ECG Case 004

Main Abnormalities

• Broad complex tachycardia, rate ~ 130 bpm.
• The rhythm is likely sinus tachycardia with a 1st degree AV block — note the “camel hump” appearance to the T waves indicating a hidden P wave.
• Interventricular conduction delay (QRS duration > 100ms, not typical LBBB / RBBB morphology)
• Right axis deviation.
• Secondary R’ wave in aVR > 3 mm.

Diagnosis

In the context of a patient presenting with seizures and hypotension, the combination of…

• QRS broadening > 100 ms
• R’ wave in aVR > 3 mm

… is highly suggestive of poisoning with a sodium-channel blocking agent — e.g. tricyclic antidepressant.

The sinus tachycardia may be due to the anticholinergic effects of the TCA.

In the context of sodium channel blockade:

• A QRS duration > 100 ms is predictive of seizures.
• A QRS duration > 160 ms is predictive of cardiotoxicity.

This patient is already manifesting life-threatening toxicity and needs aggressive resuscitation, including:

• Serum alkalinisation with NaHCO3 to reverse pH-dependent toxicity.
• Intubation and hyperventilation aiming for alkaline arterial pH (e.g. 7.45 to 7.55).
• Seizure management with benzodiazepines.
• BP management with fluid boluses +/- pressors.