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Myocardial metabolism and ventricular function following cold potassium cardioplegia
Insights
Coronary bypass surgery can cause temporary heart metabolism and function changes. Avoid early post-surgery stress to prevent further heart injury and support recovery.
Area of Science:
- Cardiology
- Cardiac Surgery
- Physiology
Background:
- Cold potassium cardioplegia is standard for myocardial protection during coronary bypass grafting.
- Transient myocardial dysfunction and metabolic alterations can occur post-surgery despite adequate protection.
Purpose of the Study:
- To investigate myocardial metabolism and ventricular function after coronary bypass grafting using cold crystalloid cardioplegia.
- To evaluate the impact of early postoperative hemodynamic stress on myocardial recovery.
Main Methods:
- Serial hemodynamic measurements and coronary sinus catheterization in 90 patients.
- Thermodilution coronary sinus flow measurements in 33 patients.
- Nuclear ventriculography in 43 patients to assess ventricular function and metabolic changes.
Main Results:
- Cardiac index initially decreased then increased postoperatively, with rising oxygen consumption.
- Myocardial lactate production shifted to extraction post-reperfusion; coronary sinus blood flow increased.
- Early hemodynamic stress (volume loading, pacing) impaired lactate extraction and decreased diastolic compliance.
Conclusions:
- Myocardial metabolism recovery is slow after coronary bypass grafting with cold crystalloid cardioplegia.
- Early postoperative hemodynamic stress can exacerbate ischemic injury.
- Avoiding stress in the early period is crucial for optimal myocardial recovery.
Abstract:
Transient alterations in myocardial metabolism and ventricular function were observed after elective coronary bypass grafting despite apparently adequate intraoperative protection with cold potassium cardioplegia. Ninety patients had serial hemodynamic measurements and coronary sinus catheters inserted. Thirty-three patients had thermodilution coronary sinus flow catheters inserted to measure coronary sinus blood flow and to evaluate the myocardial utilization of oxygen and lactate. Nuclear ventriculograms were performed in 43 patients to assess ventricular function. Cardiac index fell after discontinuation of cardiopulmonary bypass and then rose between 2 and 24 hours postoperatively. Myocardial oxygen consumption steadily increased during this period. Myocardial lactate production reverted to lactate extraction 30 minutes after reperfusion. Reactive hyperemia was present during the first 10 minutes after cross-clamp release, and coronary sinus blood flow increased gradually during the first 24 hours postoperatively. The response to the stress of volume loading (the infusion of 250 to 500 ml of a colloid solution) and atrial pacing (at a rate of 110 beats/min) was evaluated 2 to 4 hours postoperatively (EARLY) and between 4 to 6 hours postoperatively (LATE). Volume loading resulted in a decrease in lactate extraction EARLY and an increase LATE (EARLY: -0.07 +/- 0.35 mmol/L; LATE: 0.08 +/- 0.32 mmol/L, mean +/- standard deviation not significant). Atrial pacing resulted in a decrease in lactate extraction EARLY and an increase LATE (EARLY: -0.11 +/- 0.34 mmol/L; LATE: 0.14 +/- 0.36 mmol/L, p less than 0.05). Diastolic compliance (the relation between the end-diastolic volume index) decreased between EARLY and LATE. Systolic function (the relation between the systolic blood pressure and the end-systolic volume index) and myocardial performance (the relation between the left ventricular stroke work index and the end-diastolic volume index) were unchanged. Ejection fraction correlated inversely with the end-diastolic volume index and did not represent an independent index of contractility. After elective coronary bypass grafting and cold crystalloid cardioplegia, myocardial metabolism recovered slowly. Hemodynamic stresses should be avoided in the early postoperative period to prevent progressive ischemic injury.