TRICYCLIC POISONING - the QRS DURATION ON THE FIRST limb-lead ecg CAN SnNout SEIZURES AND VENTRICULAR ARRHYTHMIAS

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TRICYCLIC POISONING - THE QRS DURATION IN THE FIRST LIMB-LEAD ECG CAN SnNout SEIZURES AND ARRHYTHMIAS

Clinical Bottom Line:

Measure the QRS-duration in the limb leads of the first ECG taken after admission to the hospital.

If it is < 0.10 seconds, the patient is unlikely to develop grand mal seizures (95% CI = 0% to 14%).

If it is < 0.17 seconds, the patient is very unlikely to develop ventricular arrhythmia (95% CI 0% to 6%).

Re-Appraised by: Dave Sackett; 17 April 1998

The Studies:

49 patients (reported to the Massachusetts Poison Control Centre) seen within 24 hours of a tricyclic overdose who had limb-lead ECGs, blood screens, and follow-up observation.
8 additional similar patients reported in a letter to the Editor following publication of Study 1.

The Evidence:

QRS duration on first ECG (limb lead)	Numbers	Grand Mal Seizures (95% confidence interval)	Ventricular Arrhythmia (95% confidence interval)
< 0.10 seconds	13 + 7 = 20	0% (0% to 14%)	0% (0% to 14%)
> 0.10 seconds	36	33% (18% to 49%)	14% (3% to 25%)
< 0.17 seconds	39 + 7 =46		0% (0% to 6%)
> 0.17 seconds	10		50% (19% to 81%)

Comments:

Patients who are going to get into trouble do so by 6 hours after ingestion.
The worst ECG is the first ECG, and once normal it never got worse again.
ECG out-performed drug levels.

Expiry date: as soon as Interlibrary Loans (17 April 1997) give us more numbers

References:

Boehnert MT, Lovejoy FH Jr: Value of the QRS duration versus the serum drug level in predicting seizures and ventricular arrhythmias after an acute overdose of tricyclic antidepressants. NEJM 1985;313:474-9.
Hedges JR et al: Letter to the Editor NEJM 1986;314:988.
Pentel P, Sioris L: Incidence of late arrhythmias following tricyclic anti-depressant overdose. Clin Toxicol 1981;18:543-8 (pending)

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