Sinus node dysfunction

Sinus node dysfunction

Symptoms of sinus node dysfunction

Most frequent symptoms are syncope and presyncope. Other possible symptoms are fatigue, angina and shortness of breath. Elderly patients may present with subtle symptoms like gastrointestinal distress or a change in mental status. Symptoms can be intermittent and documentation can be difficult at times. Marked sinus bradycardia / pause may be asymptomatic occasionally.

Investigations in sinus node dysfunction

Noninvasive methods of investigation include ECG, 24 hour Holter monitoring, exercise testing and autonomic testing. If symptoms are infrequent, invasive electrophysiologic testing or the use of an implantable monitor (implantable loop recorder) may be needed for documentation.

Monitoring the ECG and correlating bradycardia during syncope is diagnostic of sinus node dysfunction. But this is rarely achieved from the simple ECG. If symptoms are frequent a 24- or 48-hr ambulatory Holter monitoring is useful. It is essential to document symptoms in a diary during Holter monitoring for correlation. Futility of treating asymptomatic pauses has to be borne in mind. Length of the pause has poor correlation with symptoms and prognosis. If symptoms are infrequent a loop recorder, a home recording device or an implantable loop recorder is needed to pick out the pauses.

Autonomic Testing in sinus node dysfunction

Pharmacologic interventions / maneuvers test reflex responses of the heart rate. Carotid sinus massage causing pauses of more than 3 seconds is considered significant. Occasionally such pauses may occur in asymptomatic elderly individuals. Intrinsic heart rate (IHR) is the heart rate during complete autonomic blockade with atropine, 0.04 mg/kg + propranolol, 0.20 mg/kg.

Intrinsic heart rate (IHR) = 118.1 – (0.57 × age [in years])

In a case of clinical bradycardia, a low IHR suggests intrinsic sinus nodal dysfunction while a normal IHR indicates abnormal autonomic regulation.

Invasive testing is reserved for symptomatic patients whose bradycardia cannot be documented by noninvasive means. Sinus node recovery time and sinoatrial conduction time are measured. But the ability to provide a definitive diagnosis by these parameters is limited.

Concomitant AV nodal disease is seen in about 17% of patients with sinus nodal dysfunction. New AV conduction abnormalities develop at the rate of 2.7% / year.