Reliability of the continuous ECG after cardiopulmonary bypass and CABG surgery.

Because of ECG changes associated with phenomena such as myocardial stunning or reperfusion injury in patients undergoing coronary artery bypass graft (CABG) surgery, Holter recordings may not detect postoperative myocardial ischemia with the same sensitivity and accuracy achieved in patients undergoing noncardiac surgery. This study details the reasons for decreased sensitivity of Holter recordings under such circumstances and suggests guidelines for inclusion of patients undergoing CABG into future studies. Continuous ECG (Holter) recordings were obtained in 617 analyzable patients before, during, and for 24 to 48 hours after CABG surgery. Uninterpretable tracings occurred with greatest frequency in the immediate period after electrical defibrillation and decreased progressively thereafter; only 50% of recorded tracings were interpretable and the percent of interpretable recordings increased progressively for the next 9 hours and then remained constant. This study confirmed the great frequency with which ECG abnormalities occur in the early postoperative period following bypass or coronary artery revascularization; it supports the suitability of Holter monitoring in patients who undergo cardiopulmonary bypass and CABG only if rigorous criteria for ECG interpretability and patient exclusion are used. In addition, because precise data were available for analysis for two thirds of all recruited patients, these results should provide valuable guidelines for estimating the appropriate sample size in the design of future studies similar to this one.