EKG Diagnosis of TCA Toxicity
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þ Terminal RBB more sensitive for EKG Widening for TCAs?
 - rightward deviation of the terminal 40 mS of the QRS is more sensitive than
   QRS widening for TCA intoxication, as shown by sIrR pattern (s-wave in lead
   I, R wave in lead aVR) although not correlated with toxixity.
   [Wolfe TR, Caravati EM, Rollings DE. Terminal 40-ms frontal plane QRS axis
   as a marker for tricyclic antidepressant overdose. Ann Emerg Med
   1989;18(4):348-351.]
 - Dan Brooks says "[rude noise] You can tell from the end of the bed whether
   they're anticholinergic or not." (CEM J Club 1/21/03) Consensus: about as
   useful as detecting hypothermia with an EKG showing an Osoborn wave instead
   of a thermometer.

þ EKG findings useless for TCA OD?
 -
   [Lavoie FW, Gansert GG, Weiss RE. Value of initial ECG findings and plasma
   drug levels in cyclic antidepressant overdose. Ann Emerg Med
   1990;19(6):696-700.]

"I'll stick with the QRS100msec. criteria. Having said this, I agree that
there are no prospective trials showing benefit. But let's look at what we
do have: Boehnert at al give a 34% incidence of seizures when QRS100,
Hulten et al find a 27% incidence of QRS100 with 6-7%mortality, Ellison et
al finds that 13% exhibit 'pronounced cardiovascular deterioration' during
or soon after seizure. Thus, I perceive that this QRS100msec group to be a
high-risk group and alkalinization (IV or vent) is warranted. I have no
evidence or "belief" that this will decrease the incidence of seizures, but
alkalemia may be cardioprotective during the seizure with its attendent
metabolic acidosis. The above ratioale may be locally biased, as the QRS
criteria is also used by the NYC Poison group - Goldfrank, Hoffman, et al. 
  
1) It is my belief that TCA's prolong QTc only if it prolongs QRS duration.
Certainly not the case in my experience, and I've found a few references that
point to *both* of these criteria being useful (Refs 5-7). Forget beliefs;
respect cold hard evidence only! ;-) I'll grant you this. From the abstracts,
their respective incidences are different. I'll get back to you when I have
more time to read the entire articles.
 
2) rightward axis deviation of the terminal 40msec (terminal R in AVR, S in I,
etc.) is only an indicator of exposure to TCAs and not predictive of toxicity.
Perhaps, but from my (quick) perusal of abstracts, I'm not sure you can say
that it is much worse than QTc and QRS duration, unless we're talking QRS
duration160 ms. In fact I found one abstract that completely contradicts this
statement (Ref 5) I stand with my statement. The 'qualitative' assessment of a
right T40, as stated above, is only evidence of exposure. Look at your
reference, the minor toxicity group had a mean  120 degrees. Having said this,
it does appear that the more right the axis is (quantitative assessment), the
higher the risk. I'm not sure we can make much of this in the individual
patient.
 
Daniel Joyce, MD 
EM-3  Mt. Sinai Program,  NYC 
djoyce@pipeline.com 
 
(1*) Ellison-DW et al; Clinical features and consequences of seizures due
to cyclic antidepressant overdose. Am J Emerg Med 7(1):5, January 1989. 
 
(2*) Niemann-JT et al; Electrocardiographic criteria for tricyclic
antidepressant cardiotoxicity. Am J Cardiol 1986 May 1; 57(13):1154-9. 
 
(3) 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. N-Engl-J-Med. 1985 Aug 22; 313(8):
474-9.

(4) Hulten BA; Heath A. Clinical aspects of tricyclic antidepressant
poisoning.  Acta Med Scand 1983; 213: 275-8.

(5) Caravati-EM; Bossart-PJ. Demographic and electrocardiographic factors
associated with severe tricyclic antidepressant toxicity.
J-Toxicol-Clin-Toxicol. 1991; 29(1): 31-43

(6) Kresse-Hermsdorf-M; Muller-Oerlinghausen-B. Tricyclic neuroleptic and
antidepressant overdose: epidemiological, electrocardiographic, and
clinical features--a survey of 92 cases. Pharmacopsychiatry. 1990 Jan; 23 Suppl 1:
17-22

(7) Pellinen-TJ; Farkkila-M; Heikkila-J; Luomanmaki-K. Electrocardiographic
and clinical features of tricyclic antidepressant intoxication. A survey of 88
cases and outlines of therapy. Ann-Clin-Res. 1987; 19(1): 12-7

R in avR more than 3 mm means toxicity according to one study.
Another study showed GCS of 8 or less