Found drowsy at home with an empty packet of her own tablets

62-year-old woman. Found drowsy at home with an empty packet of her own tablets

Amitriptyline for post-herpetic neuralgia and ramipril for hypertension. Lives alone, no cardiac history, no previous overdose.

Stage 1 of 2

Bronwen Ellis was found by her daughter at midday, slumped in a chair and difficult to rouse. An empty amitriptyline packet was on the table beside her. She opens her eyes to voice, mumbles, and moves all four limbs. The pupils are dilated, the chest is clear, and the skin is warm and dry. This twelve-lead was recorded as she was moved onto the resus trolley, and a venous gas taken at the same time gives a potassium of 4.1.

Tracing 1 of 2 for the quiz “Found drowsy at home with an empty packet of her own tablets”. — Twelve-lead recorded on arrival in resus, 25 mm/s, 10 mm/mV. Open this tracing in the studio

Bloods

Lactate (mmol/L): 2.4
Potassium (mmol/L): 4.1

What does the tracing show?

AMonomorphic ventricular tachycardia Your answer
BSupraventricular tachycardia with rate-related aberrancy Your answer
CSinus tachycardia with drug-induced QRS widening Correct answer Your answer
DSinus tachycardia with hyperkalaemic QRS widening Your answer

The rhythm is sinus tachycardia at about 112 beats per minute with a markedly widened QRS of 152 ms and a rightward axis of about 112 degrees. In the context of a tricyclic antidepressant overdose, this pattern reflects sodium-channel blockade rather than a primary ventricular tachycardia. The potassium is normal at 4.1, making hyperkalaemic widening unlikely. Supraventricular tachycardia with aberrancy would not explain the extreme rightward axis shift.

Which feature on the paper places the driver above the ventricle?

AA rightward axis, unusual for a ventricular focus Your answer
BA P wave before every complex at a constant interval Correct answer Your answer
CA rate of 112, at the slow end for ventricular tachycardia Your answer
DA QRS of 152 ms, at the narrow end for ventricular tachycardia Your answer

A P wave is visible before every QRS complex at a constant interval, confirming that the sinus node is driving the ventricle through the normal conduction system, however slowly. The rate of 112 is within the range for both sinus tachycardia and slow ventricular tachycardia, so it does not discriminate. Likewise, a QRS of 152 ms overlaps with both diagnoses. A rightward axis can occur in ventricular tachycardia and does not exclude it.

She remains drowsy with a systolic pressure of 96. What do you give?

AAmiodarone 300 mg intravenously, over twenty minutes Your answer
BSodium bicarbonate 8.4%, repeated against the QRS width Correct answer Your answer
CSynchronised cardioversion, under procedural sedation Your answer
DMagnesium sulfate 2 g intravenously, over ten minutes Your answer

Sodium bicarbonate 8.4% is the specific treatment for tricyclic-induced sodium-channel blockade. It works by increasing the extracellular sodium concentration and by alkalinising the plasma, both of which reduce the drug's binding to the sodium channel. The endpoint is narrowing of the QRS, not a target pH. Amiodarone would worsen the sodium-channel blockade, and cardioversion is not indicated because this is sinus tachycardia, not a re-entrant arrhythmia. Magnesium is the treatment for torsades de pointes, which is not present here.

Stage 2 of 2

Sodium bicarbonate 8.4% is given as 50 ml boluses through a large cannula, with the ECG repeated after each. She is intubated for airway protection before the third bolus and sedated for transfer. This tracing was recorded twelve minutes after the first bolus.

Tracing 2 of 2 for the quiz “Found drowsy at home with an empty packet of her own tablets”. — Twelve-lead repeated after treatment, 25 mm/s, 10 mm/mV. Open this tracing in the studio

Observations

HR: 96
SpO₂ (%): 99
Respiratory rate: 14
Temperature (°C): 36.3
Systolic BP (mmHg): 104
Diastolic BP (mmHg): 62

Bloods

Potassium (mmol/L): 3.6

What does comparing the two tracings show?

AThe sedation has slowed the rate Your answer
BThe ventricular tachycardia has converted to sinus rhythm Your answer
CThe QRS has narrowed while the rhythm stayed sinus Correct answer Your answer
DThe rate-related aberrancy has resolved as the rate fell Your answer

The QRS has narrowed from 152 ms to 104 ms and the axis has returned towards normal, while P waves remain visible before every complex at both time points, confirming sinus rhythm throughout. This proves the widening was a reversible drug effect. The rate has fallen from 112 to 96, but attributing that to sedation alone would miss the point: the QRS narrowing is the therapeutic response. The rhythm was never ventricular tachycardia, so it has not converted.

Diagnosis

Tricyclic antidepressant poisoning with sodium-channel blockade

The combination of sinus tachycardia, QRS widening and a rightward axis shift in the context of a tricyclic antidepressant overdose is the classic triad of sodium-channel blockade. A QRS duration above 100 ms is associated with an increased risk of seizures and above 160 ms with ventricular arrhythmia. The treatment is intravenous sodium bicarbonate, titrated against the QRS width, not against the pH.

The second tracing confirms the response: the QRS has narrowed from 152 ms to 104 ms while the rhythm has stayed sinus throughout. This is the proof that the widening was a drug effect reversed by sodium loading, not a ventricular tachycardia that required cardioversion or amiodarone.

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. N Engl J Med. 1985;313(8):474-479.
Bruccoleri RE, Burns MM. A literature review of the use of sodium bicarbonate for the treatment of QRS widening. J Med Toxicol. 2016;12(1):121-129.

Found drowsy at home with an empty packet of her own tablets

The case

On arrival

Bloods

Observations

Bloods

Diagnosis

References

Discussion