An Abrupt Doubling of Heart Rate.

CASE SUMMARY: Sinoatrial exit block is one manifestation of sick sinus syndrome. The impulse generated by the sinus node either fails to depolarize the atria or does so with delay. Sinoatrial exit block could vary in severity from first-, to second-, to third-degree. We here present a case of one type of sinoatrial block that is rarely encountered. The patient had atrial fibrillation and several other cardiac and medical comorbidities, which may complicate management. The patient had other conduction abnormalities, but no evidence of atrioventricular disease.

TAKE-HOME MESSAGE: Doubling/halving of the heart rate should raise suspicion of 2:1 sinoatrial block, indicating sinus node dysfunction.