18MWT Contributes Valuable Feedback in Setting of PAH

The 18-meter walk test (18MWT), in conjunction with the 6-minute walk test (6MWT), was an effective method of evaluating disease severity in patients with pulmonary arterial hypertension (PAH) and shows promise at predicting who among these patients has a higher risk of clinical worsening, according to recent findings.¹

The 18MWT was first proposed in a 2017 study, which measured its utility among 144 patients with symptomatic heart failure and found it had positive predictive ability for adverse events, symptoms, and health status.²

According to the authors who published their findings recently in Pulmonary Circulation, “While the 6MWT is being extensively utilized clinically, it does have several weaknesses… [It] primarily focuses on exercise endurance rather than exercise speed, indicating its inadequacy for evaluating exercise intolerance. Several studies have demonstrated the significant association between exercise speed and skeletal muscle strength, and its important role in mediating exercise intolerance in PAH.”¹

To be included in this study, the patients (N = 117) recruited from Gansu Provincial Hospital in China needed to have received a confirmed diagnosis of precapillary pulmonary hypertension by right heart catheterization between January 2018 and December 2022, be 18 years or older, and have data from both tests. Their mean (SD) age was 41.4 (15.0) years, mean body mass index was 22.1 (4.3) kg/m², and 65% were female patients. The most common reason for their PAH was congenital heart disease (52%).

Three methods of evaluation were used to gauge the utility of the 18-meter walk test (18MWT) as a complement to the 6-minute walk test: Spearman correlation, Cox regression, and Kaplan–Meier analysis. | Image Credit: © Microgen-stock.adobe.com

Overall, it took a median (IQR) 12.8 (11.3-14.6) seconds to complete the 18MWT, and the median 6MWT distance was 370 (324-420). There was a negative association between time on the 18MWT and 6MWT distance (r_s = –0.60; P < .001). According to a Bland-Altman analysis, –0.400 (95% CI, –0.897 to – 0.098) was the mean difference between the walking speeds of both tests, and from among 117 data points, just 6 were outside the limits of agreement, “indicating that 94.9% of the data points were within the acceptable range, suggesting relatively good agreement between both walk tests.”

Significant correlations were seen for World Health Organization (WHO) functional class and NT-proBNP level with both 6MWT distance (r_s = –0.51; P < .001; r_s = –0.26; P = .004, respectively) and 18MWT time (r_s = 0.35; P < .001; r_s = 0.26; P = .005). Further, of the 17.1% of all patients who experienced clinical deterioration over the 2-year study follow-up, their PAH worsened in 12.0% and the remaining died.

A simplified risk score that encompassed 6MWT distance, WHO functional class, NT-proBNP level, and 18MWT completion time was predictive of outcomes at year 1 (P < .001). Also, in one model that replaced the 6MWT with the 18MWT, statistically significant improvement was not seen (P = .051).

When considering the impact of chronic obstructive pulmonary disease history, NT-proBNP, and mean right atrial pressure, each extra second increased the risk of an adverse event by 10% (HR, 1.10; 95% CI, 1.01-1.21). Also, the high-risk group of patients—those for whom the 18MWT time was more than 16 seconds—under 4 models, their prognosis was significantly worse vs the intermediate group (18MWT time of 12-16 seconds):

• Model 1: HR, 4.30 (95% CI, 1.55-11.96; P = .005)
• Model 2: HR, 4.46 (95% CI, 1.57-12.65; P = .005)
• Model 3: HR, 3.16 (95% CI, 1.06-9.44; P = .040)
• Model 4: HR, 4.98 (95% CI, 1.41-17.61; P = .013)

There was also significant interaction between 18MWT time and 6MWT distance (P < .001) and 18MWT time and pulmonary vascular resistance (P < .001), and the effect of the 18MWT time was more pronounced in patients whose distance on the 6MWT exceeded 370 meters (HR, 1.99; 95% CI, 1,47-2.70) vs 370 meters or less (HR, 1.05; 95% CI, 1.00-1.10).

Combining results from both tests, the study investigators found the 6MWT-to-18MWT ratio has significant associations with WHO functional class (r_s = −0.50; P < .001), NT-proBNP (r_s = −0.23; P = 0.012), right atrium area (r_s = −0.23; P = .023), and mixed venous oxygen saturation (r_s = 0.26; P = .004).

Potential limitations on these findings are that 52.1% of the overall patient cohort had coronary heart disease; this was a single-center, retrospective analysis; and there was a short follow-up and small sample size.

The authors found the 18MWT to be easy to administer and clinically relevant, with their study group exhibiting better exercise capacity compared with the 2017 study in which it was first investigated. Its effectiveness also was validated through its correlations with WHO functional class, NT-proBNP, right atrium area, and mixed venous oxygen saturation.

“This study has demonstrated the potential clinical utility of the 18MWT, a novel walk test to assess exercise capacity in predicting adverse events and disease severity in patients with PAH as a complement to the 6MWT,” they wrote. “Compared to the 6MWT, the 18MWT is more time‐efficient and provides new insight into the assessment of exercise capacity by evaluating walking speed, another feature of exercise intolerance in PAH.”

References

1. Jin J, Mi Y, Wang A, et al. Role of a new walk test in pulmonary arterial hypertension: a retrospective cohort study. Pulm Circ. 2025;15(2):e70087. doi:10.1002/pul2.70087

2. Harris KM, Krantz DS, Kop WJ, et al. A new clinically applicable measure of functional status in patients with heart failure: the 60-foot walk test. JACC Heart Fail. 2017;5(6):411-420. doi:10.1016/j.jchf.2017.02.005