Adding objectivity to Submaximal Exercise testing by Assessment of heart Rate ReCovery—a Healthy volunteer study (SEARCH)

Abstract

Preoperative exercise testing is widely used to assess perioperative risk. ‘Maximal’ exercise tests, such as cardiopulmonary exercise testing, can place an unnecessary burden on patients and are not always well tolerated. To overcome this sub-maximal exercise tests (SET) are increasingly being utilised. Although potentially better tolerated, being ‘submaximal’, results may be dependent on patient motivation and effort. Measuring heart rate recovery (HRR) after SETs could potentially add objectivity and provide further insight into patient myocardial fitness. Quantifying HRR by calculating the difference between HR on exercise cessation and at 1/2 min into the recovery period (HRR1/HRR2)1 has been widely described. This study sought to assess the influence of SET effort level on the reproducibility of HRR and evaluate the reproducibility of novel methods for quantifying HRR. Thirty-four healthy volunteers underwent three 6-min SETs on a cycle ergometer. Individuals on beta-blockers or with contraindications to exercise testing were excluded. The first test was used to familiarise the volunteer with the exercise test protocol and was undertaken at 20% of the volunteers predicted maximum wattage (Wmax). The following two tests were delivered in a randomised order at 40% or 60% Wmax. Data on HRR were collected for 5 min on test cessation. Area under the (HR vs time) curve (AUC) and an effort corrected version of AUC (EC-AUC) were derived as novel indices of HRR. To ascertain the reproducibility of HRR indices, the intra-class correlation coefficient (ICC) and paired t-tests were estimated. The median age of the study population was 39 (range, 22–72) yr with 15% of the population possessing chronic co-morbidities. The ICC for HRR1 was 0.15 [95% confidence interval (CI), 0–0.43], mean difference 9.7 (P≤0.001; 95% CI, 4.3–15.1). For HRR2 the ICC was 0.35 (95% CI, 0–0.68), mean difference 15.4 (P≤0.001; 95% CI, 11.1–19.7). The novel AUC method achieved an ICC of 0.61 (95% CI, 0.27–0.8), mean difference 646 (P=0.05; 95% CI, 245.4–1038.2). EC-AUC achieved an ICC of 0.46 (95% CI, 0.14–0.69), mean difference 0.03 (P=0.01, 95% CI, 0.05–0.01). HRR1/HRR2 demonstrated poor reproducibility across differing effort levels, suggesting they are influenced by level of exertion. The AUC methods displayed moderate reproducibility and therefore may be a superior way to quantify HRR after SET. Further work is required to explore the effect of differing exercise regimes on the AUC methods of quantifying HRR and assess their utility as a perioperative risk predictor in patient cohorts. Medical Research Scotland Vacation Scholarship. 1.Adabag S, Pierpont GL. Heart 2013; 99: 1711–2