Yesterday I had a 21 yo female come in by BLS crew, tachycardic with a GCS of 3, spontaneously breathing with equal and reactive pupils bilaterally at ~ 6mm, with vomitus around her airway.  She was found down at home after her significant other called EMS due to concern that she was going to attempt suicide.  Report received that she was found with multiple empty pill bottles nearby.  No response to Narcan either in the field or in Room 9.

Here is her ECG: Calculated QTc (automated) is 401 ms, rate is 143.   The accepted normal value for QTc is: below 450ms for men and below 460ms for women.  The 99th percentile of normal: 470ms (men) and 480 ms (women).

Just how does the computer calculate this?

By using the Bazett formula: QTc = QT / sqrt( R-R interval in seconds)

This means of course that if our rate is 60 BPM, then our R-R interval would be 1000ms, (or 1 second), and thus our QTc = QT/sqrt(1); and therefore in this situation QTc equals QT.

In our particular case: the R to R interval is 10.5 boxes (thus 420 ms, or in seconds: 0.420).  The QT was autocalculated at 260 ms, and when using the Bazett equation, this gives us a QTc of 401 ms.

What if you cannot rely on the computer calculated QT (which certainly can be inaccurate)? Then calculate the QT yourself by finding the tangential intersection of the T wave downslope with the ECG baseline, and measuring the intersection distance from the start of the QRS.  See the diagram below:

Using this measurement principal, and (in our case) using the lead V2 where the p wave and T wave are 180 degrees out of phase, we obtain a QT ranging from 8-9 boxes (320-360 ms).  When using the Bazett, this gives us a calculated QTc of 493-555. Of course qualitatively we can tell the QTc seems long as it exceeds half the R-R interval, quantitatively this is an increased QTc of 38% from the auto calculated, and is certainly in the significantly prolonged QTc range.

Follow-up: TCAs and benzos positive on her drug screen.  She was started on a bicarb drip in the ED (placed 3 amps of bicarb in a bag of D5); pH 7.34, lactic acid 1.2.  She is supposedly on Flexeril (similar in structure to TCA and will light up as TCAs on the drug screen), treated the same, however appears to be less cardiogenic in toxicity:J Emerg Med 1995;13(6):781-5.  Pt is intubated and stable currently.

Click here for the EMCrit on TCAs (overview below):

1. Bicarb drip:  Goals: QRS duration <100, hemodynamically stable, Na ~150, pH ~7.5.  Sodium and bicarb don’t rise significantly in severe toxicity, her repeat showed no change in either.
2. Magnesium: may help, though risk of Torsades is low as long as the patient remains tachycardic.
3. Lidocaine: even though lidocaine is another Na-Channel Blocker, it will antagonize the effects of the TCA-like medications.
4. Watch the electrolytes (decreases expected in both K+ and Ca+):  Lytes and ABG Q1H; (My pt’s Ca+ dropped from 9.8->8.5 over 4 hours).
5. Intubation: hyperventilate to ensure no hypercapnia (want alkalosis).  Sedate with versed or propofol to raise seizure threshold.
6. ECMO: If everything else fails.