Flecainide cardiotoxicity precipitated by electrolyte imbalance. Caution with thiazide diuretics

Area of Science:

• Cardiology
• Clinical Pharmacology

Background:

• Flecainide is an antiarrhythmic drug that blocks sodium channels.
• Electrolyte disturbances, particularly hypokalaemia, are known to increase flecainide cardiotoxicity.
• The interaction between flecainide, hyponatraemia, and diuretic use has not been previously documented.

Observation:

• A patient presented with syncope, weakness, and fatigue, exhibiting QRS widening, hyponatraemia, and hypokalaemia.
• Medications included long-term bendroflumethiazide and recently initiated flecainide.
• Symptoms and ECG changes resolved upon correction of electrolyte levels.

Findings:

• The presentation was consistent with flecainide cardiotoxicity, likely precipitated by severe electrolyte disturbances.
• Hyponatraemia may contribute to flecainide toxicity by reducing sodium availability for channel antagonism.
• Bendroflumethiazide and flecainide may act synergistically to cause profound electrolyte imbalance.

Implications:

• Early recognition of flecainide cardiotoxicity is essential due to its potential for significant mortality.
• This case highlights the critical importance of maintaining strict electrolyte balance in patients treated with flecainide.
• Concomitant use of flecainide and bendroflumethiazide should be approached with caution or discouraged.