Utility of Isoproterenol to Provoke Outflow Tract Gradients in Patients With Hypertrophic Cardiomyopathy

It is important to identify patients with hypertrophic cardiomyopathy (HC) who have labile left ventricular outflow tract (LVOT) obstruction for consideration of ventricular septal reduction therapy. Although Doppler echocardiography has become the diagnostic modality to assess LVOT obstruction, it may not identify all patients with labile obstruction. This study assessed the diagnostic value of cardiac catheterization using isoproterenol challenge in 25 patients with HC in whom an LVOT obstruction (gradient ≥50 mm Hg) was clinically suspected, but not diagnosed using Doppler echocardiography. These patients underwent cardiac catheterization using a transseptal approach with isoproterenol challenge. During isoproterenol infusion, the gradient increased to ≥50 mm Hg in 14 patients and remained <50 mm Hg in 11 patients. Ten patients subsequently underwent surgical myectomy, 6 patients underwent alcohol septal ablation, and 9 patients were managed medically. Median follow-up was 26 months. Of patients who had a provoked gradient >50 mm Hg during isoproterenol infusion, 8 patients who underwent septal myectomy and 5 of 6 patients who underwent alcohol septal ablation had sustained alleviation of symptoms at follow-up. In conclusion, cardiac catheterization with isoproterenol challenge may identify patients with HC who may benefit from septal reduction therapy for whom the initial noninvasive evaluation does not show severe obstruction.