Effects of seasonal variations on coronary artery surgery.

Background: In this study, we compared profiles and early results of patients who underwent coronary artery bypass graft surgery (CABG) during the winter season with those who underwent CABG during the summer season. We also investigated whether possible seasonal variations in performance of health care professionals had any effects on surgical outcome.

Methods: The data from patients who had undergone CABG surgery in the winter (group A) and summer (group B) seasons of the period from December 1998 to August 2001 were analyzed retrospectively. Preoperative, perioperative, and postoperative data were compared. Preoperative factors analyzed included sex, age, diabetes mellitus, hypertension, New York Heart Association status, unstable angina pectoris, and left ventricle ejection fraction. Perioperative factors included graft number, internal mammary artery use, cross-clamp time, and cardiopulmonary bypass time. Postoperative factors included mediastinal reexploration, blood use, inotropic support, intraaortic balloon pump support, perioperative myocardial infarctus, cardiac arrest, infection and other complications, duration of hospital stay, and early mortality.

Results: The preoperative demographic data were identical in the 2 groups, with the exception of incidence rate of hypertension (26.8% in group A versus 15.7% in group B, P <.01). The incidence rates were higher in group B than group A for postoperative infection (8.8% versus 5.2%, P <.05), mediastinal reexploration for bleeding (6.9% versus 4.2%, P <.05), and transfusion blood use (7.3 +/- 6.2 U/patient versus 6.0 +/- 3.9 U/patient, P <.05). There were no differences between the 2 groups in early mortality rates.

Conclusion: Despite the fact that frequency and occurrence of cardiovascular events traditionally have been reported to be higher in the winter than the summer, our data show no major differences in early surgical outcome among those patients who had undergone CABG in the winter or summer. We did not encounter any seasonal patterns. However, an interesting finding was that the patients who underwent surgery in the summer had a higher incidence of infection and bleeding.