Prevalence and clinical manifestations of autonomic dysregulation of the sinoatrial node leading to syncope

to determine the structure of autonomic dysregulation of the sinoatrial node in patients without structural heart disease.

A total of 190 patients aged 18–55 years (mean age 36.5 ± 1.9 years) were examined, including 106 women (55.7%) and 84 men (44.3%), who underwent ambulatory 24-hour ECG Holter monitoring (HM ECG). All patients were referred for HM ECG after cardiology or family physician consultation. Clinical assessment included general examination, ECG, echocardiography (EchoCG), 24-hour ECG monitoring lasting 1–7 days, and laboratory testing, neurological consultation, tilt-table testing, and ambulatory blood pressure monitoring were performed as clinically indicated.

Among all patients, 65 (34.2%) reported sensations of irregular heartbeat, 58 (30.5%) had dizziness or syncopal episodes, and 67 (35.3%) complained of palpitations. Based on Holter monitoring data, 74 patients (38.9%) demonstrated signs of sinoatrial node dysregulation: persistent sinus bradycardia below 60 bpm throughout the day was observed in 5 (2.6%) patients; type I second-degree sinoatrial block in 24 (12.6%); type II second-degree sinoatrial block with pauses up to 2.5 seconds in 18 (9.5%) asymptomatic individuals. Episodes of asymptomatic sinus bradycardia with HR < 35 bpm during both active and rest periods with appropriate chronotropic response to exercise were found in 5 (2.6%) patients. Inappropriate sinus tachycardia was detected in 22 (11.5%) patients, and pacemaker migration in 12 (6.3%).

Tilt-table testing was performed in 58 patients with syncope or presyncope. Various types of autonomic dysregulation were found in 33 (17.3%) individuals, including sinoatrial node dysfunction in 9 (4.7%). Specifically, 2 (6.2%) patients were diagnosed with postural orthostatic tachycardia syndrome (POTS), 3 (9%) with cardioinhibitory syncope, 5 (15.1%) with mixed-type vasovagal syncope (VVS), and 6 (18%) with vasodepressor-type VVS. Patients in whom the cause of symptoms remained unclear were referred for further investigations, including brain MRI, extended laboratory diagnostics, and event ECG monitoring.

Autonomic dysfunction of sinoatrial node regulation is a common condition that impacts patients’ quality of life. Its main clinical manifestations include palpitations, fatigue, dizziness, syncope, and dyspnea, typical of inappropriate sinus tachycardia, postural orthostatic tachycardia syndrome, and vasovagal syncope of cardioinhibitory or mixed types. Among all patients undergoing Holter monitoring, 38.9% demonstrated various forms of sinoatrial node autonomic dysregulation. After additional tilt-table testing, vasovagal syncope associated with sinoatrial regulatory disorders was confirmed in 13.7% of patients.