Axis Illusion

Report:

Sinus rhythm

VEBs, frequent, multiform

Bigeminy

Concordant precordial pattern

Ventricular tachycardia 120/min (4 beats at the onset of recording)

Possible bidirectional ventricular tachycardia

Comment:

The two beats with marked superior (left) axis flanking the broad VEB with right axis are themselves abnormal beyond a mere LAHB, inscribing a monophasic R wave in Lead 1 and a QS in Lead 3. If they were conducted supraventricular impulses their morphology would be that of incomplete LBBB. Subsequent sinus beats show, however, that there is no hemiblock or incomplete bundle branch block present.

There is another abnormal beat preceding the triplet, but only its T wave is visible, at the very start of the recording; hence the presumption of (at least) four-beat VT. An alternative interpretation is, as always, possible: the broad right-axis VEB could be interpolated - the sinus P wave is clearly visible in its ST segment - and the subsequent left-axis beat could, then, represent an incomplete LBBB aberrancy. Or the beat is not interpolated, but causes reentry (echo) beat with LBBB aberrancy. The same mechanism could account for the preceding left-axis beat’s morphology. This cannot be ruled out, but remains unlikely.

The term axis illusion is sometimes used to describe marked left axis deviation in emphysema; here it is merely borrowed because the original reporter succumbed to an illusion. A rhythm strip would have helped him.

The VEBs can be narrow; those making the bigeminal pattern in the rest of the trace are no longer than 0.12”. What makes the diagnosis of ventricular ectopy is, in this case, the positive concordant precordial pattern. The next day, similar VEBs are still present, but have obligingly broadened to 0.16” for easy recognition (Fig 53a).