Ventricular Tachycardia: Pseudo P Waves at Either Complex End

Report:

Sinus rhythm 84/min.

Ventricular tachycardia 132/min.

Complete AV dissociation.

Comment:

The broad-complex tachycardia has QRS duration 0.20", extreme "Northwest" axis and, best of all, taller left rabbit ear in V1 to declare its ventricular origin. There is also dissociated atrial activity, almost certainly of sinus origin (upright in inferior leads, biphasic in V1). It accounts for the irregular cannon waves in the JVP (atrial contractions against closed tricuspid valve).

In lead 1, the initial QRS resembles an atrial P wave, complete with a PR interval; in the inferior leads and aVR, terminal QRS mimics retrograde 1:1 conduction. At times, only a 12-lead ECG, especially with simultaneous sets of leads, can enable one to tell the true QRS duration. Like in Case 75 above (same patient), AV dissociation identifies the true, movable P wave and makes the diagnosis possible even in a single rhythm strip. The "pseudo P waves" can cause considerable diagnostic confusion61.

Although such dissociation is present in majority of ventricular tachycardias and only a small number of junctional tachycardias with aberrancy (that may be confused with them), it is rarely as visible as in this trace, where the ventricular rate is relatively slow at 132/min.

Its presence supports the diagnosis of VT but does not, per se, prove it: "You cannot tell a pacemaker by the company she doesn't keep!"77. It could still be a dissociated junctional tachycardia with aberrant conduction. On the other hand, the morphology in this case lends little support for any particular form of aberrancy: this is a VT one can bet on.

A trace in sinus rhythm is shown below (Fig 79a). It has 1o AVB, LAA and LVH with ST/T changes as well as an IVCD and probable old inferior infarction producing LAD.