ECG for atrial extrasystole
Atrial ectopic impulse leads to the appearance of a premature R wave. The place of its occurrence and, consequently, the direction of propagation of the atrial activation wave will differ from those during sinus rhythm, so that the premature R wave will differ in shape from the P wave of sinus origin.
Because atrial ectopic teeth P are premature, they can overlap the T wave of the anterior ventricular complex and thus deform it. Careful analysis of the ECG plays a key role in identifying ectopic P waves; Often the most appropriate for such an analysis is lead V1.
Atrioventricular and intraventricular conduction. Usually, a premature atrial impulse is conducted through the AV connection and along the legs of the His bundle in the same way as if the atria were activated by the sinus node. Therefore, the PR interval and the QRS complex atrial extrasystoles are similar to those of sinus rhythm.
If the QRS complex of sinus origin is deformed due to the blockade of the legs, then the QRS complex of the atrial beats will be the same.
However, sometimes atrial extrasystoles, especially those that occur very early in the cardiac cycle, can reach the AV connection or the bundle of the His bundle at a time when their conductivity has not yet recovered after the previous atrial impulse and which thus remain partially or completely refractory to arousal.
Partial or complete refractoriness of an AV connection will lead to a prolongation of the PR interval or blockage of the atrial extrasystole, respectively. The ECG pattern observed in cases where the atrial extrasystoles are not carried out on the ventricles can be mistakenly interpreted as an indication for an EKS!
Partial or complete refractoriness of one or another of the bundle of His (usually the right leg) may be accompanied by the appearance of signs of a partial or complete blockade of the leg, respectively. This phenomenon of functional blockade of the bundle of the His bundle is called “phase aberrant intraventricular conduction”.
As a result, QRS complexes of atrial extrasystoles become wide and, thus, if the premature P wave preceding the ventricular complex cannot be detected, atrial extrasystoles can be mistaken for ventricular ones.
Value. Atrial extrasystoles occur in many heart diseases, but are also common in people with a healthy heart, especially in the elderly. Usually they are benign, however, frequent atrial premature beats can be a precursor of atrial fibrillation (AF) or atrial tachycardia.