Practice recommendations
- Following inconclusive cardiovascular and neurological testing, an echocardiogram, stress test with Holter monitor, and possibly tilt table testing are appropriate ways to determine whether a vasovagal response is to blame for a young athlete’s exercise-induced fainting episodes (C).
- Advise patients with exercise-induced syncope to increase fluid and salt intake while exercising (B). Strength training can also be helpful (B). Most drug therapies, such as beta-blockers, vasoconstrictors, and anti-arrhythmics, have inconsistent results (A). use of permanent pacemakers are not effective (B).
Strength of recommendation (SOR)
- Good-quality patient-oriented evidence
- Inconsistent or limited-quality patient-oriented evidence
- Consensus, usual practice, opinion, disease-oriented evidence, case series
An 18-year-old woman was referred to us for evaluation after fainting on several occasions during a track workout. She’d been a competitive athlete for several years, and the episodes began 3 months earlier. She reported that they happen shortly after she started to run. She also told us that just before a spell, she had a sense of fatigue and severe leg pain.
Bystanders who witnessed one of the episodes reported that her eyes rolled upwards right before she fell; they saw no tonic-clonic activity that would indicate a seizure. We learned that the spells were short-lived and followed by immediate recovery with no mental deficits, such as confusion. On several occasions, she suffered superficial skin abrasions, but fortunately no serious injuries had occurred.
We suspected exercise-induced syncope
Prompt diagnosis of syncope in athletes is essential as it may be a marker for sudden cardiac death. The differential diagnosis, however, is broad (TABLE). Syncope in adolescents is often associated with fasting and eating disorders, excessive heat, alcohol, abdominal straining, exercise, hypoglycemia, growth spurts, lack of sleep, and low blood pressure.
TABLE
Differential diagnosis for exercise-induced syncope
| Anaphylaxis | Hypertrophic cardiomyopathy |
| Aortic stenosis | Hypoglycemia |
| Atrial fibrillation | Hypoxia |
| Brugada syndrome | Left ventricular hypertrophy |
| Cardiac dilatation | Pulmonary hypertension |
| Cardiac ischemia | Sick sinus syndrome |
| Catecholamine-dependant polymorphic ventricular tachycardia | Vasodepressor reflex |
| Commotio cordis | Ventricular fibrillation |
| Dehydration | Ventricular tachycardia |
| Eating disorders | Wolff-Parkinson-White abnormality |
Few clues from her history and exam
The clinical evaluation requires a careful and detailed history, including taking a family history to exclude familial causes of sudden death, such as long QT syndrome. In our patient’s case, there was no family history of sudden death or arrhythmias. She was a nonsmoker, nondrinker, and denied using any illicit drugs. She had been taking phenytoin for suspected seizure activity, but the spells continued.
On further investigation, we discovered that our patient would faint predictably 14 minutes into a competitive 5K run. She had recently adopted a more aggressive “early breakaway” strategy: she would run the initial part of the race at a pace of about 6 minutes per mile and slow down gradually towards the end.
We also learned that she had never fainted during weight training or when running at a less aggressive pace. Other than fatigue and extreme leg pain, she could not recall any other symptoms before falling, such as nausea, dizziness, weakness, or palpitations.
Her resting seated left arm blood pressure was 110/60 mm Hg and her heart rate was regular at 53 bpm. On cardiac auscultation, we heard no murmurs or abnormal cardiac sounds in the supine or standing positions. Cardiac palpation did not reveal a distal point of maximal impulse, which can suggest cardiac dilatation or cardiomyopathy.
On examination, she had normal results for muscle strength and reflexes. A sensory exam also had normal results. We ordered blood work; her CBC, electrolytes, thyroid-stimulating hormone level, creatinine phosphokinase, and liver function tests all had normal results.
The next step: Cardio, neuro tests
If the patient’s history and physical examination yield normal results, he or she will require further tests, including the ones listed below.
Exclude arrhythmias and myopathy
Electrocardiogram (ECG). All patients should have an ECG. Most young patients and athletes have a variation in the sinus rate due to sinus arrhythmia. This is a normal finding and does not suggest a cause of syncope.
Prolongation of the PR interval or QRS duration may suggest the presence of atrioventricular nodal or conduction disease, respectively. A prolonged PR interval or left bundle branch block is very unusual in young patients; in the presence of syncope, these require further evaluation. The presence of isolated right bundle branch block is a less significant finding.1
The presence of a short PR interval and slurring of the QRS upstroke suggests Wolff-Parkinson-White syndrome. Abnormalities in the QRS morphology may suggest left ventricular hypertrophy or hypertrophic cardiomyopathy. You should also exclude abnormalities in repolarization such as prolonged QT interval, Brugada syndrome, and catecholamine-dependent polymorphic ventricular tachycardia.