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Normothermic ischemia in coronary revascularization
S V Lichtenstein1, J G Abel, S E Fremes
1Division of Cardiovascular and Thoracic Surgery, St. Paul's Hospital Heart Centre, University of British Columbia, Vancouver, Canada.
Insights
Warm heart surgery using intermittent normothermic blood cardioplegia is safe for coronary artery bypass grafting. Limiting single ischemic intervals to under 13 minutes may protect the heart during these procedures.
Area of Science:
- Cardiovascular Surgery
- Cardiac Anesthesia
- Myocardial Protection
Background:
- Warm heart surgery with continuous normothermic blood cardioplegia offers an alternative to hypothermic methods for myocardial protection.
- Interruption of coronary flow during surgery facilitates distal coronary anastomoses, a common practice in coronary revascularization.
Purpose of the Study:
- To evaluate the safety and efficacy of intermittent warm blood cardioplegia during coronary artery bypass grafting in a large patient cohort.
- To determine the impact of specific cardioplegia interruption parameters on patient outcomes.
Main Methods:
- Analysis of 720 patients undergoing coronary artery bypass surgery with intermittent warm blood cardioplegia and electromechanical arrest.
- Measurement of aortic cross-clamp time, total cardioplegia interruption time, and longest single time off cardioplegia (LTOC).
- Correlation of percent time off cardioplegia (PTOC) and LTOC quartiles with a composite outcome of mortality, myocardial infarction, and low output syndrome.
Main Results:
- An average of 3.2 grafts were constructed with a mean aortic cross-clamp time of 61.8 minutes.
- The mean total time off cardioplegia was 28.5 minutes, representing 48.2% of the cross-clamp time.
- While increased PTOC showed a protective trend (p=0.07), longer LTOC (p=0.046) was borderline harmful, with intervals < 13 minutes associated with better outcomes.
Conclusions:
- Intermittent normothermic myocardial ischemia with electromechanical arrest is well-tolerated in coronary artery bypass surgery.
- Limiting single periods of ischemia to less than 13 minutes appears to be protective against adverse outcomes.
- These findings support the judicious use of warm blood cardioplegia in complex coronary revascularization procedures.
Abstract:
Warm heart surgery-continuous perfusion with normothermic blood cardioplegia-was introduced as an alternative to conventional intermittent hypothermic perfusion for myocardial protection. Interruption of global coronary flow, however, greatly facilitates the performance of distal coronary anastomoses and is the method that has evolved with many surgeons using warm blood cardioplegia for coronary revascularization. We present results (mean +/- SD) in 720 patients undergoing coronary bypass surgery protected with intermittent warm blood cardioplegia and exposed to normothermic ischemia but with electromechanical arrest. An average of 3.2 +/- 0.9 grafts were constructed per case with an average aortic cross clamp time of 61.8 +/- 22.2 minutes. Cardioplegia was interrupted a total of 28.5 +/- 12.4 min per operation. The percent time off cardioplegia (PTOC) expressed as a proportion of the cross clamp was 48.2 + 18.6%. The longest single time off cardioplegia (LTOC) was 11.4 +/- 4.0 min per patient. Calculated mean cardioplegia delivery during the cross clamp period was 75 ml/min. PTOC and LTOC were divided into quartiles (PTOC: < 36, 36-49, 50-62, > 62%; LTOC: < 10, 10-11, 12-13, > 13 min) and related to prespecified composite outcome of mortality, enzymatic myocardial infarct and low output syndrome. PTOC was protective (event rate/quartile 16.1%, 17.2%, 9.4%, 10.6%, p = 0.07) and longer LTOC (event rate/quartile 13.5%, 10.3%, 10.9%, 19.0%, p = 0.046) borderline harmful. The data suggest that when necessary multiple periods of normothermic myocardial ischemia in the presence of electromechanical arrest are well tolerated and potentially protective provided that any single ischemic interval is < 13 min.