Author + information
- Michael Mok, MBBS†,
- Luis Nombela-Franco, MD†,
- Marina Urena, MD†,
- Robert DeLarochellière, MD†,
- Daniel Doyle, MD†,
- Henrique Barbosa Ribeiro, MD†,
- Mélanie Côté, MSc†,
- Philippe Pibarot, PhD†,
- Hugo DeLarochellière, MS†,
- Louis Laflamme, MS†,
- Paul Poirier, MD†,
- Eric Dumont, MD† and
- Josep Rodés-Cabau, MD†,⁎ ()
- ↵⁎Quebec Heart & Lung Institute, Laval University, 2725 Chemin Sainte-Foy, G1V4G5 Quebec City, Quebec, Canada
To the Editor:
Determination of individual patient risk for early-term and midterm outcomes following transcatheter aortic valve implantation (TAVI) has predominantly centered on baseline comorbidities, cardiac surgery risk algorithms, and peri-procedural complications. However, there is currently no scoring system or uniformly accepted framework for the complex decision-making process involved to determine whether a patient is at too high risk for TAVI.
The 6-min walk test (6MWT) is an objective submaximal assessment of exercise functional capacity in patients with cardiopulmonary disease (1). Two previous studies showed the feasibility and safety of using the 6MWT in patients with severe symptomatic aortic stenosis who were considered at very high or prohibitive surgical risk and showed significant improvement in the 6MWT following successful TAVI (2,3). However, it is unknown whether a pre-TAVI objective evaluation of exercise capacity can predict clinical outcomes. The objective of this study was thus to evaluate the prognostic role of the baseline 6MWT in TAVI.
To test our hypothesis, we studied 260 consecutive patients who underwent TAVI at our center. A balloon-expandable valve (Edwards SAPIEN or SAPIEN-XT, Edwards Lifesciences Inc., Irvine, California) was used in all cases. A total of 212 patients (82%) had a pre-procedural 6MWT within the month before TAVI, and all were performed in accordance with the American Thoracic Society protocol (1). Clinical follow-up was conducted by clinical visits and/or telephone consultation at 1, 6, and 12 months and annually thereafter, with no patient lost to follow-up.
Univariate and multivariate Cox proportional hazard model analyses were used to determine the predictive factors of cumulative mortality. The multivariate model included baseline and procedural variables that exhibited a p value <0.05 in the univariate analysis. Survival curves at the 1-year follow-up are presented as Kaplan-Meier curves. Results with p values <0.05 were considered significant.
The mean age of the study population was 79 ± 9 years, 54% of the patients were female, and the mean logistic EuroSCORE and Society of Thoracic Surgeons scores were 21.3% (IQR: 10.1% to 28.3%) and 7.0% (IQR: 4.0% to 8.6%), respectively. The 6MWTs were performed without complications, and the mean distance walked was 182 ± 108 m. Three in 5 patients attained a distance <200 m, and only 14% of the patients achieved a baseline distance of >300 m.
Procedural success and 30-day mortality rates were 94.3% and 7.1%, respectively. Male (73% vs. 44%; p = 0.033), chronic obstructive pulmonary disease (60% vs. 25%; p = 0.007), shorter 6MWT distance (105 [IQR: 60 to 191] m vs. 173 [IQR: 107 to 249] m; p = 0.038), and life-threatening bleeding (47% vs. 7%; p < 0.001) were associated with a higher 30-day mortality.
In total, 50 patients (23.6%) had died at a median follow-up of 12 (interquartile range: 4 to 24) months. The variables associated with a higher cumulative mortality in the univariate and multivariate analyses are shown in Figure 1A. The 6MWT distance was the most important independent predictor of mortality in the multivariate analysis (hazard ratio: 1.08 for each decrease in 10 m; 95% CI: 1.04 to 1.13; p = 0.001). At 1-year follow-up, 25% of patients who walked <182 m at baseline had died compared with 9% among those who achieved ≥182 m (p = 0.016) (Fig. 1B).
This is the first study to specifically investigate the prognostic value of the 6MWT in TAVI candidates, and it demonstrated that a poorer baseline functional capacity predicted worse clinical outcomes at 1-year follow-up. A shorter distance walked in the 6MWT may be a marker of frailty (4), which may in turn translate into worse outcomes. Also, we postulate that the ability of the 6MWT to predict mortality in patients with severe aortic stenosis may mirror the pathophysiology of patients with left ventricular failure. Among patients with moderate to severe heart failure, a significant correlation exists between distances walked during the 6MWT and peak oxygen consumption as measured by cardiopulmonary exercise test (CPET). Among patients with symptomatic severe aortic stenosis, the 6MWT may actually represent a “maximal” functional test, similar to the CPET, and thus may predict clinical outcomes (5).
Nearly one-fifth of the patients did not have a baseline 6MWT and were excluded from the study. Of note, those patients not able to perform the baseline test (severely limited mobility [n = 17], New York Heart Association class IV [n = 15], recent myocardial infarction [n = 3], and logistic reasons [n = 13]) had poorer outcomes (cumulative mortality of 45.8% vs. 23.6%; p = 0.004). Although the results of this study may be applicable to the vast majority of patients undergoing TAVI, confirmatory studies will be required. Also, larger series will be needed to determine the most appropriate 6MWT cut-off distance to predict worse outcomes.
The 6MWT is a simple and safe way to assess functional capacity in patients with severe symptomatic aortic stenosis considered to be at very high or prohibitive surgical risk. In TAVI candidates able to perform a baseline 6MWT, the test provided important additional prognostic information over that of conventional risk assessment algorithms. The inclusion of an objective functional based assessment such as the 6MWT may provide a more accurate risk assessment of the patient undergoing TAVI.
Please note: Dr. DeLarochellière is a consultant for St. Jude Medical, Dr. Dumont is a consultant for Edwards Lifesciences Inc., and Dr. Rodés-Cabau is a consultant for Edwards Lifesciences Inc. and St. Jude Medical. All other authors have reported that they have no relationships relevant to the contents of this paper to disclose.
- American College of Cardiology Foundation