You are on your PEM shift overnight when a 9 year old boy with history of behavior disorder, BIBEMS only moments (<30min) after witnessed ingestion of 500mg of his grandmother’s amitriptyline. On arrival, ABC’s intact, and the patient is sleepy but easily arousable. Normal vitals for his age. An EKG is performed, which appears normal. QRS 92 and the terminal R wave in aVR is <3mm. You are just about to given charcoal when the patient has a tonic-clonic seizure.
The EKG was normal right?
Oops. This EKG is technically not normal. Among other differences, pediatric patients have shorter QRS intervals, and according to this chart, this patient actually has a widened QRS based on his age. (This chart can also be found in the Harriet Lane Handbook, 20th edition, 2015 – Chapter 7)
Don’t try to remember this chart… just know it’s out there and that, as with many things, EKGs in kids are not the same as in adults.
So what does this kid need right now?
ABC support, benzos, sodium bicarb.
The activity of sodium bicarb in TCA overdose is two-fold:
- Sodium Loading. Hypertonic sodium directly competes with the TCA (a sodium channel blocker) at the sodium channel.
- Serum Alkanization. Increases intravascular pH which favors the non-ionized state of TCA’s, decreasing its availability to bind at the Na-channel
While many EKG changes can occur in TCA overdose, widening of the QRS is the primary indicator of toxicity on an EKG and should help guide your management. In adults, we give bicarb when QRS>100ms.
But isn’t a normal QRS in an adult between 80 and 120ms?
Yes, it is.
But in adults with TCA overdose, we give bicarb when the QRS>100. Why?
This widely accepted number is at least partly based on this 1984 prospective study of 49 patients. Patients with TCA toxicity were divided into two groups. Group A had QRS duration <100ms, while Group B had QRS duration >100 ms. These two groups were then observed. Group A had zero seizures or ventricular arrhythmias. In group B, 34% of patients had seizures and 14% had VA. In patients with QRS>160ms, 50% experienced VA. (1)
So, if QRS durations are different in kids, what QRS interval should we use to guide sodium bicarb administration?
No idea. There is basically no evidence out there I could find that adequately addresses this question. If you find some, please let me know (firstname.lastname@example.org). However, if you talk to a toxicologist (like I did), they will likely tell you to give sodium bicarb to kids with TCA overdose for any QRS that is prolonged based on the patient’s age.