ST/T Alternans: Tricyclic Overdose

Report:

Broad complex tachycardia of uncertain origin

QRS 0.28”

Probable atrial ? sinus tachycardia

ST/T alternans

Comment:

The patient was in coma, but not fitting; in shock, but not circulatory collapse; the QRS was well over 0.16”, but there were as yet no malignant ventricular arrhythmias; hypoventilating and hypercarbic, but still breathing spontaneously. The logical first step was to intubate him and optimise the pH and the intravascular volume. That done, the alternans became hardly noticeable on 12-lead ECG (Fig 93a).

Although QRS prolongation over 0.16” is a marker of serious morbidity87, its potential causes and mechanisms are many and the patients whose prolongation is due to tricyclics almost always have other, more obvious, reasons for being in the ICU88.

The arrhythmia recorded appears to have atrial waves in front of the broad complexes; they appear biphasic and may even be of sinus origin. Retrograde conduction from the ventricles, however, cannot be completely dismissed. A 12-lead ECG would have - as always - helped; but I wanted to ventilate the patient first. The 12-lead ECG, once taken as the patient was improving (Fig 93a), supported the diagnosis of probable sinus tachycardia. It is of interest that the tracing below has the same morphology as that of the idiopathic Brugada syndrome – an entity not entirely unrelated to tricyclic antidepressants89.

Repolarisation alternans is an ominous sign of impending arrhythmias.