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TAVR in Patients With Low-Gradient Aortic Stenosis
Study Questions:
What is the impact of transcatheter aortic valve replacement (TAVR) performed in low-gradient (LG) severe aortic stenosis (AS) compared to patients with high-gradient (HG) AS?
Methods:
Severe AS was defined by an aortic valve area ≤0.8 cm2 and an AS index ≤0.5 cm2/m2. LG AS patients (defined as mean AS gradient of <40 mm Hg and peak velocity <4 m/s) had been excluded from the US Pivotal Extreme Risk trial and were enrolled in the CoreValve Expanded Use Study (EUS) reported here. The comparison group of HG patients had been enrolled in either the CoreValve Pivotal Extreme Risk Trial or Continued Access Study (collectively referred to as the Reference Studies). The reference group included typical HG AS (n = 1,986) and dobutamine responder HG AS (n = 279). For the EUS study, patients were stratified by left ventricular ejection fraction (LVEF). LG-normal EF (LG-NEF) (n = 116) was defined as LG AS with LVEF <50%. Nonresponder AS (NR–AS) (n = 46) was defined as LG AS with LVEF <50% that failed to augment pressure gradients to the severe range with dobutamine. The primary study endpoint was a composite of all-cause mortality and major stroke. Secondary endpoints included all-cause mortality, cardiac mortality, valve-related mortality, stroke, bleeding, and other safety events. All patients were implanted with a self-expanding CoreValve prosthesis (Medtronic, Minneapolis, MN).
Results:
Compared to HG patients, LG–NEF patients as well as responder and nonresponder patients were more commonly male, had a larger body surface area, higher Society of Thoracic Surgeons score, and a higher prevalence of comorbidities including diabetes, coronary artery disease, prior pacemaker, myocardial infarction, and prior bypass. At 30 days, all-cause mortality or major stroke rate was lowest in the HG patients (7.9%). LG–NEF patients had a 9.5% 30-day primary event rate (p = 0.54) compared to 13% in the responders and 17.4% in nonresponders (p = 0.004 and 0.02, respectively). At 1 year, the only difference in the composite primary endpoint was between the HG and responder group. Among the four groups, baseline New York Heart Association functional classification was worse in the responders group when compared to the HG group. An improvement in heart failure status in all four groups was maintained through 1 year; however, there remained a difference between responders and HG patients. All groups had an excellent hemodynamic result following TAVR with mean gradients <10 mm Hg at 1 year.
Conclusions:
TAVR provides EUS patients significant hemodynamic relief with 1-year survival and quality-of-life outcomes comparable to that seen in typical HG AS patients who were enrolled in the reference studies.
Perspective:
This study is the first to perspectively report outcomes for prespecified outcomes in patients not considered appropriate candidates for the earlier reference trials. This included patients with LG AS either with preserved or reduced EF. These patients have been considered to be at substantially higher risk of events and potentially to derive less benefit than classic HG AS, and the role of TAVR has not been well-defined in this subset. This study demonstrated equivalent 1-year outcomes for the LG population with the unexpected exception of those who were dobutamine responders. All four groups had improved outcomes when compared to medically treated patients from prior trials. A surprising finding in the study was the poor outcome in dobutamine responders compared to the other three groups. “Conventional wisdom” is that dobutamine response confers a favorable outcome following valve replacement compared to nonresponders who were considered to represent end-stage disease. The underlying mechanism for this finding is unclear, but suggests that the ability of myocardium to respond to pharmacologic stimulation may not translate to recovery of function following relief of outflow obstruction. The bottom line from this study is that LG AS patients who are not appropriate surgical candidates, and who previously were excluded from consideration for TAVR, may after careful evaluation be candidates for TAVR and expected to have equivalent 1-year all-cause and cardiovascular mortality as well as major stroke rate compared to HG AS.
Keywords: Aortic Valve Stenosis, Body Surface Area, Cardiac Surgical Procedures, Coronary Artery Disease, Diabetes Mellitus, Diagnostic Imaging, Dobutamine, Heart Failure, Heart Valve Diseases, Heart Valve Prosthesis, Myocardial Infarction, Pacemaker, Artificial, Quality of Life, Stroke, Stroke Volume, Transcatheter Aortic Valve Replacement
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