Syncope During Exercise

Syncope occuring during exertion is a warning sign that there may be a serious and potentially life threatening underlying cause.

Approximately 5% of syncopal presentations occur during physical exertion. When syncope presents during exercise the risk of a serious cardiac cause is increased 3-fold relative to non-exertional syncope. Exertional syncope should serve as a warning symptom for two reasons:

• Firstly, it is more likely that there is underlying heart disease such as ischaemic heart disease, aortic stenosis, hypertrophic cardiomyopathy (HOCM) or pulmonary hypertension.
• Secondly, in the seemingly “normal” heart there is the possibility of conditions affecting the electrical activity of the heart, such as Long QT syndrome, which may be challenging to diagnose.

It must be remembered that even in the group with syncope occurring during exercise, benign causes are far more common particularly in the absence of structural heart disease. However, because of the increased relative risk in this group, appraisal by a specialist in the field (Cardiac Electrophysiologist) is essential.

Listed in Table 1 are the conditions which have been associated with an increased risk of premature death and may present as syncope during exercise. Each of these conditions is rare but should be contemplated in this clinical setting. A number of clinical features aid in appraising these possibilities:

History:

This is critically important in the evaluation of syncope.

• It is important to elucidate whether the syncope occured during exercise or immediately afterwards.
• Syncope occurring immediately following exercise is common and is almost always benign (see below).
• Myocardial ischaemia, Hypertrophic Cardiomyopathy and pulmonary hypertension may be associated with exertional intolerance and/or chest pains preceding syncope or dizziness.

Disease associations which may assist in diagnosis:

• There is a strong association between events which occur whilst swimming and long QT syndrome type 1 (LQT1).
• Arrhythmias due to catecholaminergic polymorphic ventricular tachycardia (CPVT) are also far more prevalent during exercise, swimming or emotional stress.
• Other conditions such as Brugada Syndrome and LQT2 are more likely to occur during sleep or rest.

Family history:

• The majority of the listed conditions have an autosomal dominance inheritance.
  • This means that there is a strong possibility that family members are affected.
  • In addition to an inquiry about cardiac events and premature death, the physician should ask about a family history of epilepsy given that convulsive syncope is frequently misdiagnosed as epilepsy. Specific inquiry should also be made about single vehicle motor vehicle accidents, drownings, still birth and apparent SIDS.
• Absence of a family history does not exclude any of these conditions.
  

Physical examination:

• This will frequently be normal but characteristic signs of HOCM, pulmonary hypertension or mitral valve prolapse (MVP) may be evident.
  • It should be noted that whilst MVP is commonly associated with ventricular ectopy, it remains controversial as to whether there is an excess in sudden death.
    

Electrocardiogram (ECG):

• This is a critical part of the assessment.
  • Most of the conditions listed in Table 1 have unique ECG abnormalities.
  • These may be subtle and specialist interpretation should be sought.
• Although a normal ECG does not completely exclude these conditions, a normal ECG further stratifies patients into a favourable prognostic group.
  

Echocardiogram:

• This is important for excluding structural heart disease such as HOCM, ARVC, dilated or ischaemic cardiomyopathy or pulmonary hypertension.

Exercise stress test:

• This should be performed in most cases of exertional syncope both as a means of reproducing the symptoms and in evaluating for arrythmias in this setting.
• Sprints on the treadmill can be helpful if CPVT is suspected.
• The QT response to stress and recovery can also be assessed.

Specialised testing:

A number of specialised tests may be indicated dependant upon the findings the aforementioned evaluation. These may include:

• Coronary angiography
• Cardiac MRI
• Pharmacological challenges if CPVT or Brugada are suspected
• Invasive electrophysiology studies to assess for inducible arrhythmias.
• Tilt table testing of a neurally mediated mechanism is suspected and other tests are normal.
• Implantable loop recorders may aid in diagnosis in difficult cases.

Special Considerations:

Age:

The relative likelihood of a serious cardiac cause for exertional syncope is greatly influenced by age.

• Serious inheritied causes should be strongly condsidered in children or adolescents presenting with exertional syncope
• Patients middle aged and older should be carefully evaluated for ischaemic or structural heart disease as, in this age group, these conditions are far more likely than inherited causes.
  • It should be remembered that in those with structural heart disease, exertional syncope is highly specific for a cardiac cause.

Post-exertional syncope:

This needs to be carefully differentiated from syncope during exertion. If correctly recognised, extensive investigation and patient anxieties may be averted.

• Post exercise hypotension (PEH) is a common physiological phenomenon.
• Post exercise systolic blood pressure falls by approximately 20mmHg in hypertensive subjects and around 10mmHg in normotensive subjects.
  • It is believed to be due to a relative imbalance between parasympathetic and sympathetic activation in a manner akin to neurocardiogenic syncope.
  • In most people, this is a favourable phenomenon which may contribute to the improved blood pressure control seen in those engaged in habitual exercise.
  • In some, the fall in blood pressure is profound and may be associated with bradycardia and/ or asystole resulting in dizziness or syncope.

The differentiation between PEH and neurally mediated syncope is somewhat academic and, although symptoms may be troublesome, both have an excellent prognosis.

Exertional syncope in the absence of heart disease:

If serious structural and electrical disorders of exertional syncope are excluded, then a benign (hypotensive) cause is likley even if syncope is recurrent.

• This seems particularly true of athletes in whom syncope during exercise is not uncommon and is frequently neurally mediated in origin.

Implantable loop recorders can be beneficial in this group to exclude an arrhythmic cause when syncope is recurrent and investigations are unremarkable.