Syncope and the runner.

Abstract

Syncope is a sudden, unexpected and grave medical episode that warrants thorough diagnostic investigation. Among runners, post-race syncope is frequently of neurocardiogenic origin (vasovagal syncope). Syncope occurring during the race tends to he more ominous. Even with extensive diagnostic work-ups, the cause of syncope is still unidentified in up to 38% of all athletic patients. A return to careful running is only recommended when the necessary tests are negative.

Keywords: neurocardiogenic (vasovagal) syncope, diagnosis, athletes.

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Syncope is a sudden, transient loss of consciousness that is accompanied by loss of postural tone with spontaneous recovery. It can be dangerous, disabling, and difficult to diagnose. Most tests for syncope have a low diagnostic yield. In most patients, a careful history (especially by witness) , physical examination, baseline blood tests, and ECG will provide a sufficient diagnosis, or determine whether further diagnostic testing is necessary. In sports medicine, syncope is often recognized as an Exercise-Associated Collapse(l, 2, 3).

Exercise-related syncope requires investigation because it may be the only symptom that precedes a sudden cardiac death. Syncope that occurs during exercise tends to be more ominous than that occurring in the post-exertional state(2). Neuro-cardiogenic (vasovagal) syncope is generally regarded as the most common Form of syncope in young adults. It occurs secondary to a sudden reflex vasodilation or bradycardia, or both. Neurocardiogenic syncope is also implicated in the majority of exercise-related syncopal events, particularly those that occur after exercise(2).

The major causes of syncope among runners would be cardiac, neurologic or metabolic. In neurologic syncope, a careful examination will yield a history of seizure activity, prolonged loss of consciousness, diplopia, headache, muscle aches, and postictal symptoms. However, seizure can occur as a result of hypertension and reduced cerebral perfusion, and therefore does not always indicate that epilepsy is the underlying cause(l). Neurologic tests include EEG, brain imaging (MRI, MRA, CT scans), and neurovascular studies (Doppler, ultrasound).

Metabolic syncope is frequently seen during the event and has readily identifiable conditions. Heat exhaustion and dehydration related to hyponatremia are the main concerns. Serum electrolytes, osmolality, and simple vital signs will provide diagnostic clues(2).

The majority of the patients suffer from cardiac syncope. Patients with organic heart diseases--such as coronary, valvular, or congenital heart diseases--or cardiomyopathy, are easier to diagnose than patients with cardiac conduction system disease (arrhythmia). Since arrhythmia may be episodic, finding asymptomatic brief arrhythmias or the lack of finding such arrhythmia does not exclude a rhythmic disturbance as a cause of the syncope(l). A major problem with the use of ambulatory ECG monitoring in the diagnosis of arrhythmia is that symptomatic correlation is rarely found (4% in Holter monitoring). Patient-activated intermittent loop recorders that can be worn for several weeks are the most useful diagnostic tools for those with multiple occurrences of syncope(1,4). Physically vigorous treadmill testing can be used for provoking exercise-induced tachyarrhythmias in exertional syncope. However, this test is rarely useful for arrhythmia detectioa(l). Other diagnostic tools include upright tilt testing, which is used to induce vasovagal syncope(5); and electrophysiological studies, which are expensive and should be reserved as a last resort for diagnosing arrhythmia. In the latter, test results are more likely to be abnormal in patients with underlying heart disease (1).

Drugs could precipitate a syncopal attack, and a detailed medication history including recreational drug use is essential. The drugs most likely to induce syncope include nitrates, vasodilators and b-blockers(1).

Even with exhaustive tests, a cause of syncope is not diagnosed in as many as 47% of the patients. However, a careful history and physical examinations leads to the identification of 55% to 85% of the causes. In the remaining patients, the aforementioned arrhythmia detection is the central issue(1).

Among runners with post-race syncope, diagnostic features should include: post-exertional occurrence, nonrecurrent syncope, unremarkable family history, normal cardiac examination, and normal ECG. Even with thorough diagnostic investigations, the cause of syncope is unknown in 38% of athletic patients with a one-year mortality rate of about 6%. If the syncopal event was clearly post-exertional, and necessary tests are negative, the patient may safely return to vigorous activity, with careful observations (2)

Note: The syncope described above actually happened to the author, Dr. Ough. After that incident, he ran nine marathons in two years, including Boston and Alaska.

References

(1.) Kapoor, W. N., Evaluation and Management of the Patient with Syncope, Journal of the American Medical Association, 1992; 268: 2553-2560.

(2.) O'Conner, F.G., and Oriscello, R.G., Exercise-related Syncope in the Young Athlete: Reassurance, Restriction Or Referral?, American Family Physician, 1999; 60:2001.2022.

(3.) Linzer, M., et al, Diagnosing Syncope Part 1: Value of History, Physical Examination, and Electrocardiography, Annals of Internal Medicine, 1997; 126: 989-996.

(4.) Lowe, P., syncope after Effort, Postgraduate Medical Journal, 2000; 76: 164-165.

(5.) Benditt, D., et al, Tilt table testing for Evaluation of Neurally Mediated (cardioneurogenic) Syncope: Rationale and Proposed Protocols, Pacing and Clinical Electrophysiology, 1991; 14:1528-1534.