] the United Kingdom,^[118] and Denmark^[119] were 0.56%, 2.29%, 0.49%, and 1.21%, respectively. The mean was 1.14% per year, which can be estimated to be society’s risk tolerance for driving. This is similar to the past and current CCS guideline risk tolerance for a syncopal episode while driving (< 1% per year). Fitness to drive recommendations in the setting of syncope are summarized in Table 9.

Syncope and MVAs

The results of all studies are weakened by 3 problems. First, syncope is a symptom, not a disease. Patients with a cardiac or other medical cause of syncope should not be included in risk models, and this can happen because of administrative coding. This is on the basis of the assumption that when a diagnosis is made, appropriate interventions will be put in place and the statistical risk shifts to the underlying diagnosis. This leaves vasovagal syncope, related disorders, and heretofore undiagnosed syncope to consider.

Second, all studies reported few hard outcomes, whether they be MVAs due to syncope or serious injuries due to syncope-associated MVAs. Third, many studies report retrospective data preceding medical assessment, and these likely do not reflect the prospective risk after assessment.

The most focused, rigourously collected data are from the Prevention of Syncope Trial (specifically, POST trials 1 and 2), which included 418 patients with 3 or more lifetime vasovagal syncopal episodes.^[118] These individuals were high-risk patients, with an average of 10 lifetime syncopal episodes and a median of 3 syncopal episodes in the preceding year. The risk of syncopal episodes while driving was 0.62% per driver-year and there was no serious injury detected. The risk of serious harm was estimated to be < 0.0035% per driver-year. This is a population in whom approximately 40% fainted in the year after study entry, and many had recurrent episodes of syncope.

In 4 clinical or administrative studies^{[118],[120]–[122]} of patients with syncope the yearly likelihood of fainting while driving (Table 9) was 0.62%, 0.33%, 0%, and 1% (mean 0.32%). In 6 clinical or administrative studies of patients with syncope^{[118]–[123]} the yearly likelihood of fainting while driving causing an MVA was 0.62%, 0%, 0.26%, 0%, 1.06%, and 2.2% (mean 0.69%). In 5 clinical or administrative studies of patients with syncope^{[118]–[123]} the yearly risk of a syncope-associated MVA causing serious injury or death was 0%, 0%, 0%, 0%, and 0.007% (mean 0.0015%).

Overall, the compiled new and old data on the risk of motor vehicle collisions in patients with syncope in conjunction with societal tolerance for the risk of motor vehicle collisions suggest we reduce the driving restrictions for these patient populations in low-risk private vehicles. The mean yearly risk of serious injury or death due to a syncope-associated MVA after assessment is 0.0015%, 50-fold less than the societally tolerated risk of 0.075% and the historical CCS benchmark of < 0.005%.^[3],[4]