Validation of Heart Rate Recovery as a Peri-operative Risk Measure

There are approximately 1.5 million major operations carried out in the NHS every year. As the population ages, and surgical technique becomes more advanced, more patients are undergoing operations which carry a high risk of complications. Currently, doctors predict this risk by asking patients about medical problems and their level of physical fitness. If an operation is very high risk, a patient may undergo cardiopulmonary exercise testing (CPET) where the patient rides an exercise bike to maximum effort (exhaustion) whilst their heart and lung function is measured. This gives the doctor specific numbers which can be discussed with the patient about the risk of complications after surgery. However, CPET is expensive and not all patients are able to do it, for example due to joint or circulation problems. Patients can also find attempting to reach maximal effort demanding and uncomfortable.

Heart rate recovery (HRR) after maximal exercise has been shown to indicate post-operative risk of complications, and is also related to life-expectancy in people with heart failure. The utility of HRR after submaximal exercise however has not been investigated as extensively. One group demonstrated that submaximal HRR predicts post-operative complications after lung surgery, and submaximal HRR also predicts life-expectancy in healthy individuals. There is less information about submaximal HRR as the methods of measuring it are not standardised. Previous work by our group has confirmed the reproducibility of submaximal HRR in a healthy population, and demonstrated different ways in which to measure it. We believe that submaximal HRR provides a "middle-ground" method of assessing how fit a patient is for surgery.

With informed consent, 95 patients across four hospitals in the West of Scotland will perform a step test pre-operatively. The step test will involve non-invasive measurement of the heart rate. Patients will exercise until approximately two-thirds of their predicted maximum heart rate is reached and then recover sitting, whilst the rate of their heart rate recovery is recorded. Patients will have pre- and post-operative troponin values measured (blood marker of strain/injury to the heart). Alongside the blood tests, patients will also answer questionnaires related to their quality of life, and information regarding other post-operative complications will be recorded.

Our study aims to demonstrate that submaximal HRR is predictive of post-operative myocardial injury (stress/injury to the heart wall due to the body's response to the operation) and that is it a valid measure when compared to the scores, blood tests and exercise tests that are currently in use in the NHS. In the future, submaximal exercise testing with HRR measurement may be offered to patients unable to perform CPET and will guide shared decision-making between patient, surgeon and anaesthetist to ensure the best outcome for the patient regarding their surgical options.