Last update: April 2020

Exercise-induced AV block

  Relatively uncommon condition.

  Second- or third-degree atrioventricular (AV) block may be seen
during exercise.

  Clinically, exercise intolerance, effort-related dizziness, shortness of breath during exercise or syncope may be seen.

  About 1/3 of patients have right bundle branch block (RBBB) in resting ECG.

Mechanisms of exercise-induced AV block

  Diseased infranodal His-Purkinje system: With exercise, increased sympathetic tone and vagolysis lead to improved conduction velocity and decreased refractory period in the AV node. Unlike the AV node, the His-Purkinje system is relatively devoid of autonomic innervation, and the refractory period decreases to a lesser extent during exercise. In a normal conduction system, these differences typically do not interfere with normal conduction. In a diseased system, however, the differences in refractoriness between the AV node and the His-Purkinje system are amplified and can result in the precipitation or worsening of infranodal block, as manifested by nonconducted P waves and AV block on ECG.

  Myocardial ischemia due to coronary artery stenosis.

  Superior vena cava stenosis: This may trigger paradoxical bradycardia, due to activation of a brainstem reflex, as a result of increased intracranial pressure.



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