Propoxyphene Toxicity

Report:

Supraventricular tachycardia, possibly sinus, 118/min

First degree AV block

PR 0.24”

Intraventricular conduction defect

QRS 0.15”

Comment:

This probably is a sinus tachycardia with P waves masked in many leads through prolonged QT interval; in V1-2, however, there is a distinct atrial hump that suggests a sinus P wave. The QRS is non-specifically prolonged although a fascicular block (e.g., atypical RBBB and a hemiblock) cannot be excluded. It matters little: there is no specific action required. The QT interval is prolonged, but the peak of the T wave occurs quite soon, almost abolishing the ST segment; this may be analogous to situation in myocarditis (Case 40).

An hour later, sinus mechanism became obvious (Fig 44a below); its PR interval is still long, at 0.20”, for rate. The IVCD is now only borderline, but retains its RAD +125o.

Dextropropoxyphene (Doloxene, Darvon) excess has marked cardiotoxicity. Its weak analgesic effects45 do not justify its use. It has quinidine-like actions, with prolonged intervals, arrhythmias and myocardial depression; these are not reversible with opiate antagonists like naloxone.

Over the next three days the T waves became inverted (Figs 44b, 44c) but the global hypokinesia resolved and the patient was handed over to psychiatrists.