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Invited Commentary
April 2016

Syncope and the Risk of a Subsequent Motor Vehicle Crash

Author Affiliations
  • 1Department of Medicine, University of Toronto, Toronto, Ontario, Canada
  • 2Evaluative Clinical Sciences Program, Sunnybrook Research Institute, Toronto, Ontario, Canada
  • 3Institute for Clinical Evaluative Sciences, Toronto, Ontario, Canada
  • 4Division of General Internal Medicine, Sunnybrook Health Sciences Centre, Toronto, Ontario, Canada
  • 5Center for Leading Injury Prevention Practice Education & Research, Toronto, Ontario, Canada
JAMA Intern Med. 2016;176(4):510-511. doi:10.1001/jamainternmed.2015.8617

A 44-year-old man was driving northbound along Interstate I-81 in Pennsylvania under clear sunny skies in the mid-afternoon on Wednesday, November 25, 2015 (the day before the Thanksgiving holiday).1 He fell unconscious, crossed a grassy median, and crashed into an oncoming tractor-trailer truck. He died instantly, as did his 12-year-old child passenger. This case is not unique and now becomes one more anonymized statistic among the 90 traffic fatalities that occur on an average day in the United States.2 About a third involve drivers known to have an underlying medical illness such as a cardiac, neurologic, or psychiatric disorder.3 Almost all of these drivers visit a physician in the year before their motor vehicle crash.3

Numé et al4 in this issue provide a rigorous analysis of 41 039 adults diagnosed with syncope and followed for a median of 2 years. The primary outcome was a serious motor vehicle crash, defined as an event sending a patient to the hospital (not necessarily admitted). The main findings suggest a doubling of risk relative to the population norm, equal to an absolute rate of about 1 serious motor vehicle crash per 50 patients with syncope annually. The increased risk extended for up to 5 years of follow-up and was particularly high for older men. The research is distinctive because syncope was based on International Classification of Diseases codes that excluded cases of third-degree heart block, epileptic convulsions, carotid sinus dysfunction, or orthostatic hypotension.

These findings are consistent with past research suggesting that syncope leads to a significant increase in the risk of a motor vehicle crash. A population-based study from Maryland (n = 7750) suggests that patients with syncope have about quadruple the crash risk of the population norm.5 A population-based study from Canada (n = 25 422) suggests that patients with syncope have about triple the crash risk of the population norm.6 A clinical trial from the United States (n = 559) suggests that patients diagnosed with life-threatening arrhythmias have about twice the risk of a crash comparing the year before to the year after intervention.7 American Medical Association guidelines based on expert opinion also list syncope as a “red flag” that justifies counseling patients on temporary driving cessation.8

All of these studies have inherent limitations due to potential confounding because (1) traffic safety cannot be explored by animal experiments, (2) patients were not randomized to diseases, and (3) a driver’s risk also depends on all others who share the road at the same time. One possibility is that syncope is a marker for additional disorders such as alcoholism or substance abuse, so that treating syncope would not be expected to normalize a patient’s traffic risks. A different interpretation is that patients are aware of the risks, have compensated to a substantial degree, and the actual risks associated with syncope are even greater. Regardless of explanation, health policy tightening is likely forthcoming because dangerous driving imposes risks on others.

The new data from Numé et al4 have several strengths. First, the study examines life-threatening crashes rather than minor crashes that cause vehicle damage without injuries. Second, the analysis distinguishes individuals with a particular diagnosis rather than classifying all traffic as the flow of similar motor vehicles. Third, the text is written in an easy manner that facilitates understanding and is not relegated to the engineering literature in a manner difficult for physicians to access. Finally, the analysis avoids the ecologic fallacy that confounds much of the literature on motor vehicle crashes where the statistics compare risks for different road segments rather than the risks for different specific individuals.

Extending these European data to the United States raises 2 further issues. The baseline rate of traffic deaths per 100 000 individuals annually is 2 times higher in America than in Denmark (10.9 vs 4.6).9 Indeed, no state has a baseline that matches Denmark, and some are 5 times higher (eg, Montana).2 This means that the absolute risks for drivers with syncope may be greater in the United States. In addition, not all states mandate physicians to counsel patients with serious medical conditions and notify a driver’s licensing agency. California requires the reporting of patients with disorders characterized by lapses of consciousness,8 whereas Massachusetts is a counterexample that has no mandate for physicians and no immunity for the breach in confidentiality.8

Applying the findings of Numé et al4 to individual patients requires further clinical judgment, since no patient is exactly the average and since some patients with syncope can be diagnosed and cured. At a minimum, physicians could consider asking patients about driving when eliciting a medical history. The findings also suggest that physicians practicing in California, Delaware, Georgia, Maine, Nevada, New Jersey, Oregon, and Pennsylvania may be obliged to counsel and report syncope patients to the driver’s licensing agency.8 The findings may also encourage other states to reconsider their own policies about medically unfit drivers. For example, physicians in Ontario, Canada, counsel about 50 000 patients with medical conditions each year on road safety (mandate first enacted in 1968).6

Numé et al4 provide a timely reminder for clinicians to consider traffic safety when managing a patient with syncope. Doing so will not clarify the diagnosis but might help prevent a life-threatening complication. Prior research suggests that physician counseling of patients with medical conditions about their driving capabilities may lead to about a 45% reduction in the patient’s subsequent risk of a serious motor vehicle crash.6 Other interventions based on detailed driving tests are less certain. Physician counseling requires tact, of course, so that an effective intervention does not compromise patient quality of life or the physician-patient relationship. Traffic fatalities (such as in the opening scenario) can be prevented for thousands of patients living with heart disease, cancer, or other illnesses.

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Article Information

Corresponding Author: Donald A. Redelmeier, MD, FRCPC, MSHSR, Sunnybrook Health Sciences Centre, 2075 Bayview Ave, G-151, Toronto, ON M4N 3M5, Canada (dar@ices.on.ca).

Published Online: February 29, 2016. doi:10.1001/jamainternmed.2015.8617.

Conflict of Interest Disclosures: None reported.

Funding/Support: This article was supported by a Canada Research Chair in Medical Decision Sciences, the Canadian Institutes of Health Research, and the Comprehensive Research Experience for Medical Students at the University of Toronto.

Role of the Funder/Sponsor: The funding organizations had no role in the design or conduct of the study; collection, management, analysis, or interpretation of the data; and preparation, review, or approval of the manuscript.

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