Association between preoperative ambulatory heart rate and postoperative myocardial injury: a retrospective cohort study

Background: Resting heart rate is well established as a predictor of morbidity and mortality in the general population. However, the relationship between preoperative heart rate and perioperative outcomes, specifically myocardial injury, is unclear.

Methods: This retrospective cohort study included patients undergoing elective major non-cardiac surgery from 2008 to 2014 at a multisite healthcare system. The exposure was ambulatory heart rate measured during the outpatient preoperative clinic visit, whereas the outcome of interest was myocardial injury (peak postoperative troponin I concentration >30 ng L^-1). Covariates included patient characteristics, comorbidities, and preoperative medications. We constructed several multivariable regression models that each modelled heart rate in a different manner, including as a simple continuous variable, categories, and fractional polynomials.

Results: The cohort included 41 140 patients, of whom 4857 (11.8%) experienced myocardial injury. Based on pre-specified heart categories thresholds, a heart rate ≥90 beats min^-1 was associated with an elevated odds of myocardial injury compared with a heart rate <60 beats min^-1 (adjusted odds ratio, 1.22; 95% confidence interval, 1.06-1.39; P=0.005). This result was consistent regardless of the method used for categorisation. When fractional polynomials were used to model heart rate, a 'J-shaped' relationship between heart rate and odds of myocardial injury was observed.

Conclusions: This cohort study found that both very high preoperative heart rates, and possibly also very low heart rates, are associated with increased risk of myocardial injury. Whether heart rate is a modifiable risk factor, or rather simply a marker of underlying cardiac pathology, needs to be determined in further research.