BOF: 2.57
A 32-year-old female is admitted as an emergency having
taking an overdose of dosulepin.
In this condition which on of the following correlates
with the severity of the poisoning?
a)
Plasma drug concentration
b)
Width of the QRS complex on ECG
c)
Degree of metabolic acidosis
d)
Degree of respiratory acidosis
e)
Urinary retention
Answer:
b)
Dosulepin (a tricyclic antidepressant) is toxic in
overdose.
The main mechanism of toxicity is cardiac sodium channel
blockade. This increases the duration of the cardiac action potential and
refractory period and delays atrioventricular conduction.
ECG changes in overdose are as follows
·
Prolongation of the PR interval
·
Prolongation of the QRS interval
·
Prolongation of the QT interval
·
Non-specific ST segment and T wave changes
·
Atrioventricular block
·
Right axis deviation of the terminal 40ms vector of the QRS
complex in the frontal plane (T 40ms axis)
·
Brugada pattern (downsloping of the ST segment elevation in
leads V1-V3 with right bundle branch block)
Maximal changes in the QRS duration and the T 40ms axis
usually occur within 12 hours of ingestion. These changes may take up to a
week to resolve.
Sinus tachycardia is the most common arrhythmia. This is
due to anticholinergic activity and inhibition of norepinephrine
(noradrenaline) uptake by tricyclic antidepressants.
Bradyarrhythmias (due to atrioventricular block) and
tachyarrhythmias (supraventricular and ventricular) may occur.
Torsade de pointes may occur uncommonly.
Hypotension occurs as a result of decreased myocardial
contractility and reduced systemic vascular resistance caused by
alpha-adrenergic blockade.
Life-threatening arrhythmias and death due to tricyclic
antidepressant poisoning usually occur within 24 hours of ingestion.
Rapid deterioration is common.
Predictors of Severity
·
Level of consciousness at presentation is the most sensitive
clinical predictor of serious complications.
·
A QRS duration >100ms and a rightward T 40ms axis appear to be
better at predicting cardiovascular toxicity than the plasma tricyclic drug
concentration although they have moderate sensitivity and specificity for
predicting the onset of complications.
