Six-Minute Walk Test Distance Predicts Peak VO2 in Patients Supported with Left Ventricular Assist Devices

Friday, 26 July 2013: 10:35 AM

Roslyn A. Prichard, RN, BA, Grad Dip CCU/ICU
Heart Lung Clinic, St Vincent's Hospital Sydney, Darlinghurst, Australia
Robyn M. Walker, MN, RN, CTcert, DipApSci, BHSci
Department of Cardiology, St VIncents Hospital, Xavier level 4,, St Vincent's Hospital,Sydney, Darlinghurst, NSW, Australia
Marcus Juul, BSc
Lung Function Laboratory, St. Vincent's Hospital Sydney, Sydney, Australia
Patricia Mary Davidson, RN, BA, MEd, PhD, FRCNA
Centre for Cardiovascular and Chronic Care, University of Technology Sydney, Broadway, NSW, Australia
Christopher S. Hayward, BMedSc, MBBS, MD, FRACP, FCANZ, MD
Heart Failure and Transpant Unit, St Vincent's Hospital, Sydney, Darlinghurst, Australia

Learning Objective 1: Have an increased awareness of procedures that can be undertaken by patients with LVADS,

Learning Objective 2: Understand use of Bland Altman analysis to compare methods.

Purpose: To examine the correlation between six minute walk test distance (6MWTD) and peak VO2 results in patients supported with Left Ventricular Assist Devices.  Two algorithms from the literature which predict VO2 max from 6MWTD in heart failure, are tested for validity in this group. 

Methods: We studied eight  patients supported with VentrAssist LVAD pumps. Each patient underwent 3 days of testing that included a 6MWT and cardiopulmonary test at Normal, High or Low speed. Data sets included,

  1. The distance achieved at each visit and pump speed, paired with the corresponding VO2 max result.
  2. The VO2 Max predicted from 6MWT using  the Cahalin et al algorithm.
  3. The VO2 max predicted from 6MWT using the Maldono-Martin et al algorithm.
  4. Resting left ventricular end diastolic dimensions (LVEDD)
  5. Resting serum Pro BNP levels.

24 data pairs were examined for  correlation between 6MWD and VO2 Max using linear regression. Student T Tests were used to examine the significance of differences in  Left Ventricular end diastolic dimensions and Pro BNP amongst patients who demonstrated response to increasing pump speed and non-responders.  Bland Altman plots established how well the equations of Cahalin and Maldonado-Martin predicted our VO2 max results.

Results:  There was a significant relationship between VO2 max and 6MWT distance (r2=0.32, p=0.004). However In subjects who showed a concomitant increase or decrease in VO2 Max with changing pump speed, there was no relationship found between VO2 and 6MWD.

Conclusion: 6MWD correlates significantly with VO2 Max in LVAD supported patients. Correlation increases when subjects with higher resting Pro BNP levels and larger LVEDDs are excluded. The Cahalin regression equations derived from, transplant wait listed patients, tended to overestimate VO2 Max in  LVAD patients. While the Maldonado-Martin equation overestimated VO2 Max in LVAD subjects with a lower VO2 Max.