Topical classification of extrasystoles
Types of premature heart beats are conventionally distinguished in strict dependence on the anatomic location of the ectopic pacemaker. According to the topical classification, there are three main localizations:
- Atrial.
- Atrioventricular (forming in the atrioventricular node).
- Ventricular.
In routine medical practice, atrial and atrioventricular rhythm disturbances are always grouped together as supraventricular extrasystoles. Such a grouping is justified due to the commonality of their clinical characteristics.
Progression to paroxysmal tachycardia
The formal diagnostic criterion for supraventricular tachycardia is the registration on the electrocardiogram of a specific "run" — a series of three or more consecutive supraventricular extrasystoles.
In cases of pronounced tachycardia, a serious terminological and visual problem arises. Due to the high heart rate, it is often impossible to distinguish the P wave on the ECG. As a result, the clinician cannot reliably differentiate true atrial tachycardia from atrioventricular tachycardia. For this reason, all such conditions are grouped under a single clinical term — "supraventricular paroxysmal tachycardia".
The main pathophysiological mechanisms of such tachyarrhythmias are:
- Circulation of the excitation wave (re-entry) directly within the AV junction.
- Presence of Wolff-Parkinson-White (WPW) syndrome.
- Presence of other accessory conduction pathways in the myocardium.
How to distinguish functional arrhythmia from organic?
Proper clinical and electrocardiographic evaluation allows the attending physician to accurately determine the true nature of the arising rhythm disturbance. It is especially important to timely differentiate functional extrasystoles, which have a number of characteristic clinical markers:
- Age of manifestation: The arrhythmia most commonly first presents in patients during the prepubertal and pubertal periods.
- Inconstancy: Rhythm disturbances are markedly transient in nature.
- Response to exercise: This is a key differential sign. During physical activity or changes in body position, functional extrasystoles either completely disappear without a trace or their total number sharply decreases.
- Topography: The overwhelming majority of benign premature beats have a supraventricular origin or, in some cases, originate from the right ventricle.
Electrophysiological effects of antiarrhythmic therapy
Medical suppression of arrhythmias is based on altering the basic parameters of cardiac function. Drugs of this group exert a comprehensive effect on all parts of the heart without exception, providing a systemic therapeutic effect.
The key mechanisms of their therapeutic action include:
- Reduction of pathological automatism in ectopic nodes.
- Slowing of the velocity of electrical conduction.
- Significant increase in the effective refractory period (ERP).
Due to their versatility and wide range of indications, antiarrhythmic agents are highly effective in rhythm disturbances of absolutely any origin. They are successfully used in both supraventricular and ventricular extrasystoles and tachyarrhythmias.
The word "supra" (above) means that the ectopic focus is located "above the ventricles." If three or more such extrasystoles are registered consecutively on the ECG, it is classified as tachycardia rather than isolated premature beats.
Class and exam questions
What mechanisms underlie supraventricular paroxysmal tachycardias?
The main pathophysiological causes are circulation of the excitation wave (re-entry phenomenon) in the AV junction, Wolff-Parkinson-White (WPW) syndrome, and the functioning of other accessory abnormal conduction pathways.
How to differentiate functional extrasystole using stress tests?
The most important diagnostic sign of functional extrasystole is its response to physical exertion. During activity or a change in body position, the number of premature contractions sharply decreases or they completely disappear.
Which parts of the heart are affected by antiarrhythmic drugs?
Antiarrhythmic drugs have a systemic effect and influence all parts of the heart. They reduce automatism, slow conduction, and increase the effective refractory period.
What else to study on this topic
- Pathogenesis of excitation wave circulation (re-entry) in the AV junction
- Electrocardiographic features of Wolff-Parkinson-White (WPW) syndrome
- Clinical significance of the effective refractory period (ERP)
- Topical classification of ventricular extrasystoles
- Features of arrhythmia manifestation in the prepubertal age
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