Symptoms and diagnosis of sinus node weakness syndrome

In half of the patients, sick sinus syndrome is asymptomatic, and the manifestations characteristic of sick sinus syndrome are detected by chance. The remaining patients seek medical attention due to complaints of syncope, dizziness, attacks of weakness, a feeling of interruptions and pain in the heart, and headaches. In cases where previously recorded ECGs could be obtained, it was found that 4-5 years before visiting the clinic, the children already had at least sinus bradycardia or pacemaker migration. Thus, in the absence of treatment, i.e., with the natural course of the disease, sinus node dysfunction gradually progresses from sinus bradycardia and pacemaker migration to the appearance of sinoatrial block in 40% of cases, as well as substitution rhythms against the background of complete failure of the sinus node. All this allows us to doubt the harmless nature of the initial electrophysiological phenomena. In most patients in childhood, despite the asymptomatic course, the sick sinus syndrome progresses. A conjugacy of the degree of damage to the sinus node and the AV node has been established. Such generalized inclusion of various levels of the conduction system in the pathological process is due to the commonality of embryonic development, the genetic program of morphogenesis and the development of vegetative innervation of the conduction structures. ECG manifestations of the syndrome include a wide range of disorders: bradycardia, rhythm migration, sinus node arrests and rhythm pauses, sinoatrial block, escape rhythms, supraventricular tachycardia, ventricular and supraventricular extrasystoles, AV conduction disorders of varying degrees.

Syndrome variant I (sinus node dysfunction) is characterized by the least pronounced deviations from the norm in terms of rhythm and AV conduction. Up to 30% of children complain of syncopal or presyncopal states (vasovagal mechanism of fainting).

In the natural course, the next stage may be characterized by the formation of both variants II and III of the sick sinus syndrome. This depends on the specific electrophysiological situation in each child. In the presence of latent additional pathways and other conditions for the formation of an abnormal electrophysiological mechanism of myocardial excitation, variant III develops - tachycardia-bradycardia syndrome. Both variants (II and III) are characterized by similar parameters of the basic sinus rhythm, including average daytime and average nighttime heart rate values, duration of rhythm pauses, reactivity of the sinus rhythm under drug and stress tests. With each of these variants, substitution rhythms appear as a compensatory phenomenon. Only in some cases they are represented by single contractions or slow rhythms from the lower parts of the cardiac conduction system (variant II), and in others, as a rule, by re-entry and ectopic tachycardias (variant III).

The most pronounced disorders are typical for the IV variant of the sick sinus syndrome. They are manifested by persistent bradycardia of about 40 per minute or less, periods of asystole more than 2 s. In some cases, rhythm pauses can reach 7-8 s or more. In some children (IV variant), sinus rhythm is not recorded or single sinus complexes are detected. This variant includes a constant bradycardic form of atrial fibrillation-flutter. In these cases, to diagnose the syndrome, it is important to evaluate the ECG recorded on a sinus rhythm. The diagnosis is valid if bradycardia, asystole or sinoatrial block are detected. Almost all children with the IV variant of the syndrome have signs of damage to the underlying parts of the cardiac conduction system and electrical instability of the myocardium: prolongation of the QT interval, alternans of the T wave, depression of the ST segment. ventricular extrasystole. This group of children has the most severe course of the sick sinus syndrome. Dizziness, attacks of severe weakness with clouding of consciousness are noted in 44% of children, in 50% of cases they are accompanied by severe cerebrovascular accidents - syncopal states. Unlike children with variant I of the syndrome, attacks of loss of consciousness in variant IV are caused by a sudden cessation or a sharp slowdown of the heart - Morgagni-Adams-Stokes attacks. They are accompanied by a sharp sudden pallor, sometimes respiratory arrest, convulsions. The duration of the attacks is from several seconds to several minutes. If it is impossible to stop them, they lead to sudden cardiac death of the child. The prevalence of the lesion, including all levels of the cardiac conduction system and the working myocardium, in conditions of a gross violation of the neurovegetative regulation of the heart rhythm allows us to classify variant IV as a cardioneuropathy.

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