Causes of sinus node weakness syndrome

While sick sinus syndrome in adults is predominantly of ischemic origin and manifests itself as atrial fibrillation, in most cases in children it develops in the absence of organic pathology of the cardiovascular system. Disturbances of the pacemaker in childhood are often caused by vegetative imbalance with a predominance of parasympathetic influences and age-related involution of the sinus node, as a consequence of inflammatory lesions of the myocardium, metabolic pathologies, autoimmune damage by specific antibodies to the cardiac conduction system. According to etiological factors, the following types of sick sinus syndrome are distinguished.

• Sick sinus syndrome of organic origin (in collagenosis, cardiomyopathy, amyloidosis, coronary heart disease, cardiac tumors, surgical injuries to the sinus node area, hormonal and metabolic cardiotoxic disorders and other pathological conditions).
• Regulatory (vagal) dysfunctions of the sinus node (vegetative-vascular dystonia with a predominance of parasympathetic influences on the heart, hypervagotonia with increased intracranial pressure, cerebral edema, vasovagal reflexes in organ pathology).
• Sick sinus syndrome as a consequence of toxic effects (antiarrhythmic drugs, cardiac glycosides, tricyclic antidepressants, sleeping pills, poisoning with malathion and other compounds that block cholinesterase).
• Dysfunction of the sinus node in children after cardiac surgery.
• Congenital dysfunction of the sinus node.
• Autoimmune disorders of sinus node function.
• Idiopathic disorders (cause not established).

In the first four cases, there is the so-called secondary syndrome of sick sinus node, its elimination is directly dependent on the effectiveness of the therapy of the underlying disease. The development of the syndrome in children who have undergone cardiac surgery is most often progressive and requires interventional treatment (implantation of a pacemaker).

In pediatric cardiology practice, it is often impossible to detect any disease that could secondarily lead to dysfunction of the sinus node. In these cases, it is customary to speak of a primary or idiopathic variant.

It is often extremely difficult to distinguish between organic and functional changes without morphological confirmation. This applies fully to the syndrome described. The criterion for differential diagnosis, in addition to the severity of the lesion, the assessment of which is often quite arbitrary, is considered to be the reversible and irreversible nature of the changes. For a long time, in addition to the term "sick sinus syndrome", the concept of "sinus node dysfunction" was widely used, implying irreversibility in the first case and reversibility in the second. It can be assumed that the so-called idiopathic sick sinus syndrome in children is a slowly ongoing degenerative lesion of the cardiac conduction system, in which the earliest and most pronounced changes occur, apparently, in the innervation of the sinus node. Hereditary predisposition can concern both the formation of vegetative pathology and primary electrophysiological changes in the cardiac conduction system.

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