Blocked premature atrial complexes

ECG: This ECG shows a bradycardia; there is sinus activity with left atrial enlargement (wide P wave > 120 ms, bifid in V5, V6 and widened negative component > 40 ms in V1); repeated succession of 2 sinus beats followed by a premature atrial complexe (atrial beat in the T wave with marked modification of the pattern of this T wave); there is an atrial trigeminy; the atrial complexes are very premature and blocked (not conducted to the ventricle) explaining the bradycardia measured by radial measurement;

Comments: This patient presented blocked premature atrial complexes leading to a bradycardia diagnosed by pulse measurement. It is thus an elevated automaticity disorder and not a conduction disorder. There is no sinus node dysfunction in this patient and the indication for pacemaker implantation should not be considered. Indeed, the slowing of the rate is related to the physiological sinus pause following the extrasystole, the purported treatment being possibly the introduction of an antiarrhythmic drug. This tracing shows that, in the presence of any tracing suggestive of a sinus node dysfunction, a careful analysis of the tracing is necessary, with particular attention to the morphology of the T wave and its variations, so as to eliminate the differential diagnosis represented by the presence of blocked atrial extrasystoles.

The coupling interval of the extrasystole is fixed with an alternation between two sinus activities and one extrasystole, thus constituting a trigeminy.

Take-home message: Premature atrial complexes can be isolated, in pairs or in bursts with a fixed or variable coupling interval. An atrial bigeminy corresponds to the alternation between a complex of sinus origin and a premature atrial complex. There is trigeminy when a premature atrial complex repeatedly occurs after two complexes of sinus origin.