[The bradycardia-tachycardia syndrome].

Disorders of the heart rhythm which consist basically of sinus bradicardia or sinus arrest correspond to a syndrome which has been named the sick sinus syndrome. Within the framework of this syndrome, there is a subgroup of alternating atrial bradycardia with episodes of atrial tachyarrhythmia. Generally known as the bradycardia-tachycardia syndrome, this subgroup is both electrophysiologically interesting and therapeutically challenging. This report is concerned with the experience obtained at the emergency ward and coronary care unit of the Instituto Nacional de Cardiología de México on the diagnosis and management of 8 patients with this syndrome. Various underlying heart conditions were present with predominance of ischemic heart disease. The clinical picture was dependent upon the hypoperfusion of vital organs secondary to the cardial arrhythmia. The most common symptoms were derived from cerebral circulatory deficit and coronary insufficiency. Half of the patients had moderate cardiac failure. All patients had spontaneous and transient loss of sinus function which lasted more than 2,000 msec. in seven. The bradycardia had a rate below 50 beats per minute in all cases except one. The tachyarrhythmias observed were atrial flutter, atrial fibrillation and paroxysmal supraventricular tachycardia. Three of the patients had more than one of these these tachyarrhythmias during the period of study. A discussion is made on the diagnosis of this syndrome by means of atrial pacing and interventions which modify either vagal or sympathetic tone. Considerations are also made on the frequent associated abnormality of the A-V functional tissues. Emphasis is placed on the problems encountered in the management of these patients. It is concluded that, in most cases, a satisfactory result may be obtained by the implantation of a permanent demand pacemaker associated to the administration of antiarrhythmic drugs.