Disopyramide in HCM — EECC MCQ

Correct answer: B — Disopyramide (class IA antiarrhythmic) has potent negative inotropic properties that reduce LVOT gradient in obstructive HCM by decreasing contractility; anticholinergic side effects (dry mouth, urinary retention, constipation, blurred vision) are common and dose-limiting

Disopyramide is a class IA antiarrhythmic (sodium channel blocker) with potent NEGATIVE INOTROPIC properties — this otherwise undesirable effect is therapeutically exploited in obstructive HCM. Mechanism: reduced contractility decreases the dynamic LVOT obstruction (less forceful ejection → less Venturi effect → less SAM). The 2023 ESC Cardiomyopathy Guidelines recommend disopyramide as add-on therapy to beta-blocker for refractory symptomatic LVOT obstruction (Class IIa) before invasive options (myectomy/ASA/mavacamten). Dose: 300-600 mg daily (modified-release formulations preferred). Side effects: anticholinergic effects (muscarinic blockade) are the major limitation — dry mouth (80%), urinary retention (particularly in older men with BPH), constipation, blurred vision. QT prolongation: class IA effect requires ECG monitoring. Disopyramide should NOT be used with verapamil (additive negative inotropy → severe hypotension). Mavacamten is emerging as an alternative/successor with a more favourable side-effect profile.

Reference: ESC (2023): Cardiomyopathies Guidelines