Adding objectivity to submaximal exercise testing by assessment of heart rate recovery—a healthy volunteer study – II (SEARCH-II)

Introduction: Exercise testing is a widely used preoperative risk assessment tool in thoracic and vascular surgery. Submaximal exercise tests (SETs) offer an easier to conduct and better tolerated alternative to ‘maximal’ cardiopulmonary exercise testing (1). Quantifying heart rate recovery (HRR) is a potentially objective method of assessing cardiopulmonary fitness following SETs. HRR1 and HRR2 (calculated as heart rate (HR) on exercise cessation minus HR at 1 and 2 minutes of rest) are commonly used methods for quantifying HRR, however previous work indicates they may be effort dependent (2,3). This study assessed the reproducibility of a novel effort correction of HRR1 and HRR2 across different modes of SET. Methods: Thirty-one healthy volunteers underwent three SETs of differing modalities in a randomised order; Bike, Step and Walk test. Individuals on beta blockers or with contraindications for exercise testing were excluded. HR was measured at 30 second intervals for 6 minutes of rest following cessation of exercise. HRR was quantified using HRR1 and HRR2. Effort corrected (EC) versions were produced by dividing raw HRR1 and HRR2 by the effort ratio (HR on exercise cessation divided by age-predicted maximum HR). Reproducibility was assessed by calculating Pearson's correlation coefficient (r) and the intra-class correlation coefficient (ICC). Results: The median age of the study population was 26 (range 18 - 74) years with 16.1% of the population possessing chronic co-morbidities. Raw HRR1 and HRR2 demonstrated poor reproducibility across all three comparisons. Effort correction improved the reproducibility HRR1, showing moderate reproducibility. Despite a modest improvement, the reproducibility of EC-HRR2 remained poor (Table 1.) Discussion: Effort correction improved the reproducibility of both HRR1 and HRR2 suggesting EC methods may be a superior way of quantifying HRR. Further work is required to explore the effect of differing exercise times on reproducibility of novel EC methods for quantifying HRR. Ascertaining this will allow adoption of a standardised protocol for SETs. Future work could be to assess the use of novel EC methods as perioperative risk predictors in patient cohorts.