Sinus node disease: ECG patterns and diagnosis

A healthy sinus node (SN) is the physiological principal site of electrical impulse formation in the heart, owing to its ability to sustain a regular generation of spontaneous depolarization at faster rates than other latent cardiac pacemakers. Structural disease (or senescence) of the SN and sinoatrial junction may cause SN disease (SND). The electrocardiographic (ECG) manifestations of SND are usually intermittent and can be easily missed. The ECG patterns of SND include: (1) periods of spontaneous, often pronounced, sinus bradycardia; (2) sinus pause due to sinus arrest or sinoatrial exit block; and (3) tachycardia-bradycardia syndrome. There is no standardized set of diagnostic criteria for SND. Since the symptoms of SND are non-specific, and the initial ECG may not be diagnostic, establishing a correlation between symptoms and the underlying heart rhythm at the time of symptoms is essential for the diagnosis, provided that any potentially reversible cause(s) of transient SN dysfunction have been excluded (or identified and treated). Invasive electrophysiological studies are not routinely used for the evaluation of SND, due to a limited sensitivity, and may be considered in patients with a mismatch of symptoms and ECG findings. When reversible causes have been excluded, SND should be distinguished from ‘physiological’ bradycardia (particularly in well-trained athletes), neurocardiogenic syncope with a pronounced cardioinhibitory component, or carotid sinus hypersensitivity. Carotid sinus hypersensitivity can be established by carotid sinus massage resulting in a pause of longer than 3 s or a symptomatic drop in blood pressure, or both.

Carotid sinus syndrome: clinical presentation, diagnosis, and management

Carotid sinus syndrome (CSS) accounts for 9% of patients presenting with syncope unexplained by the initial evaluation. It is often not considered as a possible diagnosis which can only be made by carotid sinus massage (CSM) when cardioinhibition and vasodepression occur with reproduction of symptoms. CSS must not be confused with carotid sinus hypersensitivity which is where CSM is positive in a subject without symptoms. Cardioinhibitory CSS is well treated by dual-chamber pacing but recurrence of syncope is more frequent if tilt testing is positive. Vasodepressor CSS is treated by fluids, salt, and reduction of hypotensive medication.