Acquired loss of cardiac vagal activity is associated with myocardial injury in patients undergoing noncardiac surgery: prospective observational mechanistic cohort study.

BACKGROUND: Myocardial injury is more frequent after noncardiac surgery in patients with preoperative cardiac vagal dysfunction, as quantified by delayed heart rate (HR) recovery after cessation of cardiopulmonary exercise testing. We hypothesised that serial and dynamic measures of cardiac vagal activity are also associated with myocardial injury after noncardiac surgery. METHODS: Serial autonomic measurements were made before and after surgery in patients undergoing elective noncardiac surgery. Cardiac vagal activity was quantified by HR variability and HR recovery after orthostatic challenge (supine to sitting). Revised cardiac risk index (RCRI) was calculated for each patient. The primary outcome was myocardial injury (high-sensitivity troponin ≥15 ng L-1) within 48 h of surgery, masked to investigators. The exposure of interest was cardiac vagal activity (high-frequency power spectral analysis [HFLn]) and HR recovery 90 s from peak HR after the orthostatic challenge. RESULTS: Myocardial injury occurred in 48/189 (25%) patients, in whom 41/48 (85%) RCRI was <2. In patients with myocardial injury, vagal activity (HFLn) declined from 5.15 (95% confidence interval [CI]: 4.58-5.72) before surgery to 4.33 (95% CI: 3.76-4.90; P<0.001) 24 h after surgery. In patients who remained free of myocardial injury, HFLn did not change (4.95 [95% CI: 4.64-5.26] before surgery vs 4.76 [95% CI: 4.44-5.08] after surgery). Before and after surgery, the orthostatic HR recovery was slower in patients with myocardial injury (5 beats min-1 [95% CI: 3-7]), compared with HR recovery in patients who remained free of myocardial injury (10 beats min-1 [95% CI: 7-12]; P=0.02). CONCLUSIONS: Serial HR measures indicating loss of cardiac vagal activity are associated with perioperative myocardial injury in lower-risk patients undergoing noncardiac surgery.

Individualised oxygen delivery targeted haemodynamic therapy in high-risk surgical patients: a multicentre, randomised, double-blind, controlled, mechanistic trial.

BACKGROUND: Morbidity after major surgery is associated with low oxygen delivery. Haemodynamic therapy aimed at increasing oxygen delivery in an effort to reduce oxygen debt, tissue injury, and morbidity, is controversial. The most appropriate target for this strategy is unclear and might have several off-target effects, including loss of neural (parasympathetic)-mediated cellular protection. We hypothesised that individualised oxygen delivery targeted haemodynamic therapy (goal-directed therapy) in high-risk surgical patients would reduce postoperative morbidity, while secondarily addressing whether goal-directed therapy affected parasympathetic function. METHODS: In this multicentre, randomised, double-blind, controlled trial, adult patients undergoing major elective surgery were allocated by computer-generated randomisation to a postoperative protocol (fluid, with and without dobutamine) targeted to achieve their individual preoperative oxygen delivery value (goal-directed therapy) or standardised care (control). Patients and staff were masked to the intervention. The primary outcome was absolute risk reduction (ARR) in morbidity (defined by Clavien-Dindo grade II or more) on postoperative day 2. We also assessed a secondary outcome focused on parasympathetic function, using time-domain heart rate variability measures. Analyses were done on an intention-to-treat basis. The trial was registered with Controlled Clinical Trials (number ISRCTN76894700). FINDINGS: We enrolled 204 patients between May 20, 2010, and Feb 12, 2014. Intention-to-treat analysis of the 187 (92%) patients who completed the trial intervention period showed that early morbidity was similar between goal-directed therapy (44 [46%] of 95 patients) and control groups (49 [53%] of 92 patients) (ARR -7%, 95% CI -22 to 7; p=0·30). Prespecified secondary analysis showed that 123 (66%) of 187 patients achieved preoperative oxygen delivery (irrespective of intervention). These patients sustained less morbidity (ARR 19%, 95% CI 3-34; p=0·016), including less infectious complications. Goal-directed therapy reduced parasympathetic activity postoperatively (relative risk 1·33, 95% CI 1·01-1·74). INTERPRETATION: Achievement of preoperative oxygen delivery values in the postoperative phase was associated with less morbidity, but this was not affected by the use of an oxygen delivery targeted strategy. Reduced parasympathetic activity after goal-directed therapy was associated with the failure of this intervention to reduce postoperative morbidity. FUNDING: Academy of Medical Sciences and Health Foundation Clinician Scientist Award.