Post-Ectopic Sino-Atrial Depression

Report:

Sinus rhythm 74/min

SVEBs, one RBBB-aberrant

Marked post-ectopic SA depression (overdrive suppression)

Left bundle branch block

Comment:

The 7th beat’s P’ distorts the T wave of the preceding sinus beat. The pause containing the SVEB is more than twice the sinus cycle length. The next SVEB is aberrantly conducted – rsR’ pattern – undoubtedly led into aberration by the long preceding pause (phasic aberrant conduction). The pause associated with it is even longer – more than three sinus cycles. Presumably the SA node was still recovering from the original surprise when it was surprised again.

All pacemakers tend to slow down when prematurely discharged by an ectopic impulse. The degree of depression in this case is clearly pathological and can lead to symptomatic bradycardia. It is a manifestation of sick sinus syndrome. Below (Fig 142a) is another recording, very similar except that the pauses are terminated by junctional escape beats, one dissociated from the half-buried P wave preceding it (arrow). Some are preceded by P’ waves of junctional origin.

The LAD is not reportable with LBBB; about one half LBBBs have it. The RBBB aberrancy is somewhat unusual in this setting, but not, exactly, unheard of. Perhaps the IVCD is not a true LBBB in the first place, but a LAHB with IVCD. Whatever the case, the tall narrow R in V2 is a marker of myocardial infarction or cardiomyopathy.

Fig 142a. More SA suppression.

Fig 142b. More SA suppression, another RBBB aberrancy.

Fig 142c. Episode of atrial flutter – now a full “bradycardia-tachycardia syndrome”.

Fig 143. 22 year old lady with history of multiple procedures for tricuspid atresia.