Sick sinus syndrome

ECG 1: Supraventricular tachycardia with irregular atrioventricular conduction; ventricular rate of 95 beats/minute; rapid and regular atrial activity corresponding to atrial tachycardia; complete right bundle branch block (QRS duration of 125 ms, rSR’ pattern in V1, septal q wave and widened S wave in V6);

ECG 2: Bradycardia 25 beats/minute; atrial escape rhythm from the coronary sinus region (negative atrial activity in inferior leads, reflecting an activation arising from the inferior aspect of the atrium), narrow QRS (morphological pattern similar to that of a tachycardia QRS but narrower);

Comments: Sick sinus syndrome or tachycardia-bradycardia syndrome is characterized by alternating episodes of supraventricular tachycardia (atrial tachycardia, AF, common flutter) and episodes of bradycardia related to sinus node dysfunction. Symptomatology combines secondary clinical signs with tachycardia (palpitations, heart failure) and bradycardia (fatigue, cognitive disorders, dyspnea, lipothymia, syncope). This association suggests the presence of diffuse organic atrial lesions with degenerative impairment of the automatic cells of the sinus node but also fibrosis extending to the atrial myocardium and occasionally to the specific tissue of the atrioventricular junction explaining the putative concomitant observation of atrioventricular conduction disorders.

It is common to differentiate sick sinus syndrome (absence of a chronological link between tachycardia occurence and bradycardia occurence), post-tachycardia pauses (sinus pauses observed exclusively directly after termination of atrial arrhythmia) and vagal arrhythmias (episodes of arrhythmia observed solely after a sinus slowing of vagal origin).

Take-home message: Sick sinus syndrom reflects the presence of a widespread alteration of the atrium affecting the sinus node (explaining the bradycardia) and atrial myocardium (explaining the supraventricular arrhythmias).