Assessment for QRS widening

QRS widening is a significant effect of some poisonings and indicates cardiac conduction delay. QRS widening in the setting of poisoning is associated with ventricular arrhythmias and other effects (eg seizures, bradycardia), and is a marker of high serum drug concentrations.

Drug-induced QRS widening on ECG is most commonly due to drugs that cause sodium channel blockade—see Drugs associated with QRS widening for drugs associated with QRS widening.

QRS widening may be associated with QT-interval prolongation, but such QT-interval prolongation is not usually clinically significant1.

Assess the QRS complex on a 12-lead ECG. A QRS complex wider than 120 milliseconds is generally regarded as abnormal. If the QRS complex is wider than 120 milliseconds, commence continuous ECG monitoring and assess serial 12-lead ECGs for early detection of arrhythmias. For treatment of QRS widening due to poisoning, see here.

Table 1. Drugs associated with QRS widening

Drug class

Drug

antidepressants

tricyclic antidepressants

venlafaxine

antiepileptic drugs

carbamazepine

lamotrigine

antihistamines

diphenhydramine, dimenhydrinate

antipsychotic drugs

chlorpromazine [NB1]

cardiovascular drugs

flecainide

propranolol

local anaesthetics

bupivacaine

ropivacaine

others

bupropion

chloroquine, hydroxychloroquine and quinine

cocaine

orphenadrine

potassium (oral)

Note: NB1: Chlorpromazine can cause QRS widening, but this is not usually clinically significant.
1 QT-interval prolongation may be an artefact of QRS widening if the QRS complex is the only section that is prolonged. Measurement of the QT interval should be corrected for heart rate to give a corrected QT interval (QTc). Heart rates faster than 110 beats per minute can prolong the QTc as an artefact, but this cause of prolonged QTc does not lead to torsades de pointes.Return