Disease of the sinoatrial node associated with bradycardia, asystole, syncope, and paroxysmal atrial fibrillation.

SINUS bradyeardia has been associated with a number of entities, both normal and pathologic; however, it is usually of a transient nature. It has been found in 30 per cent of healthy young males,' the well-trained athlete,2 and has been associated with pregnancy, particularly the post partum period.3 Its incidence markedly exceeds what might be expected in starvation, myxedema, jaundice, increased intracranial pressure, beriberi, labyrinthitis, convalescence from certain infectious diseases, and bilateral thoracic sympathectomy.4-8 In a series of 6,786 medical hospital admissions Kirk and Kuorning' found sinus bradyeardia in 515 patients, or 7.6 per cent; syncope due to the sinus bradyeardia occurred in only 1 patient. Sinus bradyeardia due to arteriosclerotic heart disease is rare. As can be seen from examination of the above list of entities, there are diverse causes of sinus bradyeardia. These causes may be classified as neurogenic or non-neurogenic. By blocking of vagal activity with atropine increased vagal activity has been demonstrated in young men,7 starvation,4 and increased intracranial pressure.8 Short9 describes 4 patients with alternating sinus bradyeardia associated with a variety of tachyeardias. Sinus standstill was present in 2 patients and a wandering pacemaker in 3 patients. Atropine, effort, or emotion was found to accelerate the rate considerably, usually to a normal sinus rhythm, in all these patients. Asystole with normal sinus rhythm and nodal rhythm have been described respectively by Laslett'0 and Wedd and Wilson."1 These