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

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.

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.

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.

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.