Pseudoventricular Tachycardia

Report:

Atrial tachycardia 145/min

Left bundle branch block

Primary ST/T changes consistent with ischæmia

Comment:

The sole evidence for the ectopic ventricular provenance of the tachycardia resides in the broad R wave in lead V1 (Rosenbaum’s ‘normal’ pattern). This shifts the nadir of the S wave to almost 0.08”, virtually diagnostic of ventricular ectopy. The computer and the Cardiology Registrar reported VT – not unexpected in a patient with documented recurrent myocardial infarctions.

The S wave, itself, has a sharp descent and slow upstroke in V1, in keeping with standard LBBB morphology. In all the other leads, QRS is typical of LBBB morphology. The patient did have a pre-existing LBBB. A look at other ECGs, as usual, helps: below (Fig 118a) is a typical atrial tachycardia with block (PAT with block), with P waves characteristically visible only in lead V1. It runs at the same rate as the putative VT and its P waves have the same rounded upright contour as the primary R waves of the VT; they hug the onset of each QRS complex of the “VT” and are conducted, over the top105,106, to the next QRS with PR interval of 0.46” – reasonable for PAT with block. The P waves are thus just superimposed on the initial QRS complex, in what Wagner (but nobody else) would call fusion107.

This patient had other interesting tracings. In Fig 118b there is junctional rhythm with retrograde conduction, producing another unlikely LBBB morphology – rSr’ in V1. The retrograde P is too shallow to be distinguished from terminal QRS in other leads – but in V1 we know that it cannot be part of the LBBB complex. The trace also has the rather uncommon low-voltage LBBB QRS in the frontal leads. This may be due to the patient’s fluid overload108.

In 118c there is a sinus rhythm, to be used as a baseline for viewing the V1 QRS complex.