Patient	Date	Description
Twin A	Index date	Patient seen for the first time after referral by patient’s primary cardiologist. Patient diagnosed with basal septal hypertrophic cardiomyopathy
		Resting left ventricular outflow tract (LVOT) gradient 83 mmHg
		Metoprolol succinate 50 mg twice daily, verapamil 120 mg daily, and disopyramide phosphate 100 mg twice daily started over a period of 1 month
	1–3 months	Metoprolol dose decreased and verapamil discontinued due to sinus bradycardia
		Disopyramide phosphate dose increased
	8 months	No resting LVOT obstruction
		Valsalva-induced gradient 60 mmHg
		No further dosing adjustments
	24 months	Valsalva-induced gradient 76 mmHg
		Disopyramide phosphate increased to 600 mg in three divided doses
	32 months	Severe resting LVOT gradient of 108 mmHg
		Alcohol septal ablation recommended
	33 months	Patient had alcohol septal ablation
		No more resting or provocable LVOT obstruction
	40 months	Cardiac magnetic resonance imaging showed patchy delayed gadolinium enhancement of the basal septum
	96 months	No resting or Valsalva-induced LVOT obstruction
Twin B	Index date	After her twin sister’s diagnosis, patient seen for the first time. Patient diagnosed with basal septal variant of hypertrophic cardiomyopathy
		Resting LVOT gradient of 146 mmHg
		Metoprolol succinate 50 mg daily started
	1 month	Resting LVOT gradient improved to 100 mmHg. Metoprolol dose increased.
	2 months	Resting LVOT gradient 90 mmHg
		Disopyramide phosphate 100 mg twice daily added
	4 months	Resting LVOT gradient stable at 90 mmHg.
		Disopyramide phosphate dose increased; verapamil 180 mg daily added.
	6 months	No more resting or provocable LVOT obstruction.
	20 months	Cardiac magnetic resonance imaging shows patchy delayed gadolinium enhancement of the basal septum.
	84 months	No resting or Valsalva-induced LVOT obstruction.