Intraoperative Provocative Testing in Patients with Obstructive Hypertrophic Cardiomyopathy Undergoing Septal Myectomy

Abstract

Background: Resolution of left ventricular outflow tract (LVOT) obstruction predicts symptom relief postmyectomy. Intraoperative measurement of LVOT gradients thus is essential for surgical guidance. We hypothesized that (1) hypertrophic cardiomyopathy patients have lower LVOT gradients when measured intraoperatively with transesophageal echocardiography (TEE) compared with preoperative measurements with transthoracic echocardiography (TTE) and that (2) intraoperative provocative testing can help evaluate the adequacy of surgical resection.

Methods: We compared resting LVOT gradients on preoperative TTE to intraoperative TEE. We also compared intraoperative resting and provoked gradients pre- and postresection. Either isoproterenol 10 μg/kg/min or dobutamine 20 μg/kg/min was used. Patients with provoked LVOT gradients >30 mm Hg were considered for further resection based on LVOT/mitral valve morphology and clinical comorbidities.

Results: Of 315 patients identified, 293 patients were included in the analysis. There was a statistically significant difference between preoperative TTE and intraoperative TEE resting LVOT gradients (60.9 ± 39.4 mm Hg vs 42.0 ± 30.5 mm Hg, P < .0001). Out of 197 patients who had significant resting obstruction preoperatively, 82 (41.6%) demonstrated mild or no dynamic obstruction under general anesthesia. Provocative testing with both isoproterenol and dobutamine increased peak gradients (116.8 ± 33 mm Hg isoproterenol vs 107.5 ± 33 mm Hg dobutamine, P = .03). Post-cardiopulmonary bypass, seven patients (2.3%) had LVOT gradients > 30 mm Hg at rest, while 63 patients (21.5%) had residual gradients >30 mm Hg only with provocation. Elevated gradients, persistent systolic anterior motion of the mitral valve with near contact, and/or significant mitral regurgitation with provocative testing resulted in return to cardiopulmonary bypass in 41 patients (14%).

Conclusions: Resting intraoperative TEE LVOT gradients are significantly lower than preoperative TTE gradients, with systolic anterior motion of the MV and outflow obstruction often not visualized after inducing general anesthesia. Intraoperative pharmacologic provocation can identify patients who may benefit from further surgical intervention, facilitating procedural success.

Keywords: Dobutamine; HCM; Intraoperative provocative testing; LVOT gradients; Transaortic septal myectomy.