Classification of sinus node weakness syndrome

Most often, the classifications of sick sinus syndrome suggested using the presence or absence of clinical manifestations, ECG patterns on a standard ECG or during Holter monitoring, and an increase in heart rate during exercise tests. Since the early 1990s, pediatric cardiology practice has been dividing this pathology into clinical and electrocardiographic variants of sick sinus syndrome in children depending on the nature, sequence of increase, and severity of changes in the cardiac conduction system, taking into account a stable combination of ECG manifestations, circadian rhythm changes according to Holter monitoring, heart rate response to exercise, and concomitant lesions of the cardiac conduction system.

Clinical and electrocardiographic variants of sick sinus syndrome in children

Disorders of functions

Sinus node	Lower levels of the cardiac conduction system
Option I. Sinus bradycardia with a heart rate less than 20% below the age-appropriate value, rhythm migration. Rhythm pauses during Holter monitoring up to 1.5 sec. Adequate increase in sinus rhythm during physical exertion.	Slowing of AV conduction to 1st degree AV block. Alternation of AV conduction
Option II. Sinoatrial block, escape contractions and accelerated rhythms. Rhythm pauses during Holter monitoring from 1.5 to 2 s. Inadequate increase in heart rate during physical exertion.	AV dissociation, AV block II-III degree
Option III. Tachycardia-bradycardia syndrome. Rhythm pauses during Holter monitoring from 1.5 to 2 s.	AV dissociation, AV block II-III degree
IV variant. Rigid sinus bradycardia less than 40 per minute, ectopic rhythms with single sinus contractions, atrial fibrillation-flutter. No restoration of stable sinus rhythm and its adequate acceleration during physical exertion. Rhythm pauses during Holter monitoring more than 2 s	AV and intraventricular conduction abnormalities. Secondary prolongation of the QT interval. Repolarization process abnormalities (ST segment depression, decreased T wave amplitude in the left chest leads)

In children, four stable clinical and electrocardiographic variants of sinus node dysfunction have been identified:

• Option I includes minimal manifestations in the form of sinus bradycardia and rhythm migration;
• Option II - replacement rhythms, sinus node arrest, sinoatrial block against the background of more pronounced depression of the main rhythm;
• Option III - a combination of sinus bradycardia with supraventricular heterotopic tachycardia;
• Option IV - cardioneuropathy with rigid pronounced sinus bradycardia, multiple replacement rhythms, asystoles and impaired myocardial repolarization.

Each of these variants in a fairly high percentage of cases is characterized by the addition of AV conduction disorders. The stage-by-stage formation of sinus node dysfunctions in children was confirmed: from I to II (or III, depending on the presence of electrophysiological conditions for the development of tachyarrhythmias) and IV variants.

In 2007, experimental studies by V. M. Pokrovsky and co-authors yielded a model for the development of sick sinus syndrome, in which a progressive increase in the severity of electrocardiographic changes was associated with a weakening of the central nervous system influence on rhythmogenesis. It was confirmed that the functional capabilities of the sinus node decrease sequentially. At stage I, rhythm migration appears, at stage II, escape beats, and at stage III, tachycardia-bradycardia syndrome is formed. The maximum decrease in the functional activity of the sinus node occurs under conditions of a significant decrease in central influences and is manifested by rigid bradycardia. Thus, the stages of progression of the pacemaker activity disorder of the sinus node in the experimental study exactly correspond to the above-described stages of development of sick sinus syndrome in children, which confirms the scientific and clinical significance of the classification proposed for pediatrics.

[ 1 ], [ 2 ], [ 3 ], [ 4 ], [ 5 ], [ 6 ], [ 7 ]