Introduction The Incremental Shuttle Walk Test (ISWT) has been evaluated in a number of diseases and found to be a safe, reproducible test which correlates better with VO2 max than the Six-Minute Walk Test (6MWT). We aimed to evaluate the utility of the ISWT as a prognostic indicator in pulmonary hypertension (PH).
Methods Data was retrieved for consecutive cases of PH diagnosed in our unit from 2001–2010, a cohort previously described.1 ISWT was performed routinely as part of baseline assessment according to a modified protocol of Singh et al.2 Data was analysed in 5 Groups according to the distance achieved based on ISWT level. A p-value of was deemed statistically significant.
Results 1002 of 1,344 patients diagnosed with PH underwent baseline ISWT within 3 months of cardiac catheterization and prior to pulmonary vascular therapy. Complete baseline data was available for 998 patients.
Kaplan-Meier analysis showed that increasing level of ISWT was associated with increased survival (Figure 1), including the PAH sub-group, with no ceiling effect.
ISWT distance correlated with WHO Functional Class, right atrial pressure, pulmonary vascular resistance, cardiac index, mixed venous oxygen saturation and percent predicted carbon monoxide diffusion (DLco) (p all ≤0.01). Multivariate Cox regression survival analysis including sex, body mass index, age, haemodynamic parameters and percent predicted DLco, demonstrated that ISWT distance was an independent predictor of survival.
One year follow-up data was available for 397 patients. Kaplan-Meier analysis showed that ISWT level on treatment at 1 year was predictive of survival (p < 0.001). Survival was also superior in patients whose ISWT distance improved from baseline ≥30 m compared to those whose distance remained stable (-20 to +20 m) or declined by ≥30 m (p = 0.20).
Conclusion Baseline ISWT distance correlates with WHO functional class and pulmonary haemodynamics with no ceiling effect. It is an independent predictor of survival and change in ISWT predicts outcome. These features make it a viable alternative to the 6MWT in the assessment of patients with pulmonary hypertension, with a number of potential advantages.