Concealed and Manifest Retrograde Conduction

Report:

Sinus rhythm

VEBs, one interpolated

Reentry (echo) beat of ventricular origin

Borderline left atrial abnormality (LAA)

Comment:

The ectopic beats are just about 0.14” long, with QR morphology in V1 and monophasic R in standard lead 1. Both, at first glance, appear interpolated, but only the second one actually is. It imparts a slight but definite prolongation to the subsequent PR interval and is sandwiched in an R-R cycle longer than its neighbours. The PR prolongation attests to concealed retrograde conduction of the VEB to the AV node. It is called concealed because it is not evident per se but only through its effect on the subsequent beat.

The first VEB occupies the shortest R-R cycle, making, to an experienced observer, interpolation unlikely except during a rampant sinus arrhythmia. And then, it is obviously followed by a retrograde P wave (inverted in leads 2 and 3) which precedes the next, supraventricular-looking, QRS. It thus displays a manifest retrograde conduction, which in turn reactivates the ventricles. The supraventricular-looking QRS is an echo beat. The retrograde P wave is itself premature and causes slowing of the sinoatrial pacemaker.

The patient’s dizziness could thus be due to a tachyarrhythmia: a VT (suggested by the presence of VEBs) or a reentry SVT, on the strength of the echo beat observed in this trace. Some sort of monitoring (Holter, transtelephonic, etc.) is indicated if other causes of giddiness are excluded.