Tricyclic Cardiotoxicity Treated With Sodium Bicarbonate
A 19-year-old woman presented to the hospital after deliberate ingestion of 3.15 g of dosulepin (Prothiaden). Initial findings were a Glasgow coma scale of 6, a pulse rate of 132/min, and blood pressure of 80/50 mm Hg. An ECG showed broad complexes with a QRS interval of 223 ms (Figure, A). Initial treatment included invasive ventilation and intravenous hydration. Intravenous sodium bicarbonate was administered in a dose of 150 mL ×8.4% (150 mmol bicarbonate), causing rapid resolution of the electrocardiographic abnormalities (Figure, B) and restoration of systemic blood pressure. Ventilatory support was discontinued at 12 hours after ingestion, and the patient was discharged home 1 day later after formal psychiatric review.
Poisoning by tricyclic antidepressants may cause fatal arrhythmia attributable to blockade of cardiac sodium channels, causing prolongation of the cardiac action potential, refractory period, and atrioventricular conduction. Cardiovascular features include sinus tachycardia, which is caused by anticholinergic activity and inhibition of norepinephrine uptake, and hypotension, which is caused by reduced myocardial contractility and peripheral vascular α-adrenergic blockade.1 A variety of electrocardiographic abnormalities have been described, including prolongation of the PR, QRS, and QT intervals; nonspecific ST-segment and T-wave changes; atrioventricular block; right-axis deviation of the terminal 40-ms vector of the QRS complex in the frontal plane; right bundle-branch block; and the Brugada pattern. When taken in overdose, dosulepin is more likely than other antidepressants to be cardiotoxic, and the minimum fatal dose in adults is reported to be 750 mg.2,3
Prolongation of the QRS duration >100 ms predicts a higher risk of arrhythmia and is an indication for systemic sodium bicarbonate administration. Serum alkalinization favors dissociation of the tricyclic away from myocardial sodium channels, and the extracellular sodium load improves sodium channel function.4 In patients at risk of arrhythmia, consideration should be given to intravenous administration of 50 mL of sodium bicarbonate 8.4%, and the dose may be repeated every 15 minutes until the ECG normalizes or the arterial pH is ≥7.45.1,4 This is normally sufficient to allow restoration of normal cardiac rhythm and blood pressure, without a need to resort to other antiarrhythmic agents.