Validation of submaximal heart rate recovery as a perioperative risk measure

Hughes, Cara Mae (2025) Validation of submaximal heart rate recovery as a perioperative risk measure. MD thesis, University of Glasgow.

Abstract

The number and complexity of patients presenting for surgery is increasing, with postoperative morbidity placing considerable burden on the health service, as well as negatively impacting patients’ quality and length of life. Effective preoperative risk stratification assesses the likelihood of poor postoperative outcomes so appropriate perioperative strategies can be implemented to reduce the incidence and severity of complications. Current risk stratification modalities include risk scores, biomarkers and assessment of cardiorespiratory fitness via exercise testing. The predictive value of these modalities however is variable. Preoperative risk scores involve a degree of subjectivity, particularly in the assessment of functional capacity. Cardiorespiratory fitness as measured by cardiopulmonary exercise testing (CPET) is an objective measure and associated with postoperative outcome. However, CPET is resource-intensive and not appropriate for all patients.

The aim of this thesis was to assess the utility of heart rate recovery (HRR) after submaximal exercise as a preoperative risk measure. Heart rate recovery is a marker of cardiac vagal tone and is prognostic for mortality and cardiovascular events in patients with cardiovascular disease and the general population. Systematic review performed as part of this thesis demonstrated that impaired HRR is associated with poor postoperative outcomes in individual studies, although evidence is limited (Chapter 2). Subsequently it was hypothesised that submaximal HRR could provide an objective preoperative risk prediction measure with broad applicability.

The validity of submaximal HRR in the perioperative population was investigated. The study was performed in three hospitals in the West of Scotland. Eighty-four patients (aged over 50 years) performed a submaximal step test in pre-assessment clinic or the ward prior to elective noncardiac surgery, with continuous electrocardiography for determination of HRR parameters. Perioperative data was collected, including cardiac troponins for the primary outcome of postoperative myocardial injury (PMI). Criterion, predictive, face, construct and concurrent validity were assessed in a series of investigations.

The first investigation of this thesis (Chapter 6) explored the predictive value of submaximal HRR in a cohort of 64 patients who underwent the step test and surgery, with PMI data for analysis. A range of different HRR parameters were assessed for predictive value for PMI, including absolute values, area under the heart rate recovery versus time curve and effort-corrected values, to both proportion of age-predicted maximum HR and proportion of predicted maximum power output reached. Six of the parameters demonstrated predictive value for PMI (area under the receiver operator curve (AUROC) > 0.64 for all), comparable to preoperative risk prediction measures currently in use. Submaximal HRR measured one minute after exercise cessation (HRR1) demonstrated fair predictive value for PMI (AUROC 0.69, 95% confidence interval 0.55 – 0.82). Furthermore, addition of submaximal HRR1 improved the predictive performance of a selection of preoperative risk scores in current use.

Secondary analyses (Chapter 7) explored the face validity of submaximal HRR in 72 patients who underwent both the step test and surgery. Submaximal HRR1 was associated with renal complications and intensive care admission, indicating face validity. However, there was no association between other secondary outcomes and HRR parameters.

The third investigation (Chapter 8) explored construct validity of submaximal HRR in 81 patents who underwent the step test and NT-ProBNP measurement, DASI, SORT, RCRI and POSSUM risk calculation. Submaximal HRR1 demonstrated construct validity via significant association with SORT mortality; ACS NSQIP SRC risk of any postoperative complication and length of hospital stay; DASI; RCRI and POSSUM mortality and morbidity risk.

The fourth investigation (Chapter 9) explored both criterion and concurrent validity of submaximal HRR in 12 patients who underwent the submaximal step test and CPET. Submaximal HRR did not demonstrate association with anaerobic threshold (AT), peak oxygen consumption or the ventilatory equivalent of carbon dioxide at AT and so criterion validity was not demonstrated. Concurrent validity was not reliably demonstrated, which may reflect the different aspects of cardiorespiratory fitness measured by HRR and CPET. Patients tolerated both exercise tests well but found the step test more comfortable and acceptable to perform (Chapter 10).

The work within this thesis confirms that submaximal HRR is a well-tolerated, feasible and valid measure in the perioperative population. From the range of HRR parameters measured, submaximal HRR1 consistently performed well, demonstrating predictive, face and construct validity. Future work may focus on the incorporation of submaximal HRR1 into preoperative risk assessment models; HRR measurement in the community; and integration of submaximal HRR into prehabilitation programmes.

• Item Type: Thesis (MD)
• Qualification Level: Doctoral
• Additional Information: Supported by funding from the Vascular Anaesthesia Society of Great Britain and Ireland.
• Subjects: R Medicine > R Medicine (General)
• Colleges/Schools: College of Medical Veterinary and Life Sciences
• Funder's Name: Vascular Anaesthesia Society of Great Britain and Ireland
• Supervisor's Name: Shelley, Dr. Benjamin
• Date of Award: 2025
• Depositing User: Theses Team
• Unique ID: glathesis:2025-85182
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 13 May 2025 13:51
• Last Modified: 12 Jun 2025 13:59
• Thesis DOI: 10.5525/gla.thesis.85182
• URI: https://theses.gla.ac.uk/id/eprint/85182