Subvalvular Left Ventricular Outflow Obstruction for Patients Undergoing Aortic Valve Replacement for Aortic Stenosis: Echocardiographic Recognition and Identification of Patients at Risk

Persistently high gradients after aortic valve replacement (AVR), potentially caused by prosthesis-patient mismatch or superimposed but unrecognized nonvalvular obstruction, are associated with adverse clinical outcomes. Concomitant valvular and subvalvular left ventricular outflow obstruction was first hypothesized in 1957, and identified and further characterized in the 1960s, before the availability of echocardiography. Although obstruction as a result of subvalvular hypertrophy complicating valvular aortic stenosis has been subsequently described using echocardiography, it has largely fallen from consciousness in the preoperative and intraoperative echocardiographic assessment of patients undergoing AVR for aortic stenosis. As such, subvalvular left ventricular outflow obstruction complicating valvular aortic stenosis is a potentially preventable cause of persistently high gradients that remains relatively frequently encountered after AVR. This review is intended to draw attention to this phenomenon, to describe its mechanisms, and to provide guidance for its preoperative or intraoperative recognition using echocardiographic imaging techniques, with the goal that recognition and appropriate intervention at the time of AVR will decrease its clinical impact.