LOW GRADIENT SEVERE AORTIC STENOSIS: DIAGNOSIS AND MANAGEMENT
Hari P. Chaliki, M.D., Mayo Clinic, Arizona, USA
According to the most recent American College of Cardiology/American Heart Association guidelines, peak velocity greater than 4 m/sec, a mean gradient of more than 40 mmHg and a valve area of less than 1.0 cm2 is considered severe aortic stenosis (AS). Aortic valve surgery should be done promptly in symptomatic patients or patients with reduced left ventricular ejection fraction (EF) with severe AS because of a dismal prognosis without operation. However, diagnosis of severe AS is difficult in some due to mismatch between transvalvular mean gradient and aortic valve area. Specifically, some patients present with low trans-valvular gradient and yet have a calculated valve area of less than 1.0 cm2. This scenario can occur due to low stroke volume in patients with reduced left ventricular EF, termed “low-flow, low-gradient, severe AS.” More recently, it has been recognized that some patients, often women with hypertension and concentric hypertrophy, have preserved left ventricular EF and yet have severe AS with low gradient due to low stroke volume (SVI <35 ml/m2), termed “paradoxical low-flow, low-gradient severe AS”. Diagnosis of these two entities can be challenging given that mild aortic valve stenosis may also result in similar hemodynamic variables due to lack of aortic valve excursion from poor stroke volume. When the left ventricular EF and stroke volume are reduced, one can use Dobutamine challenge to augment the stroke volume to differentiate patients with true severe AS from “pseudo” stenosis (mild stenosis). In the scenario of patients with normal left ventricular EF and reduced stroke volume, one may need to consider an alternative method of AS severity assessment such as multi-slice computed tomography to measure the aortic valve calcium score and/or Dobutamine challenge to confirm the diagnosis of severe AS before subjecting the patient to aortic valve intervention.